Research on Honey Pots with regard to proofing security

Battling hackers and technological experts who use their knowledge for stealing information and hacking can always be troublesome and costly. Why waste time, effort, energy and risk losing out thousands of dollars in profits. The use of honey pots and honey tokens can eliminate the need for such risks and enhance the security of the system. Honey tokens and honey pots are not computer systems. In fact, they are software that is designed to interact with unauthorized users and counter their activity. They give you the ability to allow hackers and crackers into the system and make them feel as if they have broken into the system. They hold false data that is kept there for that malicious user to use and steal. The honey pot then actively saves all the actions performed by the unauthorized user. Using such honey pots and combining it with the data on their actions, many potential takeovers can be subdued. Several malicious invasions can be countered using such honey pots, and at the same time, the illegal user commending on his capabilities on managing to break into the company’s security. A honey pot works by trapping the actions of an intruder by setting a fallacious database that has honey pots are just software that tackles crackers intelligently without them knowing that they have been tracked. The cracker can do whatever they like with data that is as fallacious as dummy data. There is no sensitive data provided to such a cracker and the hacker’s actions will be under review all the while he is snooping around in the system. They are relatively easy to install and do not require a lot of high technological cost or monitoring. But they are highly effective in countering illegal break-ins to sensitive data. As soon as there is an access to the system through any undefined way, the honey pot gets activated and provides the user with databases that is of no use to the company and is actually in place to fool the hacker. Therefore, Mr. Lloyd, given the obvious benefits of sugar coating an illegal user and then finding the security holes that they used in breaching the system, the company should consider implementing the honey pot system. Using this we can then fix our security holes so that they can stop other crackers breaching our security again. Bibliography 1.  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   What is honey pot? a definition from Whatis.com. Retrieved March 17, 2008, from Search Security Web site: http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci551721,00.html 2.  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Dynamic Honeypots Retrieved March 17, 2008, from Security Focus Web site: http://www.securityfocus.com/infocus/1731

Reciprocating Engine

224 C H A P T E R 6 RECIPROCATING INTERNAL COMBUSTION ENGINES 6. 1 Introduction Perhaps the best-known engine in the world is the reciprocating internal combustion (IC) engine. Virtually every person who has driven an automobile or pushed a power lawnmower has used one. By far the most widely used IC engine is the spark-ignition gasoline engine, which takes us to school and work and on pleasure jaunts. Although others had made significant contributions, Niklaus Otto is generally credited with the invention of the engine and with the statement of its theoretical cycle.Another important engine is the reciprocating engine that made the name of Rudolf Diesel famous. The Diesel engine, the workhorse of the heavy truck industry, is widely used in industrial power and marine applications. It replaced the reciprocating steam engine in railroad locomotives about fifty years ago and remains dominant in that role today. The piston, cylinder, crank, and connecting rod provide the geometric basis of the reciprocating engine. While two-stroke-cycle engines are in use and of continuing interest, the discussion here will emphasize the more widely applied four-stroke-cycle engine.In this engine the piston undergoes two mechanical cycles for each thermodynamic cycle. The intake and compression processes occur in the first two strokes, and the power and exhaust processes in the last two. These processes are made possible by the crank-slider mechanism, discussed next. 6. 2 The Crank-Slider Mechanism Common to most reciprocating engines is a linkage known as a crank-slider mechanism. Diagramed in Figure 6. 1, this mechanism is one of several capable of producing the straight-line, backward-and-forward motion known as reciprocating.Fundamentally, the crank-slider converts rotational motion into linear motion, or vice-versa. With a piston as the slider moving inside a fixed cylinder, the mechanism provides the vital capability of a gas engine: the ability to compress and expand a gas . Before delving into this aspect of the engine, however, let us examine the crank-slider mechanism more closely. 225 It is evident from Figure 6. 2 that, while the crank arm rotates through 180Â °, the piston moves from the position known as top-center (TC) to the other extreme, called bottom-center (BC).During this period the piston travels a distance, S, called the stroke, that is twice the length of the crank. For an angular velocity of the crank,
, the crank pin A has a tangential velocity component
S/2. It is evident that, at TC and at BC, the crank pin velocity component in the piston direction, and hence the piston velocity, is zero. At these points, corresponding to crank angle  = 0Â ° and 180Â °, the piston reverses direction. Thus as  varies from 0Â ° to 180Â °, the piston velocity accelerates from 0 to a maximum and then returns to 0.A similar behavior exists between 180Â ° and 360Â °. The connecting rod is a two-force member; hence it is evident that there ar e both axial and lateral forces on the piston at crank angles other than 0Â ° and 180Â °. These lateral forces are, of course, opposed by the cylinder walls. The resulting lateral force component normal to the cylinder wall gives rise to frictional forces between the piston rings and cylinder. It is evident that the normal force, and thus the frictional force, alternates from one side of the piston to the other during each cycle.Thus the piston motion presents a challenging lubrication problem for the control and reduction of both wear and energy loss. The position of the piston with respect to the crank centerline is given by x = (S/2)cos + Lcos [ft | m] (6. 1) where yA = (S/2)sin = Lsin can be used to eliminate  to obtain x/L = (S/2L)cos + [1? (S/2L)2 sin2  ]? [dl] (6. 2) Thus, while the axial component of the motion of the crank pin is simple harmonic, xA = (S/2)cos, the motion of the piston and piston pin is more complex. It may be 226 seen from Equation (6. ), however , that as S/L becomes small, the piston motion approaches simple harmonic. This becomes physically evident when it is recognized that, in this limit, the connecting rod angle,  , approaches 0 and the piston motion approaches the axial motion of the crank pin. Equations (6. 1) and (6. 2) may be used to predict component velocities, accelerations, and forces in the engine. The volume swept by the piston as it passes from TC to BC is called the piston displacement, disp. Engine displacement, DISP, is then the product of the piston displacement and the number of cylinders, DISP = (n)(disp).The piston displacement is the product of the piston cross-sectional area and the stroke. The cylinder inside diameter (and, approximately, also the piston diameter) is called its bore. Cylinder bore, stroke, and number of cylinders are usually quoted in engine specifications along with or instead of engine displacement. It will be seen later that the power output of a reciprocating engine is proport ional to its displacement. An engine of historical interest that also used the crank-slider mechanism is discussed in the next section. 6. 3 The Lenoir CycleAn early form of the reciprocating internal combustion engine is credited to Etienne Lenoir. His engine, introduced in 1860, used a crank-slider-piston-cylinder arrangement 227 in which a combustible mixture confined between the piston and cylinder is ignited after TC. The resulting combustion gas pressure forces acting on the piston deliver work by way of the connecting rod to the rotating crank. When the piston is at BC, combustion gases are allowed to escape. The rotational momentum of the crank system drives the piston toward TC, expelling additional gases as it goes.A fresh combustible mixture is again admitted to the combustion chamber (cylinder) and the cycle is repeated. The theoretical Lenoir cycle, shown in Figure 6. 3 on a pressure-volume diagram, consists of the intake of the working fluid (a combustible mixture) fro m state 0 to state 1, a constant-volume temperature and pressure rise from state 1 to state 2, approximating the combustion process, an isentropic expansion of the combustion gases to state 3, and a constant-pressure expulsion of residual gases back to state 0.Note that a portion of the piston displacement, from state 0 to state 1, is used to take in the combustible mixture and does not participate in the power stroke from state 2 to state 3. The engine has been called an explosion engine because the power delivered is due only to the extremely rapid combustion pressure rise or explosion of the mixture in the confined space of the cylinder. Hundreds of Lenoir engines were used in the nineteenth century, but the engine is quite inefficient by todays standards. In 1862, Beau de Rochas pointed out that the 228 fficiency of internal combustion could be markedly improved in reciprocating engines by compression of the air-fuel mixture prior to combustion. In 1876 Niklaus Otto (who is thou ght to have been unaware of Rochas? suggestion) demonstrated an engine that incorporated this important feature, as described next. 6. 4 The Otto Cycle The Otto cycle is the theoretical cycle commonly used to represent the processes in the spark ignition (SI) internal combustion engine. It is assumed that a fixed mass of working fluid is confined in the cylinder by a piston that moves from BC to TC and back, as shown in Figure 6. . The cycle consists of isentropic compression of an air-fuel mixture from state 1 to state 2, constant-volume combustion to state 3, isentropic expansion of the combustion gases to state 4, and a constant-volume heat rejection back to state 1. The constant-volume heat rejection is a simple expedient to close the cycle. It obviates the need to represent the complex expansion and outflow of 229 combustion gases from the cylinder at the end of the cycle. Note that the Otto cycle is not concerned with the induction of the air-fuel mixture or with the expulsion of residual combustion gases.Thus only two mechanical strokes of the crank-slider are needed in the Otto cycle, even when it is used to represent an ideal four-stroke-cycle Otto engine. In this case the remaining strokes are used to execute the necessary intake and exhaust functions. Because it involves only two strokes, the Otto cycle may also represent a two-stroke-cycle engine. The two-stroke-cycle engine is in principle capable of as much work in one rotation of the crank as the four-stroke engine is in two. However, it is difficult to implement because of the necessity of making the intake and exhaust functions a part of those wo strokes. It is therefore not as highly developed or widely used as the four-stroke-cycle engine. We will focus on the fourstroke- cycle here. The simplest analysis of the Otto cycle assumes calorically perfect air as the working fluid in what is called the Air Standard cycle analysis. Following the notation of Figure 6. 4, the compression process can be represented by the isentropic relation for a calorically perfect gas, Equation (1. 21), as p2/p1 = (V1/V2)k [dl] (6. 3) where the compression ratio, CR = V1/V2, is a fundamental parameter of all reciprocating engines.The diagram shows that the expansion ratio for the engine, V4 /V3, has the same value, V1/V2. The clearance volume, V2, is the volume enclosed between the cylinder head and the piston at TC. Thus the compression ratio may be expressed as the ratio of the sum of the clearance and displacement volumes to the clearance volume: CR = [V2 + (V1 ? V2)]/V2 Thus, for a given displacement, the compression ratio may be increased by reducing the clearance volume. The efficiency of the cycle can be most easily determined by considering constantvolume- process heat transfers and the First Law cyclic integral relation, Equation (1. ). The heat transferred in the processes 2
3 and 4
1 are q2
3 = cv (T3 ? T2) [Btu/lbm | kj/kg] (6. 4) and q4
1 = cv (T1 ? T4) [Btu/lbm | kJ/kg] (6. 5) B oth the expansion process, 3
4, and the compression process, 1
2, are assumed to be isentropic. Thus, by definition, they are both adiabatic. From the cyclic integral, the net work per unit mass is then: w = q2
3 + q4
1 = cv (T3 ? T2 + T1 ? T4) [Btu/lbm | kJ/kg] (6. 6) 230 As before, the cycle thermal efficiency is the ratio of the net work to the external heat supplied: Otto = w/q2
3 = cv (T3 ? T2 + T1 ?T4) / [cv (T3 ? T2)] = 1 + (T1 ? T4) / (T3 ? T2) = 1 ? T1/T2 = 1 ? 1 / CR k-1 [dl] (6. 7) where Equation (1. 20) has been used to eliminate the temperatures. Equation (6. 7) shows that increasing compression ratio increases the cycle thermal efficiency. This is true for real engines as well as for the idealized Otto engine. The ways in which real spark ignition engine cycles deviate from the theoretical Otto cycle are discussed later. EXAMPLE 6. 1 An Otto engine takes in an air-fuel mixture at 80Â °F and standard atmosphere presssure. It has a compression ratio of 8.Using Air Stan dard cycle analysis, a heating value of 20,425 Btu/lbm, and A/F = 15, determine: (a) The temperature and pressure at the end of compression, after combustion, and at the end of the power stroke. (b) The net work per pound of working fluid. (c) The thermal efficiency. Solution We use the notation of Figure 6. 4: (a) p2 = p1(V1/V2)k = 1(8)1. 4 = 18. 38 atm T2 = T1(V1/V2)k ? 1 = (540)(8)0. 4 = 1240. 6Â °R T3 = T2 + qa /cv = T2 + (F/A)(HV)k/cp = 1240. 6 + 1. 420,425/150. 24 = 9184Â °R p3 = p2T3 /T2 = 18. 38(9184/1240. 6) = 136. 1 atm T4 = T3 /CRk? 1 = 9184/ 80. 4 = 3997. Â °R p4 = p3 /CRk = 136. 1/81. 4 = 7. 4 atm (b) The constant-volume heat addition is governed by the fuel-air ratio and the fuel heating value: qa = HV(F/A) = 20,425/15 = 1361. 7 Btu/lbm of air 231 qr = cv (T1 ? T4) = (0. 24/1. 4)( 540 ? 3997. 4) = ? 592. 7 Btu/lbm w = qa + qr = 1361. 7 + ( ? 592. 7) = 769 Btu/lbm (c) The cycle termal efficiency may then be determined from the definition of the heat engine thermal efficiency or Equation (6. 7): th = w/qa = 769/1361. 7 = 0. 565 th = 1 ? 1/80. 4 = 0. 565 _____________________________________________________________________ In view f the discussion of gas properties and dissociation in Chapter 3, the values of T3 and T4 in Example 6. 1 are unrealistically high. Much of the energy released by the fuel would go into vibration and dissociation of the gas molecules rather than into the translational and rotational degrees of freedom represented by the temperature. As a result, significantly lower temperatures would be obtained. Thus, while the analysis is formally correct, the use of constant-low-temperature heat capacities in the Air Standard cycle makes it a poor model for predicting temperature extremes when high energy releases occur.Some improvement is achieved by using constant-hightemperature heat capacities, but the best results would be achieved by the use of real gas properties, as discussed in several of the references. 6. 5 Combustion in a Reciprocating Engine The constant-volume heat transfer process at TC in the Otto cycle is an artifice to avoid the difficulties of modeling the complex processes that take place in the combustion chamber of the SI engine. These processes, in reality, take place over a crank angle span of 30Â ° or more around TC.Let us consider aspects of these processes and their implementation in more detail. Normally, the mixture in the combustion chamber must have an air-fuel ratio in the neighborhood of the stoichiometric value for satisfactory combustion. A more or less homogeneous mixture may be produced outside the cylinder in a carburetor, by injection into the intake manifold, or by throttle-body injection into a header serving several intake manifolds. In the case of the carburetor, fuel is drawn into the engine from the carburetor by the low pressure created in a venturi through which the combustion air flows.As a result, increased air flow causes lower venturi pressure and hence in creased fuel flow. The fuel system thus serves to provide an air-fuel mixture that remains close to the stoichiometric ratio for a range of air flow rates. Various devices designed into the carburetor further adjust the fuel flow for the special operating conditions encountered, such as idling and rapid acceleration. Maximum fuel economy is usually attained with excess air to ensure that all of the fuel is burned. A mixture with excess air is called a lean mixture.The carburetor 232 usually produces this condition in automobiles during normal constant-speed driving. On the other hand, maximum power is achieved with excess fuel to assure that all of the oxygen in the air in the combustion chamber is reacted. It is a matter of exploiting the full power-producing capability of the displacement volume. A mixture with excess fuel is called a rich mixture. The automotive carburetor produces a rich mixture during acceleration by supplying extra fuel to the air entering the intake manifold. The equivalence ratio is sometimes used to characterize the mixture ratio, whether rich or lean. The equivalence ratio,
, is defined as the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. Thus
> 1 represents a rich mixture and
< 1 represents a lean mixture. In terms of air-fuel ratio,
= (A/F)stoich /(A/F). Homogeneous air-fuel mixtures close to stoichiometric may ignite spontaneously (that is, without a spark or other local energy source) if the mixture temperature exceeds a temperature called the autoignition temperature.If the mixture is brought to and held at a temperature higher than the autoignition temperature, there is a period of delay before spontaneous ignition or autoignition This time interval is called the ignition delay, or ignition lag. The ignition delay depends on the characteristics of the fuel and the equivalence ratio and usually decreases with increasing temperature. In spark-ignition engines, compression ratios and therefore the temperatures at the end of compression are low enough that the air-fuel mixture is ignited by the spark plug before spontaneous ignition can occur.SI engines are designed so that a flame front will propagate smoothly from the spark plug into the unburned mixture until all of the mixture has been ignitied. However, as the flame front progresses, the temperature and pressure of the combustion gases behind it rise due to the release of the chemical energy of the fuel. As the front propagates, it compresses and heats the unburned mixture, sometimes termed the end-gas. Combustion is completed as planned when the front smoothly passes completely through the end-gas without autoignition. However, if the end-gas autoignites, a pinging or low-pitched sound called knock is heard.The avoidance of knock due to autoignition of the end-gas is a major constraint on the design compression ratio of an SI engine. If hot spots or thermally induced compression of the end-gas ignite it before the flame front does, there is a more rapid release of chemical energy from the end-gas than during normal combustion. Knock is sometimes thought of as an explosion of the end gas that creates an abrupt pulse and pressure waves that race back and forth across the cylinder at high speed, producing the familiar pinging or low-pitched sound associated with knock.Knock not only reduces engine performance but produces rapid wear and objectionable noise in the engine. Thus it is important for a SI engine fuel to have a high autoignition temperature. It is therefore important for SI engine fuel to have a high autoignition temperature. Thus the knock characteristics of commercially available fuels limit the maximum allowable design compression ratio for SI engines and hence limit their best efficiency. The octane number is a measure of a gasoline’s ability to avoid knock. Additives such as tetraethyl lead have been used in the past to suppress engine knock.However, the accumulation of lead in the environment and its penetration into the food cycle has 233 resulted in the phaseout of lead additives. Instead refineries now use appropriate blends of hydrocarbons as a substitute for lead additives in unleaded fuels. The octane number of a fuel is measured in a special variable-compression-ratio engine called a CFR (Cooperative Fuels Research) engine. The octane rating of a fuel is determined by comparison of its knocking characteristics with those of different mixtures of isooctane, C8H18, and n-heptane, C7H16.One hundred percent isooctane is defined as having an octane number of 100 because it had the highest resistance to knock at the time the rating system was devised. On the other hand, n-heptane is assigned a value of 0 on the octane number scale because of its very poor knock resistance. If a gasoline tested in the CFR engine has the same knock threshold as a blend of 90% isooctane and 10% n-heptane, the fuel is assigned an octane rating of 90. In combustion chamber de sign, the designer attempts to balance many factors to achieve good performance.Design considerations include locating intake valves away from and exhaust valves near spark plugs, to keep end-gas in a relatively cool area of the combustion chamber and thereby suppress hot-surface-induced autoignition tendencies. Valves are, of course, designed as large as possible to reduce induction and exhaust flow restrictions. More than one intake and one exhaust valve per cylinder are now used in some engines to improve ? engine breathing.? In some engines, four valves in a single cylinder are employed for this purpose.The valves are also designed to induce swirl and turbulence to promote mixing of fuel and air and to improve combustion stability and burning rate. Pollution and fuel economy considerations have in recent years profoundly influenced overall engine and combustion chamber design. Stratified-charge engines, for example, attempt to provide a locally rich combustion region to control peak temperatures and thus suppress NOx formation. The resulting combustion gases containing unburned fuel then mix with surrounding lean mixture to complete the combustion process, thus eliminating CO and unburned hydrocarbons from the exhaust.These processes occur at lower temperatures than in conventional combustion chamber designs and therefore prevent significant nitrogen reactions. 6. 6 Representing Reciprocating Engine Perfomance In an earlier section, the theoretical work per unit mass of working fluid of the Otto engine was evaluated for a single cycle of the engine, using the cyclic integral of the First Law of Thermodynamics. The work done by pressure forces acting on a piston can also be evaluated as the integral of pdV. It is evident therefore that the work done during a single engine cycle is the area enclosed by the cycle process curves on the pressure-volume diagram.Thus, instead of using the cyclic integral or evaluating pdV for each process of the cycle, the work o f a reciprocating engine can be found by drawing the theoretical process curves on the p? V diagram and graphically integrating them. Such a plot of pressure versus volume for any reciprocating engine, real or theoretical, is called an indicator diagram. 234 In the nineteenth and early twentieth centuries a mechanical device known as an engine indicator was used to produce indicator cards or diagrams to determine the work per cycle for slow-running steam and gas reciprocating ngines. The indicator card was attached to a cylinder that rotated back and forth on its axis as the piston oscillated, thus generating a piston position (volume) coordinate. At the same time a pen driven by a pressure signal from the engine cylinder moved parallel to the cylinder axis, scribing the p-V diagram over and over on the card. The work of high speed engines is still evaluated from traces of pressure obtained with electronic sensors and displayed on electronic monitors and through digital techniques.T he work done per cycle (from an indicator card, for instance) can be represented as an average pressure times a volume. Because the displacement volumes of engines are usually known, an engine performance parameter known as the mean effective pressure, MEP, is defined in terms of the piston displacement. The mean effective pressure is defined as the value of the pressure obtained by dividing the net work per cylinder per cycle at a given operating condition by the piston displacement volume: MEP = W/disp [lbf/ft2 | kPa] (6. 8)Thus the MEP is a measure of the effectiveness of a given displacement volume in producing net work. The power output of an engine with identical cylinders may be represented as the product of the work per cycle and the number of cycles executed per unit time by the engine. Thus if the engine has n cylinders, each executing N identical thermodynamic cycles per unit time, and delivering W work units per cylinder, with a piston displacement, disp, the power outpu t is given by P = n
N
W = n
N MEP  disp [ft-lbf /min | kW] (6. 9)Expressed for the entire engine, the engine displacement is DISP = ndisp and the engine work is MEP DISP. Hence the engine power is: P = N MEPDISP [ft-lbf /min | kW] (6. 10) where N, the number of thermodynamic cycles of a cylinder per unit time, is the number of crank-shaft revolutions per unit time for a two-stroke-cycle engine and one-half of the revolutions per unit time for a four-stroke-cycle engine. The factor of ? for the four-stroke-cycle engine arises because one thermodynamic cycle is executed each time the crank rotates through two revolutions. EXAMPLE 6. 2What is the displacement of an engine that develops 60 horsepower at 2500 rpm in a four-stroke-cycle engine having an MEP of 120 psi? 235 Solution From Equation (6. 10), the displacement of the engine is DISP = P/(N MEP) = (60)(33,000)(12)/[(2500/2)(120)] = 158. 4 in3 Checking units: (HP)(ft-lbf/HP-min)(in/ft)/[(cycles/min)(lbf/in2)] = in3 ________ _____________________________________________________________ If the work is evaluated from an indicator diagram the work is called indicated work; the MEP is called the indicated mean effective pressure, IMEP; and the power is indicated power, IP.Note that the indicated work and power, being associated with the work done by the combustion chamber gases on the piston, do not account for frictional or mechanical losses in the engine, such as piston-cylinder friction or the drag of moving parts (like connecting rods) as they move through air or lubricating oil. Brake Performance Parameters Another way of evaluating engine performance is to attach the engine output shaft to a device known as a dynamometer, or brake. The dynamometer measures the torque, T, applied by the engine at a given rotational speed.The power is then calculated from the relation P = 2rpm T [ft-lbf /min | N-m/min] (6. 11) A simple device called a prony brake, which was used in the past, demonstrates the concept for the measurement of the shaft torque of engines. Figure 6. 5 shows the prony brake configuration in which a stationary metal band wrapped around the rotating flywheel of the engine resists the torque transmitted to it by friction. The product of the force measured by a spring scale, w, and the moment arm, d , gives the resisting torque. The power dissipated is then given by 2(rpm)w d.Modern devices such as water brakes and electrical dynamometers long ago replaced the prony brake. The water brake is like a centrifugal water pump with no outflow, mounted on low-friction bearings, and driven by the test engine. As with the prony brake, the force required to resist turning of the brake (pump) housing provides the torque data. This, together with speed measurement, yields the power output from Equation (6. 11). The power dissipated appears as increased temperature of the water in the brake and heat transfer from the brake. Cool water is circulated slowly through the brake to mainta in a steady operating condition.The torque measured in this way is called the brake torque, BT, and the resulting power is called the brake power, BP. To summarize: while indicated parameters relate to gas forces in the cylinder, brake parameters deal with output shaft forces. Thus the brake power differs from the indicated power in that it accounts for the effect of all of the energy losses in the engine. The difference between the two is referred to as the friction power, FP. Thus FP = IP ? BP. 236 Friction power varies with engine speed and is difficult to measure directly.An engine is sometimes driven without fuel by a motor-dynamometer to evaluate friction power. An alternative to using friction power to relate brake and indicated power is through the engine mechanical efficiency, m: m = BP/IP [dl] (6. 12) Because of friction, the brake power of an engine is always less than the indicated power; hence the engine mechanical efficiency must be less than 1. Clearly, mechanical e fficiencies as close to 1 as possible are desired. The engine indicated power can also be expressed in terms of torque, through Equation (6. 11). Thus an indicated torque, IT, can be defined.Similarly, a brake mean effective pressure, BMEP, may be defined that, when multiplied by the engine displacement and speed, yields the brake power, analogous to Equation (6. 10). Table 6. 1 summarizes these and other performance parameters and relations. The thermal efficiency, as for other engines, is a measure of the fuel economy of a reciprocating engine. It tells the amount of power output that can be achieved for a given rate of heat release from the fuel. The rate of energy release is, in turn, the product of the rate of fuel flow and the fuel heating value.Thus, for a given thermal efficiency, power output can be increased by employing a high fuel flow rate and/or selecting a fuel with a high heat of combustion. If the thermal efficiency is evaluated using the brake power, it is called t he brake thermal efficiency, BTE. If the evaluation uses the indicated power, it is called the indicated thermal efficiency, ITE. 237 It is common practice in the reciprocating engine field to report engine fuel economy in terms of a parameter called the specific fuel consumption, SFC, analogous to the thrust specific fuel consumption used to describe jet engine performance.The specific fuel consumption is defined as the ratio of the fuel-mass flow rate to the power output. Typical units are pounds per horsepower-hour or kilograms per kilowatt-hour. Obviously, good fuel economy is indicated by low values of SFC. The SFC is called brake specific fuel consumption, BSFC, if it is defined using brake power or indicated specific fuel consumption, ISFC, when based on indicated power. The SFC for a reciprocating engine is analogous to the heat rate for a steam power plant in that both are measures of the rate of energy supplied per unit of power output, and in that low values of both are d esirable.Volumetric Efficiency The theoretical energy released during the combustion process is the product of the mass of fuel contained in the combustion chamber and its heating value if the fuel is completely reacted. The more air that can be packed into the combustion chamber, the Table 6. 1 Engine Performance Parameters Indicated Brake Friction Mean effective pressure IMEP BMEP FMEP = IMEP – BMEP
m = BMEP / IMEP Power IP BP FP = IP – BP
m = BHP / IHP Torque IT BT FT = IT – BT
m = BT / IT Thermal efficiency ITE BTE
m = BTE / ITE Specific fuel consumption ISFC BSFC
m = ISFC / BSFC more fuel that can be burned with it.Thus a measure of the efficiency of the induction system is of great importance. The volumetric efficiency, v, is the ratio of the actual mass of mixture in the combustion chamber to the mass of mixture that the displacement volume could hold if the mixture were at ambient (free-air) density. Thus the average mass-flow rate of air through a cylinder is v (disp) aN. Pressure losses across intake and exhaust valves, combustion-chamber clearance volume, the influence of hot cylinder walls on mixture density, valve timing, and gas inertia effects all influence the volumetric efficiency.EXAMPLE 6. 3 A six-cylinder, four-stroke-cycle SI engine operates at 3000 rpm with an indicated mean effective pressure of five atmospheres using octane fuel with an equivalence ratio 238 of 0. 9. The brake torque at this condition is 250 lbf? ft. , and the volumetric efficiency is 85%. Each cylinder has a five inch bore and 6 inch stroke. Ambient conditions are 14. 7 psia and 40Â °F. What is the indicated horsepower, brake horsepower, and friction horsepower; the mechanical efficiency; the fuel flow rate; and the BSFC? Solution The six cylinders have a total displacement ofDISP = 6? 52? 6/4 = 706. 86 in3 Then the indicated horsepower is IP = MEP? DISP? N /[12? 33,000] [lbf /in2][in3][cycles/min]/[in/ft][ft-lbf /HP-min] = (5)(14. 7)(706 . 86)(3000/2)/[12? 33,000] = 196. 8 horsepower The brake horsepower, from Equation (6. 11), is: BP = 2 ? 3000 ? 250 / 33,000 = 142. 8 horsepower Then the friction power is the difference between the indicated and brake power: FP = 196. 8 ? 142. 8 = 54 horsepower and the mechanical efficiency is m = 142. 8/196. 8 = 0. 726 The ambient density is a = 14. 7 ? 144/ [53. 3 ? 500] = 0. 0794 lbm /ft3 nd the mass flow rate of air to the engine is ma = 0. 85? 0. 0794? 706. 86? (3000/2)/1728 = 41. 4 lbm /min For octane the stoichiometric reaction equation is C8H18 + 12. 5O2 + (12. 5? 3. 76)N2
8CO2 + 9H2O + (12. 5? 3. 76)N2 The fuel-air ratio is then F/A = 0. 9? [(8? 12) + (18? 1)]/[12. 5(32 + 3. 76? 28)] = 0. 0598 lbm-fuel /lbm-air 239 The fuel flow rate is mf = ma (F/A) = 41. 4 ? 0. 0598 = 2. 474 lbm /min The brake specific fuel consumption is BSFC = 60 mf /BHP = 60? 2. 474/142. 8 = 1. 04 lbm /BHP-hr ____________________________________________________________________ 6. Spark-Ignition E ngine Performance A typical indicator diagram showing intake and exhaust processes, valve actuation, and spark timing for a four-stroke-cycle SI engine is shown in Figure 6. 6. It is assumed that an appropriate air-fuel mixture is supplied from a carburetor through an intake manifold to an intake valve, IV, and that the combustion gas is discharged through an exhaust valve, EV, into an exhaust manifold. The induction of the air-fuel mixture starts with the opening of the intake valve at point A just before TC.As the piston sweeps to the right, the mixture is drawn into the cylinder through the IV. The pressure in the cylinder is somewhat below that in the intake manifold due to the pressure losses across the intake valve. In order to use the momentum of the mixture inflow through the valve at the end of the intake stroke to improve the volumetric efficiency, intake valve closure is delayed to shortly after BC at point B. Power supplied from inertia of a flywheel (and the other rotat ing masses in the engine) drives the piston to the left, compressing and raising the temperature of the trapped mixture.The combustion process in a properly operating SI engine is progressive in that the reaction starts at the spark plug and progresses into the unburned mixture at a finite speed. Thus the combustion process takes time and cannot be executed instantaneously as implied by the theoretical cycle. In order for the process to take place as near to TC as possible, the spark plug is fired at point S. The number of degrees of crank rotation before TC at which the spark occurs is called the ignition advance. Advances of 10Â ° to 30Â ° are common, depending on speed and load.The spark advance may be controlled by devices that sense engine speed and intake manifold pressure. Microprocessors are now used to control spark advance and other functions, based on almost instantaneous engine performance measurements. Recalling the slider-crank analysis, we observ that the piston vel ocity at top center is momentarily zero as the piston changes direction. Therefore no work can be done at this point, regardless of the magnitude of the pressure force. Thus, to maximize the work output, it is desired to have the maximum cylinder pressure occur at about 20Â ° after TC.Adjustment of the spark advance (in degrees before TC) allows some control of the combustion process and the timing of peak pressure. For a fixed combustion duration, the combustion crank-angle interval must increase with engine speed. As a consequence, the ignition advance must increase with increasing engine speed to 240 maintain optimum timing of the peak pressure. Following combustion, the piston continues toward bottom center as the high pressure gases expand and do work on the piston during the power stroke. As the piston approaches BC, the gases do little work on the piston as its velocity again approaches zero.As a result, not much work is lost by early opening of the exhaust valve before BC ( at point E) to start the blowdown portion of the exhaust process. It is expedient to sacrifice a little work during the end of the power stroke in order to reduce the work needed to overcome an otherwise-high exhaust stroke cylinder pressure. Inertia of the gas in the cylinder and resistance to flow through the exhaust valve opening slow the drop of gas pressure in the cylinder after the valve opens. Thus the gases at point E are at a pressure above the exhaust manifold pressure and, during blowdown, rush out through the EV at high speed.Following blowdown, gases remaining in the cylinder are then expelled as the piston returns to TC. They remain above exhaust manifold pressure until reaching TC because of the flow resistance of the exhaust valve. The EV closes shortly after TC at point C, terminating the exhaust process. The period of overlap at TC between the intake valve opening at point A and exhaust valve closing at point C in Figure 6. 6 allows more time for the intake and exh aust processes at high engine speeds, when about 10 milliseconds may be available for these processes.At low engine speed and at idling there may be some mixture loss through the exhaust valve and discharge into the intake manifold during this valve overlap period. The combined exhaust and induction processes are seen to form a ? pumping loop? that traverses the p-V diagram in a counterclockwise direction and therefore 241 represents work input rather than work production. The higher the exhaust stroke pressure and the lower the intake stroke pressure, the greater the area of the pumping loop and hence the greater the work that must be supplied by the power loop (clockwise) to compensate.Great attention is therefore paid to valve design and other engine characteristics that influence the exhaust and induction processes. Volumetric efficiency is a major parameter that indicates the degree of success of these efforts. Performance Characteristics A given ideal Otto-cycle engine produce s a certain amount of work per cycle. For such a cycle, MEP = W/disp is a constant. Equating the power equations (6. 9) and (6. 11) shows that the average torque is proportional to MEP and independent of engine engine speed.Therefore power output for the ideal engine is directly proportional to the number of cycles executed per unit time, or to engine speed. Thus an Otto engine has ideal torque and power characteristics, as shown by the solid lines in Figure 6. 7. The characteristics of real engines (represented by the dashed lines) tend to be similar in nature to the ideal characteristics but suffer from speed-sensitive effects, particularly at low or high speeds. Torque and power characteristics for a 3. 1 liter V6 engine (ref. 9) are shown by the solid lines in Figure 6. 8.Note the flatness of the torque-speed curve and the expected peaking of the power curve at higher speed than the torque curve. Rather than present graphical characteristics such as this in their 242 brochures, automobile manufacturers usually present only values for the maximum power and torque and the speeds at which they occur. Engine characteristics such as those shown in the figure are invaluable to application engineers seeking a suitable engine for use in a product. 6. 8 The Compression-Ignition or Diesel Cycle The ideal Diesel cycle differs from the Otto cycle in that combustion is at constant pressure rather than constant volume.The ideal cycle, shown in Figure 6. 9, is commonly implemented in a reciprocating engine in which air is compressed without fuel from state 1 to state 2. With a typically high compression ratio, state 2 is at a temperature high enough that fuel will ignite spontaneously when sprayed directly into the air in the combustion chamber from a high-pressure fuel injection system. By controlling the fuel injection rate and thus the rate of chemical energy release in relation to the rate of expansion of the combustion gases after state 2, a constant243 pressure pro cess or other energy release pattern may be achieved as in Figure 6. . For example, if the energy release rate is high, then pressure may rise, as from 2 to 3’, and if low may fall to 3’’. Thus constant-pressure combustion made possible by controlling the rate of fuel injection into the cyclinder implies the use of a precision fuel injection system. Instead of injecting fuel into the high-temperature compressed air, the cycle might be executed by compression of an air-fuel mixture, with ignition occurring either spontaneously or at a hot spot in the cylinder near the end of the compression process.Inconsistency and unpredictability of the start of combustion in this approach, due to variations in fuel and operating conditions, and to lack of control of the rate of heat release with the possibility of severe knock, makes the operation of such an engine unreliable, at the least, and also limits the maximum compression ratio. The Diesel engine therefore usually emp loys fuel injection into compressed air rather than carbureted mixture formation. In the Air Standard cycle analysis of the Diesel cycle, the heat addition process is at constant pressure: q2
3 = cp(T3 ? T2) [Btu/lbm | kJ/kg] (6. 13) nd, as with the Otto cycle, the closing process is at constant volume: q4
1 = cv(T1 ? T4) [Btu/lbm | kJ/kg] (6. 14) 244 The net work and thermal efficiency are then: w = q2
3 + q4
1 = cp(T3 ? T2) + cv(T1 ? T4) = cvT1[k(T3/T1 ? T2/T1) + 1 ? T4/T1] [Btu/lbm | kJ/kg] (6. 15) Diesel = w/q2
3 = 1 + q4-
1/q2
3 = 1 + (cv/cp)(T1 ? T4)/(T3 ? T2) = 1 ? (1/k)(T1/T2)(T4/T1 ? 1)/(T3/T2 ? 1) [dl] (6. 16) The expressions for the net work and cycle efficiency may be expressed in terms two parameters, the compression ratio, CR = V1/V2 (as defined earlier in treating the Otto cycle) and the cutoff ratio, COR = V3/V2.The temperature ratios in Equations (6. 15) and (6. 16) may be replaced by these parameters using, for the constant-pressure process, COR = V3/V2 = T3/T2 an d by expanding the following identity: T4 /T1 = (T4/T3)(T3/T2)(T2 /T1) = (V3 /V4)k-1(V3/V2)(V1/V2)k-1 = [(V3/V4)(V1/V2)]k-1COR = (COR)k-1COR = CORk where the product of the volume ratios was simplified by recognizing that V4 = V1. Thus the nondimensionalized net work and Diesel-cycle thermal efficiency are given by w /cvT1 = kCRk-1(COR ? 1) + (1 ? CORk) [dl] (6. 17) and Diesel = 1 ? (1/k)[(CORk ? 1)/(COR ? 1)]/CRk-1 [dl] (6. 8) where the cutoff ratio, COR, is the ratio of the volume at the end of combustion, V3, to that at the start of combustion, V2. Thus the cutoff ratio may be thought of as a measure of the duration of fuel injection, with higher cutoff ratios corresponding to longer combustion durations. 245 Diesel-cycle net work increases with both compression ratio and cutoff ratio. This is readily seen graphically from Figure 6. 9 in terms of p-V diagram area. As with the Otto cycle, increasing compression ratio increases the Diesel-cycle thermal efficiency. Increasing cutof f ratio, however, decreases thermal efficiency.This may be rationalized by observing from the p-V diagram that much of the additional heat supplied when injection is continued is rejected at increasingly higher temperatures. Another view is that heat added late in the expansion process can produce work only over the remaining part of the stroke and thus adds less to net work than to heat rejection. EXAMPLE 6. 4 A Diesel engine has a compression ratio of 20 and a peak temperature of 3000K. Using an Air Standard cycle analysis, estimate the work per unit mass of air, the thermal efficiency, the combustion pressure, and the cutoff ratio.Solution Assuming an ambient temperature and pressure of 300K and 1 atmosphere, the temperature at the end of the compression stroke is T2 = (300)(20)1. 4 ? 1 = 994. 3K and the combustion pressure is p2 = (1)(20)1. 4 = 66. 3 atm Then the cutoff ratio is V3/V2 = T3/T2 = 3000/994. 3 = 3. 02 The expansion ratio is calculated as follows: V4 /V3 = (V1/V2)/(V 3 /V2) = 20/3. 02 = 6. 62 T4 = T3 (V3 /V4)1. 4 ? 1 = 3000/6. 620. 4 = 1409K w = 1. 005(3000 ? 994. 3) + (1. 005/1. 4)(300 ? 1409) = 1219. 6 kJ/kg qa = 1. 005(3000 ? 994. 3) = 2015. 7 kJ/kg th = w/qa = 1219. /2015. 6 = 0. 605, or 60. 5% _____________________________________________________________________ 246 6. 9 Comparing Otto-Cycle and Diesel-Cycle Efficiencies A reasonable question at this point is: Which cycle is more efficient, the Otto cycle or the Diesel cycle? Figure 6. 10 assists in examining this question. In general notation, the cycle efficiency may be written as th = wnet /qin = wnet /(wnet + |qout|) = 1 /(1 + |qout| /wnet) [dl] (6. 19) Comparing the Otto cycle 1? 2? 3? 4 and the Diesel cycle with the same compression ratio 1? 2? 3’? , we see that both have the same heat rejection but that the Otto cycle has the higher net work. Equation (6. 19) then shows that, for the same compression ratio, the Otto cycle has the higher efficiency. It has been observed that Diesel-cycle efficiency decreases with increasing cutoff ratio for a given compression ratio. Let us examine the limit of the Diesel-cycle efficiency for constant CR as COR approaches its minimum value, 1. We may write Equation (6. 18) as Diesel = 1 ? 1 /(kCRk-1) f (COR) where f(COR) = (CORk ? 1)/(COR ? 1). Applying L’Hospital’s rule, with primes 247 esignating differentiation with respect to COR, to the limit of f(COR) as COR
1, yields lim f(COR) = lim (CORk ? 1)’/ Lim (COR? 1)’ = lim kCORk ? 1 = k COR
1 COR
1 COR
1 and limDiesel = 1 ? 1 /CRk ? 1 COR
1 = Otto Thus the limit of the Diesel-cycle efficiency as COR approaches 1 is the Otto cycle efficiency. Hence Equation (6. 18) shows that the efficiency of the Diesel cycle must be less than or equal to the Otto-cycle efficiency if both engines have the same compression ratio, the same conclusion we reached by examination of the p-V diagram.Suppose, however, that the compression ratios are not the same. Compare the Otto cycle 1? 2’? 3’? 4 with the Diesel cycle 1? 2? 3’? 4 having the same maximum temperature in Figure 6. 10. The Otto cycle has a smaller area, and therefore less work, than the Diesel cycle, but the same heat rejection. Equation (6. 19) demonstrates that the Otto cycle has a lower thermal efficiency than the Diesel cycle with the same maximum temperature. The conclusion that must be drawn from the above comparisons is quite clear. As in most comparative engineering studies, the result depends on the ground ules which were adopted at the start of the study. The Otto cycle is more efficient if the compression ratio is the same or greater than that of the competing Diesel cycle. But knock in spark-ignition (Otto) engines limits their compression ratios to about 12, while Diesel-engine compression ratios may exceed 20. Thus, with these higher compression ratios, the Air Standard Diesel-cycle efficiency can exceed that of the Otto cycle. In practice, Diesel engines tend to have higher efficiencies than SI engines because of higher compression ratios. 6. 0 Diesel-Engine Performance In 1897, five years after Rudolph Diesel’s first patents and twenty-one years after Otto’s introduction of the spark-ignition engine, Diesel’s compression-ignition engine was proven to develop 13. 1 kilowatts of power with an unprecedented brake thermal efficiency of 26. 2% (ref. 7). At that time, most steam engines operated at thermal efficiencies below 10 %; and the best gas engines did not perform much better than the steam machines. Diesel claimed (and was widely believed) to have developed his engine from the principles expounded by Carnot.He had developed â€Å"the rational engine. † Whether his claims were exaggerated or not, Diesel’s acclaim was well deserved. He had developed an engine that operated at unprecedented temperatures and pressures, had proven his concept of ignition of fuel by injection into the c ompressed high-temperature air, and had overcome the formidable problems of injecting a variety of fuels in appropriate 248 amounts with the precise timing required for satisfactory combustion. His is a fascinating story of a brilliant and dedicated engineer (refs. 7, 8).In the Diesel engine, the high air temperatures and pressures prior to combustion are attributable to the compression of air alone rather than an air-fuel mixture. Compression of air alone eliminates the possibility of autiognition during compression and makes high compression ratios possible. However, because of the high pressures and temperatures, Diesel engines must be designed to be structurally more rugged. Therefore, they tend to be heavier than SI engines with the same brake power. The energy release process in the Diesel engine is controlled by the rate of injection of fuel.After a brief ignition lag, the first fuel injected into the combustion chamber autoignites and the resulting high gas temperature susta ins the combustion of the remainder of the fuel stream as it enters the combustion chamber. Thus it is evident that the favorable fuel characteristic of high autoignition temperature for an SI engine is an unfavorable characteristic for a Diesel engine. In the Diesel engine, a low autoignition temperature and a short ignition delay are desirable. Knock is possible in the Diesel engine, but it is due to an entirely different cause than knock in a spark-ignition engine.If fuel is ignited and burns as rapidly as it is injected, then smooth, knock-free combustion occurs. If, on the other hand, fuel accumulates in the cylinder before ignition due to a long ignition lag, an explosion or detonation occurs, producing a loud Diesel knock. The cetane number is the parameter that identifies the ignition lag characteristic of a fuel. The cetane number, like the octane number, is determined by testing in a CFR engine. The ignition lag of the test fuel is compared with that of a mixture of n-ceta ne, C16H34, and heptamethylnonane, HMN (ref. 0). Cetane, which has good ignition qualities, is assigned a value of 100; and HMN, which has poor knock behavior, a value of 15. The cetane number is then given by the sum of the percentage of n-cetane and 0. 15 times the percentage of HMN in the knock-comparison mixture. A cetane number of 40 is the minimum allowed for a Diesel fuel. 6. 11 Superchargers and Turbochargers The importance of the volumetric efficiency, representing the efficiency of induction of the air-fuel mixture into the reciprocating-engine cylinders, was discussed earlier.Clearly, the more mixture mass in the displacement volume, the more chemical energy can be released and the more power will be delivered from that volume. During the Second World War, the mechanical supercharger was sometimes used with SI aircraft engines to increase the power and operational ceiling of American airplanes. Today supercharging is used with both Diesel engines and SI engines. The super charger is a compressor that supplies air to the cylinder at high pressure so that the as density in the cylinder at the start of compression is well above the free-air density. The piston exhaust gases are allowed to expand freely to the atmosphere through the exhaust manifold and tailpipe. The supercharger is usually driven by a belt or gear train from the engine crank shaft. 249 Figure 6. 11 shows a modification of the theoretical Otto cycle to accommodate mechanical supercharging. The supercharger supplies air to the engine cyclinders at pressure p7 in the intake process 7
1. The processes 4
5
6 purge most of the combustion gas from the cylinder.The most striking change in the cycle is that the induction-exhaust loop is now traversed counterclockwise, indicating that the cylinder is delivering net work during these processes as well as during the compressionexpansion loop. It should be remembered, however, that part of the cycle indicated power must be used to drive the ex ternal supercharger. The turbosupercharger or turbocharger, for short, is a supercharger driven by a turbine using the exhaust gas of the reciprocating engine, as shown schematically in Figure 6. 12. A cutaway view of a turbocharger is shown in Figure 6. 3(a). Figure 6. 13(b) presents a diagram for the turbocharger. Compact turbochargers commonly increase the brake power of an engine by 30% or more, as shown in Figure 6. 8, where the performance of an engine with and without turbocharging is compared. There, a substantial increase in peak torque and flattening of the torque-speed curve due to turbocharging is evident. For a supercharged engine, the brake power, BP, is the indicated power (as in Figure 6. 11) less the engine friction power and the supercharger shaft power: BP = DISP  IMEP  N ? Pm ?FP [ft-lbf /min | kJ/s] (6. 15) 250 where Pm is the supercharger-shaft mechanical power supplied by the engine (0 for a turbocharger). The IMEP includes the positive work contribution of the exhaust loop. The exhaust back pressure of the reciprocating engine is higher with a turbocharger than for a naturally aspirated or mechanically supercharged engine because of the drop in exhaust gas pressure through the turbine. The engine brake power increases primarily because of a higher IMEP due to the added mass of fuel and air in the cylinder during combustion.Intercooling between the compressor and the intake manifold may be used to further increase the cylinder charge density. Turbocharging may increase engine efficiency, but its primary benefit is a substantial increase in brake power. In a turbocharged engine, a wastegate may be required to bypass engine exhaust gas around the turbine at high engine speeds. This becomes necessary when the compressor raises the intake manifold pressure to excessively high levels, causing engine knock or threatening component damage. Thirty to forty percent of the exhaust flow may be bypassed around the turbine at maximum speed and load (ref. ). 251 252 6. 12 The Automobile Engine and Air Pollution Since the Second World War, concern for environmental pollution has grown from acceptance of the status quo to recognition and militance of national and international scope. Among other sources, causes of the well-known Los Angeles smog problem were identified as hydrocarbons (HC) and oxides of nitrogen (NOx) in exhaust emissions from motor vehicle reciprocating engines. As a result, national and California automobile air pollution limits for automobiles have been established and toughened.Prior to the Clean Air Act of 1990, the U. S. federal exhaust-gas emissions standards limited unburned hydrocarbons, carbon monoxide, and oxides of nitrogen to 0. 41, 3. 4, and 1. 0 g/mile, respectively. According to reference 12, today it takes 25 autos to emit as much CO and unburned hydrocarbons and 4 to emit as much NOx as a single car in 1960. The reference anticipated that, led by existing California law and other factors, futur e engine designs should be targeted toward satisfying a tailpipe standard of 0. 5, 3. 4, 0. 4 g/mile. Indeed, the 1990 Clean Air Act (refs. 15,16) specified these limits for the first 50,000 miles or five years of operation for all passenger cars manufactured after 1995. In addition to the regulations on gaseous emissions, the Clean Air Act of 1990 adopted the California standard for particulate matter of 0. 08 g/mile for passenger cars. The standards on particulates are particularly difficult for the Diesel engine, because of its of soot-producing tendency.The automobile air pollution problem arises in part because the reactions in the exhaust system are not in chemical equilibrium as the gas temperature drops. Oxides of nitrogen, once formed in the cylinder at high temperature, do not return to equilibrium concentrations of nitrogen and oxygen in the cooling exhaust products. Likewise, CO formed with rich mixtures or by dissociation of CO2 in the cylinder at high temperature does not respond rapidly to an infusion of air as its temperature drops in the exhaust system. Their concentrations may be thought of as constant or frozen.Unburned hydrocarbons are produced not only by rich combustion but also by unburned mixture lurking in crevices (such as between piston and cylinder above the top piston ring), by lubricating oil on cylinder walls and the cylinder head that absorbs and desorbs hydrocarbons before and after combustion, and by transient operating conditions. Starting in 1963, positive crankcase ventilation was used in all new cars to duct fuel-rich crankcase gas previously vented to the atmosphere back into the engine intake system. Later in the ? 0s, various fixes were adopted to comply with regulation of tailpipe unburned hydrocarbons and CO, including lowering compression ratios. In 1973, NOx became federally regulated, and exhaust gas recirculation (EGR) was employed to reduce NOx formation through reduced combustion temperatures. At the same time, HC and CO standards were reduced further, leading to the use of the oxidizing catalytic converter. Introduction of air pumped into the tailpipe provided additional oxygen to assist in completion of the oxidation reactions.In 1981, a reducing catalytic converter came into use to reduce NOx further. This device does not perform well in an oxidizing atmosphere. As a result, two-stage catalytic converters were applied, with the first stage reducing NOx in a near-stoichiometric mixture and the 253 second oxidizing the combustibles remaining in the exhaust with the help of air introduced between the stages. This fresh air does not the increase NOx significantly, because of the relatively low temperature of the exhaust.The three-way catalytic converter using several exotic metal catalysts to reduce all three of the gaseous pollutants was also introduced. The use of catalytic converters to deal with all three pollutants brought about significant simultaneous reductions in the three major ga seous pollutants from automobiles. This allowed fuel-economy-reducing modifications that had been introduced earlier to satisfy emission reduction demands to be eliminated or relaxed, leading to further improvements in fuel economy.Catalytic converters, however, require precise control of exhaust gas oxygen to near-stoichiometric mixtures. The on-board computer has made possible control of mixture ratio and spark timing in response to censor outputs of intake manifold pressure, exhaust gas oxygen, engine speed, air flow, and incipient knock. The oxygen, or lambda, censor located in the exhaust pipe upstream of the three-way converter or between the two-stage converters is very sensitive to transition from rich to lean exhaust and allows close computer control of the mixture ratio to ensure proper operation of the catalytic converter.Computer control of carburetors or fuel injection as well as other engine functions has allowed simultaneous improvement in fuel economy and emissions i n recent years. Thus, while emissions have been drastically reduced since 1974, according to reference 11 the EPA composite fuel economy of the average U. S. passenger car has nearly doubled; although this improvement has not come from the engine alone. Despite the hard-won gains in emissions control and fuel economy, further progress may be expected. EXAMPLE 6. 5 The 1990 NOx emissions standard is 0. grams per mile. For an automobile burning stoichiometric octane with a fuel mileage of 30 mpg, what is the maximum tailpipe concentration of NOx in parts per million? Assume that NOx is represented by NO2 and that the fuel density is 692 kilograms per cubic meter. Solution For the stoichiometric combustion of octane, C8H18, the air-fuel ratio is 15. 05 and the molecular weight of combustion products is 28. 6. The consumption of octane is mf = (692)(1000)(3. 79? 10-3)/ 30 = 87. 4 g/mile [Note: (kg/m3)(g/kg)(m3/gal)/(mile/gal) = g/mile. The concentration of NOx is the ratio of the number of moles of NOx to moles of combustion gas products: mole Nox /mole cg = (mNOx /mf)(mf / mcg)(Mcg /MNOx) = (0. 4/87. 4)(28. 6/46)/ (15. 05 + 1) = 0. 0001773 254 or 177. 3 parts per million (ppm). _____________________________________________________________________ Bibliography and References 1. Heywood, John B. , Internal Combustion Engine Fundamentals. New York: McGraw-Hill, 1988. 2. Ferguson, Colin R. , Internal Combustion Engines. New York: Wiley, 1986. 3. Adler, U. , et al. , Automotive Handbook, 2nd ed. Warrendale, Pa. Society of Automotive Engineers. , 1986. 4. Lichty, Lester C. , Internal Combustion Engines. New York: McGraw Hill, 1951. 5. Crouse, William H. , Automotive Engine Design. New York: McGraw-Hill, 1970. 6. Obert, Edward, Internal Combustion Engines, Analysis and Practice. Scranton, Pa. : International Textbook Co. , 1944. 7. Grosser, Morton, Diesel: The Man and the Engine. New York: Atheneum, 1978. 8. Nitske, W. Robert, and Wilson, Charles Morrow, Rudolph Diesel: Pioneer of the Age of Power. Norman, Okla. : University of Oklahoma Press, 1965. 9. Demmler, Albert W. Jr. , et al. , ? 989 Technical Highlights of Big-three U. S. Manufacturers,? Automotive Engineering. Vol. 96, No. 10, October 1988, p. 81. 10. Anon. , ? Ignition Quality of Diesel Fuels by the Cetane Method,? ASTM D 613-84, 1985 Annual Book of ASTM Standards, Section 5. 11. Amann, Charles A. , ? The Automotive Spark Ignition Engine-A Historical Perspective,? American Society of Mechanical Engineers, ICE-Vol. 8, Book No. 100294, 1989. 12. Amann, Charles A. , ? The Automotive Spark-Ignition Engine-A Future Perspective,? Society of Automotive Engineers Paper 891666, 1989. 13. Amann, Charles A. , ?The Passenger Car and the Greenhouse Effect,? Society of Automotive Engineers Paper, 1990. 14. Taylor, Charles Fayette, The Internal Combustion Engine in Theory and Practice, 2nd ed. , revised. Cambridge, Mass. : MIT Press, 1985. 255 15. Public Law 101-549, ? An Act to Amend the Clean Air Ac t to Provide for Attainment and Maintenance of Health, Protection, National Air Quality Standards, and Other Purposes,? November 15, 1990. 16. Anon. , ? Provisions? Clean Air Amendments,? Congressional Quarterly, November 24, 1990. EXERCISES 6. 1 Plot dimensionless piston position against crank angle for S/2L = 0. , 0. 4, 0. 3, and 0. 2. 6. 2* Obtain expressions for the piston velocity and acceleration as a function of the crank angle, constant angular velocity, and S/2L ratio. Use a spreadsheet to calculate and plot velocity and acceleration against crank angle for S/2L = 0. 5, 0. 4, 0. 3, and 0. 2. 6. 3 Determine the equation for the piston motion for a scotch yoke mechanism in terms of crank angle. Obtain an equation for the piston velocity for a crank that turns with a given angular velocity,
. 6. 4 Derive an equation for the Otto-engine net work by integration of pdV for the Air Standard cycle.Compare with Equation (6. 6). 6. 5* Use a spreadsheet to calculate and plot cycle ef ficiency as a function of compression ratio for the Diesel cycle for cutoff ratios of 1, 2, and 3. Indentify the Otto-cycle efficiency on the plot. Explain and show graphically from the plot how a Diesel engine can be more efficient than an Otto engine. 6. 6 A single-cylinder Air Standard Otto engine has a compression ratio of 8. 5 and a peak temperature of 3500Â °F at ambient conditions of 80Â °F and one atmosphere. Determine the cycle efficiency, maximum cylinder pressure, and mean effective pressure. 6. A six-cylinder engine with a compression ratio of 11 runs at 2800 rpm at 80Â °F and 14. 7 psia. Each cylinder has a bore and stroke of three inches and a volumetric efficiency of 0. 82. Assume an Air Standard, four-stroke Otto cycle _______________________ * Exercise numbers with an asterisk indic

Markets; Price determination and resource allocation Essay

Markets; Price determination and resource allocation - Essay Example The diagram below presents the picture of a market. Each variable is shown as interrelated to each other. Things to be produced are determined by the decisions of the buyers whether to purchase or not the available products like food, clothing and housing. Adjustments on product creation basically depends on the demand in the goods market. The method of production applied in creating the product are decided based on the level of competition of producers. Efficiency is the fundamental criteria in choosing for the method and it depends on the prices prevailing on factors of production like land, labor and capital and the prices of the output like food, clothing and housing. Producers would want to minimize cost to meet the price competition. Concerns regarding for whom the products are depend on the nature of supply and demand for inputs. Prices of inputs serve as income and ascertain the ability to purchase product. As a whole, a competitive market presents the price system brought ab out by correspondence of supply and demand and resources are allocated efficiently without intervention. Given the mechanisms of a market, the law of supply and demand enters to present information of market equilibrium. The law of supply and demand asserts that the equilibrium market price of a certain commodity is where supply equals demand. Equilibrium, on the other hand, is a state which when attained will be maintained. As shown in the succeeding diagram, the demand curve is negatively sloping because an increase in price reduces the amount of purchases. The demand curve shifts to the right because of several factors: increase in the price of substitutes, decrease in the price of complements, increase in income, change in preference for the product and special influences in favor of the product. The reverse causes the shift of the demand curve to the left. Looking at the diagram, the supply curve is shown to slope positively because a price increase stimulates production.

Start Up Shoe Business Essay Example | Topics and Well Written Essays - 2000 words

Start Up Shoe Business - Essay Example high heel, medium heel and low heel. All these three heights can be adjusted in a single product. The heel of this innovative product will be of hard plastic. It can be rotated to adjust the desired heights from three default sizes. This feature is the key attractive feature of the product. Manufacturing cost of this product would be $25. The company will manufacture this product through their own production unit. It will source leather and other required raw materials from the local suppliers. The quality of this multi-featured shoe will be of premium standard so that it can be positioned in the market among the premium brands. Quality will be checked by the expertise of the company’s manufacturing department. Quality control activity involves checking of quality of lather and pasting. These two components of a shoe determine the overall quality of the product. Customers’ feedbacks about the product at initial stage need to be evaluated to find out necessary revisions in production process or product raw materials. Quality control is one of the most important parts of production process. The quality control department always needs to focus on the industry quality standard and position the brand by comparing general feedback of the customers about quality of this product with respect to other brands. This product will be offered in the market with high standard of customer service like 6 months after sales warranty for any kind of damages of the shoe. New shoe will be provided in case of major damages within 6 months. Production flow of this product will be controlled on the basis of the demand of the product in the market. This strategy will be adapted to faster liquidation of the inventory and lower inventory cycle. Customers’ feedback will be given higher priority for further product development in terms of quality and design of this innovative product. Location HIGHLOWS shoe will be manufactured in Springfield, MA. Springfield is one of the most popular cities in England. The manufacturing unit of this product will be established in this location. Therefore, availability of resources needs to be analyzed in this location. For developing manufacturing and warehousing unit, a large hall will be leased for the next 5 years, and the interior of the hall will be designed. This includes separating the total space into two different divisions like manufacturing unit and warehouse. In the manufacturing unit, required machineries will be installed. Electric wearing will be fixed before the installation of the machineries. The generator facility will be necessary to ensure 24 hour electric supply. Renting the required building will be cost effective for this new business as the initial investment needs to be allocated in various activities like marketing, transportation, working capital management etc. Therefore, the cost of developing a building will be allocated in other operating activities. It is the most effective busi ness strategy for a new business to use rented fixed assets at initial stages, which also helps the company to easily withdraw the business in case of the worst case scenario in terms of market demand of the product. 2 to 3 vehicles are necessary for carrying raw material and also for supplying the products to the wholesalers as well as retailers. Again, to reduce initial capital requirements, this service will be outsourced from local transport service providers. To avoid delayed supply of raw materials, local suppliers will be involved in the production of this product. Legal Environment In order to obtain the licensing of the shoe business, an experienced attorney will have to be hired in order that all the legal requirements of the business are fulfilled and necessary

Empirical research Essay Example | Topics and Well Written Essays - 250 words

Empirical research - Essay Example The researcher should test these predictions using appropriate experiments. The results of these experiments will determine whether the conclusions of the empirical research are logically supported or not, depending on whether the theory that informed the hypothesis and predictions is supported by the results or not. In an empirical research, the conclusions are logical if the evidences that support them are logical and there are proper inferences and hypothesis (Goodwin, 2005). Conclusions that are not logically supported do not invalidate the entire study. It is imperative that a conclusion should be arrived at in a logical way, having followed a systematic approach to conduct research, for a study to be fully valid. However, this does not mean that an entire study will be invalid if the conclusions are not logically supported. There will be some confusion because the conclusions are not logically supported, but the study will still be valid to some extent because the research was based on observations and experiences. If these observations and experiences are not logically supported by the theory that informed the research, it does not mean that the entire research is invalid (Becker & Lazaric,

The Net Present Value (NPV) Assignment Example | Topics and Well Written Essays - 1500 words

The Net Present Value (NPV) - Assignment Example Therefore, discounting gives us the present value of money that is consequently useful in determining the net present value of any given project. d) Approximately 25% discount rate gives a zero NPV. This rate is the Internal Rate of Return and rates below this give a positive NPV hence showing the viability of a project. On the other hand, rates above 25% give a negative NPV and such projects should not be undertaken. This model could be extended by adding the effect of the energy bill on an individual’s disposable income. The higher the bill, the higher the cost implications on the individual’s net disposable income. A Decision Support System (DSS) is a computer-based information system that is used in organisations to assist in making decisions. A DSS is an interactive computerized system that supports the decision-making activities of decision makers using technology, documents, data and knowledge to complete their tasks. The 2012 London Olympics involved a lot of logistical arrangements that the organisers had to consider in order for the games to be a success. One aspect of the games that had to be carefully planned out was transport. Given the number of people that flocked the country and the city of London in particular, the transport infrastructure had to be well laid out so that there was order in the city. The road network, public transport and the effects of disrupting transport for businesses and other services had to be of particular interest to the organisers of the games. Additional or new resources have to be deployed in the areas related to incident detection and also the DSS for network managers. The transport legacy after the games should be of three types. First and foremost is the physical infrastructure that would be made to enhance the rail and road networks and vehicle fleets. There are also the enhancements to the operations and systems by designing and deploying state of the art techniques in order to detect

Marketing Concepts and Planning-- Apple IPods Assignment

Marketing Concepts and Planning-- Apple IPods - Assignment Example Features and benefits have long been the idea of improving sales and through promotional materials, however in today’s market pricing should be given much more emphasis by making it much more transparent to consumers in a variety of ways. This report identifies these proposed changes. The company’s mission is simple: Apple â€Å"recognizes that by integrating sound environmental health and safety management practices into all aspects of our business, we can offer innovative technological products and services while conserving and enhancing resources for future generations† (Lee, 2008, p.5). The objectives are to improve sales volumes through creative promotion, effective distribution, and to build consumer interest in mass market groups. The strengths of the iPod are in areas of innovation by remaining a step ahead of competition by updating features, memory and other important benefits for consumers. Research and development talent is an internal strength. Fortunately for Apple, competition is considerably weak and this is a major strength for the business! Weaknesses include, though not a fault of Apple, weakened economic conditions both domestically and internationally, posing a potential risk for future iPod (and iPad) sales. Additionally, minimal television advertising, despite the potential cost and time investment, is another weakness in regards to reaching more mass market customers. Threats to the iPod include the sudden resurgence of consumer use of auction websites such as eBay, creating a form of self-competition for budget-minded, mass market buyers as well as failure of retail partners to be more interactive in the sales/promotion process. These are external failures, however they definitely impact sales volume in certain market territories. As identified, segmentation for the iPod begins with identifying specific groups with

Capitalism Essay Example | Topics and Well Written Essays - 750 words

Capitalism - Essay Example This essay explores the United States plunged into an economic crisis in 2008 and 2009. This situation escalated, and it became an irresistible opportunity for the United States to pronounce the failure of the type of capitalism that had emerged towards the end of the twentieth century. The French President, Nicolas Sarkozy once said, â€Å"One had expected competition and abundance for everyone, but instead one got scarcity, the triumph of profit-oriented thinking, speculation and dumping." According to Sarkozy, the then economic crisis had signaled the return of the state and brought an end to public impotence illusions. Notably, economists regard the state of capitalism as one in which the governments are limited in controlling markets and posing property rights. The majority of political economists usually make strong emphasis on private property, wage labor, power relation, class, and the uniqueness in the historical formation of capitalism. Generally, capitalism encourages eco nomic growth, and the failure of our economy in 2008 should not be laid at Capitalism’s door. For one year that is between June 30, 2009, and July 1, 2008, the United States’ total economic output experienced escalating inflation that led to drop in the economy at an annual rate of 3.8 percent. Historically, this was the worst twelve months in economic decline that the United States had experienced since the year 1946. The rate of unemployment that had started declining in the year 2008 at the rate of five percent per annum doubled at the fall of the year 2010. This led to a fall in the number of jobs, a situation that lasted for about twenty one consecutive months. Towards the end, of May 2010, the median workers were relieved off their duties for a period of twenty-three weeks this is compared to ten weeks when United States had experienced depths of recessions; that is, between 1973 and 1975. All these economic hard times should not be pegged on capitalism, but on p oor governance and poor approach in resolving economic problems (Ingham 89). Shortly after the election of Ronald Reagan in the United States, a norm of a quarter century become operational, and this is the time or period when the free market approach to economic proved to be superior to economies of state directions (Ingham 43). During this period, the America’s income tax rate was halved; thus, reducing burdens from regulation. Notably, during the same period, the United States experienced a tremendous spread and growth of free market economy. This encouraged, free trade, which produced a remarkable stability and significant prosperity. Between the period 1983 and 2008, the gross domestic product experienced a growth of an average of 3.2 percent per year. It is only once within this period that the output of the United States fell in a calendar year; this only resulted when the percentage was being adjusted to two-tenths point (Ingham 104). Unfortunately, the assets of the real estate exploded resulting to varnishing of growth and stability. This drove the United States into a worse economic crisis. As President Sarkozy said, many would see this recession as an economic setback that could be as well regarded as a death blow (Ingham 119). The policies of conservative economy aimed at reducing the government power and liberating the private sector. Therefore, the introduction of the free market could have been regarded as a way of managing a state economy, but it was extremely brief. The surprising reversal of the economic down fall of the United States actually reached a point of no return in the year 2010. All these cannot or could not be blamed on capitalism, but on Americans who were only â€Å"profit oriented.† American is now convinced that the government has failed to solve the economic crisis; in fact, it has worsened the situation. It is liberal economic policies not conservativeness that is in a quick jeopardy (Ingham 342). Most of the Americans had lost faith in the federal government, and the majority had believed

Mandatory Mediation in Common and Civil Law Countries Essay

Mandatory Mediation in Common and Civil Law Countries - Essay Example Common law system countries use mandatory mediation more prevalently than civil law countries who proceed with considerable caution. The process of litigation is a complex process, which is usually avoided by many people. The civil justice system in the UK is already exhausted of cases, which have not been resolved because of various legal justifications. This negatively impacts on the involved parties because of the increase in the cost of the various court cases as time elapses. Mediation can reform the civil justice system of the UK because it ensures there is efficiency in the dispensation of justice. Consequently, savings are made and time management is upheld.In this respect, the aggrieved parties are satisfied with the mediation dispute resolutions. The mutual satisfaction of the concerned parties is never achieved in a trial setting. The introduction of mandatory mediation in civil cases aims at reducing the backlog of unresolved cases in courts of law. Mandatory mediation is a demonized element in many legal jurisdictions, although it does not affect the delivery of justice to the parties in the civil cases. Darbas (2010) asserts that the cost of mandatory intervention justifies the use of this method in the resolution of many cases. It is a better method compared to the trial because in the trial of a case, the judges can give a subjective ruling, which must be accepted. In mandatory mediation cases are resolved in an amicable manner without favor.

MBNQA Assignment Example | Topics and Well Written Essays - 250 words

MBNQA - Assignment Example This is by carrying out focus groups, gathering data from web users and analyzing trends of the call center. The Access Center established by AtlantiCare in 2006 is a good example of the benefits used in overcoming the challenges. The Center was established after a research conducted by a focus group stated that customers were frustrated when navigating and using the health care system (Duarte, Goodson & Dougherty, 2014, pg. 27). This effective approach resulted in AtlantiCare increasing its revenues, getting a high market share and increased satisfaction from their customers. Other organizations can learn that providing quality and constant improvement in the health care field is vital. These organizations need to make sure that their customers are well satisfied and served according to the needs they have. Moreover, offering effective healthcare is necessary. These organizations should realize that they need to improve community wellness and health by offering better services. Additionally, by training and recruiting well and qualified staff will enhance performance in these organizations as seen in AtlantiCare. Duarte, N. T., Goodson, J. R., & Dougherty, T. M. P. (2014). Managing innovation in hospitals and health systems: Lessons from the Malcolm Baldrige National Quality Award Winners. International Journal of Healthcare Management, 7(1),

Sherlock Holmes stories Essay Example for Free

Sherlock Holmes stories Essay Can the continued popularity of the Sherlock Holmes stories be explained by the similarity to modern television detectives? Discuss this statement with reference to The Speckled Band. The Sherlock Holmes saga has a huge inspirational impact on todays television detective stories. The reason why the Sherlock Holmes mysteries are so successful is because they contain many qualities of a classic mystery genre. It is a fair presumption if one was to say that the stories always follow a certain pattern and that in normal circumstances it is expected of the reader to lose interest, but Sherlock managed to obtain his popularity even to present day. A clear sign of how cleverly crafted Arthur Conan Doyle made these crime stories. Sherlock Holmes is a crime detective who has the ability to solve the hardest of criminal equations with the minimalist of facts, using his somewhat superb observational skills and his incredible method of scientific deduction. There is no mystery, my dear madam, said he, smiling. The left arm of your jacket is spattered with mud in no less than seven places. The marks are perfectly fresh. There is no vehicle save a dog-cart which throws up mud in that way, and then only when you sit on the left-hand side of the driver. Quoted from The Speckled Band. Holmes is a realistic and believable character, bringing the novels to life. Holmes always inspires a sense of confidence in other characters and indeed the reader as he shares a certainty of his attitude towards the mystery and the way he doesnt suffer fools gladly, always using his own initiative. This makes the reader feel as if Holmes is very confident about himself, thus making the reader confident and ultimately it makes them read on, a perfect example of Arthur Conan Doyles ability to captivate his readers. Always accompanying Holmes was his loyal companion and entrusted sidekick Dr Watson. With his old fashioned values and his consistent reliability, Watson is the perfect partner for Holmes. Watson shows a sense of amazement towards Holmess abilities and although he explains his deductions and predictions, Watson still could not do it himself. In terms of solving the crime, Watson seems rather useless. And as most of the time it seems as if Watson does not know whats going on inside Sherlocks mind, this adds suspense to the story. Arthur Conan Doyle has cleverly used Watson as a tool Holmes explains his methods and deductions to Watson and therefore to the reader. Watson is also the narrator of the story. Holmes appears in four novels and fifty-seven short stories. Arthur Conan Doyle got tired of writing about Holmes and so he killed him off in 1893 by having him fall to his death over the Reichenbach Falls in Switzerland. The stories had stop in production over one hundred years ago but still to this day they are very successful. Sherlock Holmes was modeled on and originated from Dr Joseph Bell, a surgeon in Edinburgh who had an extraordinary ability to deduce the backgrounds and occupations of his patients from minute details of their appearance. An excellent example of how the Sherlock Holmes saga has influenced modern crime story structures is Inspector Morse, a recently finished epic of mystery/crime television programs. Spanning 14 years, the ever-popular series shared a certain similarity to Holmes. Written by Colin Dexter and starring John Thaw (Left) as Inspector Morse and Kevin Whately as his trusted side kick Lewis (Right), Inspector Morse captivated viewers of all ages and class, again, very similar to Holmes. Morse and Lewis appear in thirty-three episodes and the stories are also available in other formats, such as paperback novels, paperback omnibuss and audio books as are the Holmes stories. Here is a description of the Speckled Band, one of the many successful Holmes stories written by Arthur Conan Doyle, and Deadly Slumber one of the thirty-three stories written by Colin Dexter, purposely to give a clear contrast of the similarities,: Deadly Slumber When Dr. Brewster is found dead in his car in his locked garage, everyone but Chief Inspector Morse writes the doctors death off as a suicide. A comment by the doctors wife troubles Morse, and he thinks the good doctors death anything but suicide. The chief inspectors suspicions are quickly confirmed by the autopsy it was murder. His investigation of the family soon uncovers a grudge against the family after a botched surgery on the daughter of Michael Steppings, a millionaire businessman who became a semi-reclusive following his daughter Avrils surgery that left her in a vegetative state. Steppings vowed to avenge his daughters condition on all parties involved in the surgery after losing a civil suit against the doctor and his clinic. Steppings goes so far as to send threatening letters to the doctor, but not the two other people on the surgical team the day of the operation. This oversight puzzles Morse. Steppings becomes Morses prime suspect and just as quickly is cleared by Morse and Sgt. Lewis. Then Morse is pointed in one direction by the family and another by his former prime suspect in Daniel Boyles extremely well crafted script. The last twenty minutes of Deadly Slumber is a roller coaster ride as the evidence leads Morse to one suspect after another. The adventure of the Speckled Band The speckled band leaves Helen Stoners twin sister in a state of occult horror just before her marriage. Now its Helens marriage and the same whistling sounds that her sister had heard in the nights preceding her death have come back to Stoke Moran. Her estranged stepfather seems to be the only culprit as the only other inhabitants of the old English stately home are the wild baboon and leopard. Holmes and Watson are quickly on the case, and come to the strange conclusion that it was a rare and highly venomous snake that was to blame for the mysterious deaths. As you can see both stories share the same basic structure, with the build up of suspense and the analysis of the deduction. Though perhaps one might say that the endings of the Holmes stories were somewhat more imaginative and dramatic in comparison to Morses more down to earth, realistic conclusions. To conclude, the continued popularity of the Sherlock Holmes stories, in my opinion, can be explained by the similarity to modern television detectives, as the modern television detectives are too similar to Holmes to dismiss as being created from a different origin. Taking into account the Sherlock Holmes stories were created over one hundred years ago it is fair to presume that modern day crime/mystery authors get there inspirations from the likes of Arthur Conan Doyle.

Education - Gymnasium Essay Example for Free

Education Gymnasium Essay Title Education is everywhere in the world. Individuals are learning here and there. Everyone would agree that education is a fundamental way of life. Education is obtained learning from multiple people such as parents, friends, teachers and even other surroundings. Every individual is educated and taught differently. Education should be built not only on the text that lies within a book, but should also be base with everyday life. Agree on McCullough and Oliphant perspectives because grades and how life is not revolved around grades. | Grades should not be based on how smart an individual is. Although Oliphant â€Å"Letter to a B Student† wrote â€Å"Your performance is generally assumed to correspond to the knowledge you have acquired and will retain (137). † They could be really intelligent or ignorant, but the letter grade they receive defines who they are. The letter grade that most individuals want to receive is an A, but others settle for the best they can receive. In McCullough speech â€Å"You’re Not Special† he says â€Å"Where good is no longer good enough, where a B is the new C, and where the midlevel curriculum is called Advanced College Placement (McCullough). † Even the ones that try their hardest on something might have a difficult time trying to comprehend the material. They worry about the grade they might receive and it stresses them out. There are individuals that just brush off or brag about the grade they received to make the others feel bad about themselves. For example, one student might have taken an exam that they studied for and failed; the other student did not study and passed. Individuals like to brag about their grades that they probably do not deserve. | How life is not revolved around grades because it is more than that to life. Oliphant said â€Å"Your grade does not represent a judgment of your basic ability or of your character (137). † People think that individuals such as students that do not make a high grade that they are not trying their best at what they are doing. There are a lot of wealthy people that are wealthy without grades defining them. Some of them could have made low grades when they were younger and people said they would not be successful it because they are failing everything. There are a handful of successful individuals that did not make it far in school, but is doing something good with their life. Individuals should not judge people because of several failing grades they could be more intelligent than everyone thinks they are. McCullough talks about â€Å"You’re not special, because everyone is (McCullough). †In conclusion, grades should not define a person on what they make on a paper. People should not judge a person by a low grade or high grade. Agreeing with McCullough and Oliphant perspectives. People are more intelligent than individuals think they are. | Works CitedMcCullough, David. â€Å"You’re Not Special. † Myfoxboston. com. Fox Television Stations, Inc. 6 June 2012. Web. 22 Feb. 2013. Oliphant, Robert. â€Å"Letter to a B Student. † Writing on the River: An Anthology. 3rd ed. Boston: McGraw-Hill, 2012. 136-142. Print.

The Brand Of Christian Louboutin Fashion Essay

The Brand Of Christian Louboutin Fashion Essay Christian Louboutin, sounds familiar? Has to be for the top shots of the fashion world, and for the ladies who are in vogue with the latest trends in the fashion world, and of course how can the footwear lovers not be conversant with this world famous brand! When asked whether you have any idea about this brand? or whether you would like to have a pair of Christian Louboutin? the answers by most of the fashion conscious ladies would be a unanimous yes! Founded in 1991, this French based company made it big in the competitive shoe business by taking the customised approach of shoe building. Before starting his own range of products by his own name, he used to work for same renowned designers like Chanel, Yves Saint Laurent, but a trivia is associated with his initiative to start this company. It is said that he once saw a notice at a museum saying that high heels were not allowed because they damage the floor, this infuriated him and he decided to take these people to task and started designing high heels, under his own brand name! Page 2 The man behind this world renowned brand, Christian Louboutin himself, was born and brought up in Paris, France. After finishing his academics, he started his career as an apprentice to the noted shoe designer Roger Vivier and as a freelance shoe designer for another celebrated shoemaker Chanel. After gaining considerable knowledge and experience in this line he kicked off with his own line of shoe wears, and opened the first store in paris in 1991. It is believed that being the only brother to three sisters played an influential role in developing his taste for fashion and appreciation for feminism. He was very much fascinated by this glamorous world of fashion and started making sketches at an early age, even neglecting his studies, as a result getting expelled from his school. But he hardly cared, as he knew he was destined to the next big name in the glam world. I didnt care because I felt so different from my peers. He said in an interview to Harpers Bazaar. He learnt a lot from Vivier. He once told Vivier taught me that the most important part of the shoe is the body and the heel. He also drew inspirations from extensive travelling to forbidden countries like Syria and Uzbekistan. Page 3 He famously explained his initiative to start his signature red soles which went on to become iconic in the industry in his application of U.S trademark. He quoted, In 1992 I incorporated the red sole into the design of my shoes. This happened by accident as I felt that the shoes lacked energy so I applied red nail polish to the sole of a shoe. This was such a success that it became a permanent fixture. He justified that he chose red over all the other colours because red is more than a colour. It is a symbol of love, of blood, of passion. One of the most reputed journals on shoe wears Footwear News stated that the brands signature red sole was a subtle status symbol and caught the fascination of many celebrities across the globe, even beating the big luxury brands. Throwing light on his idea of red soles he once said I did not really choose the red sole. Its more like the red sole came to me and had to stay with me. It started as a happy accident, which I kept. I was very inspired b y pop art so all my drawings were really full of colours. Even the leader in dolls Barbie came out with a special Louboutin edition with red heels! Page 4 The Louboutin shoes had a profound influence in the fashion domain. The red soles became such a huge hit that Christian Louboutin went on to the extent of trade marking his red sole heels in the U.S.A. in 2007 so that no other company could make and sell it. Apart from his trademark stilettos and red soles he also let his imagination fly and went on to try new and innovative things like he came up with an entire range with transparent heels in which it seemed that flower petals were floating. The brand is the most fiercely desired shoe wears among the ladies with having a great celebrity clientele. He says that a womans feeling in his shoes fascinates him and gives him a reason to design shoes for them. According to him, woman want to look sexy for other, more than themselves, and this feeling gives them self confidence. Another unique feature of his shoes is that it is entirely hand-made and customised, to the extent that even the trademark is etched without any intervention of mach ines. The impact is very well testified by the fact Jeniffer Lopez released a song called Louboutin. Page 5 The Christian Louboutin shoes have a life changing impact on the lives of the women. They also make some flats apart from their trademark heels. He has very strange ideologies on shoes. He has been many a times criticised for making such high heels which are supposed to be uncomfortable. But he retorts back by saying that he hates this entire concept of comfort. He believes that not wearing heel shoes just because they are not comfortable are like saying that Well, were not really in love, but were in a comfortable relationship. According to him comfort deprives you of many ideas and should be done away with. He puts light on the small intricacies of a womans nature. He says that when a woman tries a shoe and checks it out in mirror, shes not really checking whether the shoe suits her or not, in spite of the fact that she is trying a shoe. According to him When a woman buys a pair of shoes, she never looks at the shoe. She stands up and looks in the mirror, she looks at the breast, t he ass, from the front, from the side, blah blah blah. If she likes herself, then she considers the shoe. Page 6 The large number of fake Louboutin shoes and their replicas bears a testimony to the immense acceptability of the brand, and how desperately ladies want to grab this brand. These shoes make you feel charming and your existence totally vital. It makes you feel one notch above the horde of fashionistas. In fashion industry and in glamorous world these shoes have become a synonym to quality and layout. Starting with a single store in Paris there are more than twenty-five stores as of today, apart from the online stores in the U.K. His first famous client was the Princess of Monaco, who happened to be in the store in the presence of a media journalist, and from that day onwards, there was no looking back. The famous names which grace his clientele list include Madonna, Sarah Jessica Parker, Jennifer Lopez, Elizabeth Taylor, Catherine Deneuve Cher, Princess Caroline, New York-based designer Diane von Furstenberg and, Gwyneth Paltrow just to name a few. Among these there were some who wore these shoes on the most important day of their lives, their wedding day!