Engine, pressure-volume work

Since q2>0 and q < 0, and q2 is greater in magnitude than qu the cyclic engine produces a net amount of (negative) work. From our earlier discussion of pressure-volume work, we know that the area enclosed by the cycle in a p-V plot gives the magnitude of this work.p... 

Fig. 15.2. For each mole of reactants converted into products, a certain amount of heat is converted into work. More heat is converted into work in the system which is subject to external pressure variations and which produces pressure-volume work [mode (b)]. The figure is drawn for an endothermic reaction for which the net quantity of heat flowing from the reservoir to the system (reactor tank and heat engine) is larger than...

A The combustion of gasoline within an engine s cylinders does pressure-volume work that ultimately results in the motion of the car. 

Carnot cycle The idealized reversible cycle of four operations occurring in a perfect heat engine. These are the successive adiabatic compression, isothermal expansion, adiabatic expansion, and isothermal compression of the working substance. The cycle returns to its initial pressure, volume, and temperature, and transfers energy to or from mechanical work. The efficiency of the Carnot cycle is the maximum attainable in a heat engine. It was published in 1824 by the French physicist Nicolas L. S. Carnot (1796-1832). See Carnot s principle. 

Engineers and scientists who work with gases at high pressures often cannot use the ideal-gas equation to predict the pressure-volume properties of gases because departures from ideal behavior are too large. One useful equation... 

At the root of the classical thermodynamics of engines is the fact that work is an important and measurable quantity. However, work, while measurable, is rarely predictable. The work performed by a gas expanding in an engine piston can depend on pressure, volume, temperature, speed of the piston motion, frictional forces, and other factors in complex ways that are not fully understood. 

The four cylinders of a new type of combustion engine each have a displacement of 2.50 L. (The volume of the cylinder expands 2.50 L. each time the fuel is ignited.) (a) If the pistons in the four cylinders are each displaced with a pressure of 1.40 kbar and each cylinder is ignited once per second, how much work can the engine do in 1.00 minutes (b) Is the work positive or negative with respect to the engine and its contents ... 

One way to simplify the calculation of the net work of the cycle and to provide a comparative measure of the performance of an Otto heat engine is to introduce the concept of the mean effective pressure. The mean effective pressure (MEP) is the average pressure of the cycle. The net work of the cycle is equal to the mean effective pressure multiplied by the displacement volume of the cylinder. That is,... 

An engine operates on an Otto cycle with a compression ratio of 8. At the beginning of the isentropic compression process, the volume, pressure, and temperature of the air are 0.01 m, llOkPa, and 50°C. At the end of the combustion process, the temperature is 900°C. Find (a) the temperature at the remaining two states of the Otto cycle, (b) the pressure of the gas at the end of the combustion process, (c) the heat added per unit mass to the engine in the combustion chamber, (d) the heat removed per unit mass from the engine to the environment, (e) the compression work per unit mass added, (f) the expansion work per unit mass done, (g) MEP, and (h) thermal cycle efficiency. 

Find the pressure and temperature of each state of an ideal Diesel cycle with a compression ratio of 15 and a cut-off ratio of 2, and a supercharger that compresses fresh air to 20 psia before it enters the cylinder of the engine. The cylinder volume before compression is 0.16 ft. The atmosphere conditions are 14.7 psia and 70°F. Also determine the mass of air in the cylinder, heat supplied, net work produced, MEP, and cycle efficiency. 

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