Combustion engines isentropic

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. 

The Otto cycle is a spark-ignition reciprocating engine consisting of an isentropic compression process, a constant-volume combustion process, an isentropic expansion process, and a constant-volume cooling process. The thermal efficiency of the Otto cycle depends on its compression ratio. The compression ratio is defined as r= Fmax/f min- The Otto cycle efficiency is limited by the compression ratio because of the engine knock problem. 

The ideal Brayton gas turbine cycle (sometimes called Joule cycle) is named after an American engineer, George Brayton, who proposed the cycle in the 1870s. The gas turbine cycle consists of four processes an isentropic compression process 1-2, a constant-pressure combustion process 2-3, an isentropic expansion process 3-4, and a constant-pressure cooling process 4-1. The p-v and T-s diagrams for an ideal Brayton cycle are illustrated in Fig. 4.1. 

Heat engines that use gases as the working fluid in an open system model are treated in this chapter. The modern gas turbine engine operates on the Brayton cycle. The basic Brayton cycle consists of an isentropic compression process, an isobaric combustion process, an isentropic... 

These thermodynamic processes, as they occur in useful machines, arc not often of the exact polytropic form desired. For example, an isentropic process, which is exemplified, at least theoretically, by expansion of the burned gases after the explosive combustion in the gasolme engine, is modified slightly by die interchanging of heat between gases and cylinder wall, whereas a true isentropic has no heat either added or rejected in this way. ITic particular polytropic curve that would suit these conditions of expansion would depart somewhat from the adiabatic form. 

The idealization of the gas-turbine engine (based on air, and called the Brayton cycle) is shown on a PF diagram in Fig. 8.12. Step AB is the reversible adiabatic compression of air from Pa (atmospheric pressure) to Pb- In step BC heat Qbcz replacing combustion, is added at constant pressure, raising the air temperature prior to the work-producing isentropic expansion of the air from pressure Pc to pressure Po (atmospheric pressure). Step DA is a constant-pressure cooling process that merely completes the cycle. The thermal efficiency of the cycle is ... 

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