Internal Combustion Engines. Allan T. Kirkpatrick

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Appendix F contains a listing of the program FourStrokeOtto.m, which iterates through the above four‐stroke Otto gas cycle equations to determine the cycle pressures, temperatures, and the overall thermal parameters.

      Example 2.3 Four‐Stroke Otto Cycle

      Compute the volumetric efficiency, net thermal efficiency, residual fraction, intake stroke temperature rise , and the exhaust stroke temperature decrease, , of an engine that operates on the ideal four‐stroke Otto cycle. The engine is throttled with an inlet pressure of 50 kPa and has an inlet temperature of 300 K. The exhaust pressure is 100 kPa. The compression ratio, 10. Assume an energy addition of 2500 kJ/ and 1.3. Plot the volumetric efficiency, net thermal efficiency, and residual fraction as a function of the intake/exhaust pressure ratio for .

      Solution

      The program input portion of FourStrokeOtto.m is shown below.

       four-stroke Otto cycle model Input parameters: Ti = 300; inlet temperature (K) Pi = 50; inlet pressure (kPa) Pe = 100; exhaust pressure (kPa r = 10; compression ratio qin = 2500; energy addition, kJ/kg (gas) R = 0.287; gas constant (kJ/kg K) f = 0.05; guess value of residual fraction f Tr = 1000; guess value of exhaust temp (K) tol = 0.001; convergence tolerance ....

For the above conditions, as shown in Tables 2.3 and 2.4, the computation indicates that the intake stroke temperature rise, , is about 45 K, and the exhaust blowdown temperature decrease, , is about 280 K. The volumetric efficiency, , the net thermal efficiency, , and the residual fraction, 0.053.

Table 2.3 State Variables for Four‐Stroke Example 2.3