Parametric Studies of Some Operating Variables on Spark-Ignition Engine Performance

A spark-ignition engine simulation code was used to study the effects of varying the following engine operating parameters-compression ratio, fuel-air equivalence ratio, residual mass fraction, and start of heat release/ignition timing on an individual basis on the performance of a 5.734 L, V-8 spark-ignition engine. The two-zone model was used where the same traverses the charge resulting in burned and unburned zones. The unburned zone contains the reactants (fuel and air), and there is no reaction between the constituents. The burned zone consists of the products of combustion and dissociation. The results of the present work show that maximum pressure and temperature occur at fuel-air equivalence ratio, of 1.01. Furthermore, the study shows that retarding or advancing the ignition timing from maximum brake torque causes a reduction in the power output of the cycle (indicated mean effective pressure) and hence in the cycle thermal efficiency as well. In general, it was observed that the computed results under estimated the measured values of the indicated mean effective pressures as follows: at , the computed results were between 5 and 6.86% lower than the measured engine data even though the qualitative trend was in excellent agreement with it, whereas the values of the measured indicated mean effective pressure were about 6.86-16.51% higher than the simulated results for fuel-air equivalence ratio in the range . The data reported indicate that in the range the indicated thermal efficiency, , increases, whereas the indicated thermal efficiency has an approximate inverse relationship with the fuel-air equivalence ratio, , that is, in the range . The other results from this study are summarized in the conclusion.