Generic functions for fuel consumption and engine-out emissions of HC, CO and NOx of spark-ignition engines

The prediction of fuel consumption and engine-out emissions of spark-ignition engines from characteristic relationships has been investigated. For spark-ignition engines operating on homogeneous mixtures, indicated specific fuel consumption based on gross indicated power is related to compression ratio and spark timing relative to optimum values. The influence of burn rate is largely accounted for by differences in spark timings required to phase combustion correctly. For engine-out emissions of HC, CO and NOx, generic functions have been derived that relate the emissions index in each case to air-fuel ratio, spark timing relative to the optimum and burned gas fraction present during compression. The effects of exhaust gas recirculation and residual gas dilution are accounted for. Brake specific performance maps can be generated. This requires knowledge or predictions of calibrations, cylinder volumetric efficiency, rubbing friction, auxiliary loads and exhaust back pressure. A closed set of equations and illustrative results are given.