Search Results

An analytical framework is assembled, suitable for the quantitative evaluation of engine performance (fuel consumption, WOT, NOx emissions) and the appreciation of engine performance sensitivities and trade-offs. Emphasis is placed on complete, conventional spark-ignition engines in production. The framework is assembled primarily from existing and well documented analyses that deal effectively with various specific aspects of the internal combustion engine. A new and non-conventional approach is followed in the treatment of engine breathing dynamics. The engine-manifold system is treated and documented as a sequence of many small but finite control volumes, each obeying individually the field form of conservation equations. The qualifications of the analytical framework are evaluated by an extensive comparison of analytical results to dynamometer test results of engines with fairly well known design and control parameters, which are also presented.

The subject is treated on the basis of detailed engineering test data regarding components and parameters of 1975 autos. The applicability of the simulation approach is examined by extensive comparisons with integrated vehicle test results. It is found that fuel economy, for the EPA driving schedules, is adequately simulated with 5% to 10% uncertainties. Uncertainties of the same magnitude are also encountered in performance simulations. Larger uncertainties are evident in the simulation of emissions. NOx prediction has an uncertainty up to 25% but no significant bias, while CO and HC are very substantially over-predicted and under-predicted respectively. Excepting HC and CO, several applications are made in the evaluation of sensitivities to various auto components and parameters. Evaluations are made of changes in auto weight, engine displacement and rear axle ratio, considered individually and in combinations.