Gasoline Engine and Aftertreatment Modeling and Control

This article discusses the design of control system components for gasoline engines. Gasoline or, more precisely, spark ignition engines power a large majority of personal vehicles sold worldwide. A major task for the automakers is to provide good drivability and fuel economy while meeting increasingly stringent emission requirements. Achieving low emissions requires a significant reduction in cold start emissions and employment of catalytic converters to reduce tailpipe emissions once the engine is warmed up. The catalysts are loaded with precious metals – typically platinum, palladium, and rhodium. They achieve very high conversion efficiencies, but only if the engine is operated very close to stoichiometry that corresponds to the air-fuel ratio of about 14.6 for gasoline and of 9 for ethanol. Design of a control system component requires that an appropriate model be developed. The models range from very simple low-order, linear for the inner loop to a partial-differential-equation based model for the catalyst. In general, feedback controllers tolerate and even benefit from simpler models. Feed-forward control, estimation, diagnostics, and failure mode management requires more elaborate models.