Performance and Emission Predictions for a Multi-Cylinder Spark Ignition Engine with Catalytic Converter

A mathematical model is developed to represent an oxidizing catalytic converter in the exhaust system of a spark ignition engine in which the flow is non steady. By using the basic mass transfer, heat transfer and chemical reaction rate equations on the path lines the heat generated at the catalyst surface and the friction factor are allowed for in the generalized non steady flow relations using the method of characteristics. The model is included in a multi-cylinder engine simulation program. Secondary air injection into the exhaust system is represented by a simple mixing process without chemical reaction. A series of tests were carried out on a four cylinder two litre engine with a carbon monoxide and hydrocarbon oxidizing converter and secondary air injection. Comparison of results between experiments and computer calculations shows excellent agreement when the converter is new, but that if the catalyst surface is poisoned or aged the hydrocarbon prediction deteriorates. The carbon monoxide predictions, however, remain fairly good. The tests showed that the CO levels entering the exhaust pipe are dependent on the engine condition. Prediction of the overall engine performance and emission levels is very good. The comprehensive simulation program offers an excellent tool for examining practical locations of catalytic converters.