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This paper describes a simulation guided design methodology for developing direct injection combustion systems of gasoline engines. The first step is the optimization of engine gas flow. The intake port is optimized by CFD simulations to compromise the engine breathing capacity and its tumble flow. Secondly, the piston crown shapes and the injection system designs (injection pressure, hole number, hole size and orientations) are optimized based on dedicated CFD simulation results. Thirdly, different injection strategies are used at different engine operating conditions to achieve best engine performance, such as split injections being used at cold starting and catalyst heating period to realize stratified charge combustion for fast catalyst light-off, and a single injection being used to achieve homogeneous mixture combustion at almost all other operating conditions.

Engine exhaust systems need to undergo continuous modifications to meet increasingly stricter regulations. In the past, much of the design and engineering process to optimize various components of engine and emission systems has involved prototype testing. The complexity of modern systems and the resulting flow dynamics, and thermal and chemical mechanisms have increased the difficulty in assessing and optimizing system operation. Due to overall complexity and increased costs associated with these factors, modeling continues to be pursued as a method of obtaining valuable information supporting the design and development process associated with the exhaust emission system optimization. Insufficient kinetic mechanisms and the lack of adequate kinetics data are major sources of inaccuracies in catalytic converters modeling.

Automotive exhaust emission regulations are becoming progressively stricter due to increasing awareness of the hazardous effects of exhaust emissions. The main challenge to meet the regulations is to reduce the emissions during cold starts, because catalytic converters are ineffective until they reach a light-off temperature. It has been found that 50% to 80% of the regulated hydrocarbon and carbon monoxide emissions are emitted from the automotive tailpipe during the cold starts. Therefore, understanding the catalytic converter characteristics during the cold starts is important for the improvement of the cold start performances This paper describes a mathematical model that simulates transient performances of catalytic converters. The model considers the effect of heat transfer and catalyst chemical reactions as exhaust gases flow through the catalyst. The heat transfer model includes the heat loss by conduction and convection.