How Individual Valve Timing Events Affect Exhaust Emissions

The effects of individual valve timing events on the exhaust emissions of a single-cylinder engine were determined at part-load, low-speed, test conditions. The time of opening and closing of the intake and exhaust valve was varied independently over a wide range while maintaining the other three valve timing events at conventional values. Significant changes in the induction, combustion, and exhaust processes resulted from valve timing changes. Of particular interest are the changes in engine exhaust emissions of hydrocarbons and nitric oxide under part load operation. The interactions between numerous engine parameters and valve timing are also discussed. Engine load, speed, spark advance, exhaust pressure, intake system configuration, mixture temperature, and external exhaust gas recirculation effects are included in this paper.