Variations in Exhaust Emissions and Combustion Stability with Control Parameters during Idle Operations of an SI Engine
18ICES/036

Abstract

Rapid warm up of catalyst and improved combustion stability are crucial factors for reduction of harmful exhaust emissions during cold start of an SI engine. Previous studies showed that retarded ignition timing and reduced valve overlap produced higher exhaust gas temperatures resulting in faster light-off of catalysts. This study focuses on analysis of exhaust emissions with changes of ignition and exhaust valve timings during idle operations. Pressure variations in the combustion chamber are also measured and analyzed to investigate combustion stability. A combustion analyzer, designed for this study, converts pressure data to combustion characteristics such as imep and COV. These data provide better understandings of combustion with engine control parameters. Changing effects of exhaust valve timing on residual gas fraction are also investigated using transient CFD analysis. Experimental results and numerical analysis show that proper advance of exhaust valve timing is effective to improve COV and CO emissions due to a decrease in mass fraction of residual gas. HC emissions are closely related to ignition timing. Both ignition and exhaust valve timings influence NOx emissions. It is expected that optimal control of ignition and exhaust valve timings in the cold start period and idle operation will reduce harmful exhaust emissions and improve combustion stability of the engine

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