The Characteristic of Transient HC Emissions of the First Firing Cycle During Cold Start on an LPG SI Engine 2006-01-3403

The first firing cycle is very important for cold-start. Misfire of the first firing cycle can lead to significant HC emissions and affect the subsequent cycles. The first firing cycle for Gasoline SI engine have been reported in many studies. Liquefied petroleum gas (LPG) as an alternative fuel has been widely used in commercial vehicles during the last decade. However, the properties of the first firing cycle for LPG SI engine have been seldom reported. This paper presents an investigation of the characteristics of transient HC emissions of the first firing cycle during cold start on a LPG SI engine. A fast-response flame ionization detector (FFID) was applied to measure transient HC emissions of the first firing cycle in the exhaust port of the engine. At the same time, the transient cylinder pressure and instantaneous crankshaft speed of the engine were measured and recorded. The results show that the transient HC emission of the first firing cycle displays a moderately sensitive pattern varying with the excess air factor in a wide range. The minimum exhaust HC emissions almost correspond to the maximum peak cylinder pressure occurrence. The HC emissions are increased greatly when the mixture ratio is too lean or too rich. For fixed Air/Fuel as the spark timing is retarded, the HC emissions rise to a maximum and then reduce due to significant combustion in the exhaust stroke, and the HC emissions rise hugely on set of the misfire cycle with too late spark timing.