Influence of air/fuel ration on cyclic variation and exhaust emission in natural gas SI engine

摘要

Reducing pollutant emissions of passenger cars is one of the main tasks of manufacturers. One way to reduce emissions is to operate SI engine in lean combustion with natural gas. The objectives of this work are, to investigate differences between natural gas and gasoline exhaust emissions and combustion, and then, to show the accuracy of a zero-dimensional two zones thermodynamic model for NO_x predictions. Data are acquired in a 4-cylinder, bi-fuel engine. With natural gas, SI engine operates at lower ratio than gasoline leading to a reduction in NO_x emission. The thermodynamic model calculates NO_x emissions and time burning duration from the cylinder pressure. Typical differences between natural gas and gasoline have been found. With natural gas flame ignition duration decreases and flame propagation duration increases. An improvement of NO_x formation model has been developed by locking into account cycle-to-cycle cylinder pressure in. The model predicts correctly NO_x concentration within 15% even when. Varying fuel-air ratio and spark timing.