Study on effect of fuel switch process on transient emissions for LPG engine

Due to the difficult cold start for LPG engine, most of LPG passenger cars adopt gasoline auxiliary start and automatically switch to LPG after engine warm-up. Therefore, the optimized fuel switch conditions are critical to the development of LPG passenger car meeting with National Emission IV legislation. This paper presents the effects of coolant temperature, engine speed and torque on the switch process by means of lots of experiments. The results show that they bring the transient fluctuation of excess air coefficient during switch process. Thus the fluctuation amplitude and duration have direct impact on engine tailpipe emission. If the excess air coefficient fluctuation amplitudes go beyond the high conversion efficiency window of three-way catalyst, the engine's transient emission deteriorates. Above all, the proper control of the excess air coefficient fluctuation amplitude is significant to lower engine emission during fuel switch process.