Emissions And Engine Operation Behaviors Of HEV With Different Topology

With the increasingly strict emission and fuel consumption regulations,hybrid power will be the mainstream technology of passenger vehicle power for a long time in the future.Today’s hybrid vehicles have complex technology,numerous configurations,and frequent engine start and stop,which pose great challenges to control strategy,engine development and emission.Therefore,this paper selects four types of hybrid electric vehicles with typical configurations on the market to study vehicle emission characteristics and engine operating characteristics under different cycles.The monitoring system of oil temperature,coolant temperature,exhaust temperature,engine speed,engine load and other parameters was built on a chassis dynamometer,and the gaseous emission and PN emission were collected simultaneously.Based on the WLTC cycle,the causes and rules of gaseous emission and PN emission of hybrid electric vehicles with different configurations were studied.The results show that THC and CO emissions of HEVs of all configurations are the most prominent in the first start(cold start phase),while the peak of gaseous emission concentration is not obvious in the subsequent start process.The peak NOx concentration is more concentrated in the load increasing and large load operation area.CO emission deteriorates when driving at high speed.The concentration of PN in the first start,and frequent start-stop had little effect on gaseous pollutants,but increased the emission of PN.The concentrations of PN emission and CO emission in highpower cold start are much higher than those in traditional cold start stage.The causes of nuclear particles and accumulated particles in extended-range hybrid electric vehicle were analyzed.In addition,the miniaturized range-extender presents a new challenge for TWC and oil due to the presence of high-temperature oil and exhaust.Secondly,the operating characteristics of HEV engines with different configurations are studied based on different driving cycles.The research shows that there are great differences in the operating regions of engines with different configurations,showing "point","plane",maximum fuel consumption curve and "combination of point and plane".The engine speed of range extenders(series),parallel and series-parallel hybrid electric vehicles is correlated with their vehicle speed to some extent,but the correlation of power split hybrid electric vehicles is small.The influence of high-power cold start on the engine of series-parallel hybrid vehicle was analyzed from the Angle of coolant temperature and speed.It was found that compared with the traditional cold start,the engine operated at a high speed in the environment of low coolant temperature,which might aggravate the wear between engine parts.Power-split hybrid vehicles had the most start-stop times,followed by series-parallel hybrid vehicles,parallel hybrid vehicles and extendedrange(series)hybrid vehicles had the least start-stop times.The peak concentration of PN in GDI engine was much higher than that in MPI engine.In order to achieve the balance between fuel saving and emission reduction,the engine selection of hybrid vehicles with different configurations can be considered from the perspectives of emission and start-stop.The research significance of this paper lies in the comprehensive analysis of the operating characteristics of the hybrid engine under different configurations,and the analysis of its emission rules,which provides support for the subsequent thermal management development of interactive assembly and the exploration of the hybrid efficient special engine.