Numerical Investigation On Mixture Formation Of Two-stroke LPG Direct Injection Engine Used As Range Extender For Electric Car

Compared with four-stroke engine, the two-stroke direct injection engine has the advantages of high speed, high power density, simple structure and so on. However, retrieval show that making full use of these advantages to develop the two-stroke engine into power source of generator unit for extended-range electric vehicle is almost not seen. When the two-stroke direct injection engine works as an extender range mode at high speed and uses gasoline as fuel which is injected after exhaust port closing, the mixture may not be homogeneous enough due to less evaporation time. Liquefied petroleum gas (LPG) has low boiling point and high saturation vapor pressure. When the liquid LPG is directly injected into engine cylinder, flash boiling occurs which is very helpful to accelerating the fuel-air mixing. In particular, LPG is also very easy to carry and store. To this end, this article select a two-stroke engine as the extender of light electric vehicle, and the two-stroke engine is fueled with directly injected LPG. The mixture formation process of two-stroke LPG direct injection engine is investigated.The process of mixture formation is numerically simulated after the calculation model is validated by optical experiment results. The effects of fuel injection timing on the mixture formation are investigated. The results show that, under the conditions that the fuel short-circuiting is avoided, the injection timing of 50° CA ABDC for engine start and warming (2000 rpm), and 40° CA ABDC for running as the power source of generator (4800 rpm) are appropriate. The fresh mixture is locked in the cylinder when the exhaust port is closed (73° CA ABDC) and the homogeneous mixture can be formed at spark timing.Put forward a wall guided combustion system used in two-stroke engine which different from traditional forms of crankcase scavenging structure. Use the Fire V2011 software, numerical analysis of the velocity and concentration fields when choosing different injection start time. The results show that idle speed condition, injection timing of 60° CA BTDC injection, working condition of generator set, injection timing of 60° CA BTDC-70° CA BTDC is appropriate. In this case, the stratified lean mixture with overall AFR 40, which is however rich and ignitable near spark plug, can be formed near the end of compression. Further analysis on the velocity and concentration fields are done for the engine running under start and warming (2000rpm)?the power source of generator (4800 rpm) and full load (6000rpm) conditions. The results show that by using optimized injection timing for each running condition, the fresh mixture can be locked in the cylinder when the exhaust port is closed (65° CA ABDC) and the homogeneous mixture can be formed at spark timing.Put forward a spray guided combustion system used in two-stroke engine which different from traditional forms of crankcase scavenging structure. The different distribution of 6-well injector of two-stroke "spray guided" is studied in two-stroke "spray guided" DI engine in cylinder stratified and homogeneous mixture formation. The results show that the six non-uniform distribution of injector is more suitable for two stroke "spray guided" DI engine.