| With the rapid development of automobile industry, oil resources shortage and environmental pollution has become increasingly prominent, Which has posed a severe challenge to conventional oil fuels and combustion mode of The engine of vehicle, forcing people to speed up the alternative fuel of vehicle engine development and application process. Because of low pollution emissions,abundant resources,low price of natural gas, therefore be a potential development of alternative fuels. However, there are some problems that the power and economy of CNG engine get worse compared to gasoline engine need to be solved.At present, research on CNG engines of experts and scholars in domestic and foreign under full load condition mostly, and rarely research on the performance of CNG engines in the medium and low load conditions .The gas exchange process directly influences on the power, fuel economy and emissions of CNG engines. The intake system and the valve timing system have direetly effect on the volumetric effieiency of the CNG engine, which is one of the factors in the air flow in loop scavenged process. The single fixed structure of intake manifold and fixed valve timing state of the current conventional CNG engine are changed, It can be better ventilation to improve the quality of gas exchange of CNG engine, and improving the volumetric efficiency, when the technology of variable intake manifold and variable valve timing technology is utilized, thus improving the power of CNG engine to some extent.In this paper, a gasoline engine simulation model is created based on GT-Power soft . The fuel supply and injection system of the original gasoline engine is improved, according to the physical and chemical characteristics of CNG . The new fuel depot of ethane and butane in the software is created,a simulation system of CNG engine is established .The affect of intake and exhaust system and valve timing on power and economy of CNG engine at different load is analyed based on simulation system , and propose a corresponding improvement program.After optimization on the intake and exhaust system and valve timing of CNG engine,the performance of CNG engine under different loads is improved at varying degrees. After optimization the maximum torque and maximum power of optimized CNG engine are increased by 8.2%, 11.2% compared with the former respectively, and the gas economy fell by 3.1% at 25% load; the maximum torque and maximum power of optimized CNG engine are increased by 15.1%, 14.2% compared with the former respectively, and the gas economy fell by 6.4% at 50% load; the maximum torque and maximum power of optimized CNG engine are increased by 9.1%, 11.9% compared with the former respectively, and the gas economy fell by 5.1% at 100% load.The results of this article fill some gaps on the numerical simulation of working process of CNG and optimization of the intake and exhaust system structural parameters and valve timing in the domestic, and providing a reference for a simulation of nature gas engine. It also has some referencing value for the numerical simulation of other alternative fuel engines. |
