Study On Working Process And Intake Uniformity Of Natural Gas Engine

With the increase of car ownership, automobile exhaust has become one of the main air pollution sources in China. A large area of haze and fog weather in China caused by automobile exhaust, already have serious influence on the health of people. Environmental pollution has become the price of the rapid development of Chinese economy, and it produce a lot of trouble to the Chinese government. Natural gas as vehicle fuel has many advantages, such as easy to burn, low pollution emission, lower greenhouse gas emissions, broad source, etc.In this paper, focused on6108natural gas engine, various three-dimensional calculation models for combustion system, including intake port, were designed. The process of intake, combustion were both simulated, and the influence of different geometric parameters of combustion chamber on the flow movement in engine cylinders and combustion process was analyzed. One-dimensional model of working process was established for6108natural gas engine, and the accuracy of the model was also verified. Based on the model of working process, in order to improve the dynamic performance, economy, emission performance of the engine, the valve timing of6108engine was selected optimally. In order to improve the low-speed torque, the turbocharger of the engine was matched, and the influence of various arrangement forms of inlet and exhaust system on intake uniformity of engine was studied.The calculation results of three-dimensional combustion process show that appropriate increase of squeeze flow area of combustion chamber is more beneficial to make the movement of gasflow in cylinder more strengthened, and is also good for the fast spreading of subsequent flame propagation. But the oversize of squeeze flow area of combustion chamber cause that flow vortex center of cylinder cross section is close to the axis of cylinder. If that, the spread of the flame propagation within the cylinder will be under restrictions. The simulation results reveal that structures of scheme one and scheme two are more beneficial for the formation of airflow movement in cylinder and fast spreading of flame propagation.By analyzing the effect of valve timing to engine comprehensive performance, inlet valve open time was selected optimally. The starting crank angle of inlet valve open is15°before the top dead center, and the closing crank angle of inlet valve close is20°after the top dead center. The starting crank angle of valve exhaust open is53°before the top dead center, and the closing crank angle of valve exhaust close is12°after the top dead center. Those cases are in consideration of dynamics, fuel economy, emission. Turbocharger after optimal matching works in high efficient area, stay away from the surge line. The turbine working in high efficient area is beneficial for improving the low-speed torque, which is more suitable for city bus operation mode.The calculation results of engine intake uniformity show that the middle inlet of intake manifold and the middle inlet of exhaust manifold are more beneficial for the improvement of intake uniformity for engine cylinders; Working ununiformity of natural gas engine mainly caused by the structure of intake system under whole external characteristic of operation; However, the structure of exhaust system has impact on intake process, residual gas, pumping loss, which will further affect on work capacity of the engine. Especially at high speed, distribution unevenness of intake charge and unevenness of performance ability increase with the system arrangement of the right side intake system and exhaust system.In conclusion, focused on the6108natural gas engine, combustion system, valve timing, turbocharger matching, as well as distribution evenness of intake charge of engine cylinders was carricd out. Structural parameters of combustion chamber and valve timing, which is in consideration of dynamics, fuel economy, emission, were finally determined. In order to improve the low-speed torque, the turbocharger of the engine was matched. By improving the intake and exhaust system arrangement, distribution evenness of intake charge was developed. The research results are conductive to advancing research on performance optimization for natural gas engine.