Study On The Effects Of Fuel Purification To Enhance Natural Gas Engine Performance

It is well known that the heat-power conversion efficiency of the internal combustion engine will increase with the increase of the compression ratio in a certain range. Compression ratio about 11:1, for example, it can improve the thermal efficiency for 2% to 3% of every increase unit. Under the condition of low speed and heavy load, due to the detonation limit, the design of compression ratio for the engine that using spark ignition and premixed combustion, like gasoline engine and most of the gas engine, is usually lower. If fuel octane number can be increased, it can improve the compression ratio of engine accordingly to improve the fuel economy.Based on the engine performance test bench, combustion analyzer and other related testing equipment, the paper is aim to study the performance optimization of natural gas engine with turbocharged inter-cooled, spark plug ignition, inlet manifold single point injection, and premixed combustion. First, purify the natural gas, so that it can make the fuel octane number greatly improved than the liquefied natural gas on the market. Moreover, it can improve the compression ratio and thermal efficiency of the natural gas engine in order to achieve the goal of improving power performance and fuel economy. Second, complete the vehicle test in actual work condition after obtained the best compression ratio in bench test. Modify the piston to the best compression ratio about 13.6:1, used liquid methane as fuel, and validated the results of the steady-state in bench test.This study gradually increase the compression ratio of engine from 11.6 to 12.6, 13.6, 14.6, 13.6, and test the performance of the engine, including combustion process in cylinder, the state parameter(such as the exhaust pressure, etc.) and performance parameters(power and torque, BSFC, etc.) during the entire working cycle. Then analysis of the effect of compression ratio, ignition advance angle, excess air coefficient on engine performance, fuel economy and emission performance.Through bench test and vehicle test, we can know that improving the compression ratio has little impact on power performance if the other mechanical structure and the related control parameters do not change. Meanwhile, the emission for NOx is worsened, but the fuel economy goes better and the compression ratio in 13.6:1 reaches the best. Compared with the compression ratio of 11.6:1, the BSFC falls by 4% to 6% under different speed conditions. When the compression ratio improve further, especially in using the liquid methane, the combustion in cylinder is worsen, the detonation trend is more obviously, and the fuel economy is decreased.