Study On Combustion And Emission Characteristics Of A Spark Ignition Natural Gas Engine

With the diminishing of fossil fuel reserves and growing concern with environment pollution, how to improve engine fuel economy and reduce its emissions becomes the precondition of human sustainable development. Lean burn natural gas engine is featured by good fuel economy and lower exhaust emissions and is one effective way to meet strict engine emission regulations. Therefore, it is worthing investigating the combustion and emission characteristics of natural gas engines under lean burn conditions.In this paper, a natural gas engine, which was retrofitted from a Toyota 8A gasoline engine, was established. Based on an electronical control unit, a data acquisition system and exhaust emission analyzer, the effect of throttle positions, spark timing, lambda on combustion and emission characteristics was investigated.The results show that when lambda increases, combustion duration lengthens and IMEP reduces under the same operating conditions. With increased lambda, NOx emissions increase firstly and then decrease. NOx emissions reach peak at lambda=1.1. Total hydrocarbon (THC) emissions have the opposite trend as NOx emissions. But engine-out CO emissions reduce with increased lambda. With increased throttle open position, ignition timing occurs early, combustion duration decreases and IMEP increases, but IMEP increases little over 50% throttle open position. In the meantime, NOx emissions increase, but THC and CO emissions gradually decrease. At wide open throttle, fuel injection timings have little effect on IMEP. With the decrease of throttle open position, the effect of injection timings increase. Moreover, the optimum injection timing for maximum IMEP is late when engine speed is lower and occurs early when engine speed increases.