Quantitative investigation of the effects of CR, EGR and spark timing strategies on performance, combustion and NOx emissions characteristics of a heavy-duty natural gas engine fueled with 99% methane content

摘要

A quantitative investigation of the effects of CR, EGR and spark timing strategies on performance, combustion and NOx emissions characteristics was conducted on a heavy-duty natural gas engine fueled with 99% methane content. The CR was modified by replacing pistons with different bowl volumes. The results indicate that employing higher CR results in better fuel economy, lower BSFC level, but generating higher NOx emissions. In addition, PCP linearly decreases and the location of the maximum ROHR delays with the increase of EGR rate. The influence of the above factors on the engine performance is different at different engine speeds: i.e. at lower engine speeds, the 50% combustion location, 10-90% combustion duration, and EER are only slightly affected by the EGR strategy, however, with the increase of engine speed, the influence of the EGR on performance characteristics becomes more important. Besides, the NOx emissions reduces significantly due to the increase of EGR rate and the maximum decreasing content of EER is 3.88% which happened in the 1800 r/min. Therefore, on the one hand, introduction of EGR is a good strategy to decrease NOx emissions while maintaining the BSFC. On the other hand, optimizing spark timing also plays a key role in reducing the NOx emissions.