Science Progress ( IF 1.906 ) Pub Date : 2021-06-10 , DOI: 10.1177/00368504211023640 Jiangtao Xu, Tongjun Guo, Yong Feng, Mengxin Sun
Previous studies have shown that increase compression ratio (CR) is an effective way to improve thermal efficiency of gasoline engine without changing the mechanical structure and working cycle, however, it is limited by engine knock when increasing the intake boosting under high load operation. This study aimed to solve the knock problem of gasoline engine with higher CR by application of Miller cycle, which can be implemented by either early or late intake valve closing (EIVC or LIVC). Therefore, in this paper, based on the engine with CR of 13.5 and electromagnetic valves train (EMVT), a comparative study was carried out to investigate the effects of EIVC and LIVC on engine performance, by theoretical modeling and calculation. The results show that, at high load, EIVC strategy is more preferred than LIVC owing to its lower total power consumption, which can improve the indicated mean effective pressure (IMEP) by 0.0371 bar, while enhance turbulence intensity and improve combustion. And at part load, the advantage for EIVC declines gradually, nevertheless, it can still sensitively adjust the EGR rate and thus reduce NOx. This results of quantitative analysis about two Miller cycles can provide valuable reference for engine designers and researchers.
以往的研究表明，在不改变机械结构和工作循环的情况下，增加压缩比（CR）是提高汽油机热效率的有效途径，但在高负荷运行时增加进气增压会受到发动机爆震的限制。本研究旨在通过应用米勒循环解决高 CR 汽油发动机的爆震问题，米勒循环可以通过提前或延迟进气门关闭（EIVC 或 LIVC）来实现。因此，在本文中，基于CR为13.5的发动机和电磁阀系（EMVT），通过理论建模和计算，对比研究了EIVC和LIVC对发动机性能的影响。结果表明，在高负载下，EIVC 策略比 LIVC 更受青睐，因为其总功耗较低，可以将指示平均有效压力 (IMEP) 提高 0.0371 bar，同时增强湍流强度并改善燃烧。而在部分负荷下，EIVC的优势逐渐减弱，但仍能灵敏地调节EGR率，从而降低NOx。这个关于两个米勒循环的定量分析结果可以为发动机设计者和研究人员提供有价值的参考。