Xu Jiangtao, Guo Tongjun, Feng Yong, Sun Mengxin
School of Mechanical Engineering, Nanjing Institute of Technology, Jiangning District, Nanjing, China.
School of Mechanical Engineering, Nanchang Hangkong University, Nanchang, China.
Sci Prog. 2021 Apr-Jun;104(2):368504211023640. doi: 10.1177/00368504211023640.
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.
先前的研究表明，在不改变机械结构和工作循环的情况下，提高压缩比（CR）是提高汽油机热效率的有效途径，然而，在高负荷运行时增加进气增压时，它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压缩比汽油机的爆震问题，米勒循环可通过早关进气门（EIVC）或晚关进气门（LIVC）来实现。因此，本文基于压缩比为13.5的发动机和电磁气门机构（EMVT），通过理论建模和计算，对EIVC和LIVC对发动机性能的影响进行了对比研究。结果表明，在高负荷下，EIVC策略比LIVC更具优势，因为其总功耗更低，可使指示平均有效压力（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，但仍能灵敏地调节废气再循环（EGR）率，从而降低氮氧化物排放。这两种米勒循环的定量分析结果可为发动机设计者和研究人员提供有价值的参考。
