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为了降低柴油机NO_x和颗粒排放,用数值模拟发动机试验和观察燃烧过程方法研究了柴油机燃烧的一种新概念。该概念(HiMICS:均质合理的多次喷射燃烧系统)为预混合压缩着火燃烧与多次喷射相结合的方式。用与标准的单次喷射和先导喷射的比较方法研究了HiMICS方式的燃烧特性。HiMICS方式要求在从进气行程早期到压缩行程中期这一时期内完成预先喷油形成预混合气。采用改进的KIVA-Ⅱ程序分析了每一种喷油模式对发动机性能和排放量的影响。模拟结果表明,HiMICS燃烧系统的燃油耗与NO_x排放量之间的折衷关系可获得显著的改进。为了证实模拟计算的结论,在一台装有共轨喷油系统的单缸试验机上完成了发动机试验。与模拟计算结论相反,试验表明,在正常喷油定时范围内,与标准喷油系统或先导喷油系统比较,HiMICS燃烧系统的NO_x和燃油耗之间以及NO_x和炭烟排放之间的折衷关系更为恶化。然而,从另一方面来说,当喷油定时相当大地推迟时,HiMICS燃烧系统在燃油耗和炭烟排放方面占优势,同时NO_x排放也相当低。需进一步解决的问题:预混合不够均匀,预混合气着火过早以及HC和CO排放量偏高。
In order to reduce NO_x and particle emission of diesel engine, a new concept of diesel engine combustion was studied by numerical simulation of engine test and observation of combustion process. The concept (HiMICS: homogenous and reasonable multiple injection combustion system) is a combination of premixed compression-ignition combustion and multiple injection. The combustion characteristics of the HiMICS method were compared with the standard one-shot and pilot-jet methods. The HiMICS approach requires pre-injection to complete the pre-mix during the period from the early intake stroke to the mid-compression stroke. The effect of each injection mode on engine performance and emissions was analyzed using a modified KIVA-II program. The simulation results show that there is a significant improvement in the trade-off between fuel consumption and NO x emissions in the HiMICS combustion system. In order to confirm the conclusion of the simulation, the engine test was completed on a single cylinder test machine equipped with a common rail injection system. In contrast to the results of the simulation calculations, tests have shown that during the normal injection timing, there is a trade-off between NO x and fuel consumption in the HiMICS combustion system and between NO x and soot emissions compared to a standard injection system or pilot injection system Worse. However, on the other hand, HiMICS combustion systems dominate fuel consumption and soot emissions while NOx injection is relatively low, while fuel injection timing is considerably delayed. Problems to be further addressed: Pre-mix is not uniform, pre-mixture ignition is too early and HC and CO emissions are high.