燃烧室和喷油器结构对重型柴油机性能与排放的影响

Effects of Structure of Combustion Chamber and Injector on Heavy-duty Diesel Performance and Emission Characteristics

在一台两级增压共轨重型柴油机上,重点研究燃烧室与喷油器结构参数、废气再循环(EGR)参数等因素对燃烧过程、性能和排放特性的影响。数值模拟结果表明,相比原机燃烧室(CR17.5),CR16.8和CR16.2的缸内混合气湍动能增大,油气混合更为均匀。试验结果表明,相比CR17.5和CR16.2,CR16.8能有效提高燃烧反应速率、缩短燃烧持续期而降低有效燃油消耗率(BSFC),CR16.2因压缩比降低过大,BSFC最高。综合数值模拟与试验结果发现,大负荷等EGR率时,CR17.5的NO x和碳烟(soot)生成量最高,但最终的碳烟排放量低于CR16.2。CR16.8缸内湍动能最高,NO x与碳烟之间的折衷关系明显改善。喷油器优化匹配试验结果表明,相比原机直孔喷油器,带倒锥度喷孔且孔径减小的喷油器S4和S5能显著降低碳烟,明显改善NO x与碳烟之间的折衷关系。

The experimental study on the effects of structural parameters of combustion chamber and injector, as well as EGR on combustion process, performance and emissions, was conducted on a common-rail heavy-duty （HD） diesel engine matched with two-stage turbocharger. The results of numerical simulation show that compared with CR17.5, CR16.8 and 16.2 can enhance in-cylinder turbulent kinetic energy, promote the mixture of air and fuel and lead to more homogeneous mixtures. The tested results show that compared with CR17.5 and CR16.2, CR16.8 can reduce BSFC because it can enhance burning rate, shorten combustion duration. CR16.2 will lead to an increase in BSFC due to its much lower compression ratio. The results of numerical simulation and test demonstrate that NOx and soot emissions of CR17.5 are highest of all at a given EGR rate under high load conditions. However, the final soot level of CR17.5 is lower than that of CR16.2. Compared with other combustion chambers, CR16.8 can reduce soot and improve the trade-off of NO -soot due to its higher turbulent kinetic energy. The tested results concerning fuel injector matching show that relative to the fuel injector with straight holes, soot can be reduced and the trade off of NO^-soot can be improved greatly via using S4 and S5, both of which have taper holes.