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为测试循环废气对燃油耗率、NOx和碳烟排放的影响,在一台8缸4冲程直喷式水冷船用柴油机上对不同的负荷和转速进行了试验。不管试验工况如何,试验中燃油喷射正时固定为上止点前38℃A。进气氧气浓度通过进气空气流量和废气再循环中的氧气浓度测定,废气氧气浓度在排气歧管上测定。由进气氧气与燃油耗率的比值计算的平均当量比,被用来分析评价废气再循环率（EGR）对NOx和碳烟排放的影响。结果发现比油耗受废气再循环率的影响较小,由于进气和排气氧气浓度下降以及当废气再循环率增大时当量比增大,NOx排放明显降低,而在某一给定负荷和转速下,特别是较高负荷时,碳烟排放随着EGR率的增大而加剧。基于NOx和碳烟排放这种关联关系,在不增加比油耗的条件下,在韩国重载柴油机排放标准范围内,不同的柴油机工况的最佳EGR率可以粗略估计。
To test the effect of circulating exhaust on fuel consumption, NOx and soot emissions, various loads and speeds were tested on an 8-cylinder 4-stroke direct-injection water-cooled marine diesel engine. Regardless of the test conditions, the test fuel injection timing is fixed at 38 ℃ before the top dead center A. The intake oxygen concentration is determined by the intake air flow rate and the oxygen concentration in the exhaust gas recirculation, and the exhaust oxygen concentration is measured on the exhaust manifold. The average equivalence ratio calculated from the ratio of intake oxygen to fuel consumption was used to analyze and evaluate the effect of EGR on NOx and soot emissions. It was found that the fuel consumption was less affected by the EGR rate due to a decrease in the oxygen concentration of the intake and exhaust gases and a larger equivalent ratio as the exhaust gas recirculation rate was increased while NOx emission was significantly reduced at a given load and At speed, especially at higher loads, soot emissions are exacerbated as EGR rates increase. Based on the relationship between NOx emission and soot emissions, the optimal EGR rate for different diesel engine operating conditions can be roughly estimated within the range of the Korean heavy-duty diesel emission standards without increasing the specific fuel consumption.