大功率中速米勒循环柴油机NO_x排放特性数值模拟

Numerical simulation on NO_x emission characteristics of high-power medium-speed diesel engine with Miller cycle

分别采用AVL Boost和Fire软件建立大功率中速柴油机整机及缸内仿真模型,并使用柴油机台架性能实验结果进行标定和验证,分析多种Miller正时、压缩比及喷油正时设计方案对柴油机燃烧和NOx排放的影响规律。研究结果表明:进气门关闭正时提前会使NOx排放下降且预混合燃烧部分放热率峰值升高;提高几何压缩比使Miller循环方案的预混合燃烧部分放热率峰值降低,NOx排放降低,燃油经济性提高,但会导致缸内爆压剧增;配合深度Miller正时和高压缩比,推迟喷油正时曲轴转角为2°,可在保持燃油经济性的前提下实现较低的NOx排放性。

Whole engine and in-cylinder simulation models were set up for a high-power middle-speed diesel engine with AVL Boost and Fire software, and verified and calibrated with test bench experimental data. The impact of Miller timing, compression ratio and fuel injection timing on combustion and NOx emission were analyzed. The results show that NOx emission decreases and heat release rate for premixed combustion part increases with the advancement of intake valve closing. Increasing compression ratio can lower peak of heat release rate and NOx emission for Miller cycle cases, and increase fuel efficiency. But the in-cylinder peak pressure increases dramatically. 2° fuel injection delay with deep Miller cycle and high compression ratio can realize low NOx emission while keeping fuel economy.