基于RANS和LES的汽油、柴油及其掺混燃料压燃燃烧特性数值模拟研究

Numerical Investigation on Compression Ignition Combustion and Emissions Characteristics of Diesel,Gasoline and Their Blend Using RANS and LES

研究中首先采用RANS和LES两种湍流模型对汽油、柴油及汽柴油掺混燃料的喷雾进行了气液相贯穿距的标定。基于标定好的喷雾模型,采用RANS与LES对3种燃料在发动机中的燃烧过程开展了数值模拟研究。通过对比RANS与LES对部分预混燃烧数值模拟的差异,揭示了两种湍流模型对缸内流动、燃料输运及燃烧过程的影响机理。结果表明,RANS与LES都能够对柴油及掺混燃料的燃烧过程实现较好的预测,其中LES对汽油部分预混燃烧中滞燃期及放热规律的预测与试验更为接近。同时,LES对3种燃料NOx排放的计算结果都与试验更加接近,这与燃料在缸内放热的位置密切相关。

A parametric study was first performed to validate the spray model of diesel,gasoline and their blend using two turbulence models of the Reynolds average navier-stokes(RANS)and large eddy simulation(LES).Based on the results from the spray simulation,the combustions of three fuels were simulated with both RANS and LES.The effects of the two turbulence models on flow in cylinder,fuel transport and combustion process were revealed by comparing the partial-premixed combustion processes of RANS and LES.The results show that both RANS and LES can well predict the combustion processes of diesel and blended fuel.However,the prediction of the ignition delay and combustion process of gasoline is more accurate with LES.At the same time,the calculated NO x emissions are closer to the test results for all three fuels when LES is used.This is mainly because of the different positions of in-cylinder heat release when different turbulence models are applied.