煤基合成柴油燃烧及排放特性的数值模拟研究

Based on a compression ignition engine,a simulation model was established and the combustion processes of diesel/coal-to-liquid(CTL)blends with different CTL mass fractions were studied using the three-dimensional simulation method.The results indicate that as the CTL mass fraction increases,the accumulation of OH radical is accelerated during the low-temperature reaction stage,leading to the accelerated low-temperature reaction process,the earlier ignition and the shortened ignition delay.Fuels with higher CTL mass fractions exhibit less tendencies of premixed combustion,lower combustion speeds and lower combustion temperatures.The influence factors of CTL on soot generation mainly include the fuel component and the premixed combustion ratio.On the one hand,because CTL is free from aromatics,the mass profile of benzene,which is an important soot precursor,shows a single peak feature during the combustion of CTL,rather than the double peak feature when burning diesel.The effect of aromatics on soot formation is weakened as for CTL.Therefore,compared with diesel,CTL significantly reduces soot emissions.On the other hand,more diffusion combustion occurs and more fuel-rich zones are formed after ignition for fuels with higher CTL mass fractions,making the soot emission of the fuel containing 60%CTL by mass higher than that of the fuel with 30%mass fraction.In addition,the lower combustion temperature of CTL helps to reduce NOx emissions.