Research And Application Of Simplified DME-PRF Chemical Kinetic Mechanism

The controllability of gasoline high dilution combustion process can be improved considerably with DME?Dimethyl Ether?Micro Flame Ignition,as well as its thermal efficiency.In order to research MFI?Micro Flame Ignition?combustion process from mechanism,a reduced DME-PRF?Primary Reference Fuel?blend mechanism applicable to different mixing proportion was proposed.Then,the model was applied to the simulation study of DME micro-ignition combustion process.Combining with single-cylinder engine experiment,the distribution of micro-flame source and its influence on the heat release process were explored.The present DME-PRF multi-surrogate fuel chemistry mechanism was assembled in a hierarchal manner.Starting from small radicals and molecules?C₀-C₁?,larger molecules such as C₁-C₃ transition reaction module,C₄-C₇/C₈ PRF subset and DME subset were added into it gradually.The blend fuel mechanism consists of 79species and 267 reactions.Combustion experiments of blends of PRF and DME in a shock tube were conducted.The reduced blend fuel mechanism in this work was well validated by ignition delay comparison to the experimental data in a shock tube over extensive ranges of equivalence ratio,temperature and pressure for each single fuel component and their blends.Simulations of a HCCI engine in CFD were also conducted.The results indicate overall satisfactory agreements between the simulation results and experiment data.Based on the previous study on the kinetic mechanism of DME-PRF chemical reaction,the mechanism of the influence of different micro-flame source on fuel ignition was further explored.First,the influence of DME injection time on the micro-flame ignition of hybrid combustion under different working conditions is obtained through experimental study.Then the mechanism was applied to three-dimensional CFD simulation,and the micro-ignition combustion process under different operating conditions was calculated.The results show that the experimental results agree well with the simulation results,which further proves the applicability of the mechanism model in engine simulation.The experimental and simulation results show that the effect of DME injection time on the heat release rate of MFI hybrid combustion process under different load is just similar to each other.The regular is not monotonous.There always exists a best point under different load conditions.Before this timing,with the delay of the DME injection time,the ignition delay of the mixed fuel is shortened,and the combustion phase is advanced and the peak value of the heat release rate is gradually reduced.The early stage of heat release is speed up,and the latter part of the exothermic become more moderate.But after this timing,delaying the DME injection timing will lead to a sharp decline on the main heat release rate and a longer combustion duration.