Study On The Structure Transitions And Kinetic Effects Of Premixed Dymethyl Ether/Air Charges On N-Heptane Diffusion Flames

Diffusion combustion in reactivity charge is a high efficiency combustion te-chnology.Due to the introduction of the premixed reactivity charge,it can effect-ively reduce the PM and NOx of the diffusion flame.A numerical study was implemented to investigate the effects of a premixed dymethyl ether/air reactivity charges on the combustion characteristics,the structure transitions and harmful generation of n-heptane diffusion flame.Through flame chemical kinetics calculation,The mechanism of the influence of dymethyl ether atmosphere on the kinetics of n-heptane reaction was studied.The main research contents of this paper are as following:The flame simulation results shows the following consequence:1)Two flame reaction zones aroused in the flames with the addition of air-side premixing,and the fuel-side nonpremixed reaction zone near the stagnation plane and the premixed one close to the air-side burner,could be discerned by the heat release rates and CO profiles.2)It is foundthat the?_A of 0.3 and 0.7 can be viewed as the two changeover equivalence ratios.3)It is suggested that self-sustaining behaviors of the?_A=0.5⁰.6 flames would cause explosively enhanced flame reaction rates.4)With the increase of the global flame strain rate,the flame peak temperature of the active atmosphere diffusion flame decreases,the flame thickness decreases,and the combustion zone gradually narrows,indicating that the flame stretching has the effect of compressing the flame.As the blends temperature increases,the flame peak temperature of the premixed atmosphere diffusion flame increases,the combustion area is widened and the flame thickness is widened.5)The rule of harmful generation is:with the increase of the premixed equivalent ratio,the CO,CH₂O emissions of dymethyl ether premixed flame were increased,but the emission of C₆H₆ was decreased;With the increase of the global flame strain rate,the emission of CO,CH₂O were increased,but the emission of C₆H₆was decreased.With the increase of the blends tempe,ature,the emission of CO,CH₂O,C₆H₆ were increased.The flame dynamics calculations show the following consequence:1)The peakvalue of OH+O+H and CH₃+CH₂O gradually increases with increasing equivalentratio in dymethyl ether premixed atmosphere n-heptane diffusion flame with the increase,the concentration distributions gradually bimoday,and the peak positiongradually shifts toward to oxidant side,so that the combustion is accelerated and the combustion area becomes wider.2)With the increase of the global flame strain rate,the peak value of OH+O+H and CH₃+CH₂O gradually increased,but the stretch rate increase can cause the increase of the flamethermal loss,thermal loss factors to offset the premixed gas heat release rate increased,while the increase of elongation rate will flame compression,so that the burning area gradually narrowed.3)With the rise of the blends temperature,the peak value of OH+O+H and CH₃+CH₂O gradually increased and the peak position gradually moved to the side of the oxidant.The progress rates of these reactions arevaried with the variations of the equivalence ratio and temperature of the premixed charges,and the global strain rate of flame,and consequently causing the increases or decreases in CH₂O,NO and C₆H₆ formation.