Numericalinvestigations On Combustion Characteristics And Noxformation In Flames Of Mixed Fuel Including CO

In this paper, the mixed fuel including CO was investigated, by using chemicalreaction dynamics software CHEMKIN and detailed chemical reaction mechanism(GRI-Mech3.0). The mathematical model of diffusion flames and premixed flames ofthe mixed fuel including CO were established, while the burning process of diffusionflames and premixed flames were simulated at the same time. Then theoreticalanalysis research of combustion characteristics, such as fire structure, flame limits,burning velocity, NOxformation characteristics and the suppressing measures, weremade.The diffusion flame was employed in the first part of this paper. The regularchanges of the properties, such as the flameout limit, flame structure and the nitrogenoxide emissions generated characteristics, with strain rates and mixed fuelconstituents were investigated; The influence of the flame strain rates on NO emissioncharacteristics of the mixed fuel with CO as main fuel was discussed; The effect ofH2O and H atoms on combustion properties of CO/CH4mixed fuel were investigatedby comparing the obtained results when added different amount of H2O and N2to thefuel, and then analyzed it from the chemical reaction mechanism.The calculation results show that the flame temperature dropped significantly withthe increasing strain rates. This can be attributed to the incomplete combustion of thefuel and the increasing convection heat loss caused by the shortened residence time.Along with the increasing ofCO, the generate rate of OH free radicals was decreased,resulting in the reducing of the flame temperature and combustion intensity. Atdifferent strain rates, the changes of the highest flame temperature with the CO molefraction was the comprehensive function of adiabatic balance temperature, Lewisnumber, chemical reactions and residence time; the role of water vapor added in thefuel was decided by the balance between the promoting effect of CO combustionprocess and the inhibition effect of CH4combustion process.The premixed flame was employed in the second part of this paper. Variation oflaminar burning velocity of CO/CH4mixed fuel with the increasing equivalent ratiowere investigated when under different fuel composition situation and added differentmole fraction of H2O to the fuel. Then the related factors were concrete analyzed. Theinfluences of H2O and H atoms on the laminar burning velocity of CO/CH4mixed fuel were analyzed emphatically.The calculation results show that the laminar burning velocity reaches themaximum when the equivalence ratio>1. For a certain fuel, the laminar burningvelocity increased first and then decreased after reached maximum with the increasingequivalent ratio. The influence of H2O on laminar burning velocity mainly by thesolution of H free radicals participating in the chemical reactions, changing thecombustion characteristics of the premixed flame. H2O added in the mixed fuel canreduce the amount of NO, inhibit the generation of NO. What’s more, the greater themole fraction of H2O, the more obvious the inhibition effect was, and the smaller thereduction of peak NO mole fraction was.