Fuel mixing effects on flame temperature and soot formation in coflow diffusion flames

We investigated the effects of fuel mixing on flame height and flame temperature of coflow diffusion flames which were closely related to soot formation inside the flame. Four fuels with different sooting tendencies and transport properties (CH4, C3H8, C2H4, C2H2) were diluted with nitrogen and used as component fuel gases for mixing. The main results obtained are as follows: (1) Flame tip temperature is a good qualitative measure of the intensity of soot formation inside the flame. (2) Addition of nitrogen to the fuel causes both dilution and soot suppression, which lead to the decrease and the increase, respectively, in the flame tip temperature, and at a certain addition rate the flame tip temperature attains a maximum due to their competitive action. (3) There exists a strong correlation between the degree of soot formation and adiabatic flame temperature, and when soot formation is vigorous, factors which increase this temperature promote soot formation. (4) Effects of Lewis number and preferential diffusion should be taken into account to achieve effective suppression of soot formation by mixing fuels with different transport properties.