Measurements of Oxides of Nitrogen Produced by Liquid Fuel Diffusion Flames

Abstract

Liquid fuel diffusion flames burning in a low velocity gas stream under ambient pressure were studied experimentally. Flames were established around fuel-wetted porous spheres of 1 to 6 mm diameter, porous cylinders of 3.6 to 6.7 mm diameter, and moving threads of 0.22 to 0.46 mm diameter. Burning rates and oxides of nitrogen emission indices were obtained for various geometries and conditions. The emission index was defined as the total oxides of nitrogen molar formation rate divided by the mass burning rate of the fuel. The approach stream conditions varied were velocity (0-80 cm/ s) temperature (25-650 ° ) and oxygen concentration (18.5-21 percent). Methanol, ethanol, w-pentane, andn-heptane were used as fuels. Fuel temperature was varied from 25° C to the boiling point of the fuel. The data showed that fuel temperature, air velocity, and liquid surface geometry had little effect on the emission index as compared to the much larger effects of fuel composition, approach stream temperature, and approach stream composition. Burning rates were relatively insensitive to approach stream temperature and velocity, but were sensitive to fuel temperature. Comparison of the data to calculated emission indices in the literature for spherically symmetric flames around droplets showed that such models are not accurate for flames such as the ones studied. The neglect of convection effects and detailed kinetics in the models is the probable source of disagreement.