Sooting Limit of a Droplet Flame

The soot emission problem of the diffusion flame around a fuel droplet was taken up and the droplet diameter at the sooting limit, D L, was determined using a high speed camera and an optical method of soot detection. Since no soot emission occurs from the flume if the droplet diameter is smaller than D L. the magnitude of D L might be an index to the sooting tendency of liquid fuels, just like the fuel flow rate at the sooting limit which is a useful index to estimate the sooting tendency of gaseous fuels. The effects on D L of fuel type, fuel blending, and surrounding air velocity, as well as time variations of droplet diameter and flame height during combustion, were investigated. The main findings were: (1) D, was increased and the sooting tendency was lowered with the increase in the air velocity although it promoted fuel evaporation and soot formation; (2) When two types of fuels with different sooting tendencies were blended, the concentration dependence of D L was greatly affected by the ...