Prediction of the near burner region and measurements of NO x and particulate emissions in heavy fuel oil spray flames

Abstract

Fuel oil combustion is difficult to model because of the lack of detailed knowledge about the spray. In the present article a mathematical model developed at Instituto Superior Técnico and Imperial College is described. The model is validated against data for a combustor fired by an industrial-type swirl burner, for which the initial conditions of the spray have been characterized. With this advantage it is found that a fair simulation of the subsequent aerodynamics and combustion is achieved. Systematic testing has shown that such model failings as exist are linked to the prediction of the gas phase aerodynamics. Improvements will be hard won with recourse to advanced models of turbulence. Burner designs that reduce NO x emissions are frequently found to do so at the expense of augmented particulates emissions. New data are reported for the emissions of NO x and particulates as a function of the burner swirl number. With the aid of the present mathematical model the observed trends may be explained. It is concluded that the preferred burner that minimizes the emissions of both is one that ensures rapid droplet vaporization and long residence times for particulates in the internal recirculation zone of the burner. This is an aerodynamically achievable condition.