Combustion of Droplets within Gas Turbine Combustors: Some Recent Observations onCombustion Efficiency

摘要

Gas turbine combustors usually employ liquid fuels injected as a spray of smalldroplets, which are then considered to vaporize and to burn as a vapor/air diffusion flame. The effects of droplet size on combustion efficiency in such combustors were examined through a review of the literature and experiments in scaled combustors. An examination of fuel evaporation/combustion rate equations, residence times available in combustors, and turbulent flame phenomena seems to indicate that either diffusion processes or droplet evaporation would limit the combustion. The times for the latter two processes seem to be too long to be in accord with the available times within practical combustion systems. In experimental studies on two combustors of widely different geometries and fuel systems, a series of correlations was developed to describe their combustion efficiency performance. A significant loss in correlation accuracy is noted when droplet size is included. The experimental results also showed that under steady state conditions, when droplet size was varied by changing the fuel atomizer, there was no noticeable effect on combustion efficiency attributable to the variation in droplet size. It is recognized that droplet size may be of importance in unsteady conditions and in other possible conditions not investigated in the experiments.