The Effect of Fuel Sprays on Emissions from a Research Gas Turbine Combustor

Abstract

In this program, a research gas turbine combustor is used to study the influence of individual variables (in particular, fuel spray characteristics) on the local level of emissions species concentrations within the primary zone flame. The unique combustor is designed to provide realistic conditions and to allow for independent control of drop size, fuel-air ratio, residence time, air inlet temperature, pressure and reference velocity. This is one of the few combustors in which the residence time has been measured and controlled. The simple flow pattern, with no large scale recirculation, allows for unambiguous interpretation of results

Measurements were made of the local concentrations of NO_x, CO and unburned hydrocarbons, the local gas temperatures and, using laser velocimetry, local gas velocity and turbulence levels. To explain the unexpectedly high levels of hydrocarbons and low flame temperatures that were observed, it is believed that the spray burns in a manner similar to a gaseous turbulent diffusion flame. It is concluded from the data that the effect of increasing drop size (keeping residence time and other parameters fixed) is to cause an increase in unburned hydrocarbons and a decrease in the flame temperature gradients. Increasing residence time results in sharp decreases in hydrocarbons and CO and an increase in NO_x. Increasing equivalence ratio causes an increase in temperature and NO_x and a corresponding decrease in hydrocarbons. Some unexpected trends in NO_x levels are discussed.