Fuel Effects on Aircraft Combustor Emissions

Abstract

Results of an analytical program to determine the effects of broad variations in fuel properties on the pollutant emissions generated by several prominent turbojet engine combustion systems, including both tubo-annular and annular configurations, are presented. Measurements of mean drop size conducted at representative engine operating conditions are used to supplement the available experimental data on the effects of combustor design parameters, combustor operating conditions, and fuel type, on pollutant emissions. The results of the study indicate that the fuel's physical properties that govern atomization quality and evaporation rates have a significant effect on the emissions of carbon monoxide and unburned hydrocarbons. Analysis of the available experimental data shows that the influence of fuel chemistry on the emissions of carbon monoxide, unburned hydrocarbons, and oxides of nitrogen, is small. Smoke emissions are found to be strongly dependent on combustion pressure, primary-zone fuel/air ratio, and the mode of fuel injection (pressure atomization or airblast). Fuel chemistry, as indicated by hydrogen content, is also important. Equations are presented for the correlation and/or prediction of exhaust emissions in terms of combustor size, combustor geometry, engine operating conditions, fuel spray characteristics, and fuel type.