The Effect of Primary Zone Design on the Performance of a High Heat Release Rate Propulsion Engine Combustor

Abstract

The primary reaction zone of a modern propulsion engine combustion system has a profound effect on overall combustor performance, including efficiency, lean stability, exit temperature pattern factor, and emissions production rates. A unique full-annular, throughflow combustion system with interchangeable fuel injectors, dome mixing devices, and liners was used to evaluate the effects of several primary zone design variables on efficiency and exit temperature distribution. The combustor was tested in a rig designed for extreme exit temperatures, at heat release rates up to 30 M Btu/hr-ft3-atm (0.31 kW/M3-atm) and exit temperatures in excess of 3500F (1927C), through a range of overall fuel/air ratios up to stochiometric. An automated, six-port, rotating exit gas sampling system was used to map the exit gas concentrations for determining gas temperatures and combustion efficiency. Both liquid (JP-4) and natural gas fuels were used to examine the impact of evaporation and fuel momentum effects. Gaseous fuel was injected through nozzles designed to mimic the initial fuel spatial distribution and spray cone angle of the liquid nozzles. Thick thermal barrier coatings on the liners eliminated the need for and interference of film cooling. The high reference velocity, short residence time, and absence of any dilution zone further highlighted the primary zone design impact on exit conditions. Test results show that combustor efficiency becomes volume-limited at a point lean of stochiometric, with both the shape of the efficiency curve and the fuel/air ratio for maximum efficiency dependent on the primary zone design and fuel type. The average exit temperature raidal profile was outside diameter (OD)-peaked at low fuel/air ratios, rotating toward a flat profile at stochiometric for all of the configurations.