Effects of H 2 enrichment on flame stability and pollutant emissions for a kerosene/air swirled flame with an aeronautical fuel injector

Abstract

Experimental studies were conducted on an aeronautical kerosene spray injection system, at conditions as close as possible of the idle phase of an aircraft ( P = 0.03 MPa and T = 500 K), to characterize the flame stability and pollutant emissions of two-phase kerosene/air flames. The objective was to investigate the effect of H 2 enrichment of kerosene at constant power for its application to aircraft engines. Two injection configurations were tested: a direct injection of H 2 by three pipes into the first swirler, leading to a partially premixed configuration and the formation of three hydrogen pilot flames, and a premixed configuration where H 2 was mixed with air far upstream the swirler. The experiments, at high pressure and temperature, showed that both injection systems can operate at high H 2 enrichment rates (EC = 7.4%), with a slight effect on the global flame shape. In contrast, flame stability is strongly affected by hydrogen injection and the lean blow off (LBO) limit can be reduced from 0.53 to 0.35 for the most favorable conditions. The partially premixed configuration generated a more stable flame with a wider combustion domain than the premixed configuration, highlighting the importance of the hydrogen injection system. A small amount of H 2 is sufficient to reduce CO emissions by a factor of 4 for EC = 7.4%, due to the enhancement of reactions involving hydroxyl radicals, independent of the H 2 injection configuration. NO x emission rises with the increase in H 2 concentration at constant power, even though the adiabatic flame temperature remains constant. However, this behavior is counter-balanced by lower NO x emissions, induced by the LBO limit extension The partially premixed configuration generates more NO x than the premixed one due to the presence of the pilot flames, underlining several ways to optimize H 2 injection. Such results demonstrate the value and the potential of H 2 enrichment for aeronautical kerosene spray injection systems.