NO x emissions from non-premixed, direct fuel injection methane burners at high-temperature and elevated pressure conditions

Abstract

This paper describes research efforts to acquire low-NO x emissions combustor technology for the turbojet combustor of a methane-fueled HSST propulsion system. The potential of the lean, non-premixed concept has been investigated because it is free from the problems of autoignition and flash back even at the high-temperature and pressure conditions encountered. The burner module being developed has a coaxial double swirler, and fuel was injected into the circular air jet by a multiorifice nozzle and into the outer annular air jet through holes in the wall of the outer casing of the outer swirler. Emission measurements were conducted at pressures up to 0.8 MPa and at inlet air temperatures ranging from 650 to 1100 K for a flame tube fitted with the burner and a model combustor fitted with four non-premixed burner modules. The effects of inhomogeneity of non-premixed mixtures on NO x emissions, which were small at atmospheric pressure, are increasingly important at high pressures. The effects of pressure on EINO x are reported. NO x emissions lower than 5EINO x were successfully achieved at 2000 K gas temperature for combustor inlet conditions of 1100 K and 0.8 MPa with acceptable pressure losses. At an air temperature of 1100 K and pressure of 0.8 MPa, autoignition of the methane fuel in the combustion chamber was experienced.