Shear Layer Mixing for Low Emission Gas Turbine Primary Zones

Abstract

Shear layer turbulent fuel and air mixing has been utilised in a simulated gas turbine primary zone combustor. Two methods of fuel injection and two values of the number of air injection holes have been investigated at a constant pressure loss of 4% at a reference Mach number of 0.047. The method of fuel injection and the number of air injection holes was found to influence the flame stability and NO x emissions. A large number of holes produced much higher NO x emissions which was not compensated for by the ability to operate a weaker equivalence ratios due to the greater flame stability. An optimum primary zone operating condition, for very low NO x and high combustion efficiencies involving a flame temperature of approximately 1600K was identified and there was a wide flame stability margin on this condition.

Smoke Emissions From Lean Well Mixed Gas Turbine Primary Zones

“…The Jet Mix design is a form of shear layer stabilised flame and the main variation in equivalence ratio occurs in the jet shear layers. The importance of local shear layer mixing effects on gaseous emissions has been reported previously (15).…”

“…In an associated programme of work to the present the gaseous emissions from this type of combustion system has been studied. This has involved both premixed and direct gas and liquid fuel injection tests (7)(8)(9)(10)(11)14,15).…”

Jet Shear Layer Turbulent Diffusion Flames for Ultra-Low NOx Emissions

“…Low NOx emissions have been demonstrated for non-swirling jet shear layer systems for both gas and liquid fuels (Abdul- Aziz et al, 1987 andAbdul Hussain et al, 1988) and for swirl stabilised systems Andrews, 1988, 1989). The Grid Mix technique of directly fuelling an array of shear layers was shown to have low NOx characteristics Al Dabagh et al, 1983Dabagh et al, , 1985Dabagh et al, , 1989 and the present work investigates techniques to produce further reductions in NOx emissions using lower primary zone air flows for enhanced overall combustor stability.…”

“…Al- Dabagh et al (1983Dabagh et al ( , 1984 have shown that increasing the pressure loss at a constant Mach number, by increasing the stabiliser blockage, produces an increase in the turbulence fuel and air mixing. The turbulent velocity was proportional to the square root of the fractional pressure loss and the turbulence dissipation energy which governs the molecular mixing was proportional to the pressure loss to the 1.5 power.…”

“…This results in very large temperature gradients, as shown in the internal gas composition traverses of Heitor and Whitelaw (1986) and Bicen et al (1988), which generate large NOx concentrations and high smoke emissions. The authors have previously shown that if fuel injection is arranged such that the fuel is injected into the base of jet shear layers then simultaneous mixing and flame stabilization can be achieved within the jet shear layer (Al Dabagh and Andrews, 1983;Al Dabagh et al, 1985. The locally rich mixtures were confined to the shear layers which ensured a wide stability range, but mixing was nearly complete by the end of the shear layers and the downstream combustion achieved low NOx emissions by minimising the thermal NOx in the lean primary zone.…”