Investigating the Impact of Steam Enhancement on Combustion in a Swirl-Assisted Jet-Stabilized Gas Turbine Combustor

Abstract

A newly developed gas turbine combustor system based on the swirl-assisted jet-stabilized concept using Jet A-1 and natural gas as reference fuel is tested under wet conditions to evaluate its combustion characteristics in the presence of steam. The effect of steam injection into the gas turbine combustor under both spray and superheated liquid fuel injection conditions is studied experimentally on an atmospheric test rig. The experiments are conducted at atmospheric pressure and an elevated combustion air temperature of 305 °C. To evaluate the effect of steam injection on combustion performance, the water-to-gas ratio (WGR) is varied from 0% to 32%. Even at very high WGR levels, the results show virtually no combustion thermoacoustic instability during operation. With increasing WGR = 0–16% and at stoichiometric condition, NOx reductions of −82% to −100% were observed during Jet A-1 and natural gas combustion, respectively. It is shown that the reduction of the combustion zone temperature due to the steam acting as a heat sink is the main cause of the NOx decrease. For both wet and dry conditions, CO levels remained fairly similar. Both flame length and flame height above the burner increased with increasing WGR. This is due to the reduced reactivity of the fuel–air mixture. The operating range of the burner remained fairly constant for Jet A-1 until WGR = 20% while it decreased significantly with increasing WGR for natural gas combustion. While the effect of the WGR on CO was modest, the greatest effect of the WGR was on the heat release zone intensity at a constant air to fuel ratio. In reducing the NOx levels of Jet A-1 and natural gas combustion, both thermal and chemical effects of steam injection were observed. However, steam acting as a heat sink and lowering the flame temperature, thereby reducing the thermal NO formation rate, was the dominant factor in NOx reduction.