An optically accessible secondary combustion zone for the transverse injection of reacting jets into a high-speed, vitiated crossflow within a staged, gas turbine model combustor

Abstract

Advanced gas turbine combustion strategies, such as axially staging the fuel, are of great interest due to their potential to increase cycle efficiency while maintaining low levels of pollutants. In our previous work within a staged gas turbine model combustor, we used exhaust gas emissions measurements to demonstrate a significant NOX reduction by increasing the combustor exit Mach number, even at a constant residence time. In this paper, the development of an optically accessible secondary combustion zone (SCZ) to further study the injection of a reacting jet into a high-speed vitiated crossflow is described. Measurements were targeted for a nominally 1700 K vitiated crossflow, a premixed jet at an unburnt temperature of nominally 500 K, and a combustor pressure of 500 kPa. Key aspects of this design challenge include the high-speed and high temperature crossflow leading to relatively high convective heat flux at the inner surface of the windows and the necessary use of a narrow channel for the combustion gas. Emphasis is placed on the critical design features: a double-windowed design, an air-cooling scheme based on forced convection of air between the inner and outer windows, and intricate water-cooling circuits for the metal hardware. These design features have enabled long-duration, steady-state operation despite elevated pressure, high combustion gas temperatures, and high-speed reacting flows. The SCZ has survived operation at MW thermal powers over several hours of continuous operation and over a dozen test days to date; a set of windows retained good transparency without discoloration for typically 3–4 test days. Survivability of the windows through the air-cooling design has enabled us to study the reacting jet-in-crossflow at the desired high-speed conditions, without risking disturbing the physics with a window film-cooling flow. The capability to acquire useful measurements is illustrated using chemiluminescence imaging, pressure measurements, and emissions sampling.