Dual-Pump CARS Measurements in a Gas Turbine Combustor Facility Using the NASA 9-Point Lean Direct Injector

Abstract

Lean direct injection (LDI) has been among the seve ral combustion strategies being studied by NASA Glenn Research Center (GRC) to reduce oxides of nitrogen (NO x) emissions while maintaining high combustion effic iency [1]. The NASA 9-point top-hat LDI assembly is a multiplex fuel injector c ontaining nine fuel injection tips and multiple burning zones that replace one conventiona l fuel injector. The nine injectors are placed in a 3 × 3 square matrix arrangement. We have developed a gas turbine combustor facility (GTCF) at the High Pressure Laboratory in Purdue’s Zucrow Laboratory complex. The GTCF has been modified for optical access and dual-pump coherent anti-Stokes Raman scattering (DP-CARS) measurements have been performed at supersonic cruise conditions. A window assembly has been designed, fabricated, and assembled in the GTCF at Purdue University for advanced laser diagnostic stu dies. The window assembly allows optical access from three mutually perpendicular di rections using a pair of thin and thick fused silica windows on each side. The assembly is cooled using water while filmcooling air is provided for the inside of the thin windows. The thin windows are designed for thermal load while the thick windows a re designed for pressure loading. Combusting flows are studied using the central inje ctor of the aforementioned 9-point lean direct injection (LDI) device. The combustor has been operated using Jet-A fuel at inlet air temperatures up to 725 K and combustor pr essures up to 10.2 atm. DP-CARS temperature and major species concentration measurements have been performed in the GTCF at various operating conditions. An injection -seeded optical parametric oscillator (OPO) is used as a narrowband pump laser source so as to improve the accuracy and precision of the CARS measurements. Spatial maps of temperature and major species concentrations have been obtained in high-pressure LDI flames by translating the CARS probe volume in axial and radial directions inside the combustor rig without loss of optical alignment.