Lean Premixed Prevaporized (LPP) Gas Turbine Combustor Measurements of Flame Locations and Shear Layer Properties

摘要

A Lean Premixed, Pre-vaporized (LPP) gas turbine combustor is studied in order to quantify the flame location and the strength of vortices that are shed in the shear layers. LPP combustors are known to provide reduced levels of nitric oxides, but they can experience unwanted pressure oscillations at off-design conditions. Three key governing mechanisms are: the relative locations of the Main and Pilot flames, the strength of the shed vortices in the shear layers, and the oscillations of the central recirculation zone. Flame location is important because it affects the uniformity of the temperature field , which leads to low NOx, and it determines how the heat release couples with the pressure field. Flame location also governs how the main flame is anchored by the pilot flame; improved flame anchoring can remove one of the sources of combustion instabilities. Previous LPP studies have primarily been limited to gaseous fuels, atmospheric pressure, and unrealistically simple injector geometries having only one flame. In this study a simple cylindrical combustor geometry is used, but a realistic LPP fuel injector is operated which provides a central nonpremixed Pilot flame that interacts with an outer premixed Main flame. Liquid Jet-A fuel is burned at elevated pressures and preheated air temperatures. Methods were developed to apply formaldehyde PLIF to visualize flames in this harsh environment. The following parameters were selected for measurement because they are good choices to use to assess the ability of LES codes to simulate the unsteady dynamics. a) Profile of flame surface density b) Profiles of flame brush thickness c) PDF of flame length, including its mean and variance d) PDF of strength of vortices shed in the primary shear layer, including their means and variances e) PDF of the size of the recirculation zone, including its mean and variance f) Profiles of Reynolds stresses and turbulence levels.