Preliminary Design, Ignition, and Fuel Injection for a High Temperature Recuperated Microturbine Combustor

Abstract

Recuperation and high turbine inlet temperatures could enable miniature (<20 kW) gas turbines to match the fuel efficiency and installed weight of current internal combustion (IC) engines. However, these strategies create unusual challenges for combustor development. As the engine transitions from ignition to steady state, changes in the preheated air temperature, fuel/air mixture, evaporation, and chemical timescales make operability difficult with a fixed-geometry combustor at all operational states. The flame must also be exceptionally clean in all conditions because any soot will foul the recuperator. Furthermore, preheated air is less effective for cooling, potentially creating extreme thermal loads on the liner, especially during transients, and any ignition device that protrudes into the unusually hot primary zone could melt. This paper describes the preliminary design of a combustor being developed to meet these challenges, and reviews the late progress on subsystem testing and experiments. The combustor is a single-can type with a radial swirler and single atomizer nozzle at one end. An optically accessible burner is being used to explore fundamental aspects of swirler aerodynamics, ignition strategies, liner cooling, and lean blow off behavior. Particle image velocimetry (PIV) is enabling quantitative velocity measurements of swirler jet decay and interaction with the liner wall. Two different methods for projecting an ignition source into the primary zone from outside the liner, a micro-torch and a conventional spark igniter, have been tested.