An experimental investigation was undertaken to develop a lean direct injection (LDI) combustor concept. The LDI concept consisted of a 9-point fuel injection system setup in a 3×3 array, where each point is made of a fuel nozzle fitted into a counter-rotating radial-radial swirler. Each swirler consisted of an inner, primary swirler, and an outer, secondary swirler, with opposite flow rotation. The experimental investigation consisted of atmospheric combustion and lean blow-out (LBO) tests, and high pressure combustion. All tests utilized a pressure drop of 4% across the swirlers. Parameters tested included variable swirler strengths and fuel nozzle injection depth. Fuel staging was employed on all configurations.
Two swirlers, with swirl numbers (SN) of 0.64 and 1.07, were used in the swirler array, with the baseline configuration consisting entirely of the low-SN swirlers, and configurations 2 and 3 utilizing 1 and 3, respectively, of the high-SN swirlers. Configuration 2 has the high-SN swirler at the center, whereas Configuration 3 uses three high-SN swirlers in the center row. From the atmospheric tests, flame stability and lean blowout occurred at lower equivalence ratios for configuration 2 and 3, indicating that the presence of the high-swirl swirler improved flame anchoring. Two different nozzle insertion depths were tested, with a deep insertion depth providing partial prefilming on the venturi, and a shallow insertion depth with no pre-filming. Partial pre-filming greatly aided in fuel/air mixing and produced a shorter, blue flame, which was stable, and had lower LBO limit as compared to full direct injection (shallow insertion), which resulted in more unstable, longer, yellow flames.
Emission measurements were conducted at high pressures using water cooled sampling probe, and a gas analyzer system to measure the emission indices of NOx and CO. The results showed that this LDI design produced emissions values comparable to those produced by current lean premixed prevaporized (LPP) combustor designs, well below current ICAO standards.
