Flashback, Blow out, Emissions and Turbulent Displacement Flame Speed Measurements in a Hydrogen and Methane Fired Low-Swirl Injector at Elevated Temperatures and Pressures”
This paper reports on flashback limits and turbulent displacement flame speed measurements in a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane based fuels. The goal of this study is to understand the driving physics relating turbulent flame speeds to flashback at conditions relevant to gas turbine engines. Testing was conducted in an optically accessible single nozzle combustor rig at pressures ranging from 1 to 8 atm, inlet temperatures from 290 to 600K, and inlet bulk velocities between 20 and 60 m/s for natural gas and a 90%/10% (by volume) hydrogen/methane blend. Flashback occurred for high-hydrogen flames, but not for natural gas. The firing temperature at flashback was found to be proportional to the bulk velocity and inlet temperature, and inversely proportional to the pressure. Flashback occurred when leading edge of the flame approached the nozzle exit, even in flames which showed attachment near the burner rim. The unburned velocity field was measured using a Laser Doppler Velocimeter (LDV) with water seeding. Turbulent displacement flame speeds were found to be linearly proportional to the root mean square velocity fluctuations about the mean velocity. For identical inlet conditions, high-hydrogen flames had a turbulent flame speed roughly twice that of natural gas flames. Pressure, inlet temperature, flame temperature had surprisingly little effect on turbulent flame speed.