Flashback and Turbulent Flame Speed Measurements in Hydrogen/Methane Flames Stabilized by a Low-Swirl Injector at Elevated Pressures and Temperatures

This paper reports flashback limits and turbulent flame local displacement speed measurements in flames stabilized by a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane blended fuels. The goal of this study is to understand the physics that relate turbulent flame speed to flashback events 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 600 K, and inlet bulk velocities between 20 and 60 m/s for natural gas and a 90%/10% (by volume) hydrogen/methane blend. The propensity of flashback is dependent upon the proximity of the lifted flame to the nozzle that is itself dependent upon pressure, inlet temperature, and bulk velocity. Flashback occurs when the leading edge of the flame in the core of the flow ingresses within the nozzle, even in cases when the flame is attached to the burner rim. In general the adiabatic flame temperature at flashback is proportional to the bulk velocity and inlet temperature and inversely proportional to the pressure. The unburned reactant velocity field approaching the flame was measured using a laser Doppler velocimeter with water seeding. Turbulent displacement flame speeds were found to be linearly proportional to the root mean square of the velocity fluctuations about the mean velocity. For identical inlet conditions, high-hydrogen flames had a turbulent flame local displacement speed roughly twice that of natural gas flames. Pressure, inlet temperature, and flame temperature had surprisingly little effect on the local displacement turbulent flame speed. However, the flow field is affected by changes in inlet conditions and is the link between turbulent flame speed, flame position, and flashback propensity.