Experimental study of lean ignition and lean blowout performance improvement using an evaporation flameholder

The hyperburner of a turbine-based combined cycle (TBCC) works at a relatively low temperature and high local velocity flow conditions compared with an afterburner or a ramjet combustor. Therefore, wider lean ignition and blowout limits are required in a TBCC. Both a circular and crescent-shaped evaporation tube flameholders were designed and numerically simulated. Moreover, experiments were performed to measure the lean ignition and blowout performance for the two flameholder types under conditions of T = 450-650 K and Ma = 0.1-0.4. The results indicate that a crescent-shaped evaporation tube provides steady high temperature wake flow, thereby increasing the fuel evaporation rate, and that a crescent-shaped evaporation tube flameholder is superior to a circular evaporation tube flameholder; this is because the wake flow of a crescent-shaped evaporation tube is not affected by the Mach number of the flow. This is beneficial for both reliable lean ignition and wide lean blowout limits. For flows with high Mach numbers, when compared with a circular evaporation tube flameholder, the lean ignition and blowout performance is strongly enhanced for a crescent-shaped evaporation tube flameholder. The experimental results show that a crescent-shaped evaporation tube flameholder exhibits much better performance under flow conditions where T = 450 K and Ma = 0.4. The lean ignition and lean blowout equivalence ratios of a crescent-shaped evaporation tube flameholder were only 31% and 47% that of a circular evaporation tube flameholder, respectively.