Experimental study on cooling characteristics of an air-cooled evaporative flame holder under combustion conditions

The flame holder needs an integrated design with the cooling structure in advanced ramjet or afterburner combustors. Experimental studies were carried out on the air-cooled evaporative flame holder with impingement-film-slot composite cooling structure under combustion conditions. The effects of blowing ratio M (0.54-2.74) and fuel-air ratio FAR (0.0016-0.0027) on the cooling characteristics of the flame holder were studied under mainstream inlet temperature T = 600 K, inlet Mach Number Ma = 0.15 and on-duty combustion conditions. The results show that the air-cooled evaporative flame holder can stabilize the flame after adding cold air. When the blowing ratio M increases, the wall temperature decreases and the cooling effectiveness increases. The average cooling effectiveness is only 0.237 at M = 0.54 and can reach 0.595 at M = 2.74. The distribution of cooling effectiveness on the inner surface of the flame holder is similar at different blowing ratios. Along the flow direction of the inner surface, the first row of cooling structure A uses the impingement jet and the guide ring to form the initial cooling film. The cooling effectiveness of the first row A is from 0.352 to 0.433 at M = 1.89. The next row B downstream the impingement holes and guide ring uses discrete film holes and has a high cooling effectiveness ranging from 0.578 to 0.815 at M = 1.89. The row C with discrete film holes downstream of B is close to the combustion recirculation zone and has a higher heat load. The cooling effectiveness of row C is 11.7%-23.5% lower than that of row B. The last row D with slot holes is at the trailing edge heated by the hot gas in the recirculation zone. The protective effect of the cooling film is poor in row D and the cooling effectiveness is only about 0.268-0.276 at M = 1.89. In the spanwise direction, the cooling effectiveness is higher near the cold air inlet and lower away from the cold inlet. The increase of the fuel-air ratio (FAR) mainly affects the combustion temperature and wall temperature, and has little effect on the cooling effectiveness. When the fuel-air ratio increases from 0.0016 to 0.0027, the average cooling effectiveness varies from 0.502 to 0.558. As the fuel-air ratio increases, the distribution pattern of cooling effectiveness at all measuring points has little change.