THE EFFECT OF AUXILIARY FUEL IN THE CO-FLOWING AIR STREAM ON THE FLOW STRUCTURE AND BLOWOUT LIMITS OF DIFFUSION FLAMES

摘要

The paper describes the results of an investigation on the effect of an auxiliary fuel in the co-flowing air stream on the flow structure and blowout Emits of jet diffusion flames using nozzles of different geometries. Experiments were conducted with methane as the jet fuel. The auxiliary fuel in the co-flowing air stream for she majority of the tests was also methane. The flow structure of ignited jets issuing into a co-flowing stream of very lean air and methane mixtures was experimentally studied using a laser Doppler velocimeter. These tests were conducted with circular and elliptic jets of aspect ratios of 1.38 and 1.60. The diameter of the circular nozzle was 4.6 mm and the elliptic nozzles had approximately the same exit area as that of the circular nozzle. The time-averaged velocity and r.m.s value of the velocity fluctuation in the streamwise direction were measured for a co-flowing stream velocity of 1.21 m/s which corresponds to the blowout of attached flames in an &only co-flowing stream. On the basis of these measurements, attempts were made to explain the effect of nozzle geometry on the flame blowout limits.