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Abstract

A non-premixed jet flame acoustically pulsed at the third resonant frequency of 645 Hz was studied experimentally in a wind tunnel. Flame behavior, characteristics, temperature distributions, and combustion-product distributions were investigated. The flame behavior was characterized by flame visualization. Flame dimensions were obtained from long-exposure flame images. A fine-wire, R-type thermocouple was used to probe temperature distributions while combustion product concentrations were measured using a gas analyzer. Three characteristic flame modes, I, II, and III were identified in the domain of jet pulsation intensity (Ipul). Mode I flames (0 ≦ Ipul ≦ 0.30) were not affected by pulsation, and remained similar to the non-excited flames. Mode II flames (0.30 < Ipul ≦ 0.70) were characterized by a rapidly decreasing flame length, shrinking recirculation flame, and reducing flame luminosity. Mode III flames featured highly unstable, flashing blue flames prior to blow off. Temperature and combustion-product concentrations profiles showed improved mixing as the jet pulsation was increased beyond mode I. Higher temperatures, lower carbon monoxide and slightly reduced nitric oxide concentrations were recorded. Pulsing a jet at a low jet-to-crossflow momentum flux ratio and a jet pulsation intensity above 0.30 resulted in improved combustion.

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