An experimental study on the impact of acoustics and spray quality on the emissions of CO and NO from an ethanol spray flame

The effects of frequency, sound pressure level, excess air, and spray atomization on NO and CO emissions from a spray flame in a Rijke tube combustor were investigated using an electrochemical gas analyzer and a phase-Doppler droplet sizing instrument. A large decrease in NO and CO emissions was observed in the presence of acoustic oscillations. Taking concentration values at steady conditions as a reference, per cent reductions in NO and CO varied between 52 and 100%, and 53 and 90% with average values of 79 and 73%, respectively. The largest decreases were observed with increases in sound pressure level, followed by increases in acoustic frequency, and increases in excess air. Although the overall production of these pollutants is reduced, how much reduction is obtained depends on the nozzle position with respect to the acoustic field. NO and CO emissions as a function of excess air were also reduced as the spray initial Sauter mean diameter decreased. A combustion efficiency of 99% for all acoustic modes, compared to 94% for steady operation, was obtained with an excess air of 10%. No significant variations in the combustion efficiency as a function of acoustic mode were observed. (C) 1998 Elsevier Science Ltd. All rights reserved.