STUDYING COMBUSTION OF FUEL /AIR MIXTURES PASSING THROUGH ELLIPTIC SWIRLERS

Abstract

An experimental work has been carried out to characterize the combustion performance in terms of flame length, temperatures and emissions for a triple flame structure of concentric fuel rich mixture surrounded by fuel lean mixture premixed flame combined with the cross flow stream. The combustion performance of flames with using a set of elliptical double swirlers of different angles and aspect ratios were compared to that with using a circular double Swirler to investigate the effect of swirling direction modes (co- versus counter swirl), the effects of swirl angles, and ellipticity. It was found, for counter and co-swirl, that counter swirler leads to higher enhancement of combustion process than co-swirler, due to higher levels of premixing, insignificant differences in the flame length were observed. The counter swirl induces higher levels of turbulence than co-swirl with the consequent enhancement in the mixing of the mixtures and reducing the flame peak temperatures thus decreasing NOX by 36%, CO by 29%, and UHC by 35% emissions comparison to that of the co-swirl. In addition, increasing the inner swirling angle shortens the flame length. Increasing the inner swirl favorably produces flames of higher average temperatures and lower emissions of CO and NOX emissions. In this sense, it was found that the elliptic swirl of (45oi, 30oo) produces higher flame temperatures and lower emissions concentrations of NOX by 38%, CO by 10%, and UHC by 29% compared to the elliptic swirl of (30oi, 45oo). Furthermore, it was found that the elliptic swirl shows shorter flame length than circular swirler, while the elliptic swirl of AR=1.25 produces the shortest flame length relative to other Swirlers of different aspect ratios. The effect of the ellipticity was noticeable, since it was found that the elliptic swirl of AR=1.25 produces flame of higher temperatures and lower NOXand UHC emissions than any other Swirlers of different aspect ratios. Increasing the aspect ratio leads to decrease of the concentrations of CO emission. Finally, it was concluded that double circular swirl produces higher CO, NOXand UHCthan double elliptic swirl. Regarding to changing the inner equivalence ratio, it is found that decreasing the inner equivalence ratio, from 3.6 to 2.7, has a favorable combustion performance of decreasing flame length, increasing flame temperature and decreasing the emissions. Key Words: Combustion, Premixed flames, triple flames, Swirlers, elliptic swirlers, elliptic ports.