Impact of ethanol blending on soot in turbulent swirl-stabilized Jet A-1 spray flames in a model gas turbine combustor

Abstract

Influence of ethanol addition to Jet A-1 on soot formation was investigated in swirl-stabilized spray flames in a gas turbine model combustor with 94 mm × 94 mm cross-section and 188 mm length. Two blends consisting of 10% and 20% ethanol by energy content were designed. Keeping fuel feed rates constant, two different air flow rates were used giving two distinct global air-fuel ratios. Flow field of the flames in the combustor was measured using stereoscopic particle image velocimetry, and the spray droplet size distributions were determined through the Fraunhofer diffraction technique. Spatially-resolved soot volume fraction and mean primary particle size were measured using auto-compensating laser-induced incandescence. Under identical fuel and air flow conditions, measurable differences in spray and flow field characteristics were observed between neat Jet A-1 and Jet A-1/ethanol blends. In contrast to the neat Jet A-1 spray flames in which soot was first detected at 30 mm above the burner base, soot was detected at 15 mm above the burner base in the Jet A-1/10% ethanol flames. In addition to being detected lower in the flame, soot was observed in wider spatial ranges in the flame. In each of the two flames of 10% ethanol, two distinct peaks were observed in the time-averaged soot volume fraction profiles at approximately 25 mm and 45 mm above the burner base. While the peak at 50 mm was observed in the neat Jet A-1 flame, the second peak lower in the flame was not observed. The soot detected within the fuel spray cone below 30 mm above the burner base is more characteristic of gaseous fuel combustion in swirl-stabilized flames rather than a liquid spray flame. The overall quantity of soot produced in both Jet A-1/10% ethanol blend flames is greater than the respective neat Jet A-1 flames.