Soot-free and low-NO combustion of Jet A-1 in a lean azimuthal flame (LEAF) combustor with hydrogen injection

Abstract

The quest for aeroengine technologies capable of reducing soot and NOx emissions motivates the development of novel burner concepts. The present work contributes to this line of research by presenting and characterizing a low emissions LEAF combustor fuelled with Jet A-1 and hydrogen at atmospheric condition. The inclined air injection from the top manifold creates an azimuthal flow entraining the Jet A-1 sprays from the bottom manifold and produces, under favorable conditions, a toroidal distributed reaction zone which we call LEAF. In this LEAF, the combustion of the fuel from one atomizer provides a vitiated environment to the spray of the next atomizer. The flame topology and spray characteristics are analysed by means of OH* and CH* chemiluminescence, Mie scattering and soot luminescence. The burner is operated at a constant equivalence ratio with varying thermal power and air-to-liquid massflow ratio (ALR) of the air-blast atomizers. The flame topology is significantly influenced by the atomization air, through its simultaneous effect on the spray characteristics and the flow field. At low atomization air mass flow rates, the combination of lower mixing and larger spray Sauter Mean Diameter (SMD) results in localized droplet and non-uniform spray combustion. Consequently, these inhomogeneities in the combustion process prevent the formation of a LEAF and lead to topological transition of the flame to a tubular shape. In this study, we show that by injecting hydrogen into the combustor we can stabilise a LEAF topology at low ALR. At higher ALR, smaller spray SMD and higher mixing results in a spread-out reaction of hot oxidisers and evaporated fuel, which are characteristics of flameless oxidation. Measurements of soot and NO at the combustor exhaust show very low emission of NO and unburnt fuel and no soot emission, even in absence of preheating of the combustor air.