Experimental study of local flame structures and fuel droplet properties of a spray jet flame

Abstract

An n-heptane spray jet flame is characterised through quantitative measurements using laser-based techniques. The experimental set-up is composed of an annular non-swirled air co-flow that surrounds a central hollow-cone spray injector, leading to a stable flame with well- defined boundary conditions. Phase Doppler anemometry (PDA) measurements contribute to this investigation through the analysis of air and droplet aerodynamics and OH-PLIF images describe the two dimensional flame structure. The polydisperse spray distribution yields small droplets along the centreline axis while the majority of the mass is situated as big droplets along the spray borders. The flame structure presents a classical shape, with an inner wrinkled partially premixed flame front and an outer diffusion flame front. In addition Global Rainbow Refractometry Technique (GRT) has been used to measure droplet temperature in the different regions of the spray jet flame. This technique was first applied with a continuous laser (C-GRT) to get temporally averaged values of fuel droplet temperature according to the methodology developed initially by Letty et al. [1]. This technique has been extended to measure instantaneous and local fuel droplet temperature by using a pulsed laser. Therefore, conditional averaged measurements of fuel droplet temperature according to the distance of flame front are reported for the first time by coupling instantaneous GRT (I-GRT) with OH-PLIF. New insights on the thermal droplet behaviour in a spray flame are discussed.