Investigating a methanol spray flame interacting with an annular air jet using phase-Doppler interferometry and planar laser-induced fluorescence

Abstract

An experimental investigation of the interaction of an annular air jet with a methanol spray flame was conducted using phase Doppler interferometry (PDI) to measure fuel droplet size and velocity as well as gas-phase velocity, and planar laser-induced fluorescence (PLIF) to determine instantaneous and time-averaged reaction zone location, as well as quantitative OH concentration. Temperature measurements were made using Pt/Pt-10% Rh thermocouples. PLIF imaging of the OH radical showed that the spray flame had a dual reaction zone structure with annular air off but a single reaction zone with annular air on. Peak OH concentrations were measured to be 5400 PPM, regardless of the annular air flow rate. The OH concentration peaks always occurred on the fuel-lean side of the reaction zone, while temperature peaks occurred on the fuel-rich side. Gas-phase velocity vector fields show that annular air tends to channel the flow towards the centreline, and large droplet velocity vector fields show that the large droplets follow this trend as well, suggesting that the annular air jet assists in confining large spray droplets. Overall visible flame length is reduced by over 50% with annular air, providing a flame well-suited to compact combustion chambers.