Effect of injector spacing in the light-around ignition efficiency and mechanisms in a linear swirled spray burner

The ignition behaviour of a linear swirled spray burner is investigated experimentally. The study focuses on the mechanism of light-around, namely the burner-to-burner propagation, where the effect of injector-to-injector distance on the flame propagation mechanism is considered. The existence of a switching between two different flame propagation mechanisms between injectors in the chamber is identified. The radial and arch propagation mechanisms are found in this work for n-heptane and the underlying causes are explained. High-speed visualisation, high-speed Particle Image Velocimetry (HS-PIV) and Planar Laser Induced Fluorescence on Toluene (T-PLIF) expose the variables piloting these the flame propagation mechanisms and the success of light-around. The aerodynamics and the local equivalence ratio of the flow are analysed for 4 injector-to-injector distances (d) varying from 9 to 18 cm. The modification of d imposes a change in the inner recirculation zone (IRZ) and in the mixture trajectories between injectors. The mixture formation and, thus, the equivalence ratio are directly impacted by the aerodynamics. A mixture migration effect in front of the flame front is also identified and strongly associated to the radial propagation mechanism. The flame propagation speed and its wrinkling factor highlight more differences between radial and arch propagation modes.