LAUSR

Abstract Experimental optical tests were carried out in two concentric tubes burner, to obtain a comprehensive understanding of the turbulence level effects on flame kernel propagation in partially premixed flames. Two ND-YAG lasers with first and second harmonic wavelengths were employed for laser ignition and flow field velocity measurements, respectively. For the current study two parameters were considered, first the geometrical parameter, namely turbulence generator disk diameter (ds), which changes the turbulence intensity, whilst the second parameter was the jet velocity. These parameters were investigated under constant degree of partial premixing, and Liquid petroleum gas (LPG) was used as a fuel. The effect of the equivalence ratio and the jet velocity on the minimum ignition laser energy (MILE) and flame stability maps of different turbulence generator diameters were measured and employed to determine the suitable overall equivalence ratio and the operating conditions for the current study. Based on the analysis of the MILE and the stability limits, one constant jet equivalence ratio of φ = 2 and different jet velocities were used for the whole tests. The turbulent flow field was captured using two-dimension particle image velocimetry (2D PIV) system, and after times of 150, 300, 500, 1000, 1500, and 2500 μs from the start of ignition. The results demonstrated that the MILE for LPG increased as the equivalence ratio increased, especially for rich conditions. In addition, near the stoichiometric conditions, the MILE trends were closely matched for all the jet velocities, although the MILE trends of lean condition were marginally higher. The flame stability maps of different turbulence generator diameters illustrated three extinction curves, which were separated between two regions, lifted flames and blowout. Smaller (ds) was more stable compared to other (ds). The turbulence chemistry interactions influenced the flame kernel propagation rate; at lower jet velocities chemistry effects were dominant, whilst at higher jet velocities turbulence became dominant. The propagation rate for LPG flames increased either by increasing ds or by increasing jet velocity.