New developed burner towards stable lean turbulent partially premixed flames

Abstract

A new burner was developed in order to achieve very stable lean flames at lower equivalence ratio and higher level of turbulence intensity. The air-fuel mixing process of the current burner was controlled either by using different levels of partially premixed or by changing the turbulence generator disk slit diameter, ds. Initially, the distributions of turbulent intensity and air volume fraction inside the burner were numerically investigated using three-dimensional computational fluid dynamic (CFD) modelling. Then the lean flame stability limits corresponding to the lean natural gas (NG)/air mixture at an equivalence ratio of φ = 0.6, under five degrees of partially premixed and two turbulent generators disk slit diameters were delineated. Based on the stability limits map, laser induced breakdown spectroscopy (LIBS) technique was employed for further quantitative measurements of the mixture fraction or the equivalence ratio distributions of NG/air mixture. The results indicated that the maximum burner stability for smaller ds was achieved at mixing length to diameter ratio (L/D) of 1:1, whilst for larger ds the maximum stability was achieved at L/D ratio of 2:1. Furthermore, the largest disk slit diameter yielded a homogeneous mixture fraction distribution and lower rms fluctuation, compared to that of lower disk slit diameter. Consequently, this improved the conduction effectiveness in preheating the unburned gases layers resulting in higher flame propagation speed.