Experimental investigation on heat transfer characteristics of partially premixed round methane-air impinging flame jet using Mach-Zehnder interferometry

In this study, premixed and partially premixed laminar co-flow impinging flames are studied experimentally. Methane and air were used as the fuel and oxidizer in a co-annular burner with axisymmetric configuration. For the premixed setup, the mixture of fuel-air flowed from the inner tube, while for partial premixing, the secondary air was added from the region between the inner and the outer tubes. The intention is to investigate the temperature field of impinging flame using Mach-Zehnder interferometry" and finding the Nusselt number and heat transferred to the impingement surface using this temperature field. The Mach-Zehnder method was used to find temperature field of a transparent fluid by the refraction index. The effects of operational factors such as Reynolds number, equivalence ratio, the distance of the impingement surface to the burner, burner diameter, and secondary air ratio have been studied. For validation of the experimental data processing, the temperature at different locations was measured by thermocouples, which confirmed the interferometry method. The results indicate that the maximum heat flux was transferred to the impingement surface while the impingement surface was near to the inner reaction zone. Partially premixed impinging flame has better heat transfer characteristics and 4.5-6% higher maximum flame temperature than premixed flame. The average total heat transfer enhancement by partial premixing is 10.2-13.5%.