A Reverse Flow Reactor for Turbulence/Chemistry Interaction Studies

Abstract

For the purpose of studying turbulence/chemistry infractions in a regime where the mean mixture fraction, ξ, is close to stoichiometric with fluctuations such that most of the mixture lies within the flammability limits, a reverse flow reactor (RFR) has been designed and developed to create a partially premixed flame with intense turbulent mixing. Al high turbulent mixing rates, where chemical kinetics effects on turbulent flame structure are significant, this flame can yield a bank of valuable data for testing and refinement of theoretical models. This preliminary investigation has been carried out to optimize the degree of premixing and the design parameters of the burner. The mixing characteristics and the global flame structure have been studied, using measurements of mixture fraction, ξ (or concentration ϱξ) temperature, T; and velocity field by Mie-scattering, thermocouple and LDV techniques respectively.

The data show that the final version of the burner satisfies most of its design objectives in a range of residence time of 2-5 ms (mean jet velocities of 200-80 m/s). The mixing effect of a co-flowing air can be minimized by using air co-flow velocities roughly equal to that of the exit flow coming off the opposing cup. Residual stratification of fuel in the exit wall-jet flow coming off the cup has been observed in the partially premixed jet flow which causes significant fuel entrichment in the recirculation zone. The flame is more stable with less premixing, due to the existence of rich pockets which may support the flame stabilization at low equivalence ratio. The turbulence Reynolds number is estimated to be in the range of 350-1650 with a corresponding Kolmogorov length scale, L_K, of 148-16μm