INVESTIGATION OF FUEL-AIR MIXING IN A MICRO-FLAMEHOLDER FOR MICRO-POWER AND SCRAMJET APPLICATIONS

Abstract

This thesis presents a first principles model of the fuel-air mixing process in a micro-flameholder. This model is used to identify key design parameters involved in fuel-air mixing and to characterize how mixing performance scales with the Reynolds number. The results of this analysis show that fuel-air mixing in micro-flameholders occurs primarily at low Reynolds numbers (1<Re<5x103) traditionally associated with the laminar to transitional flow regime. Mixing lengths in micro-flameholders based solely on molecular diffusion are also predicted using a modified Burke-Schumann model. The predicted mixing lengths indicate that less distance is required for fuel-air mixing as micro-flameholders get smaller. Axisymmetric CFD simulations are performed to validate the predictions of the Burke-Schumann model, and to investigate the importance of axial diffusion and viscous effects. The results of these simulations suggest that viscous shear at the wall and at the fuel-air interface can significantly impact mixing lengths in micro-flameholders.