Experimental and numerical investigation of an ultra-low NOx methane reactor

This work investigates a patented novel methane reactor, the Lean Azimuthal Flame (LEAF) Combustor. The combustor operates with non-premixed combustion where both the air and methane enter the combustor volume through small, high momentum jets. The air jets, located at the top of the combustor, are angled to create a swirling flow that mixes with the fuel entering from the bottom of the combustor. The resulting toroidal flow is intended to increase mixing and hot product recirculation within the burner to reduce operating temperatures, increase residence time, and limit the formation of NOx with preliminary emissions levels measured at sub-20 ppm. The main objectives of this paper are to: (i) experimentally characterize the combustor behaviour; and (ii) improve the physical understanding of the combustion process in the system under investigation through the use of numerical simulations. Experiments were performed at various air and fuel flow rates to determine the stability range of the combustor. Direct visualization of the combustion process indicates the formation of a low luminosity stable flame with a toroidal shape. Flame photographs and OH* chemiluminescence images are presented to provide a qualitative comparison of flame structure and reaction zone, as well as to analyse the effect of varying air and fuel flow rate on combustor operation. Numerical simulations were performed using the Large Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) sub-grid combustion model to analyse the flame behaviour within the combustion chamber. The regions around the fuel jet flow in particular were investigated to explore the phenomena of flame lift-off and local extinction in the bottom of the combustor.