Mixing and combustion in a spinning combustor

Abstract

The effect of spin on mixing and combustion in a circular diict with a primary air jet and secondary gas injection through the duct wail was studied using a spin rig, with spin rates up to 10,000 rpm. The spinning ducted flowfield was compared to stationary conditions. Spin enhanced the spreading rate of the pipe and orifice jets, resulting in a larger radial velocity component and an onset of a tangential component in the jet's core for the pipe jet and in the jet's shear layer for the orifice jet. The turbulence amplification rate was enhanced predominantly in the pipe jet. The tests showed that the duct-spin affects the flow even for a relatively short entrance duct. Measurement of the mixture ratio distribution using gas sampling probes in nonreacting tests were done with inert gas injection. Centrifugal forces affected the mixing depending on the weight of the gas relative to air. The mixing was enhanced for lighter-than-air gas and suppressed for heavier. Combustion tests included both ethylene as secondary gas and solid-fuel at the wall, In gaseous fuel combustion, the spin increased the combustion temperature due to improved mixing caused by low-molecular -weight products and reduced density. For solid-fuel combustion the spin had an adverse effect. Combustion temperatures were decreased due to reduced mixing caused by centrifugal forces acting on soot and heavy hydrocarbon products.