The role of autoignition versus flame propagation in lean premixed combustion in gas turbines

In most lean premixed (LP) gas turbine combustion, hot air from the compressor mixes with natural gas as the air is ducted through swirl devices toward the combustion section. It is widely believed that a turbulent flame propagates at a rate equal to the stream velocity in the combustion section. An alternate view is that hot premixed reactants enter the combustion section where recirculation occurs causing the hot products to "backmix" with incoming reactants. The blending of hot products with incoming reactants leads to a new mixture at a temperature between reactants and products where the new mixture may autoignite. The goal of this research is quantification of how much of the LP combustion is attributable to autoignition as opposed to flame propagation. Our approach uses two fuels that have similar properties (for example the laminar flame speed, adiabatic flame temperature, and molecular mass), but differ in their autoignition delay times. These fuels are chemical isomers of C₂H₆O: ethanol (CH₃CH₂OH) (EtOH) and dimethyl ether (CH₃OCH₃) (DME). Thus, the use of these fuels allows an investigation of the role of autoignition in flame stabilization to be made while maintaining other combustion parameters constant. Computational research has been conducted in investigation of this hypothesis, and experimental research is in progress.