Examination of Premixed Methane Air Tubular Flame Response to Elevated Pressure

Abstract

Understanding flame-flow interaction is, while complex, paramount to the development of practical combustion devices. Often such devices require combustion to operate in a turbulent and high-pressure environment. Turbulent flames present a unique problem of being both experimentally and numerically arduous for current measurement techniques and software to fully resolve. Laminar flames provide the opportunity to simplify certain aspects of combustion while maintaining enough characteristics that can be mapped in a turbulent regime. Tubular flames are highly stretched and curved similar to the turbulent flames and thus play a critical role in the refinement of chemical kinetic models in turbulent simulations. Despite numerous studies of tubular flames at atmospheric conditions, work at elevated pressures has been rare. Prior numerical efforts have shown that even with reduced mass and thermal diffusivities, the methane-air tubular flame temperature steadily increases with increasing stretch rate in the presence of a high-pressure field. Chemiluminescence images were captured and compared to one-dimensional simulations with detailed chemical kinetics and molecular transport to determine the pressure effect on flame properties. The simulations and experiments show that the flame speed, thickness, and radius decrease with increasing pressure and stretch rate. They also show that nearly equidiffusive (Le ≈ 1) methane-air tubular flame temperatures increase as a result of preferential diffusion. The greater mass flux into the wrinkled flame front increases local equivalence ratios and stretch rates that correlate to higher temperatures.