A combined experimental/computational investigation of stratified combustion in methane–air mixtures

Although the importance of stratified combustion was early realized, there are still not enough data to fully characterize it mainly due to experimental difficulties of setting up mixture stratification in a controllable manner. As a contribution toward this shortage, controllable stratification was achieved with a technique based on convective-diffusive balance in a novel chamber. The measured flame speeds in the chamber showed that there were significant deviations from quasi-homogeneous flame speeds especially for flames that experienced higher concentration gradients. The experimental results were rationalized theoretically, using appropriate flame asymptotics. The emphasis lies on the establishment of the lean flammability extension, which can lead to significant fuel economy in practical systems and to the increase in flame speeds because of the non-adiabatic flames established in stratified media.