Enhancced integral burning rate of turbulent premixed flames through stratification

Burning rate of turbulent premixed flames with compositionally inhomogeneous mixtures were investigated experimentally. Hydrogen-enriched methane-air turbulent flames with a global fuel-air equivalence ratio of 0.8 were tested. Two nozzles, each containing 4 fuel/air injection lobes were used in the experiments. The lobes of the first nozzle are straight, while those of the second nozzle are not, producing a swirling motion. The fuel is injected through several small diameter holes into the lobes, generating stratified conditions. Simultaneous OH and CH2O Planar Laser Induced Fluorescence (PLIF) along with Stereoscopic Particle Image Velocimetry (SPIV) were performed for the reacting conditions. SPIV and acetone-PLIF experiments were conducted to study the background turbulent flow characteristics and fuel-air mixing of non-reacting flow, respectively. The results show that stratification can lead to broadening of the preheat layer and generation of shredded-like heat release rate structures. Despite featuring a small intensity of burning rate, the shredded flame structure can feature a relatively large integral burning rate. This suggests some degree of stratification may enhance the stratified flames integral burning rate.