Investigations on the Formation of Planar Flames in Mesoscale Divergent Channels and Prediction of Burning Velocity at High Temperatures

Abstract

Flame stabilization studies of preheated mesoscale channels of various divergent angles and aspect ratios are reported in this article. Flame propagation modes such as planar flame and negatively and positively stretched flames were observed for a range of mixture flow rates and equivalence ratios. The present investigation is focused on the formation of the planar flames in these channels. The effect, of various parameters such as channel aspect ratio, divergence angle, and heating rate on the formation of planar flames and thereby on the prediction of laminar burning velocity of various fuel–air mixtures at high temperatures are discussed. Detailed investigations show that stretch-free planar flames can be stabilized in high-aspect-ratio channels with linear velocity and temperature gradient in the axial direction. Detailed numerical simulations confirm a negligible effect of heat loss on the burning velocity due to external preheating of the channel walls. Apparatus independence of the burning velocity is confirmed through experiments in channels of various aspect ratios and divergence angles for various fuel–air mixtures. The proposed method of burning velocity measurement at high temperature is quite promising.

Keywords:

• Divergent channels
• Flame stabilization
• Laminar burning velocity
• Laminar flame propagation
• Mesoscale combustion