Effects of local flame displacement velocity on turbulent burning velocity for lean H2-C3H8-Air mixtures

Abstract

This study was made to establish a prediction method of turbulent burning velocity for lean hydrogen-propane-air mixtures, with paying special attention to the importance of local burning velocity to turbulent burning velocity. In this study, lean hydrogen added propane air mixtures with different rates of addition of hydrogen δH and equivalence ratios Φ(0.5, 0.6 and 0.8) were prepared, where Φ includes fuel concentration below a lean flammability limit of propane-air mixtures. A two-dimensional sequential laser tomography technique was applied to obtain the relationship between the flame shape and the flame displacement in a constant-volume vessel. The local flame displacement velocity SF of turbulent flames was quantitatively measured as a key parameter of local burning velocity. It was found that the mean values of SF, SF,m, at the same u'/SL0 tended to increase as hydrogen was added to lean propane-air mixtures with Φ=0.8. The trends of SF,m against u'/SL0 also corresponded well to its turbulent burning velocities, regardless of δH and Φ. An attempt was also made to predict the turbulent burning velocity by some empirical equations. As a result, the predicted turbulent burning velocities, where the obtained SF,m was employed instead of SL0 as a local burning velocity, were in better agreement with experimental ones for lean hydrogen-propane-air mixtures.

Keywords

• internal combustion engine
• premixed combustion
• hydrogen addition
• turbulent burning velocity
• local burning velocity
• lean propane combustion