Combustion Characteristics of Lean Limit Flame Propagation in a Long Tube Under Microgravity.

Abstract

Studies on combustion of extremely lean hydrocarbon-air mixtures are very important from the viewpoint of pollution control which are prompting the development of new types of combustors and internal combustion engines. However, accurate data on combustion characteristics of such mixtures are scarce owing to difficulties inherent in conventional measuring techniques. It is well known that the flame behavior is strongly affected by buoyancy under normal gravity. This becomes more critical in the vicinity of flammability limits where flame propagation velocities are very low. Consequently, data such as flammability limits obtained under normal gravity are unreliable. In this experimental investigation carried out with a quiescent mixture contained in a long tube, flame stability and buoyancy effects in the vicinity of flammability limit have been detemined. Furthermore the study has been extended to include the effect of surface roughness on flame propagation. The experimental results show that, (1) Under microgravity, an axially symmetrical flame propagation is possible in a long tube, even at mixture conditions near the flammability limits and the combustion characteristics can be accurately determined using this method, (2) Propagation velocity with the rough surface is higher than with the smooth surface.