An Experimental Study on Burning Velocity Characteristics of Hydrocarbon-Premixed Micro-Scale Spherical Laminar Flames

Understanding of the burning velocity for micro-scale flames is inevitable in the improved design of micro-combustors for miniaturized power supplies, and also useful for modeling local burning characteristics of turbulent flames. The present study is performed to examine experimentally the burning velocity characteristics of micro-scale spherical laminar flames in the range of flame radius rf approximately from 1 to 5 mm for methane and propane mixtures as hydrocarbon fuel, and also macro-scale laminar flames with rf >7 mm for comparison. The mixtures have nearly the same laminar burning velocity at so-called unstretched flames and different equivalence ratio φ (φ=0.8-1.0 for CH4, φ=1.0-1.4 for C3H8). The radius and the burning velocity of micro-scale flames are obtained by using sequential schlieren images recorded under appropriate ignition conditions. It is found that the burning velocity of all micro-scale flames has a tendency to increase with increasing rf , and approach that of macro-scale flames. The propane mixture with φ1.4 , however, shows that the burning velocity of micro-scale flames can not be explained based on that of macro-scale flames. This suggests that the optimum size and Karlovitz number to improve the burning velocity are existed, depending on φ and fuel types.