Influence of characteristic chemical reaction time on burning velocity of hydrogen-premixed micro-scale spherical laminar flames

Comprehension of the burning velocity for micro-scale flames is inevitable in the improved design of micro-combustors for miniaturized power supplies. The pitsent study is performed to examine experimentally the burning velocity characteristics of hydrogen-pitmixed micro-scale spherical laminar flames in the range of flame mdius r1 < 5 mm, and also macro-scale laminar flames with r1>7 mm for comparison. The niixtuits have nearly the laminar burning velocity 8L0 at so-called unstmtched flames with diffeitnt equivalence mtios (ø =0.3∼12). In this experiment, the values of the 8L0 are fixed at approximately 15, 25 and 35 cmls, in order to examine the influence of characteristic chemical reaction time on micro-scale spherical laminar flames. The mdius and the burning velocity of micro-scale flames are obtained by using sequential schlieitn images itcorded under appropriate ignition conditions. The itsults show that the burning velocities of micro-scale flames with qi=ø.3 and 0.5 or 1.2 have a tendency to decrease or increase with incmasing r1 and approach that of macro-scale flames, but such a tmnd can not be seen for ø0.7 and 0.9 micro-scale flames, iritspective of 8L0 It is also found that the optimum size and Karlovitz number to improve the burning velocity are existed for ø7 and 0.9 micro-scale flames, iritspective of 8L0. © 2011 The Japan Society of Mechanical Engineers.