水素-酸素-希釈ガス混合気の微小球状伝ぱ層流火炎の基礎燃焼速度特性

概要

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This study is performed to experimentally examine the fundamental burning velocity characteristics of meso-scale spherical laminar flames in the range of flame radius rf approximately from 1 to 5 mm for hydrogen-oxygen mixtures diluted with Ar, CO2 or N2, in order to make clear an influence of dilution gas on burning velocities of meso-scale flames and a method for improving combustion of micro-meso scale flames. Macro-scale laminar flames with rf > 7 mm are also examined for comparison. The mixtures have nearly the same laminar burning velocity for unstretched flames and different equivalence ratios φ(=0.5-0.9). The radius and the burning velocity of meso-scale flames are obtained by using sequential schlieren images recorded under appropriate ignition conditions. It is found that the burning velocities of meso-scale flames for CO2 diluted mixtures (φ=0.5-0.9) have a tendency to decrease with increasing rf, and approach those of macro-scale flames. Such a trend, however, can not be seen for Ar- as well as N2- diluted mixtures of hydrogen and oxygen with φ=0.7 and 0.9, whose burning velocity of meso-scale flames can not be explained based on that of macro-scale flames. This suggests that micro-meso scale flames have the optimum size and Karlovitz number to improve the burning velocity, depending on dilution gas types in addition to φ and fuel types.