Experimental investigation on heat loss and combustion in methane/oxygen micro-tube combustor

To understand working features of a micro-tube combustor, combustion of CH4/O2 was carried out in three types of micro-tubes with the same outer diameter of 3 mm. In the tests, combustion characteristics and heat loss in micro-tubes were studied. It is shown that when equivalence ratio was lower than unity, CH4 was not completely oxidized and a great amount of gas H2 and CO was produced, which lowered the combustion heat release. If equivalence ratio is a little larger than unity, CH4 was completely oxidized to gas CO2 and water vapor, and the reaction released the maximum combustion heat. Meanwhile, heat loss of the tube wall was the largest. Heat loss of the stainless steel tube occupied 22% of the heat release at most. Since the wall emissivity of stainless steel tube was larger than that of ceramic tube, radiative heat loss was very large and the most occupied 70% of the total heat loss. Additionally, because thermal conductivity of ceramic was less than that of stainless steel, temperature gradient along axis was larger than that of stainless steel tube, which was disadvantageous to axis heat transfer and flame stabilization.