Development of planar meso-scale combustor with double narrow slit flame holder and various aspect ratios for micropower generator

Abstract

We have investigated the effects of the aspect ratio of the rectangular mesoscale combustor with a narrow slit flame holder on the flame stability limit, flame behavior and uniformity of combustor wall temperature. The combustor was made of copper with a cross-section area of 6 mm2. The combustor aspect ratio (AR) was varied as 1, 1.5, 2.67, and 6. LPG and pure oxygen were premixed and the experiment was conducted at a limited flow rate. Pure oxygen is selected as an oxidizing agent with the intention of revealing in detail the range of flame stability within a very narrow quenching distance. All observed flames were inside the combustion chamber, not outside the channel. This research used a new type of flame holder namely double narrow slit flame holder as a flame stabilizer. The flame holder with double slit and a kind of bluff body in the center helps recirculate the flow and prolong the residence time to make the flame more stable. The use of double narrow slit flame holder successfully extended the stability map to a very lean equivalence ratio (f). However, there was a dead zone near stoichiometry condition due to very high flame propagation speed. Aspect ratio had an important role for the non-circular combustor. The aspect ratio gave a great effect to determine the limit of the stability map that can be achieved at the rich mixture. The combustor with AR=1.5 had the widest range of flammability limit, while AR=6 hadthe narrowestflame stability limits. However, the latter reached the most uniform wall temperature, which is important to obtain high efficiency thermal to electric energy conversion. The results of this study can be used to determine the right fuel mixture on the mesoscale combustor as a heat source on the micro power generator/thermal electric system.