For the development of ultra-micro combustors for Ultra-Micro Gas Turbines (UMGT), heat lossreduction and hydrocarbon fuel use are the key issues. An approach for reducing the effect of heat lossin ultra-micro combustors was proposed. The heat loss ratio (HLR), which was defined as the ratio of heatloss rate from a combustor to heat release rate in the combustor, was related to the space heating rate(SHR), and experiments using some flat-flame ultra-micro combustors with hydrogen/air premixtureexhibited the relation of HLR ～SHR-0.92/l(l, characteristic length of combustor). From the viewpointof heat loss reduction, burning at high SHR in compact ultra-micro combustors is essential for a practicalUMGT combustor. As for hydrocarbon combustion, the flat-flame burning method with and without catalystwas applied to propane fuel. The flat-flame combustor, having an inner diameter of 18.5 mm, a heightof 3.5 mm, and a volume of 0.806 cm3, could form a propane flame successfully in the chamber without acatalyst and achieved an extremely high SHR of 3370 MW/(Mpa m3). Flame stable region was wideenough, and the combustion efficiency achieved was more than 99.4% between the equivalence ratios of0.5 and 0.7 at (m)a =0:06 g/s. The flat-flame combustor using a Pt-impregnated porous plate showed catalyticcombustion, but did not improve the combustion characteristic. On the other hand, the flat-flamecombustor using a nozzle whose surface was covered with Pt showed a combination of catalytic andgas-phase combustion with improved combustion efficiency for a wider range of equivalence ratios, dueto CO oxidation in the burned gas after gas-phase combustion in the chamber.
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