Engine efficiency, emission characteristics, and structural dimensions are important considerations for gas turbines that are used in transportation applications. Ultra-compact combustion technologies are attracting attention for use in the development of gas turbines due to their low emissions and low cost. This paper studies ultra-compact combustors for gas turbines through experimentation. Furthermore, an asymmetric combustor (fuelled with methane) is designed based on trapped-vortex combustion technology. In addition, four structural configurations of mainstream flame holders and three sizes of combustion zones are considered. The combustion, emission, and stability characteristics of seven combustors are experimentally studied in detail using a gas component analyser, particle image velocimetry, a dynamic pressure system, and a data acquisition system. The fuel adaptability of the combustor is analysed numerically. Under typical experimental conditions, the combustion efficiencies were higher than 94% and the emission indexes of unburned hydrocarbon and nitrogen oxide were in the range of 3-7 and 0.5-1.5 g/(kg fuel), respectively. Additionally, no combustion instability was observed for any experimental conditions. The inlet injection velocity of the mainstream zone (and the combustion power of the combustion zone) significantly influenced the emissions of carbon monoxide and unburned hydrocarbons, the combustion efficiency, and the dynamic pressure characteristics. The volume of the combustion zone, air injection velocity of the combustion zone, structural type, and blockage ratio of the mainstream flame holder all influenced the combustion and stability characteristics to different degrees.