Flame stability and emission characteristics of propane-fueled flat-flame miniature combustor for ultra-micro gas turbines

An engineering model of a propane-fueled miniature combustor was developed for ultra-micro gas turbines. The combustion chamber had a diameter of 20mm, height of 4mm, and volume of 1.26cm3. The flat-flame burning method was applied for lean-premixed propane–air combustion. To create the stagnation flow field for a specific flat-flame formation, a flat plate was set over the porous plate in the combustion chamber. A burning experiment was performed to evaluate the combustion characteristics. The flame stability limit was sufficiently wide to include the design operation conditions of an equivalence ratio of 0.55 and air mass flow rate of 0.15g/s, and the dominant factors affecting the limit were clarified as the heat loss and velocity balance between the burning velocity and the premixture flow velocity at the porous plate. CO, total hydrocarbons (THC), and NOx emission characteristics were established based on the burned gas temperatures in the combustion chamber and the temperature distribution in the combustor. At an air mass flow rate of less than 0.10g/s, CO and THC emissions were more than 1000ppm due to large heat loss. As the air mass flow rate increased, the heat loss decreased, but CO emissions remained large due to the short residence time in the combustion chamber. NOx emission depended mainly on the burned gas temperature in the combustion chamber as well as on the residence time. To reduce emissions despite the short residence time, a platinum mesh was placed after the combustion chamber, which drastically decreased the CO emissions. The combustor performance was compared with that of other miniature combustors, and the results verified that the present combustor has suitable combustion characteristics for a UMGT, although the overall combustor size and heat loss need to be reduced.