Experimental and Numerical Design Study for a Small Scale Jet-Stabilized Micro Gas Turbine Combustor

Micro gas turbines (MGT) used as combined heat and power (CHP) systems present interesting advantages over conventional CHP systems. For low power MGTs (1–3 kW_el), a single stage jet-stabilized combustor is well suited to reach low emissions despite high preheat temperatures. Although several jet stabilized combustors in this power range have already been presented in literature, the influence of single design parameters was not described yet. Therefore this paper presents a design study with different combustor geometries. Besides the number of nozzles, also the diameter of air and fuel nozzles as well as the length of the mixing zone is varied. Experiments are performed in an atmospheric combustor test rig with preheat temperatures of 730°C. Additionally RANS-CFD simulations for selected conditions are carried out. The results indicate an inverse correlation between the number of nozzles (diameter adjusted for constant inlet velocities) and the emissions, where an increase in the number of nozzles leads to lower emissions and a shorter reaction zone. Changing the air nozzle diameter and therefore the jet velocity creates a different trend. As the pressure loss decreases with smaller inlet velocities, the CO- and NO_x-emission levels increase. An extension of the mixing section as well as of the diameter of the fuel nozzles have only minor effects for the examined geometries. The knowledge acquired in this work helps to evaluate the influence of design parameter changes on the behavior of small scale jet-stabilized combustors and allows an optimization of the combustor design regarding flame length and emissions.