Experimental Investigation of the Combustion Behavior of Single-Nozzle Liquid-FLOX®-Based Burners on an Atmospheric Test Rig

Abstract

Abstract As an alternative to the commonly used swirl burners in micro gas turbines (MGT), the FLOX®-based combustion concept promises great potential for the nitric oxide emission reduction and increased fuel flexibility. Previous research on FLOX®-based MGT combustors mainly addressed gaseous fuels and there is limited knowledge available on liquid fuel FLOX®-based MGT combustors. Despite having to deal with a new set of challenges while utilizing liquid fuel in the burner, first steps are taken to gain more information on the influencing operational parameters. In this regard, a FLOX®-based liquid fuel burner is developed to fit into a newly designed combustor for the Capstone C30 MGT. The C30 combustor operates with three burners arranged tangentially to an annular combustion chamber and provides a total thermal power of 115 kW. In this work, operational properties of merely one of the three C30 liquid fuel burners are investigated and the rest of the two burners are emulated in form of hot cross–flow. As for the liquid burners, the experiments are conducted with three geometrically different single–nozzle burners at atmospheric pressure. The studied FLOX®-based burners consist of an air nozzle with a coaxially arranged fuel pressure atomizer. The cross–flow is realized by utilizing a 20–nozzle FLOX®-based natural gas combustor. Measurements include visualization of the reaction zone and analysis of the exhaust gas emissions. By detecting the hydroxyl radical chemiluminescence (OH*-CL) emissions, the position of the heat release zone within the combustion chamber is attained. Correspondingly, the flame height above burner and the flame length are calculated. The investigated design parameters include air preheat temperature up to 733 K, equivalence ratio, burner geometry, and thermal power. The work presented in this paper aims to deepen the understanding of the design parameter interactions involved within the single–nozzle liquid–FLOX®-based burners. The cross–flow is set at a constant operating point to take the influence of the circulating hot gases on the flame into account. Through variation of thermal power the effect of liquid fuel preparation, i.e., atomization, evaporation, and mixing on combustion properties and exhaust gas emissions are examined. Analyses of measurements of different burner configurations are shown. The results show that the burners with the medium diameter consistently performed remarkably at different flame temperatures and thermal powers. The lowest NOx and CO emissions for the medium diameter burner lied between 5–7 ppm and 8–10 ppm, respectively. The collected data sets can be used for the validation of numerical simulations as well.