Planar Flow Filed Measurements in Atmospheric and Pressure Combustion

Given the continuing growth of air transport and stationary power generation in conjunction with increasingly stringent requirements on fuel efficiency and emissions new developments in combustor technology are necessary. On this background the Institute of Propulsion Technology is involved in several national and European research programs that are aimed at providing industry with improved modeling tools for combustor design. A common strategy in these projects is to generate high quality CFD validation data from combustor configurations that share critical features of realistic combustors such as mixing jets, flame instabilities and increased operating pressures. An important work package within these research programs is to provide detailed information of the flow field inside the combustor. In this past this was achieved using single point measurement techniques such as laser Doppler anemometry (LDA). Planar techniques such as planar Doppler velocimetry (PDV) or particle image velocimetry (PIV) have the potential of providing this data much more cost effectively. This paper's intention is to report on the status of applicability of PIV in combustor. Two experimental facilities at the Institute of Propulsion Technology were chosen for the PIV applicability study presented in the article: (1) an atmospheric 'laboratory-scale' combustor, (2) a pressurized, single sector combustor (e.g. a single segment of a complex full scale combustor) with optical access from three sides. Both combustors are equipped with double swirl nozzles and are fired with kerosene. The former facility is rather simple in its maintenance/operation and lends itself to the optimization of laser-optical measurement equipment. However, its characteristics are not typical of realistic combustors. On the other hand the pressurized single sector combustor can be operated at up to 20 bar with air pre-heating of up to 850 K at mass flow rates of 1.3 kg/s. The observed differences in flame stability between the two combustors are reflected in the collected velocity data: While the pressurized, pre-heated flame is characterized by a strong, quiescent recirculation zone above the nozzle, the flow inside the atmospheric combustor is much more irregular. Although successful overall, the PIV applicability study presented a number of technological challenges that are typically not present in isothermal conditions. These include the treatment of increased light scattering by fuel droplets, window contamination, flame luminosity and the introduction of appropriate solid particle seeding. The encountered problems and possible solution strategies are presented in the paper