The “High-pressure Experiments“ group is experimentally investigating the autoignition of different gaseous fuels at gas turbine relevant operating conditions (pressure, temperature, flow field) in the combustor system “Reheat”. This combustion concept implemented in the largest ALSTOM gas turbine is characterized by two combustors with an expansion step in a high-pressure turbine stage in between. With temperatures higher than 1000 K in the mixing section of the second combustor, the injection of highly reactive hydrogen-rich fuels is challenging because of much higher flashback and autoignition risks in comparison with the gas turbine standard fuel natural gas. Autoignition is a spontaneous and local event which strongly increases the temperature, pressure and radical concentration.
Experiments at gas turbine relevant operating conditions are performed in a generic optically accessible reheat combustor (see photo below) implemented in the high-pressure combustor rig Stuttgart (HBK-S) which allows the application of optical diagnostics. The onset and the temporal and spatial development of autoignition kernels are recorded by high-speed imaging (a typical result is given below).