Influence of effusion cooling air on the CO production in the primary zone of a pressurized single sector model gas turbine combustor

In this study, the influence of effusion cooling air on the CO production in the primary zone of a pressurized single sector model gas turbine combustor is investigated in a parametric study using a combination of laser-based diagnostics. Three species (OH, CO, CH2O) are probed using laser-induced fluorescence (LIF). In principle, this combination of probed species allows to derive the forward reaction rate of CO oxidation and the local heat release rate from the LIF signals. Based on simulations and measurements in a laminar flame, we show that the limited optical resolution of the intensified cameras severely limits the applicability of the method for pressurized flames. However, by employing a conditioning strategy, mainly using CH2O-LIF as a marker for low temperature chemistry, it was shown that effusion cooling air affects the structure of the premixed flame at large distances from the effusion cooled liner. At higher blowing ratios, samples measured in the primary zone during the CO production phase exhibit a higher CO concentration at a given level of OH concentration. Most likely, this is caused by the strong non-linear sensitivity of OH concentration to temperature, shifting the local equilibrium towards higher CO concentrations, when fractions of the effusion cooling air are recirculated towards the inlet nozzle. In the exhaust phase, dilution effects seem to dominate, as a higher effusion cooling air mass flow systematically lowers both measured OH and CO signals.