Oscillations in Gas-Turbine Combustors; Control of Rumble, Pattern Factor and Emissions

The experiments with kerosene fuel have been stopped temporarily and the results examined. It is evident that NOx reductions up to 50% can be achieved with oscillation of the fuel, and that the amplitudes associated with reductions of this magnitude are difficult to achieve and may be undesirable in practice. Improvements in pattern factor can also be achieved, usually when the original pattern factor is poor, and are largest with low frequency oscillations as might be expected. The T-vaporiser used for kerosene fueling of the gas-turbine sector has been replaced by a double jet arrangement to allow the use of gaseous fuel and preliminary experiments show first that the pattern factors are poor as a result of the poorer mixing associated with forward injection of fuel and second that reduction is NOx emissions are again present with magnitudes of the order of 20%. Perhaps most promising is the application of oscillations to neighbouring fueling devices, but out of phase, so that the near field is subject to the oscillations and the far field is not. This appears to result in NOx reductions, since thermal NOx is produced in the near field, but without the possibly harmful effects of pressure waves throughout the combustor. p1