Pulsed fuel injection system for reducing NO.sub.x emissions

In a gas turbine combustion process in which liquid fuel is introduced through a plurality of fuel injectors to a primary combustion zone of a combustor as a fine spray, and air is compressed and introduced as primary air to the primary combustion zone with the fuel spray to form a combustible mixture, and is also introduced as secondary air to a secondary combustion zone through a multiplicity of discrete jets and cooling passageways to cool the combustor walls, assist the mixing of the fuel and air, complete the combustion of the gases from the primary combustion zone and cool and dilute them for emission, the improvement which comprises supplying a continuous flow of said liquid fuel and primary air to form a combustible mixture in said primary combustion zone, modulating the flow rate of a portion of said liquid fuel through each of said fuel injectors in the form of uniformly-spaced modulations in the fuel flow rate, sensing a condition of the combustion process representative of the extent of NO.sub.x formation, and adjusting the frequency and/or amplitude of the modulations in order to produce a controlled degree of gas flow oscillation in the form of cyclic expansion and contraction of the primary and secondary combustion zones without creating a net pressure gain throughout the combustion chamber, thereby substantially improving the gas phase mixing rate and the homogeneity of the formed fuel/air mixtures and decreasing the net extent of NO.sub.x formation normally resulting from the transitioning of fuel-air mixtures from high to low stoichiometry during combustion or oxidation.

In a gas turbine combustor apparatus comprising means for introducing liquid fuel to a primary combustion zone as a fine spray and means for compressing the introducing primary air to primary combustion zone with the fuel spray to form a combustile mixture, and means for introducing secondary air to a secondary combustion zone through a multiplicity of discrete jets and cooling passageways to cool the combustor walls, assist the mixing of the fuel and air, complete the combustion of the gases from the primary combustion zone and cool and dilute them for emission, the improvement which comprises means for modulating the flow rate of a portion of said liquid fuel in the form of uniformly-spaced increases in the fuel flow rate, with a time period between peaks in said uniformly-spaced modulations of less than about 10 milliseconds, in order to produce a controlled variation of primary zone combustion temperature and volume, resulting in a controlled degree of gas flow oscillation in the form of cyclic expansion and contraction of the primary and secondary combustion zones without creating a net pressure gain throughout the combustion chamber, thereby substantially improving the gas phase mixing rate and the homogeneity of the formed fuel/air mixtures and decreasing the net extent of NO.sub.x formation normally resulting from the transitioning of fuel-air mixtures from high to low stoichiometry during combustion or oxidation.

In a gas turbine combustor apparatus comprising a plurality of fuel injectors for introducing liquid fuel to a primary combustion zone as a fine spray and means for compressing and introducing primary air to the primary combustion zone with the fuel spray to form a combustible mixture, and means for introducing secondary air to a secondary combustion zone through a multiplicity of discrete jets and through cooling passageways to cool the combustor walls, assist the mixing of the fuel and air, complete the combustion of the gases from the primary combustion zone and cool and dilute them for emission, the improvement which comprises means for modulating the flow rate of a portion of said liquid fuel in the form of uniformly-spaced increases in the fuel supply rate, means for sensing a condition of the combustion process representative of- the extent of NO.sub.x formation, and means for adjusting the frequency and/or amplitude of the modulations, in order to produce a controlled variation of primary zone combustion temperature and volume, resulting in a controlled degree of gas flow oscillation in the form a cyclic expansion and contraction of the primary and secondary combustion zones without creating a net pressure gain throughout the combustion chamber, thereby substantially improving the gas phase mixing rate and the homogeneity of the formed fuel/air mixtures and decreasing the net extent of NO.sub.x formation normally resulting from the transitioning of fuel-air mixtures from high to low stoichiometry during combustion or oxidation.