In this paper a semi-empirical method is presented to predict the NOX emission of a pilot stabilized, technically premixed gas turbine combustor for arbitrary combustor inlet conditions. The method is based on measurement data for a reference operation cycle and ISO ambient condition. A model based correction function is used to account for the change of NOX emission, which results from combustor inlet condition and/or operation cycle deviating from reference data.
The proposed method assumes that a pilot stabilized, technically premixed flame can be simplistically modeled as two separate combustion regimes: An assumed perfectly premixed regime, and an assumed diffusion flame regime. The emission of the combustor is then modeled as a superposition of the emissions from both individual combustion regimes. The emissions from the diffusion flame regime are the dominant contribution, although only a comparably small share of fuel is burnt in this regime.
The emission of the perfectly premixed combustion regime can be modeled as a sole function of flame temperature. On the other hand, the emissions from the diffusion regime are strongly affected by combustor inlet pressure and temperature, which are in turn a function of the gas turbine operation cycle and inlet conditions. To simplify matters, only the change in NOX emission from the diffusion regime, which results from deviation of combustor inlet pressure and/or temperature from values expected for a reference operation cycle and ISO ambient condition, is modeled. NOX emission data for this reference operation cycle is necessary experimental input for the method.
The proposed method can — with minimum experimental input — predict the NOX emission of a pilot stabilized, technically premixed combustor with good accuracy for arbitrary engine operation cycles and inlet conditions. It is aimed at providing reliable NOX emission estimates without the need for time intensive CFD or expensive experimental investigations. Typical applications are the assessment of a gas turbine’s NOX potential for feasibility studies of new operation or engine concepts with a proven combustor design, and for NOX estimates for out-of-experience ambient or site conditions for existing engines.