Combustion system control

1. A method of controlling a combustion system of a gas turbine engine, the gas turbine engine having: a compressor section with an inlet; a combustor with a primary combustion zone, of which a condition in the primary combustion zone is defined by a primary zone control parameter; a turbine section having an inlet region; the method comprising:

controlling the primary zone control parameter to have a substantially constant value over a range of values of compressor inlet air temperature, the range of values of compressor inlet air temperature based on ambient temperature variation,

determining a turbine entry temperature at the turbine inlet as a function of compressor inlet temperature for a predetermined value of the primary zone control parameter, and

controlling one or more engine operating parameters to a value, or range of values, determined as a function of compressor inlet air temperature and/or turbine entry temperature; wherein the primary zone control parameter in the combustor is controlled to be substantially equal to the predetermined value of the primary zone control parameter; and wherein the determined turbine entry temperature is within a predetermined range of turbine entry temperature values.

2. The method as claimed in claim 1 ,

wherein the primary zone control parameter is one of: a primary zone temperature or a primary zone equivalence ratio.

3. The method as claimed in claim 1 ,

wherein the determined turbine entry temperature is determined from a predetermined relationship which correlates the range of compressor inlet air temperature values to the range of turbine entry temperature values for a predetermined constant value of the primary zone control parameter, wherein the relationship is defined by a:

a look up table, including interpolation between data points in the look up table; an equation; and/or

a best fit relationship of a series of values of compressor inlet air temperature and turbine entry temperature.

4. The method as claimed in claim 1 , wherein the engine operating parameter(s) is/are chosen from a list comprising:

compressor intake air flow; compressor delivery air pressure; compressor delivery temperature; fuel mass flow rate into combustor; and/or combustor air fuel ratio.

5. The method as claimed in claim 1 ,

wherein the primary zone control parameter is controlled to have a substantially constant value at a predetermined engine power condition value, or range of values.

6. The method as claimed in claim 5 , wherein the predetermined engine power condition value is substantially 100%.

7. The method as claimed in claim 5 ,

wherein the predetermined engine power condition is less than 100% and

wherein a compressor intake air flow is less than 100% of maximum compressor intake flow; or

wherein the compressor intake air flow is reduced after intake prior to delivery to the combustor.

8. The method as claimed in claim 1 , further comprising:

measuring, inferring and/or calculating compressor inlet air temperature.

9. A control system for a combustion system of a gas turbine engine comprising:

a controller, and

one or more sensors,

wherein the control system is configured to implement the method of claim 1 .

10. A control system for a combustion system of a gas turbine engine comprising:

a controller, and

one or more sensors, wherein the control system is configured to implement the method of claim 1 ,

wherein the controller is programmed to determine from a predetermined relationship which correlates the range of compressor inlet air temperature values to the range of turbine entry temperature values for a predetermined constant value of the primary zone control parameter, wherein the relationship is defined by a:

a look up table, including interpolation between data points in the look up table; an equation; and/or a best fit relationship of a series of values of compressor inlet air temperature and turbine entry temperature.

11. A gas turbine engine, comprising: a compressor section with an inlet;

a combustor with a primary combustion zone, a turbine section having an inlet region, and a control system, the control system comprising a controller and one or more sensors,

wherein the control system is configured to implement the method of claim 1 ,

wherein the controller is programmed to determine from a predetermined relationship which correlates the range of compressor inlet air temperature values to the range of turbine entry temperature values for a predetermined constant value of the primary zone control parameter, wherein the relationship is defined by a:

a look up table, including interpolation between data points in the look up table; an equation; and/or

a best fit relationship of a series of values of compressor inlet air temperature and turbine entry temperature.

12. A method of manufacturing a control system for a combustion system of a gas turbine, the gas turbine having: a compressor section with an inlet; a combustor with a primary combustion zone, of which a condition in the primary combustion zone is defined by a primary zone control parameter; and a turbine section having an inlet region; the method comprising:

determining a value of the primary zone control parameter for optimal control of NOx, CO and/or UHC;

determining a range of values of turbine entry temperature at the turbine inlet as a function of a range of compressor inlet temperatures for a predetermined value of primary zone control parameter, the range of compressor inlet air temperatures based on ambient temperature variation;

configuring the combustor and/or control system so as to:

control the primary zone control parameter over the range of compressor inlet air temperatures:

wherein the primary zone control parameter is controlled to be substantially equal to the determined value of the primary zone control parameter; and

wherein the turbine entry temperature is within the predetermined range of values for the turbine entry temperature.

13. The method as claimed in claim 12 ,

wherein the primary zone control parameter is one of: a primary zone temperature or a primary equivalence ratio.