Method and apparatus for controlling a compressor of a gas turbine engine

1. A method of operating an environmental control system, the environmental control system comprising a dedicated environmental control system compressor powered configured to provide environmental control system input air;

the method comprising:

determining a current operating point of a gas turbine engine compressor; and reducing the environmental control system input mass flow when the current operating point of the compressor is determined to be less than a first predetermined margin of the compressor surge line, and increasing the environmental control system input mass flow when the current operating point of the compressor is determined to be greater than a second predetermined margin of the compressor surge line modulating mass flow of environmental control system input air to maintain

the operating point of the gas turbine engine compressor within predetermined limits.

2. A method according to claim 1 , wherein the gas turbine engine comprises a high pressure compressor coupled to a high pressure turbine, a booster compressor coupled to a low pressure turbine, and a fan coupled to the low pressure turbine, the fan and booster compressor being coupled to the low pressure turbine by a low pressure shaft, and the high pressure compressor being coupled to the high pressure turbine by a high pressure shaft.

3. A method according to claim 1 , wherein the gas turbine engine comprises a high pressure compressor coupled to a high pressure turbine by a high pressure shaft, an intermediate pressure compressor coupled to an intermediate pressure turbine by an intermediate pressure shaft, and a fan coupled to a low pressure turbine by a low pressure shaft.

4. A method according to claim 1 , wherein the environmental control system compressor is powered by an electric motor, and wherein the electric motor is electrically powered by a gas turbine engine driven electrical generator.

5. A method according to claim 4 , wherein the gas turbine engine comprises a high pressure compressor coupled to a high pressure turbine, a booster compressor coupled to a low pressure turbine, and a fan coupled to the low pressure turbine, the fan and booster compressor being coupled to the low pressure turbine by a low pressure shaft, and the high pressure compressor being coupled to the high pressure turbine by a high pressure shaft, and

the gas turbine engine generator that provides electrical power for the electric motor is driven by one of the low and intermediate pressure shafts.

6. A method according to claim 1 , wherein the method comprises determining a combination of handling bleed valve positions and environmental control system input mass flows which maintains the operating point of the compressor at or above a minimum surge margin, or substantially matches the operating point of the compressor to the minimum surge margin.

7. A method according to claim 1 , wherein the method comprises determining the operating point by comparing one or more sensed gas turbine engine parameters to a lookup table.

8. A method according to claim 7 , wherein the sensed gas turbine engine parameters comprise one or more of pressure ratio, fuel flow, core air temperature compressor mass airflow and compressor rotational speed.

9. A method according to claim 1 , wherein the method comprises comparing a pressure difference between the determined current operating point and a surge line to determine a current surge margin.

10. A method according to claim 9 , wherein the method comprises using a lookup table comprising a relationship between environmental control system input air mass flow and current surge margin to determine an environmental control system input air mass flow required to match the operating point of the gas turbine engine compressor to the minimum surge margin.

11. A method according to claim 1 , wherein the method comprises modulating a mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor within predetermined limits only where the environmental control system input air mass flow is less than a maximum environmental control system inlet air mass flow capacity.

12. A method according to claim 1 , wherein the method comprises modulating a mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor within predetermined limits only where a difference between the environmental control system input air mass flow and an environmental control system inlet air flow set point is less than a predetermined value.

13. A method according to claim 1 , wherein the method comprises modulating a mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor within predetermined limits only where an environmental control system flow control mode is selected.

14. A method according to claim 1 , wherein the method comprises modulating a mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor within predetermined limits only where the difference between the surge margin with the modulated ECS air flow and the minimum surge margin is less than the difference between the surge margin that would be provided by opening a handling bleed and the minimum surge margin, and opening a handling bleed valve if the difference between the surge margin with the modulated ECS air flow and the minimum surge margin is greater than the difference between the surge margin that would be provided by opening a handling bleed and the minimum surge margin.

15. An environmental control system comprising:

a handling bleed valve system;

an environmental control system air input system; and

a controller configured to modulate mass flow of environmental control system input air in accordance with the method of claim 1 .

16. A method of operating an environmental control system comprising:

determining a current surge margin of a gas turbine engine compressor; and

modulating mass flow of environmental control system input air to maintain the surge margin of the gas turbine engine compressor within predetermined limits; and

modulating a proportion of environmental control system input air and recirculation air in the environmental control system to thereby maintain to maintain cabin airflow within predetermined limits.

17. An environmental control system comprising:

a handling bleed valve system;

an environmental control system air input system; and

a controller configured to modulate mass flow of environmental control system input air in accordance with the method of claim 16 .

18. A method of operating an environmental control system comprising:

determining a current surge margin of a gas turbine engine compressor; and

modulating a mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor within predetermined limits only where the difference between the surge margin with the modulated environmental control system mass flow and the minimum surge margin is less than the difference between the surge margin that would be provided by opening a handling bleed and the minimum surge margin, and opening a handling bleed valve if the difference between the surge margin with the modulated environmental control system air flow and the minimum surge margin is greater than the difference between the surge margin that would be provided by opening a handling bleed and the minimum surge margin.

19. An environmental control system comprising:

a handling bleed valve system;

an environmental control system air input system; and

a controller configured to modulate mass flow of environmental control system input air in accordance with the method of claim 18 .