Engine fuel control system
An engine fuel control system includes a fuel metering valve operable to control the flow of fuel between a supply line and a delivery line. The delivery line is configured to receive fuel from one or more fuel pumps. The engine fuel control system further includes a pressure raising arrangement which receives the fuel flow from the delivery line and raises the fuel pressure therein. The engine fuel control system further includes a pressure sensor arranged to sense the pressure of the fuel in the supply line between the one or more fuel pumps and the fuel metering valve, or to sense the pressure of the fuel in the delivery line between the fuel metering valve and the pressure raising arrangement.
1. An engine fuel control system including:
a fuel metering valve operable to control the flow of fuel between a supply line and a delivery line, the supply line being configured to receive fuel from one or more fuel pumps,
a pressure raising arrangement which receives the fuel flow from the delivery line and raises the fuel pressure therein,
a pressure sensor located downstream of the one or more fuel pumps and upstream of the fuel metering valve to sense the pressure of the fuel on the supply line, or located downstream of the fuel metering valve and upstream of the pressure raising arrangement to sense the pressure of the fuel on the delivery line, and
an engine electronic controller configured to detect an upward runaway event using the fuel pressure sensed by the pressure sensor, and implement an upward runaway curtailing procedure when the upward runaway event is detected.
2. The engine fuel control system according to claim 1 , wherein the one or more fuel pumps comprise a small displacement fuel pump and a large displacement fuel pump, the supply line having a branch from the small displacement fuel pump and a branch from the large displacement fuel pump, and the pressure sensor is located in the branch from the large displacement fuel pump to sense the pressure of the fuel on the supply line.
3. The engine fuel control system according to claim 1 further including a health monitor which uses the sensed fuel pressure to monitor the health of the fuel control system.
4. The engine fuel control system according to claim 1 , wherein the engine controller detects the upward runaway event on the basis of the value of the sensed fuel pressure and/or the rate of change of the sensed fuel pressure.
5. The engine fuel control system according to claim 1 , wherein the engine controller further implements an engine control recovery procedure using the sensed fuel pressure as an indication of fuel flow.
6. The engine fuel control system according to claim 5 , wherein the engine controller further receives an indicator of engine power output as a measure of engine overthrust, and uses the indicator of engine power output in the implementation of the engine control recovery procedure.
7. The engine fuel control system according to claim 1 , wherein the or another engine electronic controller implements an engine windmill relight procedure in which the or the another engine electronic controller determines a desired fuel delivery rate, and controls the fuel metering valve to provide a nominal fuel delivery rate which is higher than that corresponding to the desired fuel delivery rate, the or the another engine electronic controller using the sensed fuel pressure to determine the nominal fuel delivery rate.
8. The engine fuel control system according to claim 1 , wherein the or the another engine electronic controller uses the sensed fuel pressure to detect a blockage in the delivery line.
9. The engine fuel control system according to claim 3 , including a pump health monitor which uses the sensed fuel pressure to determine the health of at least one of the fuel pumps.
10. The engine fuel control system according to claim 9 , wherein the one or more fuel pumps comprise a small displacement fuel pump and a large displacement fuel pump, the supply line having a branch from the small displacement fuel pump and a branch from the large displacement fuel pump, and the pressure sensor is located in the branch from the large displacement fuel pump to sense the pressure of the fuel on the supply line, the pump health monitor using the sensed fuel pressure to determine the health of the large and the small displacement fuel pumps.
11. The engine fuel control system according to claim 1 further including a pressure drop control arrangement operable to regulate a pressure drop across the fuel metering valve, the pressure drop control arrangement maintaining, during a normal operation, a substantially constant pressure drop across the metering valve.
12. The engine fuel control system according to claim 11 , wherein the pressure drop control arrangement comprises a pressure drop control valve and a spill valve.
13. The engine fuel control system according to claim 12 , wherein the delivery line is configured to receive fuel from the one or more fuel pumps, wherein the spill valve is a combining spill valve, operable to supply fuel to the supply line from the one or more fuel pumps.
14. The engine fuel control system according to claim 1 , wherein the engine is a gas turbine engine.
15. A gas turbine engine having the engine fuel control system of claim 1 .