Patent Application
20070068170
The invention relates generally to the closing of a fuel supply in case of an emergency and, more particularly, to an emergency fuel shutoff system and method.
A fuel shutoff system is required on some engines or similar devices in order to close the fuel supply without or prior to the shutdown of the fuel pump system. In these engines, such as in gas turbine engines, a fuel shutoff system is provided to quickly close the fuel supply in case of an emergency. For instance, in a multi-spool gas turbine engine, the fuel supply must be interrupted extremely quickly in the event of a low pressure shaft shear. Because of the fast response time of gas turbine engines, a low pressure shaft shear may cause an increased fuel flow that is likely to increase the problem. Perhaps more critically, however, is that the turbine has virtually no load after shaft shear, and will thus quickly overspeed and fail catastrophically. These conditions require that the fuel supply be interrupted with the smallest possible delay.
Conventional fuel shutoff systems for gas turbine engines use cable and pulley mechanisms or solenoid systems. A probe or a similar arrangement is provided very close to the shaft and is used to detect the low pressure shaft shear. If this happens, the fuel supply is shutoff using a mechanical movement through the use of the cables and pulleys, or using an electrical signal. Although these mechanisms and systems have a relatively small response time, there is still a need for a faster arrangement.
Accordingly, there is a need to provide an improved emergency fuel shutoff system and method that can have a response time faster than existing mechanisms and systems.
In one aspect, the present invention provides an emergency fuel shutoff system for a gas turbine engine, the gas turbine engine having at least a fuel circuit, the fuel shutoff system comprising: an explosive member; a triggering circuit connected to the explosive member; and a fuel circuit interrupting device mounted on the fuel circuit, the interrupting device being activated by explosion of the explosive member.
In another aspect, the present invention provides an emergency fuel shutoff system to be mounted on a fuel circuit a gas turbine engine, the system comprising: a pyrotechnic device; means for triggering the pyrotechnic device; and means for closing the fuel circuit operational as a result of activation of the pyrotechnic device.
In another aspect, the present invention provides A method of shutting off a fuel circuit of a gas turbine engine, the method comprising: providing a fuel circuit closing device in the fuel circuit, the device having a ‘standby’ position wherein fuel may pass therethrough and a ‘interrupt’ position wherein the fuel flow therethrough is substantially impeded, the fuel circuit closing device being biased to the ‘interrupt’ position; holding a fuel circuit closing device in the ‘standby’ position using an explosive member; and triggering the explosive member to substantially remove the member from the fuel circuit closing device, thereby permitting the closing device to move to the ‘interrupt’ position.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
Another advantage of using explosive bolts is that they have an extremely small response time. Also, when the closing device 30 is designed with a small stroke and with a spring 34 having a very high preload, the response time of the piston 32 will be small as well.
In case of an emergency, the explosive bolt 36 is triggered to release the piston 32, thereby allowing it to move to the position where the fuel circuit 22 is closed. The explosive bolt 36 is selected to be completely contained upon firing, and thus minimize any effect to adjacent engine systems. The system 20 is said to be an emergency system since once exploded, the explosive bolt 36 must be replaced by a new one before the fuel circuit 22 be used once again.
A triggering circuit 40 is used for triggering the explosive bolt 36.
Each side 42a, 42b of the triggering circuit 40 comprises a corresponding power terminal 52a, 52b, a corresponding neutral or ground terminal 54a, 54b and an optional feedback terminal 56a, 56b. Each wear probe 50a, 50b is connected to the circuit 40 using a corresponding pair of terminals 58a, 58b. The optional feedback terminal 56a, 56b on each side 42a, 42b is used to confirm that they are powered. When no potential is detected upon starting the engine, the electronic engine control will note that there is a fault.
In the illustrated embodiment, the various terminals are attached to the fuel shutoff housing 28 using a two-part connector 60. This facilitates the maintenance or the replacement of the closing device 20. Each side of the triggering circuit 40 comprises a resistor 62a, 62b to keep a small current into the system. The resistors 62a, 62b are preferably located on the removable part of the connector 60 so that no accidental firing can occur when connecting or disconnecting the connector 60, should the power be on at that moment.
The explosive bolt 36 is triggered when the potential at the terminals of its detonator is sufficiently high. When both sides 42a, 42b are powered, and only one of the wear probes 50a, 50b is broken, the potential at the terminals of the explosive bolt 36 remains the same. However, when both probes 50a, 50b are worn off, the potential at the terminals of the explosive bolt 36 will be significantly higher, thereby triggering the explosive bolt 36.
If required, one side of the triggering circuit 40 can be deactivated so that the explosive bolt 36 be triggered using only the opposite wear probe 50a, 50b.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, although described as an explosive or pyrotechnic “bolt”, the device need not be a bolt, per se, as the skilled reader will understand. Also, the triggering circuit can have only one side or have more than two sides. The triggering circuit can be different from what is shown in the figures. The present invention is not limited to gas turbine engines and can be used on any other engines or machines. The fuel circuit closing device can differ from what is shown and described, such as being a rotary unit or be biased by a pressurized gas or the like. The system can include an additional firing activation which would allow the electronic engine control or even an operator, through the manual activation of a switch, to shutoff the fuel supply using the system. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
