Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
1999-07-27
2001-03-06
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
With safety device
Reexamination Certificate
active
06195978
ABSTRACT:
The present invention relates generally to fuel delivery systems for engines, especially aircraft gas turbine engines, and more particularly to an ecology system for such fuel delivery systems.
Some fuel delivery systems for gas turbine engines require an ecology function that removes a set quantity of fuel from the engine fuel manifold after engine shutdown. This is required for two reasons. First, it keeps fuel from vaporizing into the atmosphere. Second, it keeps the fuel from coking on the engine's fuel nozzles, a condition that hinders nozzle performance, leading to premature failure. A costly and complex solution is provided by prior art ecology systems which use a complex arrangement of pistons, check valves, divider valves, plumbing, reservoirs and pumps to accomplish this task, some such features being shown in Cole U.S. Pat. No. 4,206,595 and Wernberg U.S. Pat. No. 5,809,771. This type of architecture results in a high cost and weight ecology system.
It is desirable to minimize the fuel remaining in an engine fuel manifold upon cessation of engine operation and there is a demand for the provision of a compact, economical ecology function for fuel supply systems.
The present invention provides solutions to the above problems by reversing the direction of fuel flow to the engine upon engine shut-off by adding one valve to the main fuel control, and modifying the main fuel control pressurizing valve to include a pressure switching function. The valve has a movable piston defining therein a variable volume chamber and purges the engine fuel manifold by withdrawing a one piston stroke volume of fuel from the conduit coupling the valve to the engine fuel manifold when the engine is de-energized. Separate components, mounting brackets and engine plumbing are eliminated, reducing total system weight and cost.
In accordance with one form the invention, an ecology valve whose position is solely controlled by a pressurizing valve, supplies fuel from the pressurizing valve to the engine fuel manifold during normal engine operation and withdraws fuel from the engine fuel manifold during cessation of engine operation. The ecology valve includes a valve housing with an inlet port coupled to a main fuel flow outlet of the pressurizing valve, an outlet port coupled to the engine fuel manifold, and a control port connected to a control port of the pressurizing valve. The valve contains a movable piston having opposed piston faces. The piston is reciprocable between one position allowing maximum fuel flow from the inlet port to the outlet port, and another position substantially blocking any fuel flow from the inlet port to the outlet port. The piston responds to high pressure at the ecology valve control port to move toward the fuel passing position and to lower pressure at the ecology valve control port, indicative of cessation of engine operation, to move toward the fuel blocking position and, concurrently, to withdraw fuel from the engine fuel manifold. One piston face receives the control inlet pressure and the other face defines, in conjunction with the housing, a variable volume chamber in to which fuel is drawn during engine shut-down.
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Allied-Signal Inc.
Evora Robert Z.
Freay Charles G.
Palguta Larry J.
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