WO1992007179A1

WO1992007179A1 - Fuel supply system

Info

Publication number: WO1992007179A1
Application number: PCT/US1991/006363
Authority: WO
Inventors: John R. Williamson
Original assignee: Allied-Signal Inc.
Priority date: 1990-10-15
Filing date: 1991-09-05
Publication date: 1992-04-30

Abstract

A fuel supply system (10) for providing fuel flow to a gas turbine engine (12) is provided that includes a first stage electric boost pump (26), a second stage ejector pump (30) that only operates when the electric boost pump (26) is not operating and a third stage engine driven, dual displacement pump (40).

Description

FUEL SUPPLY SYSTEM TECHNICAL FIELD

This invention relates to fuel supply systems for gas turbine engines and more specifically to an improved fuel supply system and method that includes a dual displacement pump and an ejector boost pump.

BACKGROUND OF THE INVENTION

While fuel supply systems for gas turbine engines come in many configurations, a typical fuel supply system includes a fuel tank, several stages of fuel 0 pumps, and a fuel control which meters the fuel and feeds the fuel to the engine's combustor. Within these several pump stages there is usually one engine driven, positive displacement pump which is the main pump in the system and at least one low pressure pump that maintains lb a minimum pressure at the inlet to the main pump to prevent cavitation therein. Positive displacement pumps discharge fuel flow at a rate that is proportional to the rotational speed of the pump. Because this pump is driven by the engine the rotational speed of the pump is

20 proportional to the rotational speed of the engine. A problem that exists with these types of pumps is that they discharge more fuel than is required by the engines when the aircraft is operating at altitude. The reason for this is that the displacement of the pump must be

25 sized to meet the fuel flow required to light-off the engine. The term light-off refers to the point during the start sequence of a gas turbine engine at which the conditions in the combustor are suitable to support combustion. Generally, light-off occurs at an engine rotational speed which is about 10-12% of the engines full operating speed. Therefore, the pump is sized at a rotational speed of about 10-12% of the pumps operating speed. However, while the fuel discharged by the pump is linearly proportional to the speed of the pump such a relationship does not hold for the engines. Therefore, when the engine reaches its operating speed, referred to as 100% speed, the pump also reaches its 100% speed and discharges more fuel flow than is needed by the engine. This problem gets worse as the aircraft operates at altitude, because at higher altitudes ambient temperatures and pressures are less than at sea level and consequently, the engines require less fuel flow to maintain 100% speed. Under these conditions, the entire fuel flow into the pump is being pressurized while only a portion of this fuel flow is being used by the engine. The unused portion of fuel flow is usually bypassed back to the pump inlet to be recirculated through the pump. This recirculation produces large amounts of heat which increases the temperature of the fuel and represents lost energy.

In the prior art, numerous fuel supply systems are disclosed in which an attempt is made to put this lost energy to use.

LaGrone, U.S. Patent No. 4,339,917 discloses a fuel supply system which includes a first stage ejector pump, a second stage compressor and a third stage, engine driven positive displacement pump. Excess fuel exiting from the third stage pump is sent to a hydraulic turbine which drive the second stage compressor. A portion of the flow exiting the second stage compressor is used to drive the first stage ejector pump. Because all the stages are ultimately driven by the engine a reservoir of fuel just upstream of the third stage is required to supply fuel during an engine start sequence.

Symon, U.S. Patent No. 4,703,136 discloses a fuel supply system which includes a first stage ejector pump, a fuel filter, and a second stage engine driven positive displacement pump. Excess fuel exiting from the positive displacement pump is injected through the ejector pump thereby using the temperature of this fuel to prevent ice from forming in the filter.

Turner et al., U.S. Patent No. 3,736,072 discloses a fuel supply system including a first stage electric boost pump, a second stage backing pump, a third stage ejector pump and a fourth stage engine driven positive displacement pump. After the engine has been started excess fuel is directed from the fuel control back to the ejector pump. Once the ejector pump is operating, the first stage pump is shut down.

Magnus Jr., U.S. Patent No. 3,043,104 discloses a fuel supply system including a first stage ejector pump, a second stage ejector pump and a third stage engine driven, fixed displacement pump. Excess fuel is sent form the fuel control back to the ejector pumps.

In each of the above mentioned system the engine driven pump must operate at full capacity when the engine is operating at 100% speed regardless of the altitude and thereby generates a large temperature rise in the fuel.

Accordingly, a need exists for a fuel supply system that can provide sufficient fuel flow to light off a gas turbine engine at sea level and can provide fuel flows less than the system's full capacity when the gas turbine engine is at its operating rotational speed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fuel supply system that can provide sufficient fuel flow to light off a gas turbine engine at sea level and can provide fuel flows less than the system's full capacity when the gas turbine engine is at its operating rotational speed.

The present invention achieves the above-stated objective by incorporating an engine driven dual displacement pump in a a fuel supply system. A dual displacement pump, also referred to as a dual pressure pump, is a pump capable of generating two fuel flows at the same or different pressures depending on the conditions downstream of the pump's exit ports. At altitude the flow from one of the exit ports is at full pressure and is sent to the engine while the flow from the second port, which is at a lower pressure, can be recirculated. Because it is not possible to operate this lower pressure discharge port at 0 psig backpressure, this excess discharge pressure is put to use by feeding the fuel flow therefrom into an ejector pump upstream of the dual displacement pump.

These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWINGS

The single FIGURE is a partially schematic, partially cross-sectional diagram of a fuel supply system contemplated by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, a fuel supply system generally denoted by the numeral 10 is shown in conjunction with a gas turbine engine 12 having an associated gear box 14 which drives a positive displacement pump 40 through a mechanical connection shown schematically by dotted line 18. The pump 40 feeds pressurized fuel through delivery conduit 20 to a fuel control shown schematically at 22 for subsequent delivery to the engine 12.

The fuel supply system 10 further includes a fuel tank 24 having a low pressure pump 26 having driving means independent of the engine 12 and disposed within the tank 24 so that the pump 26 is gravity fed even when the tank 24 is almost empty. In the preferred embodiment, the pump 26 is an electric boost pump. Fuel is pumped by the pump 26 through a conduit 28 to an eductor type intake port 32 of an ejector or jet boost pump 30 that effects an aspirating action in drawing fuel through conduit 28 when the pump 26 is not operating. The ejector 30 further includes aspirating nozzle means in the form of a nozzle 34 disposed in alignment with an eductor type exhaust port 36. Fuel flow exiting from the exhaust port 36 is directed to the pump 40. The pump 40 is preferably a dual displacement or dual pressure gear pump comprising a housing 50 with three pumping gears 44, 46 and 48 mounted therein. The gears 44, 46 and 48 are arranged so that the gear 46 intermeshes with both gears 44 and 48. Each of the gears 44, 46, 48 are carried on rot ta le shafts, 54, 56 and 58 respectively. The shaft 56 is rotatably driven by the gear box 14. As the shaft 56 drives gear 46 counterclockwise, the gear 46 drives the gears 44 and 48 clockwise. Accordingly, the gear 44 and 46 form a first gear pump and the gears 46 and 48 form a second gear pump in parallel flow arrangement with the first gear pump. The pump 40 can be either a fixed displacement or variable displacement pump. However, the fixed displacement configuration is preferred because it is simpler, more reliable and less costly.

The housing 50 has a first inlet 51 and a first outlet 52 disposed generally on a common tangent between the gears 44 and 46, and a second inlet 53 and a second outlet 54 disposed generally on a common tangent between the gears 46 and 48. The inlets 51 and 53 are on opposite sides of the housing 50 as are the outlets 52 and 54. Both inlets 51 and 53 receive fuel flow from the exhaust port 36. The fuel exiting outlet 52 is pumped through the delivery conduit 20 while the fuel exiting outlet 54 is pumped to a valve means 60. In the preferred embodiment, the housing 50 would also enclose the ejector pump 30.

A more detailed description of a dual displacement gear pump such as pump 40 can be found in

Carter et al., U.S. Patent No. 4,204,811 which is incorporated herein by reference and which also is assigned to the assignee of the present invention. The valve means 60, shown schematically, is embodied, for example, as an actuatable, two-position valve. The valve 60 is positioned by an actuator 61 controlled from the fuel control system 22 shown schematically by dotted line 63. In a first position, the valve means 60 directs the fuel pumped through outlet 54 to the delivery conduit 20, and in a second position this fuel is directed to the nozzle 34 in the ejector 30.

During the start sequence of the aircraft engine, the electric boost pump pumps fuel from the tank 24 to the pump 30, and the valve means 60 is positioned to direct the fuel flow therethrough to the delivery duct 20. At an engine and pump speed of about 10-12% the combustor of the gas turbine engine lights-off and the engine begins to accelerate. When the rotational speed of the engine and the pump 40 reaches self sustaining speed, about 40% speed, the pump 26 is shut off and the valve means 60 is repositioned to direct the flow through the valve means 60 to the ejector 30. The fuel flow entering the ejector 30 is accelerated by the nozzle 34 so that the stream of fuel exiting the nozzle 34 has a much larger velocity than the stream of fuel flowing through the intake port 32. As these two fuel streams mix, the velocity of the slower stream is increased creating a sectioning effect which draws fuel from the fuel tank 24. A pressure relief valve 65 is provided to direct any fuel not used by the ejector back to the fuel tank 24.

The advantages of the present invention are that it can provide sufficient fuel flow at low engine speeds and also, effectively reduced fuel flows at higher engine speeds. Also, it is more efficient than the prior art systems, because at the higher engine speeds the fuel flow at outlet 54 is at a lower pressure than the fuel flow at outlet 52. Additional efficiency is gained by using the energy of this lower pressure flow to drive the ejector 30.

Various modifications and alterations to the above described system will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A fuel supply system for a gas turbine engine having a fuel control, comprising in combination: a fuel source; a low pressure pump driven independently of said gas turbine engine and operably disposed in said fuel source; an ejector pump having nozzle means, an intake port in fluid communication with said low pressure pump and an exhaust port; a dual displacement pump having an inlet in fluid communication with said exhaust port of said ejector pump and having a first and second exhaust ports, said first exhaust port feeding said fuel control; and valve means in fluid communication with said second exhaust port of said dual displacement pump, for alternately directing fuel flow from said second exhaust port to said fuel control or said nozzle means of said ejector pump.

2. The fuel supply system of Claim 1 wherein said dual displacement pump is a gear type pump.

3. The fuel supply system of Claim 1 wherein said dual displacement pump is a fixed displacement pump.

4. The fuel supply system of Claim 1 wherein said dual displacement pump is driven by said engine.

5. The fuel supply system of Claim 1 wherein said low pressure pump is driven by an electric motor.

6. The fuel supply system of Claim 2 wherein said gear type pump further comprises a first pumping gear rota ably engaging a second pumping gear, and rotatably

engaging a third pumping gear, said first and second gears being for pumping fluid from said inlet to said first exhaust port of said dual displacement pump, and said first and third gears being for pumping fuel from said inlet to said second exhaust port of said dual displacement pump.

7. A fuel supply system for delivering fuel from a fuel source to a fuel control of a gas turbine engine, comprising, pumping means for pumping fuel from an inlet of said pumping means to a first and second outlet of said pumping means; a fuel passageway extending between said fuel source and said inlet and having a first fuel flow stream therethrough; and means, disposed in said passageway, for converting the flow from said second outlet into a second flow stream within said passageway, said second flow stream having a velocity greater than the velocity of said first flow stream.

8. The fuel supply system of Claim 7 further comprising a valve means for selectively directing said flow from said second outlet to said fuel control or said converting means.

9. A fuel supply system for a gas turbine engine having a fuel control, comprising in combination: a fuel source; a low pressure pump operably disposed in said fuel source; an ejector pump having nozzle means, an intake port in fluid communication with said boost pump and an exhaust port; a third and fourth pump in a parallel flow arrangement each of said third and fourth pumps having an intake port in fluid communication with said exhaust port of said ejector pump and having an exhaust port, said exhaust port of said third pump feeding said fuel control; and valve means for alternately directing fuel flow from said exhaust port of said fourth pump to said fuel control or said nozzle means of said ejector pump.

10. A fuel supply system for a gas turbine engine having a fuel control, comprising in combination: a fuel source; a low pressure pump operably disposed in said fuel source; an ejector pump having nozzle means, an intake port in fluid communication with said boost pump and an exhaust port; and a third pump intermediate said exhaust port of said ejector pump and said fuel control and driven by said engine, having means for driving said ejector pump when said engine attains a self sustaining operating condition.

11. A fuel supply system for a gas turbine engine having a fuel control, comprising in combination: a fuel source; a low pressure pump operably disposed in said fuel source; an ejector pump having nozzle means, an intake port in fluid communication with said boost pump and an exhaust port; and a third pump intermediate said exhaust port of said ejector pump and said fuel control and driven by said engine, having means for alternately pumping fuel to said fuel control or to said ejector pump.

12. A method for transferring fuel from a fuel source to a gas turbine engine during a start sequence of the gas turbine engine comprising the steps of: drawing fuel from a fuel source by use of an low pressure pump disposed in the fuel source; feeding said fuel from said low pressure pump to an inlet of a dual displacement pump; initially delivering all the flow exiting said dual displacement pump to said gas turbine engine; and shutting off said low pressure pump when the rotating speed of said gas turbine engine attains a self sustaining operating condition and substantially simultaneously redirecting a portion of said flow exiting said dual displacement pump to an ejector pump disposed between said fuel source and said dual displacement pump.

13. The method of Claim 12 further comprising the step of continuing to draw fuel from said fuel source.