FUEL PREHEATING USING ELECTRIC PUMP

• US 20130192679A1
• Filed: 07/05/2012
• Published: 08/01/2013
• Est. Priority Date: 02/01/2012
• Status: Active Grant

• Current Assignee: United Technologies Corporation (Rtx Corporation)
• Original Assignee: Hamilton Sundstrand Corporation (Rtx Corporation)
• Inventors: Ripley, David Lloyd, Hagshenas, Behzad
• Granted Patent: US 9,206,775 B2
• Time in Patent Office: Days
• US Class Current: 137/2
• CPC Class Codes: B64D 37/34 Conditioning fuel, e.g. heating during filling B64D37/18
• CPC Class Codes: B64D 41/00 Power installations for auxiliary purposes
• CPC Class Codes: F02C 7/236 Fuel delivery systems comprising two or more pumps
• CPC Class Codes: F02M 31/166 with mechanical generation of heat, e.g. by surface friction
• CPC Class Codes: F02M 37/0052 Details on the fuel return circuit; Arrangement of pressure regulators
• CPC Class Codes: F05D 2220/50 for auxiliary power units (APU's)
• CPC Class Codes: F05D 2260/606 Bypassing the fluid
• CPC Class Codes: F05D 2260/85 Starting
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y10T 137/0324 With control of flow by a condition or characteristic of a fluid
• CPC Class Codes: Y10T 137/86139 Serial

Abstract

A fuel system for an auxiliary power unit includes a mechanical fuel pump, an electric fuel pump, and a controller. The mechanical fuel pump provides fuel flow to the auxiliary power unit and has an output dependent upon an operational speed of the auxiliary power unit. The electric fuel pump is located in flow series with the mechanical fuel pump. The controller causes the electric fuel pump to circulate and thereby warm fuel prior to start up of the auxiliary power unit.

Claims

1. A fuel system for an auxiliary power unit, the fuel system comprising:

a mechanical fuel pump for providing fuel flow to the auxiliary power unit, the mechanical fuel pump having an output dependent upon an operational speed of the auxiliary power unit;

an electric fuel pump located in series with the mechanical fuel pump; and

a controller for causing the electric fuel pump to circulate and thereby warm fuel prior to start up of the auxiliary power unit.

2. The fuel system of claim 1, wherein the electric fuel pump is located upstream of the mechanical fuel pump on a common fuel supply conduit.

3. The fuel system of claim 2, further comprising:

a bypass conduit having a first end and a second end, the first end fluidly connected to the fuel supply conduit upstream of the electric fuel pump and the second end fluidly connected to the fuel supply conduit downstream of the electric fuel pump; and

a bypass check valve located on the bypass conduit, the check valve having an open configuration for allowing fuel to flow from the first end to the second end of the bypass conduit.

4. The fuel system of claim 3, further comprising:

a relief fuel conduit having a first end and a second end, the first end fluidly connected to the fuel supply conduit downstream of the electric fuel pump and the second end fluidly connected to the fuel supply conduit upstream of the electric fuel pump; and

a relief check valve located on the relief conduit, the check valve having an open configuration for allowing fuel to flow from the first end to the second end of the relief fuel conduit.

5. The fuel system of claim 3, further comprising:

a fuel metering unit for managing the fuel flow to the auxiliary power unit, the fuel metering unit located downstream of both the electric fuel pump and the mechanical fuel pump on the fuel supply conduit; and

a recirculation conduit having a first end and a second end, the first end connected to the fuel metering unit and the second end connected to the fuel supply conduit at a location downstream of the electric fuel pump.

6. The fuel system of claim 2, further comprising:

a fuel metering unit for managing the fuel flow to the auxiliary power unit, the fuel metering unit located downstream of both the electric fuel pump and the mechanical fuel pump on the fuel supply conduit; and

a recirculation conduit having a first end and a second end, the first end connected to the fuel metering unit and the second end connected to the fuel supply conduit at a location upstream of the electric fuel pump.

7. The fuel system of claim 2, further comprising:

a boost fuel pump for increasing fuel flow to the auxiliary power unit, the boost fuel pump located on the fuel supply conduit upstream of the mechanical fuel pump.

10. The fuel system of claim 1, wherein the controller shuts the electric fuel pump off at a higher operational speed for the auxiliary power unit.

11. The fuel system of claim 10, wherein the electric fuel pump is operated from about 1-8% of a maximum engine speed.

8. The fuel system of claim 8, wherein the electric fuel pump is located upstream of the boost fuel pump.

9. The fuel system of claim 8, wherein electric fuel pump is located downstream of the boost fuel pump.

12. A fuel system for an auxiliary power unit, the fuel system comprising:

a fuel supply conduit fluidly connecting a fuel reservoir to a combustor;

a fuel metering unit located on the fuel supply conduit upstream of the combustor;

a mechanical gear driven pump located on the fuel supply conduit upstream of the fuel metering unit;

a mechanical boost pump located on the fuel supply conduit upstream of the mechanical gear driven pump;

an electric pump located on the fuel supply conduit upstream of the mechanical gear driven pump; and

a controller for commanding the electric pump to circulate and thereby warm fuel prior to start up of the auxiliary power unit.

13. The fuel system of claim 12, further comprising:

a fuel shut-off valve located on the fuel supply conduit between the fuel metering unit and the combustor, the fuel shut-off valve having an open configuration and a closed configuration; and

a relief fuel conduit fluidly connecting an outlet of the electric pump to an inlet of the electric pump, wherein fuel flows along the relief fuel conduit when the fuel shut-off valve is in the closed configuration.

14. The fuel system of claim 12, further comprising:

a starter motor, wherein the controller is configured to command the starter motor to start rotation of the auxiliary power unit after fuel is heated from flowing along the relief conduit.

15. The fuel system of claim 12, wherein the controller shuts the electric fuel pump off at a higher operational speed for the auxiliary power unit.

16. The fuel system of claim 12, wherein the electric fuel pump is operated from about 1-8% of a maximum engine speed.

17. A method for providing warmed fuel to an auxiliary power unit, the method comprising:

commanding a valve to close and prevent fuel from flowing to the auxiliary power unit;

providing power to an electric pump to circulate and thereby warm fuel prior to start up of the auxiliary power unit; and

commanding the valve to open and allow fuel to flow into the auxiliary power unit.

18. The method of claim 17, further comprising:

terminating power to the electric pump when the output of a mechanical pump provides sufficient fuel flow to sustain operation of the auxiliary power unit.

19. The method of claim 18, wherein the electric fuel pump is operated from about 1-8% of a maximum engine speed.

20. The method of claim 17, wherein the vale is commanded to open to allow the preheated fuel to the auxiliary power unit either after a predetermined period of time or the fuel reaches a desired temperature.