Fuel tank ullage purge system

1. A purge system, comprising:

an airflow source to provide an airflow; and

a fuel tank, including:

a tank volume including a tank ullage;

at least one inlet, wherein the at least one inlet is in fluid communication with the tank ullage and the airflow source to provide the airflow as an inbound airflow to the tank ullage;

at least one outlet, wherein the at least one outlet is in fluid communication with the tank ullage and an overboard location to direct the inbound airflow as an outbound airflow from the tank ullage to the overboard location; and

a heat exchanger in fluid communication with the inbound and the outbound airflows whereby the inbound airflow upstream from the tank ullage thermally communicates with the outbound airflow downstream from the tank ullage to maintain the inbound airflow below lower explosive fuel temperature limits and above fuel gelling temperatures.

2. The purge system of claim 1 , wherein the airflow source is an ambient air source.

3. The purge system of claim 1 , wherein the airflow source is a fuselage source.

4. The purge system of claim 1 , wherein the airflow source is an aircraft fan bleed air source.

5. The purge system of claim 1 , further comprising a conditioning device in fluid communication with the inbound airflow.

6. The purge system of claim 1 , further comprising a drying device in fluid communication with the inbound airflow.

7. The purge system of claim 1 , further comprising a fan in fluid communication with the airflow.

8. The purge system of claim 1 , further comprising a suction device in fluid communication with the outbound airflow to provide negative pressure to the outbound airflow.

9. The purge system of claim 8 , wherein the suction device is an ejector.

10. A method to purge hydrocarbon vapors, the method comprising:

providing a cool airflow via an airflow source;

providing a fuel tank having a tank volume with a tank ullage;

providing the cool airflow as an inbound airflow to the tank ullage via at least one purge duct of the fuel tank; and

directing the inbound airflow as an outbound airflow from the tank ullage to an overboard location via a vent of the fuel tank

providing thermal communication between the inbound and outbound airflows upstream from the at least one purge duct to maintain the inbound airflow below lower explosive fuel temperature limits and above fuel gelling temperatures.

11. The method of claim 10 , wherein the cool airflow is cooled via a conditioning device.

12. The method of claim 10 , wherein the cool airflow is further dried via a drying device.

13. The method of claim 10 , wherein the airflow source is an ambient air source.

14. The method of claim 10 , wherein the airflow source is a fuselage air source.

15. The method of claim 10 , wherein the airflow source is an aircraft fan bleed air source.

16. The method of claim 10 , further comprising a fan in fluid communication with the airflow.

17. An aircraft, comprising:

an airflow source to provide an airflow;

an aircraft body comprising a fuselage and wings extending outwardly from the fuselage in opposite directions; and

a center fuel tank disposed within the fuselage and wing tanks disposed within the wings,

the center fuel tank including a center tank volume including a center fuel tank ullage, a leading edge and at least one inlet and at least one outlet proximate to the leading edge,

each of the wing tanks respectively including a wing tank volume including a wing tank ullage, an inboard edge and at least one inlet and at least one outlet proximate to the inboard edge;

wherein each of the at least one inlets is in fluid communication with the tank ullage and the airflow source to provide the airflow to the corresponding tank ullage;

wherein each of the at least one outlets is in fluid communication with the corresponding tank ullage and an overboard location outside the aircraft to direct the airflow from the corresponding tank ullage to the overboard location; and

wherein the aircraft further comprises a heat exchanger disposed upstream from the at least one inlets and downstream from the at least one outlets, wherein airflow being provided to the center and the wing tank ullages thermally communicates with the airflow being directed to the overboard location to maintain the airflow being provided to the center and the wing tank ullages below lower explosive fuel temperature limits and above fuel gelling temperatures.

18. The aircraft according to claim 17 , further comprising:

common lines by which each of the at least one inlets are fluidly communicative with each other and the airflow source, and

common lines by which each of the at least one outlets are fluidly communicative with each other and the overboard location.