System and method for circulating fuel through a direct injection pump of a bi-fuel engine

1. A vehicle comprising:

a bi-fuel engine independently operable on any of a first fuel type, a second fuel type, or a combination of the first fuel type and the second fuel type; and

a fuel supply system coupled to the bi-fuel engine and configured for supplying the bi-fuel engine with only the first fuel type, the fuel supply system including:

a tank configured for storing a liquid supply of the first fuel type;

a lift pump in fluid communication with the tank and configured for pressurizing and circulating the first fuel type;

a direct injection pump assembly coupled to the bi-fuel engine and in fluid communication with the lift pump for receiving the first fuel type therefrom, and in fluid communication with the bi-fuel engine for supplying the first fuel type thereto; and

a cooling circuit in fluid communication with the direct injection pump assembly and configured for circulating the first fuel type through the direct injection pump assembly to cool the first fuel disposed within the direct injection pump assembly when the bi-fuel engine is operating and being fueled by the second fuel type.

2. A vehicle as set forth in claim 1 wherein the direct injection pump assembly includes a low pressure inlet for receiving the first fuel type from the lift pump, and a high pressure outlet for supplying the first fuel type to the bi-fuel engine.

3. A vehicle as set forth in claim 2 wherein the direct injection pump assembly includes a high pressure pump drivenly coupled to the bi-fuel engine and interconnecting the low pressure inlet and the high pressure outlet in fluid communication, and operable to increase the pressure of the first fuel type.

4. A vehicle as set forth in claim 3 wherein the high pressure pump includes a low pressure side in fluid communication with the low pressure inlet, and a high pressure side in fluid communication with the high pressure outlet.

5. A vehicle as set forth in claim 4 wherein the cooling circuit includes an outflow in fluid communication with the low pressure side of the high pressure pump.

6. A vehicle as set forth in claim 5 wherein the fuel supply system further includes a supply line interconnecting the lift pump and the low pressure inlet of the direct injection pump assembly in fluid communication.

7. A vehicle as set forth in claim 6 wherein the cooling circuit includes a cooling line interconnecting the outflow and the supply line in fluid communication.

8. A vehicle as set forth in claim 7 wherein operation of the high pressure pump by the bi-fuel engine circulates the first fuel type from the low pressure side of the high pressure pump, through the cooling circuit, and back to the supply line.

9. A vehicle as set forth in claim 8 wherein the cooling circuit includes a heat exchanger in fluid communication with the cooling line and configured to remove heat from the first fuel type circulating therethrough.

10. A vehicle as set forth in claim 9 wherein the cooling circuit includes a check valve configured to allow fluid communication in a direction from the low pressure side of the high pressure pump, through the cooling circuit, and back to the supply line, and configured to prevent fluid communication in an opposite direction.

11. A vehicle as set forth in claim 10 wherein the direct injection pump assembly includes a check valve disposed between the low pressure inlet and the low pressure side of the high pressure pump, and configured to allow fluid communication in a direction from the low pressure inlet toward the low pressure side of the high pressure pump, and configured to prevent fluid communication in an opposite direction.

12. A vehicle as set forth in claim 5 wherein the cooling circuit includes a return line interconnecting the outflow and the tank in fluid communication.

13. A vehicle as set forth in claim 12 wherein actuation of the lift pump circulates the first fuel type through the low pressure side of the pump, through the return line, and back into the tank.

14. A vehicle as set forth in claim 13 wherein the cooling circuit includes a back pressure relief valve configured to allow fluid communication in a direction from the low pressure side of the high pressure pump, through the cooling circuit, and back to the tank when a fluid pressure of the first fuel type is greater than a pre-determined value, and configured to prevent fluid communication in an opposite direction when the fluid pressure of the first fuel type is less than the pre-determined value.

15. A vehicle as set forth in claim 14 wherein the cooling circuit includes a flow restriction device configured to restrict fluid flow through the cooling circuit to a pre-defined fluid flow rate.

16. A vehicle as set forth in claim 1 wherein the first fuel type includes one of gasoline or diesel fuel.

17. A vehicle as set forth in claim 1 wherein the second fuel type includes one of compressed natural gas, liquefied petroleum gas, or hydrogen.

18. A method of operating a vehicle, the method comprising:

fueling a bi-fuel engine with only a second fuel type; and

circulating a first fuel type through a fuel supply system having a direct injection pump assembly coupled to the bi-fuel engine, to cool the first fuel type in the direct injection pump assembly, when the bi-fuel engine is being fueled by the second fuel type, to prevent vaporization of the first fuel type within the direct injection pump assembly, wherein the fuel supply system supplies only the first fuel type to the bi-fuel engine.

19. A method as set forth in claim 18 wherein circulating the first fuel type includes circulating the first fuel type from a low pressure side of the direct injection pump assembly to one of a fuel system supply line upstream of an inlet of the direct injection pump assembly, or a fuel storage tank.

20. A method as set forth in claim 19 where in the first fuel type is gasoline, and the second fuel type is one of compressed natural gas, liquefied petroleum gas, or hydrogen.