Liquefied petroleum gas (LPG) pump control systems and methods

1. A control system for a liquefied petroleum gas (LPG) vehicle, comprising:

a composition determination module that determines a composition of LPG in an LPG tank of the LPG vehicle based on an LPG tank pressure and a temperature of the LPG in the LPG tank;

a target rail pressure module that determines a target rail pressure based on the composition of the LPG; and

a pump control module that determines a duty cycle based on the target rail pressure and that controls operation of an LPG pump based on the duty cycle.

2. The control system of claim 1 wherein the composition corresponds to a first amount of the LPG that is propane and a second amount of the LPG that is butane.

3. The control system of claim 1 further comprising:

a minimum rail pressure module that determines a minimum rail pressure based on the composition; and

an engine load compensation module that determines a load compensation pressure based on an engine load,

wherein the target rail pressure module determines the target rail pressure based on the minimum rail pressure and the load compensation pressure.

4. The control system of claim 3 wherein the target rail pressure module determines the target rail pressure based on a sum of the minimum rail pressure and the load compensation pressure.

5. The control system of claim 4 wherein the target rail pressure module determines an integral pressure based on a difference between the sum and a measured rail pressure and determines the target rail pressure based on the sum and the integral pressure.

6. The control system of claim 5 wherein the target rail pressure module sets the target rail pressure equal to a second sum of the integral pressure and the sum.

7. The control system of claim 3 wherein LPG in a fuel rail remains in a liquid form when a rail pressure is one of greater than and equal to the target rail pressure.

8. The control system of claim 1 wherein the pump control module determines a head pressure based on the LPG tank pressure and the target rail pressure and determines the duty cycle based on the head pressure.

9. The control system of claim 1 wherein the pump control module determines the duty cycle further based on at least one of a voltage of an energy storage device of the LPG vehicle, an altitude, and an ambient temperature.

10. A control method for a liquefied petroleum gas (LPG) vehicle, comprising:

determining a composition of LPG in an LPG tank of the LPG vehicle based on an LPG tank pressure and a temperature of the LPG in the LPG tank;

determining a target rail pressure based on the composition of the LPG;

determining a duty cycle based on the target rail pressure; and

controlling operation of an LPG pump based on the duty cycle.

11. The control method of claim 10 wherein the composition corresponds to a first amount of the LPG that is propane and a second amount of the LPG that is butane.

12. The control method of claim 10 further comprising:

determining a minimum rail pressure based on the composition;

determining a load compensation pressure based on an engine load; and

determining the target rail pressure based on the minimum rail pressure and the load compensation pressure.

13. The control method of claim 12 further comprising determining the target rail pressure based on a sum of the minimum rail pressure and the load compensation pressure.

14. The control method of claim 13 further comprising:

determining an integral pressure based on a difference between the sum and a measured rail pressure; and

determining the target rail pressure based on the sum and the integral pressure.

15. The control method of claim 14 further comprising setting the target rail pressure equal to a second sum of the integral pressure and the sum.

16. The control method of claim 12 wherein LPG in a fuel rail remains in a liquid form when a rail pressure is one of greater than and equal to the target rail pressure.

17. The control method of claim 10 further comprising:

determining a head pressure based on the LPG tank pressure and the target rail pressure; and

determining the duty cycle based on the head pressure.

18. The control method of claim 10 further comprising determining the duty cycle further based on at least one of a voltage of an energy storage device of the LPG vehicle, an altitude, and an ambient temperature.