System and method for controlling an engine in a bi-fuel vehicle to prevent damage to a catalyst due to engine misfire

1. A system comprising:

a misfire detection module that detects misfire in a cylinder of an engine; and

a fuel control module that:

controls a first fuel system to deliver a first fuel to the cylinder; controls a second fuel system to deliver a second fuel to the cylinder, wherein the first fuel and the second fuel are different types of fuel; and

selectively switches from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a number of misfires detected in the cylinder over a predetermined number of engine cycles being greater than a first predetermined number.

2. The system of claim 1 wherein the fuel control module selectively switches from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder when a rate of misfire in the cylinder is greater than a predetermined rate.

3. The system of claim 1 wherein the first fuel is a first type of liquid fuel, and the second fuel is a second type of liquid fuel that is different than the first type of liquid fuel.

4. A system comprising;

a misfire detection module that detects misfire in a cylinder of an engine; and

a fuel control module that:

controls a first fuel system to deliver a first fuel to the cylinder;

controls a second fuel system to deliver a second fuel to the cylinder, wherein the first fuel and the second fuel are different types of fuel;

selectively switches from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to misfire being, detected in the cylinder;

selectively switches from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a rate of misfire in the cylinder being greater than a predetermined rate; and

switches from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a percentage of misfire over a predetermined number of engine cycles being less than a predetermined percentage.

5. The system of claim 4 wherein the second fuel system delivers the second fuel to the cylinder independent from the first fuel system.

6. The system of claim 4 wherein the fuel control module selects the predetermined percentage based on a predetermined relationship between engine speed, engine load, misfire percentage, and catalyst damage.

7. The system of claim 6 wherein the first fuel is a gaseous fuel and the second fuel is a liquid fuel.

8. The system of claim 7 wherein the fuel control module selectively continues to deliver the second fuel to the cylinder when the percentage of misfire over the predetermined number of engine cycles is greater than the predetermined percentage.

9. The system of claim 8 wherein:

the fuel control module continues to deliver the second fuel to the cylinder when a fault is detected in at least one of the first fuel system, the second fuel system, and a spark plug circuit; and

the spark plug circuit includes a spark plug that generates spark in the cylinder and electronic components that supply power to the spark plug.

10. The system of claim 9 further comprising a cylinder deactivation module that deactivates the cylinder when:

the second fuel is delivered to the cylinder; and

the cylinder is periodically misfiring.

11. The system of claim 10 further comprising a torque limit module that limits torque output of the engine when:

the second fuel is delivered to the cylinder; and

the engine is randomly misfiring.

12. A method comprising:

detecting misfire in a cylinder of an engine;

controlling a first fuel system to deliver a first fuel to the cylinder;

controlling a second fuel system to deliver a second fuel to the cylinder, wherein the first fuel and the second fuel are different types of fuel; and

selectively switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a number of misfires detected in the cylinder over a predetermined number of engine cycles being greater than a first predetermined number.

13. The method of claim 12 further comprising selectively switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder when a rate of misfire in the cylinder is greater than a predetermined rate.

14. The method of claim 12 wherein the first fuel is a first type of liquid fuel, and the second fuel is a second type of liquid fuel that is different than the first type of liquid fuel.

15. A method comprising:

detecting misfire in a cylinder of an engine;

controlling a first fuel system to deliver a first fuel to the cylinder;

controlling a second fuel system to deliver a second fuel to the cylinder, wherein the first fuel and the second fuel are different types of fuel;

selectively switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to misfire being detected in the cylinder;

selectively switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a rate of misfire in the cylinder being greater than a predetermined rate; and

switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a percentage of misfire over a predetermined number of engine cycles being less than a predetermined percentage.

16. The method of claim 15 wherein the second fuel system delivers the second fuel to the cylinder independent from the first fuel system.

17. The method of claim 15 further comprising selecting the predetermined percentage based on a predetermined relationship between engine speed, engine load, misfire percentage, and catalyst damage.

18. The method of claim 17 wherein the first fuel is a gaseous fuel and the second fuel is a liquid fuel.

19. The method of claim 18 further comprising selectively continues to deliver the second fuel to the cylinder when the percentage of misfire over the predetermined number of engine cycles is greater than the predetermined percentage.

20. The method of claim 19 further comprising continuing to deliver the second fuel to the cylinder when a fault is detected in at least one of the first fuel system, the second fuel system, and a spark plug circuit, wherein the spark plug circuit includes a spark plug that generates spark in the cylinder and electronic components that supply power to the spark plug.

21. The method of claim 20 further comprising deactivating the cylinder when:

the second fuel is delivered to the cylinder; and

the cylinder is periodically misfiring.

22. The method of claim 21 further comprising limiting torque output of the engine when:

the second fuel is delivered to the cylinder; and

the engine is randomly misfiring.

23. A method comprising:

detecting misfire in a cylinder of an engine;

controlling a first fuel system to deliver a first fuel to the cylinder;

controlling a second fuel system to deliver a second fuel to the cylinder, wherein the first fuel and the second fuel are different types of fuel; and

selectively switching from delivering the second fuel to the cylinder to delivering the first fuel to the cylinder in response to a number of misfires detected in the cylinder over a predetermined number of engine cycles being greater than a first predetermined number and less than a second predetermined number.

24. The method of claim 23 wherein the first fuel is a gaseous fuel and the second fuel is a liquid fuel.

25. The method of claim 24 further comprising continuing to deliver the second fuel to the cylinder when the number of misfires detected in the cylinder over the predetermined number of engine cycles is greater than the second predetermined number.