Fuel system diagnostics

1. A method for in situ operating an internal combustion engine comprising:

turbo-charging said internal combustion engine;

determining at least one combustion characteristic for each of a plurality of combustion chambers of said internal combustion engine, including an actual heat release signal for each of said plurality of combustion chambers;

inputting said actual heat release signal for each of said plurality of combustion chambers into a diagnostic logic tree for diagnosing changes in combustion characteristics due to at least one of:

a fuel injector of a plurality of fuel injectors associated with said plurality of combustion chambers malfunctioning,

a start of combustion timing error, and

a change in a fuel heating value; and

performing a mitigation technique to compensate for said changes in combustion characteristics,

wherein said diagnosing includes:

(i) determining whether or not each of said plurality of fuel injectors is injecting a desired amount of fuel into respective combustion chambers within a first range of tolerance; and

(ii) determining whether or not a difference between an actual intake manifold pressure and a desired intake manifold pressure is outside a second range of tolerance,

wherein, in response to determining that each of said plurality of fuel injectors is injecting said desired amount of fuel into respective combustion chambers within said first range of tolerance and that said difference between said actual intake manifold pressure and said desired intake manifold pressure is outside said second range of tolerance, said mitigation technique includes determining a fuelling correction for said plurality of fuel injectors as a function of said difference between said actual intake manifold pressure and said desired intake manifold pressure.

2. The method of claim 1 , further comprising:

determining a desired heat release signal as a function of engine operating conditions;

comparing a difference between said actual heat release signal and said desired heat release signal with a predetermined tolerance;

diagnosing said fuel injector of said plurality of fuel injectors is malfunctioning when said difference is outside a range of said predetermined tolerance; and

reporting said fuel injector is malfunctioning to an on-board diagnostic system.

3. The method of claim 1 , further comprising;

determining a desired heat release signal as a function of engine operating conditions;

comparing a difference between said actual heat release signal and said desired heat release signal with a predetermined tolerance;

diagnosing said fuel injector of said plurality of fuel injectors is malfunctioning when said difference is outside a range of said predetermined tolerance;

diagnosing that said fuel injector of said plurality of fuel injectors is: (a) introducing too much fuel when said difference is greater than a positive value of said predetermined tolerance; and, (b) introducing too little fuel when said difference is less than a negative value of said predetermined tolerance; and

reporting said fuel injector of said plurality of fuel injectors is either introducing too much or too little fuel to an on-board diagnostic system.

4. The method of claim 1 , further comprising:

determining another combustion characteristic for each of said plurality of combustion chambers, including an actual start of combustion timing; and

inputting said actual start of combustion timing for each of said plurality of combustion chambers into said diagnostic logic tree for diagnosing said start of combustion timing error.

5. The method of claim 4 , further comprising:

determining a desired start of combustion timing as a function of engine operating conditions;

comparing a difference between said actual start of combustion timing and said desired start of combustion timing with a first predetermined tolerance; and

adjusting start of injection timing for at least one fuel injector of said plurality of fuel injectors to correct for said start of combustion timing error when said difference between said actual start of combustion timing and said desired start of combustion timing is outside a range of said first predetermined tolerance.

6. The method of claim 5 , further comprising determining that said at least one fuel injector is introducing an amount of fuel within a range of a second predetermined tolerance as a precondition before adjusting said start of injection timing for said at least one fuel injector.

7. The method of claim 1 , further comprising:

calculating, for each of said plurality of combustion chambers, a cumulative heat release based on said actual heat release signal;

calculating a mean cumulative heat release for said internal combustion engine based on said cumulative heat release for each of said plurality of combustion chambers,

wherein said diagnosing further includes:

(iii) determining whether or not a difference between said mean cumulative heat release and a desired mean cumulative heat release for said internal combustion engine is outside a third range of tolerance,

wherein, in response to determining that each of said plurality of fuel injectors is injecting said desired amount of fuel into respective combustion chambers within said first range of tolerance and that said difference between said actual intake manifold pressure and said desired intake manifold pressure is outside said second range of tolerance, and determining said difference between said mean cumulative heat release and said desired mean cumulative heat release for said internal combustion engine is outside said third range of tolerance, said mitigation technique includes determining said fuelling correction as a function of said difference between said actual intake manifold pressure and said desired intake manifold pressure and said difference between said mean cumulative heat release and said desired mean cumulative heat release.

8. The method of claim 1 , further comprising:

fuelling said internal combustion engine with boil-off gas during start-up;

detecting a change in fuel quality with respect to a default fuel quality when fuelling with boil-off gas; and

switching to fuelling with a cryogenic fuel after determining one of: (a) a predetermined amount of time fuelling said internal combustion engine with said boil-off gas has elapsed or (b) vapor pressure for said boil-off gas has dropped below a predetermined value.

9. The method of claim 1 , further comprising

fuelling said internal combustion engine with one of a cryogenic fuel, a boil-off gas of said cryogenic fuel, or a combination of said cryogenic fuel and said boil-off gas of varying proportions; and

detecting a change in fuel quality with respect to a default fuel quality.

10. The method of claim 9 , further comprising:

selectively fuelling said internal combustion engine with said cryogenic fuel, said boil-off gas, or said combination of said cryogenic fuel and said boil-off gas according to at least one of:

fuelling said internal combustion engine with said boil-off gas during engine start-up;

fuelling said internal combustion engine with cryogenic fuel after a predetermined amount of time after engine start-up;

fuelling said internal combustion engine with cryogenic fuel after boil-off gas pressure decreases below a predetermined lower pressure threshold; or

fuelling with said combination of said cryogenic fuel and said boil-off gas during normal engine operation when boil-off gas pressure increases beyond a predetermined upper pressure threshold.

11. An apparatus for in situ operating an internal combustion engine comprising:

one or more accelerometer sensors associated with a plurality of combustion chambers in said internal combustion engine; and

a controller which, in operation:

receives a signal from each of said accelerometer sensors representative of pressure in a respective combustion chamber;

determines at least one combustion characteristic for each of said plurality of combustion chambers including an actual heat release signal for each of said plurality of combustion chambers;

inputs said actual heat release signal for each of said plurality of combustion chambers into a diagnostic logic tree for diagnosing changes in combustion characteristics due to at least one of:

a fuel injector of a plurality of fuel injectors associated with said plurality of combustion chambers malfunctioning,

a start of combustion timing error, and

a change in a fuel heating value; and

performs a mitigation technique to compensate for said changes in combustion characteristics,

wherein said internal combustion engine is turbo charged,

wherein said diagnosing includes said controller, in operation:

(i) determines whether or not each of said plurality of fuel injectors is injecting a desired amount of fuel into respective combustion chambers within a first range of tolerance; and

(ii) determines whether or not a difference between an actual intake manifold pressure and a desired intake manifold pressure is outside a second range of tolerance,

wherein, in response to said controller determining that each of said plurality of fuel injectors is injecting said desired amount of fuel into respective combustion chambers within said first range of tolerance and that said difference between said actual intake manifold pressure and said desired intake manifold pressure is outside said second range of tolerance, said mitigation technique includes said controller, in operation, determines a fuelling correction for said plurality of fuel injectors as a function of said difference between said actual intake manifold pressure and said desired intake manifold pressure.

12. The apparatus of claim 11 , wherein said controller, in operation:

determines a desired heat release signal as a function of engine operating conditions;

compares a difference between said actual heat release signal and said desired heat release signal with a predetermined tolerance;

diagnoses said fuel injector of said plurality of fuel injectors is malfunctioning when said difference is outside a range of said predetermined tolerance: and

reports said fuel injector is malfunctioning to an on-board diagnostic system.

13. The apparatus of claim 11 , wherein said controller, in operation:

determines a desired heat release signal as a function of engine operating conditions;

compares a difference between said actual heat release signal and said desired heat release signal with a predetermined tolerance;

diagnoses said fuel injector of said plurality of fuel injectors is malfunctioning when said difference is outside a range of said predetermined tolerance;

determines that said fuel injector of said plurality of fuel injectors is malfunctioning by one of (a) introducing too much fuel when said difference is greater than a positive value of said predetermined tolerance or (b) introducing too little fuel when said difference is less than a negative value of said predetermined tolerance; and

reports said fuel injector of said plurality of fuel injectors is either introducing too much or too little fuel to an on-board diagnostic system.

14. The apparatus of claim 11 , wherein said controller, in operation:

determines another combustion characteristic for each of said plurality of combustion chambers, including an actual start of combustion timing; and

inputs said actual start of combustion timing for each of said plurality of combustion chambers into said diagnostic logic tree for determining said start of combustion timing error.

15. The apparatus of claim 14 , wherein said controller, in operation:

determines a desired start of combustion timing as a function of engine operating conditions;

compares a difference between said actual start of combustion timing and said desired start of combustion timing with a first predetermined tolerance; and

corrects for said start of combustion timing error by adjusting start of injection timing for at least one fuel injector of said plurality of fuel injectors when said difference between said actual start of combustion timing and said desired start of combustion timing is outside a range of said first predetermined tolerance.

16. The apparatus of claim 15 , wherein said controller, in operation, determines that said at least one fuel injector is introducing an amount of fuel within a range of a second predetermined tolerance as a precondition before adjusting said start of injection timing for said at least one fuel injector.

17. The apparatus of claim 11 wherein said controller, in operation:

calculates, for each of said plurality of combustion chambers, a cumulative heat release based on said actual heat release signal;

calculates a mean cumulative heat release for said internal combustion engine based on said cumulative heat release for each of said plurality of combustion chambers,

wherein said diagnosing further includes said controller, in operation:

(iii) determines whether or not a difference between said mean cumulative heat release and a desired mean cumulative heat release for said internal combustion engine is outside a third range of tolerance,

wherein, in response to said controller determining that each of said plurality of fuel injectors is injecting said desired amount of fuel into respective combustion chambers within said first range of tolerance and that said difference between said actual intake manifold pressure and said desired intake manifold pressure is outside said second range of tolerance, and determining said difference between said mean cumulative heat release and said desired mean cumulative heat release for said internal combustion engine is outside said third range of tolerance said mitigation technique includes said controller, in operation, determines said fuelling correction as a function of said difference between said actual intake manifold pressure and said desired intake manifold pressure and said difference between said mean cumulative heat release and said desired mean cumulative heat release.

18. The apparatus of claim 11 , wherein said controller, in operation:

detects a change in fuel quality with respect to a default fuel quality when fuelling with a boil-off gas; and

causes a switch to fuelling with a cryogenic fuel after determining one of:

a predetermined amount of time fuelling said internal combustion engine with said boil-off gas has elapsed; or

vapor pressure for said boil-off gas has dropped below a predetermined value.

19. The method of claim 1 wherein, the difference between said actual intake manifold pressure and said desired intake manifold pressure results from a change in exhaust pressure due to said change in said fuel heating value.

20. The apparatus of claim 11 wherein, the difference between said actual intake manifold pressure and said desired intake manifold pressure results from a change in exhaust pressure due to said change in said fuel heating value.