Cylinder pressure based control of dual fuel engines

1. A method, comprising:

operating an internal combustion engine system including an intake system connected to an engine with a plurality of cylinders and at least two fuel sources operably connected to the internal combustion engine system to provide a flow of liquid fuel to each of the plurality of cylinders and a flow of a gaseous fuel to each of the plurality of cylinders, wherein the intake system is coupled to each of the plurality of cylinders to provide a charge flow from the intake system to a combustion chamber of the respective cylinder, the internal combustion engine system further including an exhaust system;

determining a pressure in the combustion chamber of at least one cylinder during a combustion cycle associated with the cylinder;

determining at least one operating condition of the at least one cylinder as a function of the pressure;

determining a first part of the operating condition attributable to the liquid fuel;

determining a second part of the operating condition attributable to the gaseous fuel, wherein the second part of the operating condition is determined from a difference between the operating condition in die at least one cylinder and the first part of the operating condition; and

adjusting a substitution rate of the gaseous fuel for the liquid fuel in response to the operating condition deviating from a target operating condition.

2. The method of claim 1 , wherein the pressure is an indicated mean effective pressure (IMEP), the operating condition is an energy output determined from the IMEP in response to combustion of the liquid fuel and gaseous fuel in the combustion chamber, and the first part of the operating condition is an energy contribution of the liquid fuel to the energy output determined from an amount of the liquid fuel provided during the combustion cycle and a heating value of the liquid fuel.

3. The method of claim 2 , wherein the second part of the operating condition is an energy contribution of the gaseous fuel to the energy output, and further comprising:

comparing the energy contribution of the gaseous fuel to a target contribution of the gaseous fuel to the energy output of the cylinder; and

adjusting the substitution rate of the gaseous fuel in response to the energy contribution of the gaseous fuel deviating from the target contribution.

4. The method of claim 2 , wherein the second part of the operating condition is an energy contribution of the gaseous fuel to the energy output, further comprising:

determining an air-to-fuel ratio of the charge flow from the energy contribution of the gaseous fuel and a mass air flow of the charge flow;

comparing the air-to-fuel ratio of the charge flow to a target air-to-fuel ratio of the charge flow; and

adjusting the charge flow in response to the air-to-fuel ratio of the charge flow deviating from the target air-to-fuel ratio.

5. The method of claim 4 , wherein adjusting the charge flow includes at least one of:

opening or closing at least one of an intake throttle in the intake system, a compressor bypass valve in a compressor bypass, a wastegate of a turbine in the exhaust system, a variable geometry turbine in the exhaust system; and

varying a lift profile of at least one of an intake valve and an exhaust valve of the cylinder.

6. The method of claim wherein the operating condition includes a combustion parameter in the combustion chamber of the cylinder during the combustion cycle.

7. The method of claim 6 , wherein the combustion parameter is at least one of a heat release placement, an effective expansion ratio, and a centroid of heat release during the combustion cycle.

8. The method of claim 6 , wherein the second part of the operating condition is a contribution of the gaseous fuel to the combustion parameter, and further comprising comparing the contribution of the gaseous fuel to a target contribution of the gaseous fuel to the combustion parameter, and adjusting the substitution rate of the gaseous fuel for the liquid fuel includes adjusting the substitution rate in response to the contribution of the gaseous fuel to the combustion parameter deviating from the target contribution of the gaseous fuel to the combustion parameter.

9. The method of claim 1 , wherein determining at least one operating condition includes detecting a knock intensity from the pressure in the at least one cylinder.

10. The method of claim 9 , further comprising retarding a timing of injection of the liquid fuel into the combustion chamber in response to the knock intensity exceeding a threshold amount.

11. The method of claim 9 , further comprising leaning out the charge flow into the combustion chamber in response to the knock intensity exceeding a threshold amount.

12. The method of claim 11 , wherein leaning out the charge flow includes at least one of opening an intake throttle in the intake system and closing a wastegate of a turbine in the exhaust system.

13. The method of claim 9 , further comprising lowering the substitution rate of the gaseous fuel in response to the knock intensity exceeding a threshold amount.

14. The method of claim 1 , wherein determining the at least one operating condition includes determining a peak pressure in the cylinder, and further comprising reducing a pressure of the charge flow in response to the peak pressure exceeding a threshold amount.

15. The method of claim 1 , wherein the liquid fuel is diesel fuel and the gaseous fuel is selected from the group consisting of natural gas, bio-gas, methane, propane, ethanol, producer gas, field gas, liquefied natural gas, compressed natural gas, and landfill gas.

16. A system, comprising:

an internal combustion engine including a plurality of cylinders, at least one of the plurality of cylinders including a pressure sensor in communication with a combustion chamber of the at least one cylinder;

an exhaust system configured to receive exhaust from the plurality of cylinders;

an intake system configured to direct a charge flow to the plurality of cylinders, wherein the intake system includes a compressor for compressing the charge flow;

a fuel system including a first fuel source operable to provide a liquid fuel to the plurality of cylinders and a second fuel source operable to provide a gaseous fuel to the plurality of cylinders; and

a controller connected to the internal combustion engine, the pressure sensor, the first fuel source, and the second fuel source, wherein the controller is configured to

receive a pressure signal indicative of a pressure in the combustion chamber of the at least one cylinder during a combustion cycle associated with cylinder,

determine an operating condition of the at least one cylinder as a function of the pressure,

determine a first part of the operating condition attributable to the liquid fuel,

determine a second part of the operating condition attributable to the gaseous fuel from a difference between the operating condition in the at least one cylinder and the first part of the operating condition, and

adjust a substitution rate of the gaseous fuel for the liquid fuel in response to the operating condition.

17. The system of claim 16 , wherein the liquid fuel is diesel fuel and the gaseous fuel is selected from the group consisting of natural gas, bio-gas, methane, propane, ethanol, producer gas, field gas, liquefied natural gas, compressed natural gas, or landfill gas.

18. The system of claim 16 , wherein the pressure is an indicated mean effective pressure (IMEP) in the cylinder during the combustion cycle, the operating condition includes an energy output determined from the IMEP in response to combustion of the liquid fuel and gaseous fuel in the combustion chamber, and the first part of the operating condition is an energy contribution of the liquid fuel to the energy output determined from an amount of the liquid fuel provided during the combustion cycle and a heating value of the liquid fuel.

19. The system of claim 18 , wherein the second part of the operating condition is an energy contribution of the gaseous fuel to the energy output and the controller is configured to:

compare the energy contribution of the gaseous fuel to a target energy contribution of the gaseous fuel to the energy output of the cylinder; and

adjust the substitution rate of the gaseous fuel for the liquid fuel in response to the contribution of the gaseous fuel to the energy output deviating from the target energy contribution of the gaseous fuel.

20. The system of claim 18 , wherein the second part of the operating condition is an energy contribution of the gaseous fuel to the energy output and the controller is configured to:

determine an air-to-fuel ratio of the charge flow from the energy contribution of the gaseous fuel and a mass air flow of the charge flow;

compare the air-to-fuel ratio of the charge flow to a target air-to-fuel ratio of the charge flow; and

adjust the charge flow in response to the air-to-fuel ratio deviating from the target air-to-fuel ratio.

21. The system of claim 20 , wherein the controller is configured to adjust the charge flow by controlling at least one of an intake throttle in the intake system, a compressor bypass valve in a compressor bypass, a wastegate in a turbine of the exhaust system, and a variable geometry turbine in the exhaust system.

22. The system of claim 16 , wherein the operating condition includes a combustion parameter in the combustion chamber of the cylinder during the combustion cycle.

23. The system of claim 22 , wherein the second part of the operating condition includes a contribution of the gaseous fuel to the combustion parameter in the cylinder and the controller is configured to:

compare the contribution of the gaseous fuel to the combustion parameter to a target contribution of the gaseous fuel to the combustion parameter of the cylinder; and

adjust the substitution rate of the gaseous fuel for the liquid fuel in response to the contribution of the gaseous fuel to the combustion parameter deviating from the target contribution.

24. The system of claim 16 , wherein the controller is configured to detect a knock intensity from the pressure in the at least one cylinder and retard a timing of injection of the liquid fuel into the combustion chamber in response to the knock intensity exceeding a threshold amount.

25. The system of claim 16 , wherein the controller is configured to detect a knock intensity from the pressure in the at least one cylinder and lean out the charge flow into the combustion chamber in response to the knock intensity exceeding a threshold amount.

26. The system of claim 16 , wherein the intake system includes an intake throttle downstream of the compressor and a controllable bypass around the compressor, and the exhaust system includes at least one of a variable geometry turbine and a wastegated turbine.

27. The system of claim 16 , wherein the controller is configured to detect a knock intensity from the pressure in the at least one cylinder and lower the substitution rate of the gaseous fuel in response to the knock intensity exceeding a threshold amount.

28. A method, comprising:

operating an internal combustion engine system including an intake system connected to an engine with a plurality of cylinders and at least two fuel sources operably connected to the internal combustion engine system to provide a flow of liquid fuel to each of the plurality of cylinders in a first fuelling mode and, in a second fuelling mode, to provide a flow of a gaseous fuel to each of the plurality of cylinders in addition to the flow of liquid fuel, wherein the intake system is coupled to each of the plurality of cylinders to provide a charge flow from the intake system to a combustion chamber of the respective cylinder, the internal combustion engine system further including an exhaust system;

determining a pressure in the combustion chamber of at least one cylinder during a combustion cycle associated with the cylinder;

determining at least one actual operating condition as a function of the pressure;

determining a first part of the operating condition attributable to the liquid fuel;

determining a second part of the operating condition attributable to the gaseous fuel, wherein the second part of the operating condition is determined from a difference between the operating condition in the at least one cylinder and the first part of the operating condition; and

transitioning from one of the first and second fuelling modes to the other of the first and second fuelling modes while maintaining a target operating condition during the transition as a function of the actual operating condition before the transition.

29. The method of claim 28 , wherein the at least one actual operating condition is an indicated mean effective pressure (IMEP) of the at least one cylinder and the target operating condition is a target IMEP.

30. The method of claim 28 , wherein the at least one actual operating condition is a total energy contribution of the liquid fuel and the gaseous fuel and the target operating condition is a target energy contribution of the liquid fuel and the gaseous fuel during the transition.