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Methods and systems are provided for controlling a vehicle engine to reduce cycle-to-cycle combustion variation. A predictive model is applied to predict cycle-to-cycle combustion behavior of an engine based on observed engine performance variables. Conditions are identified, based on the predicted

Methods and systems are provided for controlling a vehicle engine to reduce cycle-to-cycle combustion variation. A predictive model is applied to predict cycle-to-cycle combustion behavior of an engine based on observed engine performance variables. Conditions are identified, based on the predicted cycle-to-cycle combustion behavior, that indicate high cycle-to-cycle combustion variation. Corrective measures are then applied to prevent the predicted high cycle-to-cycle combustion variation.

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1. A method of controlling a vehicle engine to reduce cycle-to-cycle combustion variation, the method comprising: applying a predictive model to predict cycle-to-cycle combustion behaviour of an engine based on observed engine performance variables;identifying conditions that indicate high cycle-to-

1. A method of controlling a vehicle engine to reduce cycle-to-cycle combustion variation, the method comprising: applying a predictive model to predict cycle-to-cycle combustion behaviour of an engine based on observed engine performance variables;identifying conditions that indicate high cycle-to-cycle combustion variation based on the predicted cycle-to-cycle combustion behaviour; andapplying corrective measures to prevent the predicted high cycle-to-cycle combustion variation,wherein applying a predictive model to predict cycle-to-cycle combustion behaviour of an engine includes: applying a predictive model based on temperature of an engine cylinder and a cylinder charge composition at the end of a combustion cycle. 2. The method of claim 1, wherein the predicted cycle-to-cycle combustion behaviour includes an indicated mean effective pressure. 3. The method of claim 2, wherein the high cycle-to-cycle combustion variation includes an indicated mean effective pressure with a coefficient of variation that is greater than a defined threshold. 4. The method of claim 3, wherein the defined threshold is a coefficient of variation of 5%. 5. The method of claim 1, wherein the predicted cycle-to-cycle combustion behaviour includes a combustion phasing, and wherein the high cycle-to-cycle combustion variation includes a series of combustion phasing values with a standard deviation greater than a defined threshold. 6. The method of claim 1, wherein applying corrective measures to prevent the predicted high cycle-to-cycle variation includes adjusting an amount of fuel injected into the cylinder. 7. The method of claim 6, wherein adjusting the amount of fuel injected includes adjusting the amount of fuel injected for a single cycle based on the predicted cycle-to-cycle combustion behaviour of the engine. 8. The method of claim 6, wherein adjusting the amount of fuel injected includes adjusting the amount of fuel injected in every cycle based on the predicted cycle-to-cycle combustion behaviour of the engine. 9. The method of claim 1, wherein applying corrective measures to prevent the predicted high cycle-to-cycle variation includes adjusting a fuel injection timing for the cylinder. 10. The method of claim 1, wherein the cylinder charge composition includes an amount of unburned fuel at the end of a combustion cycle. 11. The method of claim 10, further comprising: estimating the amount of unburned fuel remaining in the cylinder based on one or more measured pressure values of the cylinder during the combustion cycle. 12. The method of claim 1, further comprising: estimating the temperature of the engine cylinder based on one or more measured pressure values of the cylinder during the combustion cycle. 13. A method of controlling a vehicle engine to reduce cycle-to-cycle combustion variation, the method comprising: applying a predictive model to predict cycle-to-cycle combustion behaviour of an engine based on observed engine performance variables;identifying conditions that indicate high cycle-to-cycle combustion variation based on the predicted cycle-to-cycle combustion behaviour; andapplying corrective measures to prevent the predicted high cycle-to-cycle combustion variation,determining a set of one or more engine operating conditions;comparing the set of one or more engine operating conditions to a set of defined operating regions;operating the engine in a spark ignition mode when the set of one or more engine operating conditions is within a first defined operating region; andoperating the engine in a homogenous charge compression ignition mode when the set of one or more engine operating conditions is within a second defined operating region, wherein the acts of applying the predictive model, identifying conditions that indication high cycle-to-cycle combustion variation, and applying corrective measures are performed when transitioning from the spark ignition mode to the homogenous charge compression ignition mode. 14. The method of claim 13, wherein the homogenous charge compression ignition mode includes a spark-assisted homogenous charge compression ignition mode. 15. The method of claim 13, wherein the acts of applying the predictive model, identifying conditions that indication high cycle-to-cycle combustion variation, and applying corrective measures are performed when transitioning from the homogenous charge compression ignition mode to the spark ignition mode. 16. The method of claim 1, further comprising: determining a set of one or more engine operating conditions;comparing the set of one or more engine operating conditions to a set of defined operating regions;determining that the engine is operating in a stable HCCI region when the set of one or more operating conditions is within a first defined operating region, wherein the engine is unlikely to exhibit high cycle-to-cycle combustion variation in the stable HCCI region; anddetermining that the engine is operating in an unstable HCCI region when the set of one or more operating conditions is within a second defined operating region, wherein the engine is more likely to exhibit high cycle-to-cycle combustion variation in the unstable HCCI region as compared to the stable HCCI region,wherein the acts of applying the predictive model, identifying conditions that indication high cycle-to-cycle combustion variation, and applying corrective measures are performed when the engine is operating in the unstable HCCI region. 17. The method of claim 1, wherein applying the predictive model to predict cycle-to-cycle combustion behaviour of the engine includes predicting a residual gas temperature based on the following equation: Tr⁡(k)={α⁡[1+βηm⁡(θm)⁢mf⁡(k)⁢V⁡(θm)γ-1]1γ+ζ⁢⁢mf⁡(k)⁢(1-ηm⁡(θm))}⁢Tivc⁡(k)wherein α, β, and γ are parameters defined through engine calibration,wherein θm is the crank angle at the end of combustion,wherein mf(k) is the mass of fuel in the cylinder during combustion cycle k,wherein nm(θm) is a combustion efficiency of the engine,wherein V is the volume of the engine cylinder, andwherein Tivc(k) is the temperature at intake valve closing. 18. A method of controlling a vehicle engine to reduce cycle-to-cycle combustion variation, the method comprising: determining a set of one or more engine operating conditions;comparing the set of one or more engine operating conditions to a set of defined operating regions;operating the engine in a spark ignition mode when the set of one or more engine operating conditions is within a first defined operating region;operating the engine in a homogenous charge compression ignition mode when the set of one or more engine operating conditions is within a second defined operating region; andwhen transitioning from the spark ignition mode to the homogeneous charge compression ignition mode, applying a predictive model to predict at least one of a combustion phasing and a mean effective pressure value of an engine cylinder for each of a plurality of future combustion cycles based, at least in part, on a determined cylinder temperature and a determined amount of unburned fuel remaining in a cylinder after a current combustion cycle is complete,identifying variations in the at least one of the combustion phasing and the predicted mean effective pressure values for the cylinder which indicate high cycle-to-cycle combustion variation, andadjusting at least one of an injected fuel quantity and a fuel injection timing for a subsequent combustion cycle to prevent the predicted high cycle-to-cycle combustion variation. 19. A method of controlling a vehicle engine to reduce cycle-to-cycle combustion variation, the method comprising: determining a set of one or more engine operating conditions;comparing the set of one or more engine operating conditions to a set of defined operating regions;determining that the engine is operating in a stable HCCI region when the set of one or more operating conditions is within a first defined operating region, wherein the engine is unlikely to exhibit high cycle-to-cycle combustion variation in the stable HCCI region;determining that the engine is operating in an unstable HCCI region when the set of one or more operating conditions is within a second defined operating region, wherein the engine is more likely to exhibit high cycle-to-cycle combustion variation in the unstable HCCI region as compared to the stable HCCI region; andwhen it is determined that the engine is operating in the unstable HCCI region, applying a predictive model to predict at least one of a combustion phasing and a mean effective pressure value of an engine cylinder for each of a plurality of future combustion cycles based, at least in part, on a determined cylinder temperature and a determined amount of unburned fuel remaining in a cylinder after a current combustion cycle is complete,identifying variations in the at least one of the combustion phasing and the predicted mean effective pressure values for the cylinder which indicate high cycle-to-cycle combustion variation, andadjusting at least one of an injected fuel quantity and a fuel injection timing for a subsequent combustion cycle to prevent the predicted high cycle-to-cycle combustion variation.