Predictive modeling and reducing cyclic variability in autoignition engines
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.
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; and
applying 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; and
applying 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; and
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,
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; and
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,
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:
T
r
(
k
)
=
{
α
[
1
+
βη
m
(
θ
m
)
m
f
(
k
)
V
(
θ
m
)
γ
-
1
]
1
γ
+
ζ
m
f
(
k
)
(
1
-
η
m
(
θ
m
)
)
}
T
ivc
(
k
)
wherein α, β, and γ are parameters defined through engine calibration,
wherein θ m is the crank angle at the end of combustion,
wherein m f (k) is the mass of fuel in the cylinder during combustion cycle k,
wherein n m (θ m ) is a combustion efficiency of the engine,
wherein V is the volume of the engine cylinder, and
wherein T ivc (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; and
when 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, and
adjusting 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; and
when 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, and
adjusting 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.