Embodiments of the present invention relate to real-time engine control during recompression homogeneous charge compression ignition (“HCCI”) combustion.
In one embodiment, the invention provides a method for controlling combustion performance of an engine. The method includes determining a desired fuel quantity for a first combustion cycle. One or more engine actuator settings are then identified which would be required during a subsequent combustion cycle to cause the engine to approach a target combustion phasing. If the identified engine actuator settings are within a defined acceptable operating range, the desired fuel quantity is injected during the first combustion cycle. If not, an attenuated fuel quantity is determined and the attenuated fuel quantity is injected during the first combustion cycle.
In some embodiments, the attenuated fuel quantity is determined by identifying the actuator settings necessary to cause the engine to approach the target combustion phasing if the desired fuel quantity is injected and then comparing the necessary actuator settings to the acceptable operating range.
In other embodiments, the method further includes determining a maximum fuel injection amount and a minimum fuel injection amount. The maximum fuel injection amount is the maximum amount of fuel that can be injected without requiring one or more engine actuator settings that are outside of the defined acceptable operating range. The minimum fuel injection amount is the minimum amount of fuel that can be injected without requiring one or more engine actuator settings that are outside of the defined acceptable operating range. If the desired fuel quantity is greater than the maximum fuel injection amount, the value of the attenuated fuel quantity is defined as the maximum fuel injection amount. If the desired fuel quantity is less than the minimum fuel injection amount, the value of the attenuated fuel quantity is defined as the minimum fuel injection amount.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
Internal combustion engines can be configured to operate in one or more of various combustion modes—the most well known of which is spark ignition. However, some engines are configured to operate in autoignition mode where combustion is achieved by compressing the in-cylinder gas to the point of selfignition instead of introducing a spark. In the examples described below, the internal combustion engine can selectively switch between a spark ignition mode and an autoignition (or homogeneous charge compression ignition (HCCI)) mode. In other examples, an internal combustion engine can be configured to operate in additional or other combustion modes.
As illustrated in
The ECM 105 monitors the various sensors 110, 115, 120, 125, 130, 135 and controls the actuators 140, 145, 150. The ECM 105 receives information (i.e., data captured by the sensors) and processes the received information to control the combustion performance of the engine such that a target combustion phasing (θCA50ref(k)) and a target fuel injection amount (mfdes(k)) are achieved, and predetermined constraint requirements are satisfied. The ECM 105 includes at least one processor and at least one memory module 155, shown in
u=[unvo,usoi]T (1)
where k is the current combustion cycle.
The observer 170 receives and processes the combustion phasing (θCA50(k)) of the engine 178 to estimate current combustion state information. The current combustion state information, denoted by ({circumflex over (x)}(k)), includes a temperature (Tbd(k)) and a pre-combustion charge composition (ibd(k)) associated with at least one cylinder of the engine 178.
xd=[ibd,Tbd]T (2)
An output from the pedal position sensor 115 is received and processed by the load controller 165 to determine a target fuel injection amount. In some constructions, this is accomplished by employing a torque correlation model to determine an amount of torque to be exercised based, at least in part, on the pedal position measurements. After applying the torque correlation model, the load controller 165 uses a converter to determine the target fuel injection amount (mfdes(k)) based on the determined amount of torque.
The estimated current combustion state information ({circumflex over (x)}(k)) and the determined target fuel injection amount (mfdes(k)) are received and processed by the fuel governor 175 to determine an appropriate amount of fuel to inject (mf(k)) into at least one cylinder of the engine 178. The fuel governor 175 employs a predictive model, described in further detail below, to determine whether the target fuel injection amount (mfdes(k)) would require actuator settings (u(k)) that violate predetermined constraints in order to cause the combustion phasing (θCA50(k)) of the engine 178 to approach the target combustion phasing (θCA50ref(k)). If the target fuel injection amount (mfdes(k)) would require actuator settings (u(k)) that violate predetermined constraints, the fuel governor 175 adjusts the fuel injection amount (mf(k)), as discussed in more detail below in reference to
The predetermined constraints, mentioned in the paragraphs above in reference to
unvomin≦unvo≦unvomax (3)
where unvomin is the minimum valve actuation timing and unvomax is the maximum valve actuation timing. The maximum rate for valve actuation timing, denoted by Δunvo, is given by
|unvo(k)−unvo(k−1)|<Δunvo (4)
where unvo(k) is the current value of the valve actuation timing and unvo(k−1) is the previous value of the valve actuation timing. The fuel injection timing, denoted by usoi(k), is also limited within a range of values and defined by
usoimin≦usoi≦usoimax (5)
where usoimin is the minimum fuel injection timing and usoimax is the maximum fuel injection timing. The values of minimum and maximum timing and the maximum rate thresholds are constants, which are hardware dependent. Examples of range limitations for actuators controlling valve timing (defining the negative valve overlap period) and the fuel injection timing (defined by the start of injection (“SOI”)) and how they correspond to the overall timing of the combustion cycle are partially illustrated in
Aside from the actuator component constraints, the predetermined constraints may also include the actuator control authority constraints and the combustion performance constraints. In some embodiments, the actuator control authority constraints include a relative magnitude of authority and a bandwidth for each of the plurality of actuators controlling the valve actuation timing (unvo(k)) and the fuel injection timing (usoi(k)). Additionally, in some embodiments, the combustion performance constraints include limited pressure rise rates, air-to-fuel ratios, and maximum allowable emissions.
θCA50(k)=g(xd(k),u(k),mf(k),xc(kTs)) (6)
where xd(k) is the discrete combustion state vector, u(k) is the vector of actuator settings, mf(k) is the fuel injection amount, xc is a vector of five continuous manifold states, and Ts is the engine cycle time. Based on the received input values, the combustion phasing controller 160 simultaneously regulates the exhaust valve closing (“EVC”) and the fuel injection timing (usoi(k)) to control the engine 178 during recompression HCCI combustion such that target combustion phasing (θCA50ref(k)) is achieved.
mf(k)=mf(k−1)+β(mfdes(k)−mf(k−1)) (7)
where mfdes(k) is the target fuel injection amount for the first combustion cycle, mf(k−1) is the amount of fuel injected during a previous combustion cycle, and β is the adjustment parameter used in determining an attenuated fuel quantity (mf(k)). The value of β is initially set to 1 (“one”).
If the actuator settings required during the subsequent combustion cycle to approach the target combustion phasing (θCA50ref(k)) are predicted to violate the predetermined constraints if the target fuel injection amount (mfdes(k)) is injected during the first combustion cycle (step 210), then the attenuated fuel quantity (mf(k)) is determined (steps 205-225) and injected during the first combustion cycle (step 230). If the actuator settings required during the subsequent combustion cycle to approach the target combustion phasing (θCA50ref(k)) are predicted to satisfy the predetermined constraints if the target fuel injection amount (mfdes(k)) is injected during the first combustion cycle (step 210), then the target fuel injection amount (mfdes(k)) is injected during the first combustion cycle (step 230).
If constraint violations are predicted (step 210), the ECM 105 reduces the value of the adjustment parameter (β) (step 215). Then, the ECM 105 determines a first adjusted fuel quantity based on the reduced adjustment parameter (β), the target fuel injection amount (mfdes(k)), and the amount of fuel injected during the previous combustion cycle (mf(k−1)), if such amount is known (step 205). The ECM 105 utilizes the predictive model of the nonlinear fuel governor to again determine the actuator settings required during the subsequent combustion cycle to approach the target combustion phasing (θCA50ref(k)) if the first adjusted fuel quantity is injected during the first combustion cycle (step 205). If the actuator settings required during the subsequent combustion cycle to approach the target combustion phasing (θCA50ref(k)) are still predicted to violate the predetermined actuator constraints if the first adjusted fuel quantity is injected during the first combustion cycle (step 210), then the adjustment parameter (β) is again reduced (step 215) and a second adjusted fuel quantity is determined based upon the reduced adjustment parameter (β) (step 205). This process is repeated until an adjusted fuel quantity is calculated that does not require a violation of the actuator constraints.
Once an adjusted fuel quantity is determined that satisfies the actuator constraint (step 210), the ECM 105 determines whether the value of the adjustment parameter (β) has converged toward an optimal value of β between zero and one (step 220) as it was adjusted. If the adjustment parameter (β) has not converged (step 220), the ECM 105 increases the value of the adjustment parameter (β) (step 225) and again simulates the model to determine an adjusted fuel quantity (step 205). The adjustment parameter (β) has converged when a difference between a current value of the adjustment parameter β(i) and a value of the adjustment parameter calculated during a previous iteration of the predictive model β(i−1) is less than a predetermined tolerance (ε).
|β(i)−β(i−1)|≦ε (8)
Otherwise, the adjustment parameter (β) has not converged.
This process is repeated until the value of the adjustment parameter converges toward an optimal value which can be used to calculate a fuel injection quantity that does not lead to violations of the actuator constraints. In some embodiments, the repeated acts of reducing and increasing the value of the adjustment parameter (β) are performed according to a bisectional search between the values of zero and one.
For example, the range of permissible fuel amounts for an NVO saturation constraint, denoted by Snvosat(n), is given by
Snvosat(n)=[mfmin(n),mfmax(n)] (9)
where mfmin(n) is the minimum fuel amount and mfmax(n) is the maximum fuel amount permissible for the NVO saturation constraint to be satisfied. An overall minimum fuel amount (mfmin) and an overall maximum fuel amount (mfmax) are determined (step 250) and defined by
[mfmin,mfmax]=
the overlap between the range of permissible fuel amounts for the NVO saturation constraint (Snvosat(n)), the range of permissible fuel amounts for an NVO rate constraint (Snvorate(n)), and the range of permissible fuel amounts for an SOI saturation constraint (Ssoisat(n)) for which all constraints will be satisfied.
As further illustrated in
where mfmin is the overall minimum fuel amount, mfmax is the overall maximum fuel amount, and mfdes(k) is the target fuel injection amount. As such, the amount of fuel to be injected (mf(k)) is adjusted to equal the overall maximum fuel amount (mfmax) when the target fuel injection amount mfdes(k) exceeds the overall maximum fuel injection amount (mfmax). Conversely, the amount of fuel to be injected (mf(k)) is adjusted to equal the overall minimum fuel amount (mfmin) when the target fuel injection amount mfdes(k) is below the overall minimum fuel amount (mfmin).
Thus, embodiments of the invention provide, among other things, methods and systems for controlling the performance of the engine during recompression HCCI combustion by adjusting the fuel amount injected into the engine when the fuel governor predicts that the target fuel injection amount would require actuator settings that violate the predetermined constraints.
Various features of the invention are set forth in the following claims.
This application claims priority to U.S. Provisional Application No. 61/543,544, filed Oct. 5, 2011, and titled “FUELING STRATEGY FOR CONTROLLED-AUTOIGNITION ENGINES,” the entirety of which is incorporated herein by reference.
This invention was made with Government support under grant No. DE-EE0003533 awarded by the Department of Energy. The Government has certain rights in this invention.
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