Patent Description:
Uncontrolled, damaging combustion such as engine knock, in which a large amount of energy is released in a short period of time, typically from rapid combustion of end gas, creates rapid pressure rise rates often followed by high frequency pressure oscillations. These intense pressure waves impose high stresses on engine structural components, and dramatically increase heat transfer rates, ultimately leading to engine damage. Such uncontrolled combustion may occur due to a variety of reasons such as poor fuel quality and properties, inhomogeneity of fuel-air mixture, hot spots in the combustion chamber, deposits, evaporating lube oil, unfavorable pressure-time history in the unburned gas of the cylinder charge, cylinder or cyclic variability of charge, inadequate cooling etc. Prediction of abnormal combustion is generally very difficult and is typically addressed during engine design.

<CIT> discloses a method for controlling operation of dual fuel internal combustion engine, which involves adjusting a substitution rate of gaseous fuel for liquid fuel in response to an operating condition deviating from a target operating condition.

<CIT> discloses a dual fuel engine comprising a controller, which is configured to convert the cylinder pressure input into a combustion metric indicative of the combustion occurring in the measured cylinder and to control fuel input and timing into the engine based on the combustion metric.

The concepts herein encompass the inclusion of at least one in-cylinder pressure sensor on the engine with the following combustion metrics being calculated concurrently with operation of the engine, and in some instances, in real-time: Peak Pressure, Rate of Pressure Rise, Pressure Ripple, Burn Duration, and Change Rate of Heat Release. These metrics are then combined mathematically via an equation / algorithm to determine how close the engine is operating to uncontrolled combustion. This allows the engine to be pushed to more severe operating conditions such as a richer mixture or higher substitution rates in Dual Fuel operation while maintaining safe operation. In some instances, the engine is a <NUM>-stroke or <NUM>-stroke engine and, in some instances, real-time refers to combustion metrics being calculated before completion of the next cycle, within the same cycle (e.g., before the next intake), before completion of the next stroke, or within the same stroke.

In some implementations, the concepts herein include ability to collect and process in-cylinder pressure information on a cycle-to-cycle basis as well as the following algorithms:.

Certain aspects of the present disclosure include using the combustion metrics listed above to determine a combustion intensity number that can then be used in a control loop to drive the engine safely to maximum gas substitution. In some implementations, all of these metrics are needed in order to cover many different cases that can be seen on a dual fuel engine. In some instances, the heat release change is statically determined or dynamically determined such that the inflection point of where combustion speeds up is accurately determined.

In certain aspects of the present disclosure, uncontrolled combustion (detonation) is no longer looked at from the traditional time based frequency domain, but instead from low speed direct in-cylinder pressure information which is based on practical engine limits.

One example of the present disclosure is a method of detecting uncontrolled combustion in a dual fuel internal combustion engine. The method includes sampling in-cylinder pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal, calculating a combustion intensity metric based on the corresponding pressure signal, and determining a parameter describing how close the engine is to an uncontrolled combustion condition based on the combustion intensity metric.

The dual-fuel internal combustion engine includes an in-cylinder pressure sensor configured to measure the pressure in a cylinder of the engine and generate a corresponding pressure signal, a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal, and an engine control unit couplable to the pressure sensor and the crank angle sensor. The engine control unit is configured to: sample the pressure signal, calculate a combustion intensity metric based on the corresponding pressure signal, determine a parameter describing how close the engine is to an uncontrolled combustion condition; and control a substitution rate of a first fuel and a second fuel delivered to the cylinder based on one or more of the parameter and the combustion intensity metric.

The claimed invention relates to a method of detecting uncontrolled combustion in a dual fuel internal combustion engine. The method includes sampling a pressure signal from in-cylinder pressure sensor, the pressure signal representative of a measured pressure in a cylinder of the engine, calculating a combustion intensity metric based on the pressure signal, wherein the combustion intensity metric is an indicator of the engine's proximity to an uncontrolled combustion condition, determining an engine control parameter as a function of the combustion intensity metric, and controlling the engine based on the engine control parameter.

The internal combustion engine according to claims <NUM> and <NUM> is a dual-fuel internal combustion engine and the engine control parameter includes a substitution rate of a first fuel and a second fuel based on at least one of the parameter or the combustion intensity metric.

In some instances, the first fuel is diesel and wherein the second fuel is natural gas.

In some instances, the combustion intensity metric is calculated within a same combustion cycle as the sampling of the in-cylinder pressure sensor.

In some instances, the method includes calculating, based on the pressure signal, a pressure metric, a heat release metric, and a knock metric, where the combustion intensity metric a function of the pressure metric, the heat release metric, and the knock metric. In some instances, the heat release metric comprises an adiabatic heat release rate of combustion in a cylinder of the engine.

In some instances, the method includes calculating at least one of the following combustion metrics based on the pressure signal: the peak cylinder pressure, the crank angle of peak cylinder pressure, a rate of cylinder pressure rise, a cylinder pressure ripple, the crank angle of a cylinder pressure ripple, a burn duration, a slope of heat release, the crank angle of centroid of heat release, or the crank angle of max heat release rate.

In some instances, the combustion intensity metric is a function of at least one of: the peak cylinder pressure, the crank angle of peak cylinder pressure, the rate of cylinder pressure rise, the cylinder pressure ripple, the crank angle of cylinder ripple, the burn duration, the slope of heat release, the crank angle of centroid of heat release, or the crank angle of max heat release rate.

The combustion intensity metric is a function of at least the peak pressure, the rate of pressure rise, the pressure ripple, the burn duration, and the slope of heat release.

In some instances, the method includes determining a fuel input signal, a throttle position signal, and an ignition timing signal for the engine based on at least one of the combustion intensity metric or the parameter.

The claimed invention further relates to a controller controlling operation of a dual-fuel internal combustion engine of an engine system, where the engine system includes a pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal and a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal. The controller includes a processor couplable to the in-pressure sensor and the crank angle sensor and at least one non-transitory computer readable medium storing instructions operable to cause the processor of the controller to perform operations. Where the operations include: (a) sample the pressure signal, (b) calculate a combustion intensity metric based on the pressure signal, wherein the combustion intensity metric is an indicator of the engine's proximity to an uncontrolled combustion condition, (c) determine a substitution rate of a first fuel and a second fuel delivered to the cylinder based on the combustion intensity metric, and (d) control the dual-fuel intemal combustion engine based on the substitution rate.

In some instances, first fuel is diesel and wherein the second fuel is natural gas.

In some instances, steps (b) and (c) occur within a next cycle of the cylinder.

In some instances, the instructions include calculating, based on the pressure signal, a pressure metric, a heat release metric, and a knock metric, and wherein the combustion intensity metric a function of the pressure metric, the heat release metric, and the knock metric.

In some instances, calculating the heat release metric includes calculating an adiabatic heat release rate of combustion in the cylinder of the engine.

In some instances, the instructions include calculating at least one of the following combustion metrics based on the pressure signal: the peak cylinder pressure, the crank angle of peak cylinder pressure, a rate of cylinder pressure rise, a cylinder pressure ripple, the crank angle of a cylinder pressure ripple, a burn duration, a slope of heat release, the crank angle of centroid of heat release, or the crank angle of max heat release rate.

In some instances, the peak cylinder pressure, the crank angle of peak cylinder pressure, the rate of cylinder pressure rise, the cylinder pressure ripple, the crank angle of cylinder ripple, the burn duration, the slope of heat release, the crank angle of centroid of heat release, or the crank angle of max heat release rate.

In some instances, the instructions include determine at least one of: a fuel input signal, a throttle position signal, or an ignition timing signal for the dual-fuel internal combustion engine based on at least one of the combustion intensity metric or the parameter, and control the dual-fuel internal combustion engine using at least one of: the fuel input signal, the throttle position signal, or the ignition timing signal.

Yet another not claimed example is controller for controlling operation of an internal combustion engine of an engine system, where the engine system includes a pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal and a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal. The controller includes a processor couplable to the in-pressure sensor and the crank angle sensor and at least one non-transitory computer readable medium storing instructions operable to cause the processor of the controller to perform operations. The operations include: (a) sample the pressure signal, (b) calculate a combustion intensity metric based on the pressure signal, wherein the combustion intensity metric is an indicator of the engine's proximity to an uncontrolled combustion condition, (c) determine an engine control parameter as a function of the combustion intensity metric, and (d) control the engine based on the engine control parameter.

Certain aspects of the present disclosure have the following advantages: Reduces the risk of damaging a high substitution rate dual fuel engine. The calibration effort to detect uncontrolled combustion is greatly reduced as the Combustion Intensity metric uses known mechanical engine limits. Certain aspects also allow an engine to always operate with maximum substitution control without having to add in margin for safety, which provides a much better value proposition for the dual fuel engine operator.

A new approach of detecting uncontrolled combustion is disclosed - namely combustion intensity (CI) - that monitors a mathematical combination of pressure and heat release metrics that can accurately predict the onset of uncontrolled combustion. Data from spark-ignited and dual fuel engines showcase the disadvantages of the traditional knock type, vibration frequency- based approaches, which work best at severe conditions, when there are extremely abrupt end-gas burn rates followed by high frequency oscillations. This technique falls short especially in dual fuel combustion, when there is diesel combustion ripple obfuscating the signal and at certain modes, when frequency content diminishes below normal detection thresholds. In contrast, embodiments of the CI metrics described herein provide monotonic trends as gas substitution increases across all operating points and even when gas quality, manifold air temperature, or other engine conditions changed. This provides a definitive control action path, which, in some instances, can be designed to a combustion intensity target. The gas substitution rate (GSR) at which these phases are encountered and the severity of combustion intensities may vary for different engine configurations, but the essential combustion phenomena disclosed herein should be universally relevant.

Pushing gas engines to their lean / low NOx and high BMEP limits and gas-diesel dual fuel engines to high substitution rates often leads to performance-limiting abrupt uncontrolled combustion such as knock. Understanding and detection of the progression of abnormal combustion is key to engine protection. Aspects of the present disclosure include the ability to detect the progression of uncontrolled combustion using both in-cylinder pressure in spark-ignited and dual fuel engines. For gas engines, pressure-based knock detection captures all the knock cycles while vibration-based knock detection misses a considerable percentage. For dual-fuel engines, the classical frequency-based detection approaches can detect severe combustion events, but do not provide a good continuously increasing signal. This makes engine control and calibration very difficult and therefore usually drives lower substitution rates in order to maintain a safety margin. This behavior is due to the diesel combustion process that creates pressure ripples in the cylinder.

Historically, the phrase "knock" has been used broadly to mean any form of "uncontrolled combustion" which is generally associated with "auto-ignition" phenomena due to compression and heating of combustible gas mixtures outside of the flame front. Controlled combustion would be characterized as a regular progression of the mass fraction burned that would be associated with a propagating flame. Classical knock would occur when the end-gas ahead of the flame auto-ignites due to pressure and temperature developed from the flame, but it is not in the flame. When auto-ignition occurs, it sends pressure waves across the cylinder which are detected as high frequency pressure oscillations and potential vibration noise.

Uncontrolled combustion can be characterized by a discontinuous sudden increase in the heat release rate, and this sudden increase in heat release rate will show up in the pressure trace shape, but it may or may not induce high frequency pressure oscillations. Unlike spark ignited engines, where uncontrolled combustion progressively builds in severity from incipiency to severe knock, providing enough time for a control action, onset of "uncontrolled combustion" in dual fuel engines can be sudden and non-monotonic. When this "uncontrolled combustion" occurs, high frequency oscillations are not always observed in either in-cylinder pressure or vibration-based knock sensor signals until it is often too late.

As substitution rates increase beyond a certain point, it was found that the vibration-knock signature decreases. If the engine is relying on knock for protection against excessive gas substitution rates, changing gas quality, or other influences, a robust control system is needed with progressively increasing signal feedback to maximize substitution while maintaining safe engine operation.

To achieve this, a new approach of detecting uncontrolled combustion is described that monitors a mathematical combination of pressure and heat release metrics that can accurately predict the progression of uncontrolled combustion providing a definitive control action path. With this approach, substitution rates can be maximized and maintained to a desired safety margin on a diesel dual-fuel engine.

Tests were conducted to vary the substitution rates at various speeds and loads to show the different combustion modes that can be seen in a diesel dual fuel engine. This data was used to determine a better approach to detect uncontrolled combustion in a dual fuel engine, proposing the term combustion intensity (CI). The combustion intensity metric described herein delivers a continuously increasing measure of the state of combustion to provide better controllability, while improving protection against uncontrolled combustion, since it is based upon direct monitoring of in-cylinder pressure concurrent with the combustion cycle.

For dual-fuel engines, as described above, traditional frequency based detection approaches and are able to detect severe combustion events, but do not provide a good continuously increasing signal that correlates with the severity. This makes engine control and calibration very difficult and usually drives to lower substitution rates in order to maintain a safety margin. For low gas substitution rates, the diesel combustion process dominates as diesel auto-ignition creates pressure ripple in the cylinder. As gas is added to the fresh charge, the intensity of the diesel ignited combustion increases in intensity - the gas amplifies the effect of diesel initiated combustion. However, as substitution rates increase beyond a certain point, the vibration knock signature decreases as the combustion shifts modes from "diesel like" to "premixed gas like" and the frequency based content starts to decrease with additional gas substitution. If the engine is relying on vibration base knock sensors for protection against excessive gas substitution rates, changing gas quality, or other influences, a robust control system is needed with progressively increasing signal feedback in order to maximize substitution while maintaining safe engine operation. To solve this problem, a new approach of detecting uncontrolled combustion in dual fuel engines is required.

One example solution described herein is the inclusion of at least one in-cylinder pressure sensor on the engine with the following combustion metrics being calculated concurrently with operation of the engine, and in some instances, in real-time: Peak Pressure, Location of Peak Pressure, Rate of Pressure Rise, Pressure Ripple, Location of Ripple, Burn Duration, and Slope of Heat Release, Location of Centroid of Heat Release Rate, Location of Max Heat Release Rate. In some instances, these metrics are then used together to determine how close the engine is operating to uncontrolled combustion. Based on this determination, the engine is allowed to be pushed to higher substitution rates while maintaining safe operation.

While the most demanding version of Dual fuel gas/diesel combustion refers herein to adding gaseous fuel to an existing diesel engine, the stock compression ratio, valve timing, and pistons are un-changed, this method applies to all Dual-Fuel gas/diesel engines including micro-pilot. Gas typically consists of natural gas, propane or biogas and it is introduced either at a single point - where it is fumigated into the intake system - or port injected near the intake valve. In some instances, Dual Fuel will refer to the continuous addition of natural gas to the combustion chamber of a stock diesel engine. As the gas substitution rate is increased, the diesel will "govern" by reducing the diesel quantity in equal energy ratios to maintain a target load.

Referring initially to <FIG>, an example engine system <NUM> usable with aspects of the present disclosure is shown. The engine system <NUM> includes an engine control unit <NUM>, an air/fuel module <NUM>, an ignition module <NUM>, and an engine <NUM> (shown here as a reciprocating engine). <FIG> illustrates, for example, an internal combustion engine <NUM>. For the purposes of this disclosure, the engine system <NUM> will be described as a gaseous-fueled reciprocating piston engine. In certain instances, the engine operates on natural gas fuel. The engine may be any other type of combustion engine, both in the type of fuel (gaseous, liquid (e.g., gasoline, diesel, and/or other), same phase or mixed phase multi-fuel, and/or another configuration) and the physical configuration of the engine (reciprocating, Wankel rotary, and/or other configuration). While the engine control unit <NUM>, the air/fuel module <NUM> and the ignition module <NUM> are shown separately, the modules <NUM>, <NUM>, <NUM> may be combined into a single module or be part of an engine controller having other inputs and outputs.

The reciprocating engine <NUM> includes engine cylinder <NUM>, a piston <NUM>, an intake valve <NUM> and an exhaust valve <NUM>. The engine <NUM> includes an engine block that includes one or more cylinders <NUM> (only one shown in <FIG>). The engine <NUM> includes a combustion chamber <NUM> formed by the cylinder <NUM>, the piston <NUM>, and a head <NUM>. A spark plug <NUM> or direct fuel injector or prechamber is positioned within the head <NUM> which enables the ignition device access to the combustible mixture. In general, the term "spark plug" can refer to a direct fuel injection device and/or spark plug or other ignition device within a prechamber. In the case of a spark plug, a spark gap <NUM> of the spark plug <NUM> is positioned within the combustion chamber <NUM>. In some instances, the spark gap <NUM> is an arrangement of two or more electrodes with a small space in-between. When an electric current is applied to one of the electrodes, an electric arc is created that bridges the small space (i.e., the spark gap) between the electrodes. Other types of igniters can be used, including laser igniters, hot surface igniters and/or yet other types of igniters. The piston <NUM> within each cylinder <NUM> moves between a top-dead-center (TDC) position and a bottom-dead-center (BDC) position. The engine <NUM> includes a crankshaft <NUM> that is connected each piston <NUM> such that the piston <NUM> moves between the TDC and BDC positions within each cylinder <NUM> and rotates the crankshaft <NUM>. The TDC position is the position the piston <NUM> with a minimum volume of the combustion chamber <NUM> (i.e., the piston's <NUM> closest approach to the spark plug <NUM> and top of the combustion chamber <NUM>), and the BDC position is the position of the piston <NUM> with a maximum volume of the combustion chamber <NUM> (i.e., the piston's <NUM> farthest retreat from the spark plug <NUM> and top of the combustion chamber <NUM>).

The cylinder head <NUM> defines an intake passageway <NUM> and an exhaust passageway <NUM>. The intake passageway <NUM> directs air or an air and fuel mixture from an intake manifold <NUM> into combustion chamber <NUM>. The exhaust passageway <NUM> directs exhaust gases from combustion chamber <NUM> into an exhaust manifold <NUM>. The intake manifold <NUM> is in communication with the cylinder <NUM> through the intake passageway <NUM> and intake valve <NUM>. The exhaust manifold <NUM> receives exhaust gases from the cylinder <NUM> via the exhaust valve <NUM> and exhaust passageway <NUM>. The intake valve <NUM> and exhaust valve <NUM> are controlled via a valve actuation assembly for each cylinder, which may include be electronically, mechanically, hydraulically, or pneumatically controlled or controlled via a camshaft (not shown).

Movement of the piston <NUM> between the TDC and BDC positions within each cylinder <NUM> defines an intake stroke, a compression stroke, a combustion or power stroke, and an exhaust stroke. The intake stroke is the movement of the piston <NUM> away from the spark plug <NUM> with the intake valve <NUM> is open and a fuel/air mixture being drawn into the combustion chamber <NUM> via the intake passageway <NUM>. The compression stroke is movement of the piston <NUM> towards the spark plug <NUM> with the air/fuel mixture in the combustion chamber <NUM> and both the intake value <NUM> and exhaust valve <NUM> are closed, thereby enabling the movement of the piston <NUM> to compress the fuel/air mixture in the combustion chamber <NUM>. The combustion or power stroke is the movement of the piston <NUM> away from the spark plug <NUM> that occurs after the combustion stroke when the spark plug <NUM> ignites the compressed fuel/air mixture in the combustion chamber by generating an arc in the spark gap <NUM>. The ignited fuel/air mixture combusts and rapidly raises the pressure in the combustion chamber <NUM>, applying an expansion force onto the movement of the piston <NUM> away from the spark plug <NUM>. The exhaust stroke is the movement of the piston <NUM> towards the spark plug <NUM> after the combustion stroke and with the exhaust valve <NUM> open to allow the piston <NUM> to expel the combustion gases to the exhaust manifold <NUM> via the exhaust passageway <NUM>.

The engine <NUM> includes a fueling device <NUM>, such as a fuel injector, gas mixer, or other fueling device, to direct fuel into the intake manifold <NUM> or directly into the combustion chamber <NUM>. In some instances the engine <NUM> is a dual duel engine having two sources of fuel into the combustion chamber <NUM>.

In some instances, the engine system <NUM> could include another type of internal combustion engine <NUM> that doesn't have pistons/cylinders, for example, a Wankel engine (i.e., a rotor in a combustion chamber). In some instances, the engine <NUM> includes two or more spark plugs <NUM> in each combustion chamber <NUM>.

During operation of the engine, i.e., during a combustion event in the combustion chamber <NUM>, the air/fuel module <NUM> supplies fuel to a flow of incoming air in the intake manifold before entering the combustion chamber <NUM>. The spark module <NUM> controls the ignition of the air/fuel in the combustion chamber <NUM> by regulating the timing of the creation of the arc the spark gap <NUM>, which initiates combustion of the fuel/air mixture within combustion chamber <NUM> during a series of ignition events between each successive compression and combustion strokes of the piston <NUM>. During each ignition event, the spark module <NUM> controls ignition timing and provides power to the primary ignition coil of the spark plug <NUM>. The air/fuel module <NUM> controls the fuel injection device <NUM> and may control throttle valve <NUM> to deliver air and fuel, at a target ratio, to the engine cylinder <NUM>. The air/fuel module <NUM> receives feedback from engine control module <NUM> and adjusts the air/fuel ratio. The spark module <NUM> controls the spark plug <NUM> by controlling the operation of an ignition coil electrically coupled to the spark plug and supplied with electric current from a power source. The ECU <NUM> regulates operation of the spark module <NUM> based on the engine speed and load and in addition to aspects of the present system disclosed below.

In some instances, the ECU <NUM> includes the spark module <NUM> and the fuel/air module <NUM> as an integrated software algorithms executed by a processor of the ECU <NUM>, and thereby operate of the engine as single hardware module, in response to input received from one or more sensors (not shown) which may be located throughout the engine. In some instances, the ECU <NUM> includes separate software algorithms corresponding to the described operation of the fuel/air module <NUM> and the spark module <NUM>. In some instances, the ECU <NUM> includes individual hardware module that assist in the implementation or control of the described functions of the fuel/air module <NUM> and the spark module <NUM>. For example, the spark module <NUM> of the ECU <NUM> may include an ASIC to regulate electric current delivery to the ignition coil of the spark plug <NUM>. A plurality of sensor systems exist to monitor the operational parameters of an engine <NUM>, which may include, for example, a crank shaft sensor, an engine speed sensor, an engine load sensor, an intake manifold pressure senor, an in-cylinder pressure sensor, etc. Generally, these sensors generate a signal in response to an engine operational parameter. For example, a crank shaft sensor <NUM> reads and generates a signal indicative of the angular position of crankshaft <NUM>. In an exemplary embodiment, a high speed pressure sensor <NUM> measures in-cylinder pressure during operation of the engine <NUM>. The sensors <NUM>,<NUM> may be directly connected to the ECU <NUM> to facilitate the sensing, or, in some instances are integrated with a real-time combustion diagnostic and control (RT-CDC) unit configured to acquire high speed data from one or more of the sensor and provide a low speed data output to the ECU <NUM>. In some instances, the ignition control described herein is a stand-alone ignition control system providing the operation of ECU <NUM> and the spark module <NUM>. The sensors may be integrated into one of the control modules, such as the ECU <NUM> or a RT-CDC. Other sensors are also possible, and the systems described herein may include more than one such sensor to facilitate sensing the engine operational parameters mentioned above.

<FIG> is a schematic of an engine control system <NUM> of the engine system <NUM> of <FIG>. <FIG> shows the ECU <NUM> within the engine control system <NUM> configured to control the engine <NUM>. As indicated above, high-speed pressure data <NUM> is generated by pressure sensors <NUM>, each mounted with direct access to the combustion chamber. The pressure signal <NUM> is captured at a high crank-synchronous rate, for example, <NUM>° resolution or <NUM> samples per cycle of the engine <NUM>. This synthetic crank angle signal is generated from the lower resolution crank position signal. For example, with a typical crank angle encoder <NUM> generating a crank angle signal <NUM> by sensing passage of the edge of teeth on a disk, the disk mounted to rotate with the crank, the resolution of the crank position is based on the number of teeth. A typical <NUM>-<NUM> tooth wheel has a resolution of <NUM>°. However, in some instances, interpolation is used to determine a crank angle in the space between of the edges. Thus, the spacing between edges uses the previously observed tooth period divided by the number of edges required to achieve the desired angular sampling resolution. To account for minor variability between the crank teeth that can be seen even when the average engine speed is constant, and the encoder system is re-synchronized on each edge.

In some instances, the resulting high-resolution pressure signal <NUM> is used by the combustion diagnostics routine in the Real-time Combustion Diagnostics and Control (RT-CDC) <NUM> module to produce the combustion diagnostics <NUM> on a per-cylinder, per cycle basis, for example, IMEP, Pmax, CA50, combustion quality, and combustion intensity, as discussed in more detail below. The metrics <NUM> are subsequently used by the ECU <NUM> as a feedback signal for adjusting key combustion performance characteristics by modulating engine control actuator settings <NUM>.

<FIG> is a block diagram of an example engine control unit <NUM> configured to have aspects of the systems and methods disclosed herein. The example engine control unit <NUM> includes a processor <NUM>, a memory <NUM>, a storage device <NUM>, and one or more input/output interface devices <NUM>. Each of the components <NUM>, <NUM>, <NUM>, and <NUM> can be interconnected, for example, using a system bus <NUM>.

The processor <NUM> is capable of processing instructions for execution within the engine control unit <NUM>. The term "execution" as used here refers to a technique in which program code causes a processor to carry out one or more processor instructions. In some implementations, the processor <NUM> is a single-threaded processor. In some implementations, the processor <NUM> is a multi-threaded processor. The processor <NUM> is capable of processing instructions stored in the memory <NUM> or on the storage device <NUM>. The processor <NUM> may execute operations such as calculating of a combustion intensity.

The memory <NUM> stores information within the engine control unit <NUM>. In some implementations, the memory <NUM> is a computer-readable medium. In some implementations, the memory <NUM> is a non-volatile memory unit.

The storage device <NUM> is capable of providing mass storage for the engine control unit <NUM>. In some implementations, the storage device <NUM> is a non-transitory computer-readable medium. In various different implementations, the storage device <NUM> can include, for example, a hard disk device, an optical disk device, a solid-state drive, a flash drive, magnetic tape, or some other large capacity storage device. The input/output interface devices <NUM> provide input/output operations for the engine control unit <NUM>. In some implementations, the input/output interface devices <NUM> can include an in-cylinder pressure sensor <NUM>, a crank angle sensor <NUM>, or other engine sensors.

In some examples, the engine control unit <NUM> is contained within a single integrated circuit package. An engine control unit <NUM> of this kind, in which both a processor <NUM> and one or more other components are contained within a single integrated circuit package and/or fabricated as a single integrated circuit, is sometimes called a microcontroller. In some implementations, the integrated circuit package includes pins that correspond to input/output ports, e.g., that can be used to communicate signals to and from one or more of the input/output interface devices <NUM>.

Certain aspects of the concepts described herein encompass the ability to collect and process in-cylinder pressure information on a cycle-to-cycle basis as well as the following algorithms:.

Certain aspects of the present disclosure use the combustion metrics listed above to determine a combustion intensity number that can then be used in a control loop to drive the engine safely to maximum gas substitution. All of these metrics are needed in order to cover many different cases that can be seen on a dual fuel engine.

One example of an enabling technology disclosed herein is the heat release change algorithm as well as bum duration. The heat release change can be statically determined or dynamically determined such that the inflection point of where combustion speeds up is accurately determined.

Previously, in a dual fuel engine, vibration sensors were used, but they only allow the controller to detect heavy knock due to the presence of extreme auto-ignition. Traditional solutions use accelerometers to determine the frequency and amplitude in order to detect detonation. However, the traditional solutions do not work well for dual fuel engines, as the signal reduces as you get to higher substitution rates. This makes it very difficult to understand the proximity to uncontrolled combustion. If higher substitution rates are desired, the threshold for the controller to take action must be greater than the highest signal during normal dual fuel combustion. To maintain safe engine operation, the knock threshold should be below the highest intensity, however that will limit the allowable substitution rates as shown in <FIG> shows a plot of what the processed accelerometer detection does as a function of gas substitution in an example engine, as discussed in more detail below. This technique fails especially in dual fuel combustion due to the diesel combustion ripple obfuscating the signal at certain dual fuel modes, and later when all frequency content disappears at high GSR, providing no clear indication of safety margin to uncontrolled combustion. A more robust detection methodology is needed that can capture the state of combustion. With this in mind, a combustion intensity (CI) metric was formulated.

Certain aspects of the present disclosure relate to the use of direct in-cylinder pressure measurements to calculate engine metrics that can be used in a certain combination to give an increasing detection signal as substitution rate continues to increase. This allows the engine controller to achieve maximum substitution while understanding how close the engine is to uncontrolled combustion therefore maintaining safe engine operation. One example of the CI metric is expressed weighted sum of heat release rate and pressure rise rate metrics, while including classical metrics like pressure ripple and peak pressure. In some instances the CI may be any mathematical combination of any of the parameters identified above such as a polynomial, weighted sum, sum of exponentials or power law, or a nonlinear function, CI = function (Peak Pressure, Rate of Pressure Rise, Pressure Ripple, Burn Duration, Change Rate of Heat Release, Knock Index).

One example combustion intensity metric is expressed as a linear sum of parameters such as shown below in Equation <NUM>.

This CI metric, which uses pressure-based information and heat release information and does not have the limitations of the traditional vibration-based detection. In some instances, the CI metric is a sum of pressure metrics, heat release metrics, and classical knock metrics.

In some instances, the CI metric incorporates practical engine limits that can be easily calibrated with knowledge of the mechanical limits of the engine. In some instances, this CI metric also incorporates the classical knock detection and peak pressure limits in order to have a secondary safety measure. The CI metric correlates well with the qualitative sense of combustion observable in the pressure traces during calibration in the lab. The combustion intensity metric shown in <FIG> is progressively increased from <NUM> to <NUM>% as gas substitution is increased. <FIG>, discussed in more detail below in Example <NUM>, illustrates what the combustion intensity metric does as a function of gas substitution showing the combustion intensity metric vs. classical knock intensity metrics as a measure of proximity to uncontrolled combustion. A clear linear control action path can be set to which a controller can be targeted to maximize gas substitution while maintaining a desired safety margin from uncontrolled combustion. In some instances the combustion intensity metric describes (or is used to determine) how close the engine is operating to uncontrolled combustion. This allows the engine to be pushed to higher substitution rates while maintaining safe operation by, for example, allowing the GSR to be increased while maintaining safe engine operation by using the combustion intensity metric to control the increase of the GSR without causing uncontrolled combustion. The combustion intensity metric enables this safe increase by, for example, providing a more accurate 'picture' of the current state of combustion because the CI metric increases with likelihood of uncontrolled combustion. Therefore, the use of a CI metric in an engine control can, for example, enable the selection of a target CI value and then using the CI metric in a control loop to maximize GSR within the target CI. In some instances, the CI metric reduces calibration requirements.

Aspects of the present disclosure enable uncontrolled combustion (detonation) to no longer be considered in the traditional time based frequency domain, but instead from direct in-cylinder pressure information which is based on practical engine limits. Aspects enable reduction of the risk of damaging a high substitution rate dual fuel engine. The calibration effort to detect uncontrolled combustion is greatly reduced as the Combustion Intensity metric uses known mechanical engine limits. Example implementations also allows the engine to always operate with maximum substitution control without having to add in margin for safety which provides a much better value proposition for the dual fuel engine operator.

An example improvement from vibration-based detection is the incorporation of heat release concurrent with combustion, as this is the primary effect of adding natural gas as can be seen in the plot of the smoothed heat release traces at <NUM>%, <NUM>% and <NUM>% gas substitution rate (GSR) shown in <FIG>, discussed in more detail below in Example <NUM>. As natural gas is added, the traditional diesel pre-mixed spike is reduced and then progresses to a heat release rate that is very aggressive at <NUM>%. This can be monitored in order to understand the current state of combustion intensity. At <NUM>% GSR and above, the combustion becomes completely gas dominant, and the engine behaves almost like a spark ignition engine or a micro-pilot ignited gas engine.

The CI metric is a progressive measure of the state of combustion and is a good indicator of proximity to uncontrolled combustion as can be seen in the following example.

A study of the effect of gas addition on the original diesel combustion characteristics of a diesel-natural gas dual fuel engine was conducted, where the stock engine compression ratio of the original diesel engine was left unchanged. The specifications of the dual fuel engine used in the study are shown in Table <NUM>. A Woodward knock sensor (WLEKS) and Kistler 6058A piezoelectric in-cylinder pressure sensors were used to capture any uncontrolled combustion on a Dewetron combustion analyzer, sampling at <NUM>. The engine was always brought to a stable operating condition with <NUM>% diesel targeting set points for IMEP and MAT, before gas was substituted for diesel using chemical energy split calculations. The diesel fuel was injected between <NUM> to <NUM> degrees before top dead center, depending on where in the speed load map the engine was operating. The gas substitution rate (GSR) was increased in steps of <NUM>% increments and repeated at different speed and load points. The data shown in the following figures (<FIG>) is averaged over <NUM> combustion cycles. The methane number of the natural gas used in this study was approximately <NUM>, with <NUM>% methane, <NUM>% ethane and <NUM>% propane.

An example of the raw in-cylinder pressure and vibration knock traces captured at <NUM> bar IMEP, <NUM> rpm, is plotted in <FIG> is a plot of in-cylinder pressure and vibration traces at <NUM>%, <NUM>% and <NUM>% gas substitution rate <NUM>, <NUM>, <NUM> (GSR), at <NUM> rpm and10 bar IMEP. <FIG> shows that a pressure ripple (diesel combustion) is visible at <NUM>% gas (<NUM>% diesel) operation. As the gas is increased from <NUM> to <NUM>% GSR (not shown), the overall combustion initially becomes quieter, where diesel combustion is still dominant. Further increase to <NUM>% (second curve) shows a zone of noisier diesel-gas combustion, with increased knock frequency components detected with both vibration and in-cylinder pressure sensors. This can be seen in <FIG> where the pressure and vibration knock intensity reach a maximum at <NUM>% GSR. At <NUM>% GSR, the vibration signal is at its quietest (third curve).

<FIG> is a plot of vibration and pressure knock intensity versus gas substitution ratio. <FIG> and <FIG> show the challenge: the vibration knock signature increases in intensity from <NUM> to <NUM>% GSR at this operating point, captured also in <FIG>, but then turns and decreases to its lowest value at <NUM>% substitution - just before very intense combustion knock is observed (and noted in <FIG>, but unable to record over <NUM> cycles). As the gas substitution was increased from <NUM>% to <NUM>% gas substitution, the gas combustion becomes increasingly dominating during the latter half of combustion. In this phase, all frequency content disappears as seen in <FIG>. Classical approaches of pressure ripple or knock spectral content become difficult to detect proximity to knock or uncontrolled combustion. This creates a very difficult control issue for the engine controller because it is difficult to accurately perform closed loop control when the engine operates near uncontrolled combustion. This is different from a spark-ignited gas engine where vibration based knock can detect light, medium, and heavy knock, thus giving the controller the ability to adjust engine parameters before heavy/severe knock occurs. In a dual fuel engine, vibration sensors can be used, but they only allow the controller to detect heavy knock due to the presence of extreme auto-ignition. It would be wise to use open loop tables or a much lower allowable GSR to keep the knock levels in the monotonic range. If higher substitution rates are desired, the threshold for the controller to take action must be greater than the highest signal during normal dual fuel combustion. To maintain safe engine operation, the knock threshold should be below the highest intensity; however, that will limit the allowable substitution rates as shown in <FIG>.

<FIG> is a <NUM>-D contour plot of pressure knock intensity at various speeds versus gas substitution and <FIG> is a <NUM>-D contour plots of vibration knock intensity at various speeds versus gas substitution. <FIG> and 6B indicate the non-monotonic and non-linear trends, which will prove difficult to design a robust control around. The pressure knock intensity and vibration knock intensity techniques fail in dual fuel combustion due to the diesel combustion ripple obfuscating the signal at certain dual fuel modes, and later when all frequency content disappear at high GSR, providing no clear indication of safety margin to uncontrolled combustion.

<FIG> is a graph illustrating the effect of a combustion intensity (CI) metric versus a classical knock intensity metrics as a measure of proximity to uncontrolled combustion and as a function of gas substitution. The CI metric of the present disclosure is a more robust detection methodology that can capture the state of combustion. <FIG> shows that the CI metric provides a good indicator of proximity to uncontrolled combustion, and, in some instances, the CI metric is a progressive measure of the state of combustion. The CI metric incorporates practical engine limits that can be calibrated with knowledge of the mechanical limits of the engine. In some implementation, and as show above in Equation <NUM>, the CI is a weighted sum of heat release rate and pressure rise rate metrics, in addition to including classical metrics like pressure ripple and peak pressure. In some instances, the CI metric, which uses pressure-based information and heat release information, does not have the limitations of the traditional vibration-based detection. In some instances, the CI metric also incorporates the classical knock detection and peak pressure limits in order to have a secondary safety measure. In some implementations, the CI metric correlates well with the qualitative sense of combustion observable in the pressure traces during calibration in the lab.

<FIG> is a plot of smoothed heat release traces at <NUM>% (<NUM>) , <NUM>% (<NUM>) and <NUM>% (<NUM>) gas substitution rate. A major improvement from vibration- based detection is the incorporation of real-time heat release, as this is the primary effect of adding natural gas as can be seen in the plot of the smoothed heat release traces at <NUM>%, <NUM>% and <NUM>% gas substitution rate (GSR) shown in <FIG>. As natural gas is added, the traditional diesel pre-mixed spike is reduced and then progresses to a combined heat release rate that is very aggressive at <NUM>%. This can be monitored in order to understand the current state of combustion intensity. At <NUM>% GSR and above, the combustion becomes completely gas dominant, and the engine behaves almost like a spark ignition engine or a micro-pilot ignited gas engine.

Referring again to <FIG>, the CI metric progressively increased as gas substitution is increased from <NUM> to <NUM>%. A clear linear control action path can be set to which a controller can be targeted to maximize gas substitution while maintaining a desired safety margin from uncontrolled combustion. This linearity is seen even in a <NUM>-D contour plot of combustion intensity shown in <FIG> with monotonic trends across all speeds. One of the metric in the CI calculation that helped linearize this metric is the heat release rates, as the combustion in the latter half of the burn duration gets faster as more gas is added, as shown in <FIG>.

<FIG> is a plot of angle locations of <NUM>% (<NUM>), <NUM>% (<NUM>) and <NUM>% (<NUM>) of total heat release versus gas substitution. In <FIG>, the crank angle locations of <NUM>%, <NUM>% and <NUM>% of total heat release are shown, which helps understand the combustion phasing, ignition delays and the burn rates. As diesel was replaced by gas, the start of injection (SOI) and the CA50 were not affected at this operating point, showing that the combustion phasing did not change much. The angular interval between CA90 and CA50 decreased sharply as GSR was increased, indicating a faster burn of end-gas. In addition, CA10 increased slightly showing greater ignition delay as GSR was increased from <NUM> to <NUM>%. As gas displaces the air, the oxygen concentration would be lower, so the mixture is richer and the ignition delay is longer. Correspondingly, as the gas/air mixture gets richer, the flame speed increases continuously until a very short burn duration is evident as are the conditions for end-gas auto-ignition. At the operating point shown above, end-gas auto-ignition conditions were not reached, and GSR was pushed to <NUM>% at which point the limit of diesel injector delivery was reached.

Increasing GSR leads to end-gas auto-ignition with large ripples in the pressure, as shown in pressure and heat release rate traces in <FIG>. Which show, plots of in-cylinder pressure at <NUM>% (<NUM>), <NUM>% (<NUM>) and <NUM>% (<NUM>) gas substitution rate versus crank angle, and smoothed heat release traces at <NUM>% (<NUM>), <NUM>% (<NUM>) and <NUM>% (<NUM>) gas substitution rate versus crank angle. <FIG> is a plot of combustion intensity and knock intensity metrics versus gas substitution rate (GSR), and shows that, when severe end-gas knock is present, both pressure and vibration knock intensity metrics increase sharply along with the combustion intensity. Therefore, it appears that the frequency based detection techniques, such as the spectral content in vibration or pressure ripple, are not clearly seen until intense knock occurs. At low loads, these vibration or pressure techniques fall short in clearly identifying the margin to knock as the trends were non-monotonic. If a simple threshold based severity is to be determined, this example shows that high threshold levels will only catch events of severe engine-damaging knock, which can occur abruptly. If lower threshold levels were used to quantify severity, then the engine should not be pushed past <NUM>-<NUM>% gas substitution. In contrast, the present CI metric provides a continuously increasing measure of the state of combustion to provide better controllability and increase maximum safe gas substitution (e.g., up to <NUM>% gas substitution) , while improving protection against uncontrolled combustion.

In Example, <NUM> the effect of gas quality was simulated by substituting propane in place of natural gas. <FIG> show the pressure <NUM>, <NUM>, <NUM> and smoothed heat release rate <NUM>, <NUM>, <NUM> traces as the propane substitution ratio (PSR) was increased from <NUM>% to <NUM>% at <NUM> rpm, <NUM> bar IMEP and at a fixed (overall) gas substitution of <NUM>%. The diesel contribution in this test is maintained at <NUM>%, while propane was substituted for natural gas in increments of <NUM>% PSR using chemical energy split calculations. The plots indicate that even a small percentage of propane caused drastic heat release and pressure rise rates, with large, visible pressure oscillations. <FIG> is a graph of the CI (<NUM>) and knock intensity metrics (<NUM>, <NUM>) versus propane gas substitution rate (PSR) and shows that the CI metric is still reliable as propane was added to indicate the highly unstable combustion.

<FIG> is a plot combustion intensity (<NUM>) and knock intensity metrics (<NUM>, <NUM>) versus manifold air temperature (MAT). <FIG> shows the effect of the charge air temperature or density on the detection of proximity to uncontrolled combustion. Increases in the charge air temperature can impact ignition delays, in-cylinder temperature rise rates and auto-ignition propensity of the engine. The metrics are compared as the manifold air temperature (MAT) is increased from <NUM> to <NUM>, at <NUM> rpm, <NUM> bar IMEP. The results indicate that only the CI metric increase linearly with the MAT, and can be used reliably as a proximity to uncontrolled combustion, whereas the other knock intensity metrics provide no clear trends.

A Woodward Large Engine Control Module (LECM) was used to test the CI metric on a real embedded ECU, which allowed for real-time combustion feedback to be performed using the AUX (Auxiliary) module. Two cases were tested to show the sensitivity of the CI metric to detect changes in combustion. <FIG> show the first test case, where a sine wave was commanded for the GSR (<NUM>) with an offset of <NUM>% and an amplitude of <NUM>%, as shown in <FIG> shows that the CI metric responded well to the changes as the metric went from <NUM>% to <NUM>% intensity. The amplitude was then decreased to <NUM>%, and the CI metric showed <NUM>% intensity at the peak. Then while the sine wave was still being commanded <NUM>% propane (<NUM>) was substituted for natural gas in order to simulate a gas quality change, and it can be seen that the CI metric (<NUM>) detected the change by indicating a higher intensity.

For the second case, the manifold air temperature (MAT) was allowed to increase to around <NUM> and then cooled quickly, as shown in <FIG> shows that the CI metric increased as MAT increased as expected. The results show that the CI metric detects external disturbances very well. In some instances, the CI metric is used to control the engine to a defined limit. The CI metric aspects disclosed herein can significantly reduces the amount of calibration as well as the amount of safety margin usually considered for dual fuel engines. This detection method should allow higher substitution rates to be achieved.

<FIG> is a flow chart <NUM> of an example aspect of the present disclosure. A engine controller (e.g., ECU <NUM>) sample a pressure signal from in-cylinder pressure sensor (<NUM>), calculates a combustion intensity metric based on the pressure signal, where the combustion intensity metric is an indicator of the engine's proximity to an uncontrolled combustion condition (<NUM>), determines an engine control parameter as a function of the combustion intensity metric (<NUM>), and control the engine based on the engine control parameter (<NUM>).

Implementations of the subject matter described in this specification, such as calculating a combustion intensity metric can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible program carrier, for example a computer-readable medium, for execution by, or to control the operation of, a processing system. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of them.

The term "engine control unit" may encompass all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. A processing system can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, software application, script, executable logic, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile or volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks or magnetic tapes; magneto optical disks; and CD-ROM, DVD-ROM, and Blu-Ray disks.

Claim 1:
A method (<NUM>) of detecting uncontrolled combustion in a dual-fuel internal combustion engine of an engine system, the engine system comprising an in-cylinder pressure sensor (<NUM>) configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal (<NUM>) and a crank angle sensor (<NUM>) configured to measure the crank angle of the engine and generate a corresponding crank angle signal (<NUM>), a controller comprising a processor (<NUM>) couplable to the in-cylinder pressure sensor and the crank angle sensor, the method comprising:
sampling (<NUM>) a pressure signal from the in-cylinder pressure sensor, the pressure signal representative of a measured pressure in a cylinder of the engine;
calculating combustion metrics based on the pressure signal, the combustion metrics being at least a peak cylinder pressure, a rate of cylinder pressure rise, a cylinder pressure ripple, a burn duration, and a slope of heat release;
calculating (<NUM>) a combustion intensity metric based on the pressure signal, wherein the combustion intensity metric is an indicator of the engine's proximity to an uncontrolled combustion condition, and wherein the combustion intensity metric is a function of at least the peak cylinder pressure, the rate of cylinder pressure rise, the cylinder pressure ripple, the burn duration, and the slope of heat release;
determining (<NUM>) an engine control parameter as a function of the combustion intensity metric, wherein the engine control parameter comprises a substitution rate of a first fuel and a second fuel based on the combustion intensity metric; and
controlling (<NUM>) the engine based on the engine control parameter.