Patent Description:
Internal combustion engines that can be operated at least partly on gaseous fuel include gaseous fuel internal combustion engines and dual fuel (DF) internal combustion engines. DF internal combustion engines are, for example, configured for operation with liquid fuel, such as Diesel, and gaseous fuel, such as natural gas. Incomplete combustion, such as misfires, may occur when a mixture of gaseous fuel and air in a cylinder of such an engine is only partly consumed by the flame. Incomplete combustion may be caused by a malfunction of the ignition system, such that, for example, an insufficient ignition flame is formed. Alternatively, the mixture of fuel and air may be set inappropriately, for example, due to insufficient fuel feed.

Lean mixtures of gaseous fuel and air are specifically susceptible to incomplete combustion as flame formation of those mixtures is small and the fuel may not be fully consumed within one combustion cycle. As an undesired consequence, unburnt fuel may build up in the exhaust passages of the internal combustion engine. This can lead to explosions and potential damage to the engine.

An exemplary DF internal combustion engine is disclosed, for example, in <CIT>. An overview of various engine misfire detection methods used in on-board diagnostics of internal combustion engines is given in<NPL>.

<CIT> discloses an energy transfer system of a vehicle. The energy transfer system includes an input energy computation means for determining the input energy, an output energy computation means for determining the energy output, and a comparing means for comparing the input energy with the output energy. An anomaly in the energy transfer system is determined based on the result of the comparison by the comparing means.

The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.

According to one aspect of the present disclosure, a method of detecting an incomplete combustion in an internal combustion engine operating at least partly on gaseous fuel comprises the steps of claim <NUM>.

According to another aspect of the present disclosure, an internal combustion engine operating at least partly on gaseous fuel comprises the features of claim <NUM>.

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. In the drawings:.

The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described therein and illustrated in the drawings are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of patent protection. Rather, the scope of patent protection shall be defined by the appended claims.

The present disclosure is based in part on the realization that an incomplete combustion in a cylinder of an internal combustion engine may be detectable by a combustion energy value of the combustion which may be derived from a temporal development of the cylinder pressure during combustion. The temporal development of the cylinder pressure may be observed and analyzed by an associated control system.

In general, once the incomplete combustion is detected, the associated control system may terminate the operation of the internal combustion engine, indicate a failure of the internal combustion engine to the user of the engine and/or initiate appropriate countermeasures to prevent an incomplete combustion from reoccurring. For example, the control system may increase the fuel-to-air ratio of the mixture admitted to the cylinder. In case the internal combustion engine is a DF internal combustion engine operating in gaseous fuel mode, the control system may be further configured to switch from gaseous fuel mode into liquid fuel mode or to stop switching to gaseous fuel mode.

An internal combustion engine operable at least partly on gaseous fuel and exemplary methods for controlling the same are described in the following in connection with <FIG> and <FIG>, respectively.

<FIG> shows schematically an exemplary internal combustion engine <NUM> operating at least partly on gaseous fuel, such as a DF engine (illustrated schematically in <FIG>) or a gaseous fuel engine (illustrated schematically in <FIG>).

Internal combustion engine <NUM> comprises an engine block <NUM>, a charge air system <NUM>, an exhaust gas system <NUM>, a gaseous fuel system <NUM> including a purge gas system <NUM> and/or a liquid fuel system <NUM>. Internal combustion engine <NUM> can be powered with a liquid fuel such as, for example, diesel fuel in a liquid fuel mode (LFM), and with a gaseous fuel such as natural gas provided, for example, by an LNG-system, in a gaseous fuel mode (GFM).

Engine block <NUM> comprises a plurality of cylinders. Exemplarily, four cylinders <NUM> are depicted in <FIG>. Engine block <NUM> may be of any size, with any number of cylinders, such as <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, and in any configuration, for example, "V", in-line or radial configuration.

Each cylinder <NUM> is equipped with at least one inlet valve <NUM> and at least one outlet valve <NUM>. Inlet valves <NUM> are fluidly connected to charge air system <NUM> and configured to provide charge air, or a mixture of charge air and gaseous fuel into cylinders <NUM>. Analogous, outlet valves <NUM> are fluidly connected to exhaust gas system <NUM> and configured to direct exhaust gas out of respective cylinder <NUM>.

Charge air is provided by charge air system <NUM> including an air intake <NUM>, a compressor <NUM> to charge air, and a charge air cooler <NUM>. A charge air manifold <NUM> is fluidly connected downstream of charge air cooler <NUM> and guides charge air via cylinder specific inlet channels <NUM> into respective cylinders <NUM>.

Exhaust gas system <NUM> includes an exhaust gas turbine <NUM> connected to compressor <NUM> via shaft <NUM> and an exhaust gas manifold <NUM> guiding exhaust gas from individual exhaust gas outlet channels <NUM> to exhaust gas turbine <NUM>.

Charge air system <NUM> may comprise one or more charge air manifolds <NUM>. Similarly, exhaust gas system <NUM> may comprise one or more exhaust gas manifolds <NUM>.

In addition, inlet valves <NUM> and outlet valves <NUM> may be installed within inlet channels <NUM> and outlet channels <NUM>, respectively. Inlet channels <NUM> as well as outlet channels <NUM> may be provided within a common cylinder head or individual cylinder heads covering cylinders <NUM>.

Gaseous fuel system <NUM> comprises a gaseous fuel source <NUM> connected to gaseous fuel piping <NUM>. Gaseous fuel source <NUM> constitutes a gaseous fuel feed for supplying gaseous fuel for combustion in GFM. For example, gaseous fuel source <NUM> comprises a gas valve unit and a gaseous fuel tank that contains natural gas in a pressurised state.

Gas valve unit is configured to allow, to block, and to control flow from gaseous fuel tank into gaseous fuel piping <NUM>. The gas valve unit may comprise gaseous fuel control valves, gaseous fuel shut-off valves and venting valves.

Gaseous fuel piping <NUM> is fluidly connected to a gaseous fuel manifold <NUM> which splits into a plurality of gaseous fuel channels <NUM>. Each gaseous fuel channel <NUM> is fluidly connected to one of the plurality of inlet channels <NUM>. To dose gaseous fuel into individual inlet channels <NUM>, in each gaseous fuel channel <NUM>, a gaseous fuel admission valve <NUM> is installed. In some embodiments, internal combustion engine <NUM> may comprise more than one gaseous fuel manifold <NUM>.

Each gaseous fuel admission valve <NUM> is configured to allow or to block flow of gaseous fuel into an individual inlet channel <NUM> to mix with compressed charge air from charge air system <NUM> in GFM. Thus, cylinder specific mixing zones downstream of each gaseous fuel admission valve <NUM> are generated. For example, gaseous fuel admission valves <NUM> may be solenoid actuated plate valves in which springs hold a lower surface of a movable disk against an upper surface of a stationary disk or plate, the two surfaces being configured to provide a sealed relationship in a closed state of gaseous fuel admission valve <NUM>. Each gaseous fuel admission valve <NUM> may be mounted to a cylinder head covering at least one cylinder <NUM>.

Purge gas system <NUM> (indicated in <FIG> by a dashed dotted box) comprises a purge gas tank <NUM>, a purge gas control valve <NUM>, and a purge gas shut-off valve <NUM> connected in series. Purge gas tank <NUM> constitutes a purge gas source to flush gaseous fuel piping <NUM>, gaseous fuel manifold <NUM>, etc. with a purge gas, such as nitrogen in a pressurized state.

Purge gas system <NUM> may be fluidly connected to gaseous fuel system <NUM> at various locations. For example, in <FIG> a first connection <NUM> is disposed proximal to the gaseous fuel manifold <NUM>. A second connection <NUM> is disposed proximal to gaseous fuel source <NUM>. First shut-off valve <NUM> and second shut-off valve <NUM> can block or allow a purge gas flow through first connection <NUM> and second connection <NUM>, respectively. Additional connections may be integrated in gas valve unit of gaseous fuel source <NUM>.

As previously mentioned, <FIG> illustrates a DF internal combustion engine as well as a gaseous fuel engine. In a DF internal combustion engine, liquid fuel system <NUM> comprises a liquid fuel tank <NUM> connected to liquid fuel piping <NUM>. Liquid fuel tank <NUM> may comprise a first liquid fuel tank for storing a first liquid fuel, for example, heavy fuel oil (HFO), and a second liquid fuel tank for storing a second liquid fuel, for example, diesel fuel. Liquid fuel tank <NUM> constitutes a liquid fuel source for supplying liquid fuel for combustion in LFM. Additionally, liquid fuel tank <NUM> may constitute a liquid fuel source for supplying ignition fuel in GFM.

Liquid fuel piping <NUM> is fluidly connected to a liquid fuel manifold <NUM> which splits into a plurality of liquid fuel inlet channels <NUM>. To dose liquid fuel into the combustion chamber of cylinder <NUM>, in each liquid fuel inlet channel <NUM> a fuel injection system <NUM> is installed.

In a gaseous fuel internal combustion engine, such as a spark ignited gaseous fuel internal combustion system, fuel injection system <NUM> is fluidly connected to gaseous fuel source <NUM> (indicated by a dashed line <NUM>) instead of liquid fuel tank <NUM>. In this embodiment fuel injection system <NUM> may comprise a pre-combustion chamber for providing spark ignited pilot flames <NUM> (see <FIG>) to ignite the mixture of gaseous fuel and air.

Exemplary embodiments of fuel injection system <NUM> for DF and gaseous fuel internal combustion engines are described in more detail when referring to <FIG> and <FIG>, respectively.

As shown in <FIG>, internal combustion engine <NUM> further comprises a plurality of pressure sensors <NUM> mounted at each cylinder <NUM>. Each pressure sensor <NUM> is configured to generate a signal corresponding to a temporal development of an internal cylinder pressure during the operation of the engine, for example, during combustion. The pressure sensor is further described when referring to <FIG>.

To control operation of engine <NUM>, a control unit <NUM> is provided. Control unit <NUM> forms part of a control system of the engine. Control unit <NUM> is configured to receive data of pressure sensor <NUM> via a readout connection line <NUM>. Control unit <NUM> may further be configured to control various components of engine <NUM> such as gaseous fuel admission valves <NUM> via a control connection line <NUM> and fuel injection system <NUM> via a control connection line <NUM>. Control unit <NUM> may further be configured to control valves of purge gas system <NUM>. Alternatively, a second control unit (not shown) may be configured to control the operation of engine <NUM>. Further description of the control system and additional control lines between control unit <NUM> and other components of the engine, such as the fuel injection system <NUM>, will be given in <FIG> and <FIG>.

Control unit <NUM> may further be connected to other sensors not shown in <FIG>, such as engine load sensors, engine speed sensors, temperature sensors, NOx-sensors, or fuel-to-air ratio sensors provided for each individual cylinder or for a plurality of cylinders. Control unit <NUM> may also be connected to an operator panel (not shown) for issuing a warning to the operator, indicating a failure of the engine or the like.

<FIG> shows a cylinder <NUM> of a DF internal combustion engine <NUM> which is an exemplary embodiment of internal combustion engine <NUM> of <FIG>. Elements already described in connection with <FIG> have the same reference numerals, such as engine block <NUM>, control unit <NUM>, pressure sensor <NUM>, and cylinder <NUM>.

Cylinder <NUM> provides at least one combustion chamber <NUM> for combusting a mixture of gaseous fuel and air, a piston <NUM>, and a crankshaft <NUM> which is drivingly connected to piston <NUM> via a piston rod <NUM>. Piston <NUM> is configured to reciprocate within cylinder <NUM>.

Cylinder <NUM> is connected to charge air manifold <NUM> via inlet channel <NUM> and to exhaust gas manifold <NUM> via outlet channel <NUM> (see <FIG>). Inlet valve <NUM> is disposed in inlet channel <NUM>, and outlet valve <NUM> is disposed in outlet channel <NUM>. Gaseous fuel admission valve <NUM> can supply gaseous fuel to combustion chamber <NUM> of cylinder <NUM>.

<FIG> further illustrates fuel injection system <NUM> by a dashed box. When DF internal combustion engine <NUM> is operated in LFM, fuel injection system <NUM> is used to inject liquid fuel into combustion chamber <NUM>, the liquid fuel being the sole source of energy. When DF internal combustion engine <NUM> is operated in GFM, fuel injection system <NUM> may be used to inject a pilot amount of liquid fuel into combustion chamber <NUM> to ignite the mixture of gaseous fuel and air. In GFM, fuel injection system <NUM> may therefore function as a gaseous fuel ignition system.

In <FIG>, an exemplary embodiment of such a gaseous fuel ignition system is based on a main liquid fuel injector <NUM> for injecting a large amount of liquid fuel in LFM and a pilot amount of liquid fuel into combustion chamber <NUM> to ignite the mixture of gaseous fuel and air in GFM. In other embodiments, such as for heavy duty DF internal combustion engines, gaseous fuel ignition system may comprise a separate ignition liquid fuel injector <NUM> to inject the pilot amount of liquid fuel into combustion chamber <NUM> in GFM.

Cylinder <NUM> further comprises pressure sensor <NUM> to measure a temporal development of an internal cylinder pressure during the operation of the engine, for example, during combustion. Pressure sensor <NUM> may be a capacitive pressure sensor, an electromagnetic pressure sensor, a piezoelectric pressure sensor, an optical pressure sensor or any other pressure sensor known in the art. Pressure sensor <NUM> may be mounted at any location of cylinder <NUM> convenient for measuring the cylinder pressure during combustion. For example, pressure sensor <NUM> may be mounted within a cylinder side wall or at the cylinder head face. Pressure sensor <NUM> may reach at least partly into the combustion chamber of cylinder <NUM>, for example through a bore in a cylinder side wall.

Pressure sensor <NUM> may further be disposed outside of the combustion chamber <NUM> to detect the cylinder pressure indirectly. For example, pressure sensor <NUM> may be mounted at an existing component of the engine, such as a bolt head, spark plug boss, etc. Pressure sensor <NUM> may sense stress of that component during combustion, the stress corresponding to the internal cylinder pressure during combustion.

DF internal combustion engine <NUM> additionally comprises a control system including control unit <NUM>. Control unit <NUM> is connected to main liquid fuel injector <NUM> via control connection line <NUM> and, in case of heavy duty DF internal combustion engines, also to ignition liquid fuel injector <NUM> via a separate control connection line (not shown).

<FIG> shows a cylinder <NUM> of a gaseous fuel internal combustion engine <NUM> being another exemplary embodiment of internal combustion engine <NUM> of <FIG>. Elements already described in connection with <FIG> and <FIG> have the same reference numerals. Gaseous fuel internal combustion engine <NUM> is similar to DF internal combustion engine <NUM> of <FIG>, except for the components described in the following.

Fuel injection system <NUM> comprises a pre-combustion chamber <NUM>. Pre-combustion chamber is configured to receive a pre-mixture of gaseous fuel and air outside of combustion chamber <NUM>. The pre-mixture of gaseous fuel and air is ignited, for example by a spark plug, to provide pilot flames <NUM> disposed into combustion chamber <NUM>. Pilot flames <NUM> are used to ignite the mixture of gaseous fuel and air in combustion chamber <NUM>. Control unit <NUM> is connected to pre-combustion chamber <NUM> via control connection line <NUM>. Alternatively, fuel injection system <NUM> may be a spark plug for igniting the mixture of gaseous fuel and air via an electric discharge.

In general, control unit <NUM> of an engine as disclosed in connection with <FIG> may be a single microprocessor or multiple microprocessors that include means for controlling, among others, an operation of various components of DF internal combustion engine <NUM>. Control unit <NUM> may be a general engine control unit (ECU) capable of controlling numerous functions associated with DF internal combustion engine <NUM> and/or its associated components. Control unit <NUM> may include all components required to run an application such as, for example, a memory, a secondary storage device, and a processor such as a central processing unit or any other means known in the art for controlling DF internal combustion engine <NUM> and its components. Various other known circuits may be associated with control unit <NUM>, including power supply circuitry, signal conditioning circuitry, communication circuitry and other appropriate circuitry. Control unit <NUM> may analyze and compare received and stored data and, based on instructions and data stored in memory or input by a user, determine whether action is required. For example, control unit <NUM> may compare received pressure data from pressure sensor <NUM> with target values stored in memory, and, based on the results of the comparison, transmit signals to one or more components of the engine to alter the operation of the same.

Exemplary internal combustion engines suited to the disclosed method are, for example, DF internal combustion engines of the series M46DF and M34DF or gaseous fuel internal combustion engines of the series GCM34 manufactured by Caterpillar Motoren GmbH & Co. KG, Kiel, Germany. One skilled in the art would appreciate, however, that the disclosed method can be adapted to suit other internal combustion engines as well.

In the following, operation and control of internal combustion engine <NUM> is described with reference to <FIG> in connection with <FIG>. For illustration purposes, the methods are disclosed with reference to structural elements disclosed in connection with <FIG>. However, the skilled person will understand that the respective steps can be performed on other embodiments as well.

Referring to <FIG>, a flow chart of an exemplary method of detecting an incomplete combustion in a cylinder of an internal combustion engine is illustrated.

The method includes an analysis section <NUM> and a control section <NUM>. In analysis section <NUM>, control unit <NUM> performs the steps necessary to determine whether the combustion in cylinder <NUM> is associated with an incomplete combustion (misfire) or with a complete combustion. In case the combustion was associated with incomplete combustion, control unit <NUM> performs control steps set out in control section <NUM>.

Referring to analysis section <NUM>, at step <NUM> control unit <NUM> receives a pressure data from pressure sensor <NUM> via readout connection line <NUM>. The pressure data corresponds to a temporal development of the cylinder pressure during combustion, for example over time or crank angle.

In <FIG> exemplary developments of cylinder pressure for various operating conditions of the engine are shown and will be discussed in the following. In case internal combustion engine is operated in motored operation, i.e. no combustion occurs, the time-pressure data received by control unit <NUM> is indicated by graph <NUM>. Graph <NUM> illustrates an increase of pressure up to a certain maximum compression pressure <NUM>, followed by a decay of pressure back to the initial pressure. The increase of pressure up to maximum compression pressure <NUM> corresponds to the compression of charge air only or unignited fuel-air mixture during the upward movement of piston <NUM> in cylinder <NUM>. When piston <NUM> reaches top dead center (TDC), the pressure approaches its maximum value (indicated by <NUM>). Time-pressure graph <NUM> can be measured or derived from the compression of the gaseous fuel-air mixture within cylinder <NUM> based on thermodynamic equations, such as equations for adiabatic compression or polytropic compression or can be provided as an estimate or simulation. Control unit <NUM> has stored a temporal development of cylinder pressure for motored operation of the internal combustion engine, such as graph <NUM>, and uses it as a reference for the later analysis.

In case the engine is operated under normal condition, i.e. the entire or essentially the entire mixture of gaseous fuel and air is consumed by the flame (assumed complete combustion), the time-pressure data received by control unit <NUM> will be similar to graph <NUM>. Compared to the motored operation illustrated in graph <NUM>, the heat release of the combustion causes the cylinder pressure to increase up to a maximum combustion pressure <NUM> far above the maximum compression pressure <NUM>. Additionally, peak pressure occurs at times later than TDC due to the finite combustion time. Example values for the maximum compression pressure <NUM> and maximum combustion pressure <NUM> are <NUM> bar and <NUM> bar, respectively.

In case a misfire occurs in cylinder <NUM>, the fuel-air mixture is only partly consumed by the flame. The pressure increase in cylinder <NUM> will therefore be somewhat lower than the pressure increase for complete combustion (graph <NUM>), but somewhat higher than the pressure increase for motored operation of the engine (graph <NUM>). An exemplary time-pressure data received for the case of a misfire (incomplete combustion) is given by graph <NUM> in <FIG>. Depending on how much gaseous fuel and air was consumed by the flame, time-pressure graph <NUM> may be more proximal to time-pressure graph <NUM> associated with complete combustion, or more proximal to time-pressure graph <NUM> associated with motored combustion.

At step <NUM> control unit <NUM> receives a pressure data corresponding to one of the various operating conditions of cylinder <NUM> explained above. The pressure data may be available for discrete times during the combustion cycle, e.g. for <NUM>° crank angle, or quasi-continuously depending on the temporal resolution of pressure sensor <NUM>.

At step <NUM>, control unit <NUM> derives from that pressure data a combustion energy value of the combustion. The combustion energy value may be derived as a heat release rate of the combustion, for example, by multiplying the received pressure data (graphs <NUM>, <NUM> or <NUM>) with the corresponding cylinder volume using equations given, for example, by Internal Combustion Engine Fundamentals, John B. Heywood, ISBN <NUM>. A further example of the combustion energy value is the indicated mean effective pressure (IMEP) of the cylinder <NUM>, wherein the IMEP is derived by integrating the received pressure data (graphs <NUM>, <NUM>, <NUM>) over the period of a combustion cycle. Furthermore, the combustion energy value may be derived, for example, from a pressure difference between pressure data associated with combustion (graphs <NUM>, <NUM>, <NUM>) and pressure data associated with motored operation of the engine (graph <NUM>).

Control unit <NUM> may further associate the combustion energy value with a burnt fuel energy value. In another embodiment, control unit <NUM> may additionally receive data corresponding to a total energy value of the combustion, for example by receiving data on the total mass flow rates of fuel and air admitted to combustion chamber <NUM>. Based on the total energy value of the combustion and the burned fuel energy value, control unit <NUM> yields an unburnt energy value.

At step <NUM>, control unit <NUM> determines whether the derived combustion energy value is beyond a predetermined combustion threshold level. The predetermined combustion threshold level may be stored on the memory of control unit <NUM> as a fixed value or may be determined based on empirical values typical for the engine. The predetermined combustion threshold level may further depend on the load of the internal combustion engine. In this case, control unit <NUM> may additionally be connected to engine load sensors configured to receive the load of the engine.

In some embodiments, the predetermined combustion threshold level or more precisely speaking, the predetermined combustion-cycle specific combustion threshold level, may be set by the manufacturer of the engine as an engine-type specific default parameter, and may be obtained from runs of a test engine. The default parameter may be defined during the definition of all engine-type specific operating parameters for the engine control system The test engine may be the same type or a different type than internal combustion engine <NUM>, and may be deliberately brought into a state where one or more cylinders of the test engine start to misfire. For example, during the runs of the test engine, a fuel-to-air ratio of the gaseous fuel supplied to cylinder <NUM> may be decreased until one of the cylinders starts to misfire, or the gaseous fuel ignition system and/or the gasous fuel admission valve <NUM> may be forced to stay closed. During those tests, the cylinder pressure of each or all cylinders, such as the maximum combustion pressure in cylinder <NUM>, the heat release rate or the indicated mean effective pressure - generally all data which is used to derive a combustion energy value - may be recorded. From the recorded cylinder pressure a critical cylinder pressure may be determined at which one or all cylinders of internal combustion engine <NUM> start to misfire.

For example, the predetermined combustion-cycle specific combustion threshold level may be set according to a predetermined combustion energy value associated with a misfire of any of the cylinders of internal combustion engine <NUM>. For example, the predetermined combustion energy value may be a heat release rate value, a maximum combustion pressure in cylinder <NUM>, or an indicated mean effective pressure at which misfire was detected. In some embodiments, a heat release rate value, a maximum combustion pressure in cylinder <NUM>, or an indicated mean effective pressure at which misfire is detected may be about <NUM>% to <NUM>% of the heat release rate, the maximum combustion pressure in cylinder <NUM>, or the indicated mean effective pressure during desired operation of internal combustion engine <NUM>, e.g. during operation with complete combustion. Thus, the predetermined combustion-cycle specific combustion threshold level may be set to a value at which - strictly speaking - combustion occurs; although the combustion occurs not as desired.

Moreover, because the cylinder pressure - or more generally the combustion energy value derived from the cylinder pressure - also depends on other engine parameters, such as on a load or a speed of internal combustion engine <NUM>, in some embodiments, the test runs may also be performed for various loads and speeds of internal combustion engine <NUM>. Then, for each load and each speed a critical cylinder pressure may be determined at which one or all cylinders of internal combustion engine <NUM> start to misfire. And those critical cylinder pressure values distinguishing between complete and incomplete combustion may then be stored as a function of engine speed and/or load on the memory of control unit <NUM> as part of an engine specific data bank. Thus, a predetermined combustion-cycle specific combustion threshold level map may be readily available for further steps of the control procedure.

Therefore, in some embodiments, step <NUM> (at which control unit <NUM> determines whether the derived combustion energy value is beyond the predetermined combustion-cycle specific combustion threshold level) may include a further step <NUM>' indicated as a dashed box, at which control unit <NUM> provides the predetermined combustion-cycle specific combustion threshold level and/or the associated maps from its memory. In some embodiments, those values and/or maps may be provided by reading (step <NUM>") the engine specific data bank in which the predetermined combustion-cycle specific combustion threshold level and/or the associated maps are stored.

Once the predetermined combustion-cycle specific combustion threshold level and/or the associated maps are read at step <NUM>'', during a further step (not shown) the predetermined combustion-cycle specific combustion threshold level and/or the associated maps may then be compared with the derived combustion energy value.

In the following the predetermined combustion-specific combustion threshold level may also be referred to as predetermined combustion threshold level.

Generally, the threshold companion may differ for burnt and unburnt energy values. For example, when control unit <NUM> associated the combustion energy value with a burnt fuel energy value, control unit <NUM> determines whether the burnt fuel energy value is below the predetermined combustion threshold level. In contrast, when control unit <NUM> yielded an unburnt fuel energy value, control unit <NUM> determines whether the unburnt fuel energy value is above the predetermined combustion threshold level.

Assuming acceptable combustion, control unit <NUM> determines at step 406A that the combustion energy value is not beyond the predetermined combustion threshold level, e.g. the burnt (unburnt) fuel energy value is above (below) the predetermined threshold level, and associates the combustion with a complete combustion (step <NUM>) in which case no further control steps are performed by control unit <NUM> and the analysis can be performed for further combustion processes.

In case control unit <NUM> determined that the combustion energy value is beyond the predetermined combustion threshold level (step 406B), e.g. the burnt (unburnt) fuel energy value is below (above) the predetermined threshold level, the control unit associates the combustion with an incomplete combustion (step <NUM>) and performs further control steps set out in control section <NUM>.

In some embodiments, control unit <NUM> may perform the steps of analysis section <NUM> for a series of combustion events and perform further control steps set out in control section <NUM> only when a pre-set portion of the series of combustion events was associated with incomplete combustion. The pre-set portion may be a fixed value stored on the memory of control unit <NUM> or depend on the load of the engine, such that, for example, at low engine loads a larger number of incomplete combustion events is tolerated by control unit <NUM> until control steps of control section <NUM> are performed.

In the following, control steps of control section <NUM> are explained that can be performed individually or in desired combinations. In general, once control unit <NUM> determined that the combustion event, or a pre-set portion of the series of combustion events are associated with incomplete combustion, at step <NUM> control unit <NUM> sends control tasks to the fuel system. For example, gaseous fuel admission valve <NUM> may be controlled via control connection line <NUM> to stop the flow of gaseous fuel into combustion chamber <NUM>. When internal combustion engine is a DF internal combustion engine (compare <FIG>), control unit <NUM> may send a control task to main liquid fuel injector <NUM> via control connection line <NUM> to stop the flow of liquid fuel into combustion chamber <NUM>, thus terminating the operation of LFM or GFM of the internal combustion engine. When internal combustion engine is a gaseous fuel internal combustion engine (see <FIG>), at step <NUM> control unit <NUM> may control gaseous fuel admission valve <NUM> to stop the flow of gaseous fuel and/or control pre-combustion chamber <NUM> via control connection line <NUM> to stop formation of spark ignited pilot flames <NUM>.

In <FIG>, alternative control steps performed by control unit during control section <NUM> are indicated by the dashed lines. As one example, at step <NUM> control unit <NUM> may send control tasks to the operator panel of the internal combustion engine indicating misfiring of the internal combustion engine, e.g. by a blinking warning light or by emitting a warning tone. As another example, if internal combustion engine is a DF internal combustion engine, at step <NUM> control unit <NUM> may switch from GFM to LFM by sending a control task to gaseous fuel admission valve <NUM> to stop admission of gaseous fuel to combustion chamber <NUM> and in turn send a control task to main liquid fuel injector <NUM> to increase flow of liquid fuel into combustion chamber <NUM>, thus initiating the switch.

Referring to <FIG>, a flow diagram of an exemplary method of detecting an incomplete combustion in a cylinder is shown including a further countermeasure section <NUM> with a control loop <NUM>. Steps already described in connection with <FIG> have the same reference numerals. The exemplary method of <FIG> may comprise the same analysis section <NUM> as described in <FIG>. Additional countermeasure section <NUM> may avoid incomplete combustion from reoccurring in the following combustion cycles prior the need to perform control steps of control section <NUM>. The additional steps in countermeasure section <NUM> are described as follows.

When at step <NUM> control unit <NUM> associated the combustion with an incomplete combustion, at step <NUM> it further derives from a section of the pressure data (section <NUM> in <FIG>) associated with an ignition of the fuel-air mixture an ignition energy value. Section <NUM> is typically at, but may not be limited to, times between <NUM>° and <NUM>° crank angle and particularly at times between <NUM>° and <NUM>° crank angle before TDC of piston <NUM>. The ignition energy value may be derived from a pressure difference between the time-pressure data received from pressure sensor <NUM> and the predetermined time-pressure data associated with motored operation of the engine within section <NUM>.

The ignition energy value is indicative of the operability of the gaseous fuel ignition system, such as ignition liquid fuel injector <NUM> and main liquid fuel injector <NUM> in DF internal combustion engines or pre-combustion chamber <NUM> in gaseous fuel internal combustion engines.

At step <NUM>, control unit <NUM> determines whether the ignition energy value derived from section <NUM> indicates operability or in-operability of the gaseous fuel ignition system by determining whether the ignition energy value is beyond a predetermined ignition threshold level. Predetermined ignition threshold value can be stored on the memory of control unit <NUM> as a fixed value and/or in dependence of the load of the engine.

In case the ignition energy value is beyond a predetermined ignition threshold level, control unit <NUM> determines that the ignition energy value indicates the operability of the gaseous fuel ignition system (step 604A).

In case control unit <NUM> determined at step 604A that the ignition energy value indicates operability of the gaseous fuel ignition system, control unit <NUM> further determines at step <NUM> whether the fuel-to-air ratio of the mixture admitted to cylinder <NUM> is below an upper fuel-to-air ratio threshold level. For this purpose, control unit <NUM> may be additionally connected to fuel-to-air ratio sensors. The upper fuel-to-air ratio threshold level is stored on the memory of control unit <NUM> but may be, similarly to the ignition threshold level and combustion threshold level, depending on the load of the engine. In addition or alternatively, control unit <NUM> may have stored a predetermined time-pressure data, such as graph <NUM> in <FIG>, which corresponds to the upper fuel-to-air threshold level.

In case the fuel-to-air ratio is below the upper fuel-to-air ratio threshold level (step 606A), control unit <NUM> sends control tasks to gaseous fuel admission valve <NUM> to increase the flow of gaseous fuel for the respective cylinder <NUM>, a subgroup of cylinders or all cylinders of internal combustion engine (step <NUM>). Control unit may then assess the new time-pressure data corresponding to the next combustion cycle and perform steps <NUM> and <NUM>. In case control unit <NUM> determines that the gaseous fuel ignition system is still operable, also step <NUM> is performed, until at step 606B control unit <NUM> determines that the fuel-to-air ratio can no longer be increased and leaves control loop <NUM>.

If control loop is left at step 606B, control unit <NUM> then confirms that the combustion is associable with an incomplete combustion (step <NUM>) as previously done in step <NUM>, at which point at least one of the control steps set out in control section <NUM> (<FIG>) are performed.

Similarly, in case control unit <NUM> already determined at step 604B (in any of the runs through control loop <NUM>, or even before control loop <NUM> was entered) that the ignition energy value indicates in-operability of the gaseous fuel ignition system, control loop <NUM> is left at step 604B and control unit <NUM> confirms that the combustion is associable with an incomplete combustion (step <NUM>), thus initiating at least one of the control steps of control section <NUM>.

In some embodiments where the combustion energy value and/or ignition energy value are derived for a series of combustion events, the combustion energy value and/or ignition energy value may be derived, for example, for successive combustion events or for every other, third, fourth or any other fraction of combustion events.

In some embodiments the predetermined combustion threshold level may be determined based on a certain number, such as a fixed value, a delta value below averaged time-pressure data, or it may be determined based on a predetermined combustion pressure over intake manifold pressure.

Analysis section <NUM> and control section <NUM> are, for example, relevant with respect to the safe operation of marine DF and gaseous fuel internal combustion engines. For those engines, Marine Class Society demands that in the exhaust passage of the engine the lower explosive limit (LEL) should not be exceeded to ensure safe operation of the engine. Analysis section <NUM> and control section <NUM> may ensure or at least help that engines such as DF internal combustion engines of the series M46DF and M34DF or gaseous fuel internal combustion engine of the series GCM34 comply with this regulation by initiating appropriate control steps such as a termination of the operation of the engine or, in case the engine is a DF internal combustion engine, a switch from GFM to LFM, once misfiring of the engine was detected.

Countermeasure section <NUM> may similarly be helpful in that respect, as the steps performed within this section allow to react to misfires without initiating a switch over to LFM or a termination of the operation of the engine. Using the herein disclosed aspects, one may therefore be able to reduce down time of the engine, increase maintenance intervals, and/or enlarge the operating envelope of the engine.

Claim 1:
A method of detecting an incomplete combustion in an internal combustion engine (<NUM>, <NUM>, <NUM>) operating at least partly on gaseous fuel, the method comprising:
receiving (step <NUM>) a pressure data (<NUM>, <NUM>, <NUM>) corresponding to a temporal development of a cylinder pressure during combustion within a single combustion cycle;
deriving (step <NUM>) from the pressure data (<NUM>, <NUM>, <NUM>) for that specific combustion cycle a combustion energy value of the combustion,
associating the derived combustion energy value with a burnt fuel energy value, and, optionally, receiving data corresponding to a total energy value of the combustion and yielding an unburnt fuel energy value from the total energy value of the combustion and the burnt fuel energy value;
determining (step 406B) that the burnt fuel energy value is below a predetermined combustion-cycle specific combustion threshold level, or that the unburnt fuel energy value is above the predetermined combustion-cycle specific combustion threshold level, the predetermined combustion-cycle specific combustion threshold level being based on a critical cylinder pressure determined during operation of a test engine, at which critical cylinder pressure one or all cylinders of the internal combustion engine (<NUM>, <NUM>, <NUM>) start to misfire; and
associating (step <NUM>) the combustion event with an incomplete combustion at that specific combustion cycle if the combustion energy level is beyond the predetermined combustion threshold level.