WO2015030659A1

WO2015030659A1 - Method and system for the control of an internal combustion engine

Info

Publication number: WO2015030659A1
Application number: PCT/SE2014/050977
Authority: WO
Inventors: Ola Stenlåås; Kenan MURIC
Original assignee: Scania Cv Ab
Priority date: 2013-08-29
Filing date: 2014-08-27
Publication date: 2015-03-05
Also published as: DE112014003615T5; SE1450993A1; SE1450253A1

Abstract

The present invention pertains to a method for the control of a combustion engine (101), wherein said combustion engine (101) comprises at least one combustion chamber (201) and elements (202) for the supply of fuel to said combustion chamber (201), wherein combustion in said combustion chamber (201) occurs in combustion cycles. The method comprises : - estimating, during a first part of a first combustion cycle, a first measure of specific heat capacity for said first combustion cycle, - determining, based on said first measure, a first amount of a first liquid for supply to said combustion chamber (201), and - supplying said first amount of said first liquid to said combustion chamber (201). The invention also pertains to a system and. a vehicle.

Description

METHOD AND SYSTEM FOR THE CONTROL OF &N INTERNAL COMBUSTION ENGINE

Field of the invention

The present invention pertains to combustion engines, and in particular to a method for the control of a combustion engine according to the preamble of claim 1 , The invention also relates to a system and. a vehicle, as well as a computer program and a computer program product, which implement the method according to the invention.

Backgro nd of the invention

The background description below constitutes a background description for the invention, and thus need not necessarily constitute prior art technology.

In connection with increased government interests concerning pollution and air quality, emission standards and. regulations regarding emissions from, combustion engines have been drafted in many jurisdictions.

Such emission regulations often consist of requirements defining acceptable limits for exhaust emissions in vehicles equipped with combustion engines. For example, levels of nitrogen oxides (NO_x) , hydrocarbons (HC) and carbon monoxide (CO) are often regulated. These emission regulations may also handle the occurrence of particles in exhaust emissions.

In an effort to comply with these emission regulations, exhausts caused by the combustion of the combustion, engine are treated (purified.) . By way of example, a so-called catalytic purification process may be used, so that exhaust treatment systems in e.g. vehicles and other vessels usually comprise one or more catalysts and/or other components . For example, the exhaust treatment systems in vehicles with diesel engines oft.en comprise particulate fi 11.ers, The occurrence of unwanted compounds in the exhaust flow, resulting from the combustion engine, is to a large extent caused by the combustion process in the combustion engine's combustion chamber, at least partly depending- on the amount of fuel which is consumed in the combustion.

For this reason, and due to the fact that a very large part of the operating economy of primarily heavy goods vehicles is controlled by the amount of fuel consumed., great efforts are also made to make the combustion engine's combustion more efficient in an effort to reduce emissions and fuel

consumption .

"

One objective of the present invention is to provide a method to control a combustion engine. This objective is achieved with a method according to claim. 1,

The present inventions pertains to a method for the control of a. combustion engine, where said combustion engine comprises at least one combustion chamber and elements for the supply of fuel to said combustion chamber, wherein the combustion in said combustion chamber occurs in combustion cycles. The method co prises :

- estimating, during a first part of a first combustion cycle, a first measure of specific heat capacity for said first combustion cyc.1e , - determining, based on said first measure, a first amount of a first liquid for supply to said combustion chamber, and

-^■ supplying said first amount of liquid, to said, combustion chamber .

Generally, during the combustion in a. combustion engine, a part of the energy released, at combustion will result in a work, effected on the combustion engine ' s output shaft, i.e. the force which may be used, to drive the vehicle. Also, a part of the combustion's energy will be used to heat the exhausts resulting during combustion, and a part of the energy released during the combustion will be lost in pure heat losses, i.e. to heat, the combustion engine.

Regarding the heating of the exhausts resulting during

combustion, a certain heating- may be desirable, e.g. in order for the exhaust, t eatment i an after-treatment s stem, to function in the desired manner. However, an unnecessarily large amount of energy may still be consumed for such heating of exhausts.

Regarding the pure heat losses, t ese have seve al

disadvantages. First, the heat losses reduce the efficiency of the combustion engine, with increased fuel consumption, and associated fuel costs, as a. consequence. In. addition, the heating of the combustion engine which arises must be taken care of by the vehicle's cooling system, with the associated workload on the latter. Heat losses may also occur at the expense of the available heat energy in the combustion's exhausts, where heat energy may thus be desirable, e.g. for heating of exhaust treatment components.

According to the present invention, such losses may be reduced by supplying to t e combustion said, first, liquid, which may consist of a liquid entirely consisting of water, or a liquid which at least partly or mainly consists of water. A liquid consisting of water with additives from a corrosive or frost- protection perspective, i.e. additives which do not. impact the combustion, are deemed to constitute water according to the present application. Said first liquid may, however, also comprise other types of additives. For example, it may be advantageous to add. additives that in themselves may nave an advantageous impact on e.g. t e reduction of one or several unwanted chemical compounds resulting at combustion.

The liquid may e.g. consists of an additive for reduction of nitrogen oxides resulting during combustion in said combustion chamber. During combustion in combustion engines, in

particular diesel engines, unwanted nitrogen oxides NO_K are generated, at least partly due to the excess oxygen, which is generally applied during combustion in diesel engines . The additive may e.g. be an additive containing urea, such as AdBlue . Alternatively, the liquid may consists of an additive intended for reduction of another substance resulting at combustion .

By thus supplying a liquid, which at least partly consists of water, and which is intended to evaporate during said first combustion cycle, the transition between liquid and gas will absorb heat from the combustion process and thus reduce heat losses .

According to one embodiment, the liquid is supplied at a point in time entailing that the evaporation entirely or

substantially occurs after the combustion cycle's compression phase has been completed, and thus during an expansion phase . The evaporation of liquid into gas entails a volume expansion and a pressure increase associated therewith, which, at evaporation during the expansion phase, will at least partly result in a force acting on the combustion engine ' s output shaft, and thus result in an operation with improved

efficiency as a consequence . At the same time, problems with heating, etc. are reduced. According to one embodiment, the liquid is supplied during the combustion cycle ' s compression phase, so that evaporation may at least partly occur during the compression phase. Such supply of liquid may thus entail great advantages in the use of combustion engines. It is important, however, that this supply is carried out in a controlled manner, since negative effects may otherwise arise. If e.g. at a subsequent

compression liquid remains in liquid form, and thus

substantially in an incompressible form, in the combustion chamber, substantial damage may arise, at least if the amount of remaining liquid is too great. Likewise, it should be ensured that the tem.perat.ure in t e combustion chamber is not permitted to drop to such a low level that combustion of injected fuel is impaired in an unwanted manner.

According to the present invention, the supply of liquid to the combustion chamber is controlled based on prevailing conditions in the combustion chamber during an ongoing

combustion cycle, i.e. based on conditions during the

combustion cycle during which, the injection of liquid occurs. This has the advantage that the injected amount may be adapted to prevailing conditions, so that unwanted negative effects of e.g. injection of too great an amount of liquid may be

avoided ,

According to the invention, liquid is thus injected directly into the combustion engine's combustion chamber with the use of an applicable injection element, such as preferably a separate injection element, whereby said first liquid, may be injected independently of injection of fuel. This has the advantage that injection may take place precisely at the wanted, moment, and only in situations where it is deemed to be advantageous to carry out an injection of liquid.

More specifically, injection of liquid according to the invention is carried out based on a prevailing specific heat capacity for the gas composition in the combustion chamber. By estimating specific heat, capacity during an ongoing combustion cycle it may be determined whether injection of liquid is desirable, based on the estimated specific heat capacity.

According to one embodiment, a relationship between isobar- heat capacity and isochoric heat capacity C_y is estimated, so that liquid is injected based on said relationship.

According to one embodiment, the specific heat capacity

C_r

relationship, qamma γ— κ— ----- , or a similar relationship is est imated .

At the determination of the applicable amount of liquid for injection, the injection may be carried out with the objective to control e.g. said relationship between the isobar specific heat capacity C_p and the isochoric specific heat capacity C_v toward some suitable value, and according to one embodiment the relationship is controlled toward some applicable wanted change of this relationship during the combustion cycle, where the wanted change may be determined in advance, e.g. as depending on the crank angle, for instance expressed as a function or e.g. expressed as a tabulation of for example desired values for different crank angles. Further, the estimation of specific heat capacity, e.g. said relationship gamma γ, may be arranged to be carried out at applicable points in time, such as every time a substantial change of the combustion occurs, e.g. at a change of the injected amount of fuel . According to one embodiment , the specific heat capacity is, however, substantially estimated continuously, e.g. with applicably frequent intervals, such as at each crank angle, or with more frequent or less frequent intervals. Estimation may e.g. be arranged to be carried out each time a value relating to the conditions in the combustion chamber is obtained, e.g. when a value representing t e combustion chamber's pressure is obtained.

The in ection of liquid may also be arranged to be carried out individually for each cylinder, i.e. specific heat capacity may be estimated individually for the respective combustion chamber, so that injection of liquid may be adapted

individually for the respective combustion chamber .

The invention thus enables control where e.g. differences between different cylinders may be detected, and compensated with the use of individual adjustment of the injected amount of liquid to the respective combustion chamber . It may also be the case that injection of different amounts of liquid into different combustion chambers may be desirable, e.g. in order to control certain cylinders toward the fulfilment of some criterion, and other cylinders toward some other applicable criterion, which may also be achieved according to the

invention. Further, only one or some of the cylinders may be arranged to be controlled according to the invention, while combustion in the remaining cylinders may be carried out in a customary or other applicable manner .

The method according to the present invention may e.g. be implemented with the use of one or several FPGA (Field- Programmable Gate Array) circuits, and/or one or several ASICs (Application-Specific Integrated Circuit) , or other types of circuits which may handle the desired calculation speed .

Further characteristics of the present invention and

advantages thereof will be described in the detailed

description of example embodiments set out below and in the enc1osed drawings .

Fig. 1A schematically shows a vehicle in which the present i vention may be used.

Fig. IB shows a control device in the control system for the vehicle shown in Fig. 1A.

Fig. 2 shows the combustion engine in the vehicle shown in

Fig. 1A in more detail.

Fig, 3 shows an example method according to the present

i vent ion .

Fig. 4 shows an example of the variation in the

relationship between isobar heat capacit C_P and isochoric heat capacity C_v during a combustion cycle. Detailed description of embodiments

Fig. 1A schematically shows a driveline in a vehicle 100, according to an embodiment of the present invention. The driveline comprises one combustion engine 101, which in a customary manner, via an output shaft on the combustion engine 101, usually via a flywheel 102, is connected to a gearbox 103 via a clutch 106.

The combustion engine 101 is controlled by the engine's control system via a control device 115. Likewise, the clutch 106, which may e.g. consist of an automatically controlled clutch, as well as the gearbox 103 are controlled by the vehicle's control system with the help of one or several applicable control devices (not shown.) . Naturally, the

vehicle's driveline may also be of another type, such as a type with a conventional automatic gearbox, or a type with a manual gearbox, etc.

An output, shaft 10 from, the gearbox 103 operates the driving wheels 113, 114 in a customary manner via the end gear and q driving shafts 104, 105. Fig, 1A shows only one shaft with driving wheels 113, 114, but in a customary manner the vehicle may comprise more than one shaft equipped with driving wheels, or one or more extra shafts, such as one or more support shafts. The vehicle 100 also comprises an exhaust system with an after-treatment system 200 for customary treatment

(purification) of exhaust emissions resulting from combustion in the combustion, chamber (e.g. cylinders) of the combustion engine 101.

Combustion engines in vehicles of the type shown in Fig. 1A are often equipped with controllable injectors, in order to supply the desired amount of fuel at the desired point in time in the combustion cycle to the combustion engine's combustion chamber, such as at a specific piston position (crank angle degree) in the case of a piston engine.

Fig. 2 schematically shows an example of a fuel injection system for the combustion engine 101 exemplified in Fig. 1A. The fuel injection system consists of a so-called Common Rail system, but. the invention is equally applicable in other types of injection systems. Fig. 2 shows only one

cylinder/combustion chamber 201 with a piston 203 active in the cylinder, but the combustion engine 101 consists, in the present example, of a six-cylinder combustion engine and may generally consist of an engine with any number of

cylinders/combustion chambers, e.g. any number of

cylinders/combustion chambers in the range 1-20 or even. more. The combustion engine also com.pr.ises at. least one respective injector 202 for each combustion chamber (cylinder) 201. Each respective injector is thus used for injection/supply of fuel in a respective combustion chamber 201. Alternatively, two or more injectors per combustion chamber may be used. The

injectors 202 are individually controlled, by respective actuators (not shown) arranged at the respective injectors, which, based on received control signals, e.g. from the control device 115, control the opening/closing of the

injectors 202. The control signals for the control of the actuators'

opening/closing- of the injectors 202 may be generated by some applicable control device, as by the engine control device 115 in this example. The engine control device 115 thus determines the amount of fuel which actually is to be injected at any given time, e.g. based on prevailing operating conditions in the vehicle 100.

The injection system shown in Fig. 2 thus consists of a so- called Common Rail system, which means that all injectors (and therefore all combustion chambers) are supplied with fuel from a common fuel conduit 204 (Common Rail), which, with the use of a fuel pump 205, is filled with fuel from a fuel tank (not shown) at the same time as the fuel in the conduit 204is pressurised to a certain pressure, also with the help of the fuel pump 205. When the respective injector 202 is opened, the highly pressurised fuel in the common conduit 204 is then injected into the combustion chamber 201 of the combustion engine 101. Several openings/closings of a specific injector may be carried out during one and the same combustion cycle, whereby several injections may thus be carried out during the combustion of one combustion cycle. Further, each combustion chamber is equipped with a respective pressure sensor 206, for sending of signals regarding a prevailing pressure in the combustion chamber to e.g. the control device 115. The

pressure sensor may e.g. be piezo-based and should be fast enough to be able to send crank angle resolved pressure signals, for instance at every 10th, every 5th or every crank angle degree or at another suitable interval, e.g. more f equently .

With the help of a system of the type shown in Fig. 2, the combustion during a combustion cycle in a combustion chamber may to a large extent be controlled e.g. using multiple in ections, where the times and/or duration of the injections may be controlled, and where data from e.g. the pressure sensors 206 may be taken into consideration in connection with this control. By using data from e.g. the pressure sensor the conditions in the combustion chamber may be evaluated, so that water-based liquid may be supplied to the combustion, e.g. depending on an estimation of specific heat capacity according to the below. Regarding the supply of water-based liquid according to the invention, each combustion chamber, or only a part of the combustion engine's combustion chambers, each comprise an injector 210 through the use of which the liquid may be supplied to the combustion chamber 201 from a tank 211. The liquid in the tank 211 may be arranged to be pressurised, or a pump (not shown) between tank 211 and injector 210 may be used to pressurise liquid for injection into the combustion chamber 201.

Injection of liquid according to the present invention is exemplified in Fig. 3 with an example method 300, where injection takes place based on an estimation of a specific heat capacity in the combustion chamber, and where the method according to the present example is arranged to be carried out by the engine control device 115, shown in Figs. 1A-B.

In general, control systems in modern vehicles consist of a communication bus system consisting of one or more

communications buses to connect a number of electronic control devices (ECUs) , such as the control device, or controller, 115, and various components arranged on t e vehicle. According to prior art, such a control system may comprise a large number of control devices, and the responsibility for a specific function may be distributed among more than one control device.

For the sake of simplicity. Figs. 1A-B show only the control device 115, in which the present invention is implemented in the embodiment displayed. The invention may, however, also be implemented in a control device dedicated to the present invention, or wholly or partly in one or several other control devices already existing in the vehicle. Considering the speed at which calculations according to the present invention are carried out, the invention may be arranged to be implemented in a control device which is especially adapted for real time calculations of the type described below. The implementation of the present invention has shown that e.g. ASIC and FPGA. solutions a.re suitable for and cope well with calculations according to the present invention.

The function of the control device 115 (or the control

device (s) at which the present invention is implemented.) according to the present invention, may, apart from depending on sensor signals from the pressure sensor 206, e.g. depend on signals from other control devices or sensors. Generally, control devices of the type shown are normally arranged to receive sensor signals from different parts of the vehicle, as well as from different control devices arranged on the

vehicle .

The control is often controlled by programmed instructions. These programmed instructions typically consist of a computer program., which, when executed, in a computer or control device, causes the computer/control device to carry out the desired. control action, as a method step in the process according to the present invention.

The computer program usually is a part of a computer program product, where the computer program product comprises an applicable storage medium 121 (see Fig, 13), with the computer program stored on said storage medium 121. The computer program may be stored in a non-volatile way on said storage medium. Said digital storage medium 121 may e.g. consist of any from the following group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory) , EPROM (Erasable PROM) , Flash, EEPROM (Electrically Erasable PROM), a hard disk unit, etc., and may be set up in or in combination with the control device, where the computer program is executed by the control device. By changing the computer program's instructions, the vehicle's behaviour may thus be adjusted in a specific

situation ,

An example control device (control device 115) is shown schematically in Fig. IB, and the control device in turn may comprise a calculation unit 120, which may consist of e.g. a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP) , one or several FPGA (Field-Programmable Gate Array) circuits or one or several circuits with a predetermined specific function (Application Specific Integrated. Circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121, which provides the calculation unit 120 with e.g. the stored program code and/or the stored data which the calculation, unit 120 needs in order to be able to carry out. calculations. The calculation unit 120 is also set up to store interim or final results of calculations in the memory unit 121.

Further, the control device is equipped, with devices 122, 123, 124, 125 for receiving and sending of input and output signals. These input and output signals may contain waveforms, pulses, or other attributes which may be detected by the devices 122, 125 for the receipt of input signals as

information for processing by the calculation unit 120, The devices 123, 124 for sending output signals are arranged to convert the calculation result from the calculation unit 120 into output signals for transfer to other parts of the

vehicle's control system and/or the component (s) for which the signals are intended. Each one of the connections to the devices for receiving and sending of input and output signals may consist of one or several of the following: a cable, a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus, or any other bus configuration; or of a wireless connection.

Reverting to the method 300 shown in Fig. 3, the method begins with step 301, where it is determined whether the supply, according to the invention, of liquid to the combustion chamber 201 should be carried out. The control according to the invention may e.g. be arranged to be carried out

continuously, as soon as the combustion engine 101 is started. According to one embodiment, the injection of liquid into a combustion chamber is carried out only if a combustion of fuel occurs during the same combustion cycle.

The method according to the present invention thus consists of a method for the supply of a liquid consisting of water, or which is at least water-based, to the combustion chamber of the combustion engine 101, while the combustion takes place in said combustion chamber 201 in combustion cycles. The liquid m y e . g . consist of an additive for reduction of one or several substances resulting during combustion, such as nitrogen oxide, NO_x. As is previously known, the term

combustion cycle is defined as the steps comprised in a combustion in a combustion engine, e.g. a two-stroke engine's two strokes and a four-stroke engine's four strokes. The term also includes cycles where no fuel is actually injected, but where the combustion engine is still operated with a certain engine speed, such as by the vehicle's driving wheels via the driveline, in e.g. dragging. That is to say, even if no injection of fuel is carried out, a combustion cycle is still completed for e.g. every two revolutions (for four-stroke engines) , o e.g. every revo 1 t ion (two-stroke engines) by the combustion engine's output shaft The same applies to other types of combustion engines.

In step 302, it is determined whether a combustion cycle has or will be started, and when this is the case, the method continues to step 303, where it is determined whether specific heat capacity should be estimated. If this is not the case, the method reverts to step 302. When specific heat capacity is to be estimated, the method continues to step 303. As

mentioned, this estimation may e.g. be arranged to be carried out only if combustion is to occur during the combustion cycle. According to the present example, the specific heat capacity relationship is estimated, i.e. gamma γ— κ— , but

obviously another estimation may be carried out, as for instance only isobar specific heat capacity C_p or isochoric specific heat capacity C_v , or another applicable relationshi between these.

In step 303 the substance amount is estimated, n for the combustion air being supplied during the current combustion cycle. This may e.g. be carried out substantially immediately after the one or several intake valves ave been closed, and good estimation may be obtained with the use of the general gas law, i.e.

The substance amount n may thus be expressed as: n

V , i.e. the combustion chamber's volume as a function of crank angle may advantageously be tabulated in the control system's memory,, or be calculated in an applicable manner.

The pressure p constitutes the pressure in the combustion chamber 201, which is determined with the pressure sensor 206.

R constitutes the general gas constant, and

T constitutes the temperature of the combustion gas which may be estimated with a good approximation as the inlet

temperature, which is usually determined with existing

temperature sensors, and which varies slowly and may therefore usually be deemed constant for several consecutive combustion, cycles. This tem.perat.ure may thus be determined, in a customary manner with a customarily occurring inlet temperature sensor.

The method then continues to step 304, where it is determined, whether the combustion cycle has reached a crank angle

position <pl for which gamma γ is to be determined. Gamma y may be arranged to be determined continuously, but it may also be the case that the determination of gamma γ is carried out only when e.g. the compression step has been completed or

substantially completed, i.e. at or around the top dead centre TDC for a piston engine. For example, the estimation of gamma Y may be arranged to be carried out at the earliest when the piston is within e.g. 1-20 crank angle degrees from TDC and 1 hea.ding towards this point. The reason for this is that injection of liquid is initiated only late during the

compression step, or not until during the expansion phase, in order to obtain an evaporation that contributes to the

vehicle's propagation, i.e. the evaporation occurs at least primarily during the expansion phase.

When it is thus determined that the crank angle position φΐ has been reached, the method continues to step 305, where the prevailing pressure p at the wanted crank angle position is determined. The prevailing pressure in the combustion chamber may be determined substantially continuously with the use of the pressure sensor 206, e.g. at applicable intervals every 0,1-10 crank angle degrees.

The method then continues to step) 306, where the combustion chamber's mean temperature is calculated with the use of the general gas law, as in T , where V is crank angle

nR

dependent, and where p is determined in step 305. Other parameters as per above. When the temperature has been

calculated, the method continues to step 307.

In step 307 gamma y is then calculated by calculating the specific heat capacity at a constant pressure C_p as well as at a constant volume C_v ,

These heat capacities are tabulated for different chemical substances and elements in tables issued by NASA, and are interpolated as a function of temperature, where the

temperature determined in step 306 is used. Generally, the specific heat capacity at a constant pressure C_p is tabulated in the shape: cp c

a, 7' ² + α₂Ύ- + α₃ + a₄T + α₅Τ² + α₆Γ³ + α₇Τ⁴

R (3)

The specific heat capacity for a constant volume, C_Y , may then be calculated as C_y~C_p -R , so that gamma y may thus be calculated. When gamma γ has been calculated, in step 308 the liquid injection may subsequently be carried out according to the below, as a function of gamma y, as and when required.

At the calculation of gamma γ, regard should be had to the case where an EGR recirculation is carried out, i.e. when some of the exhausts from the combustion are recirculated to the inlet side of the combustion engine, impacting the chemical composition in the combustion chamber. Control of the EGR recirculation normally consists of its own regulation, but as described below, it may be advantageous to adjust the EGR recirculation based, on the amount of liquid, supplied. When EGR recirculation is applied, e.g. the following correlation may be applied to estimate specific heat capacity at a constant pressure for EGR recirculated gas, where a and b is the number of carbon atoms a d nitrogen atoms, respectively, i the fuel used to drive the vehicle, i.e. C_aH_b , and where _gl constitutes the lambda value:

A corresponding calculation of specific heat capacity at a constant volume for pure air consists of:

CpAiR - T½ (3.773c_p¾CO + _Cpo₂(T) (5)

With the objective of obtaining a correct gamma value, the respective heat capacity is weighted according to equation (6), where EGR% constitutes the EGR. level: c_p - c_pAm * (1 - EGR%) + c_pEGR * EGR% (6)

The EGR level may e.g. be determined as an EGR level

determined during a previous combustion cycle. Alternatively, the EGR level may be determined via e.g. emission

calculations, where e.g. carbon dioxide calculations may be used to determine how large a part of the combustion air consists of recirculated exhausts. For example, this may be carried out by measuring the carbon dioxide level at the inlet to the combustion chamber and at the outlet of the combustion chamber, respectively, or further downstream in the after- treatment system., so that, the EGR level may be calculated in a manner familiar to a person skilled in the art. The EGR recirculation thus constitutes a variable which is not

calculated specifically for each combustion cycle, but which is normally available in the vehicle's control system, where this is calculated with applicable intervals. Generally, the control of the EGR recirculation is much slower than control a.ccord.ing to the present invent ion .

In case water/liquid has been supplied to the combustion chamber, this may be taken into account in the above equation by adding another term, as follows (where the liquid in the example consists of water) : a^C _PC 02 +J^CpH20÷(^Q+)(⁽½^~1)^CP02^÷3773½ ^CPN2 +^nCPH20 ™

^{CpEGR =} e +( '773¾_i-l)(e-|)+»_H2o ^{( )} where n consists of the substance amount of water, i.e. the volume for injected water divided by the molar mass.

In step 307 thus an initial value for gamma γ is determined, so that in step 308 the amount of liquid for injection may be determined, based on the gamma γ determined, in connection with or without combustion (fuel supply) .

The determination of the amount of liquid, for injection may be carried out in different ways, and e.g. consist of a

comparison between an obtained estimation of gamma γ and an expected/desired value for gamma y. When e.g. the estimated gamma y is lower than desired, an amount of liquid for

injection into the combustion chamber may be determined as a function of the difference between the desired value and the obtained, value.

According to one embodiment, the above equations are used in the determination of the applicable amount of liquid for supply to the combustion chamber, but where the unknown, substance amount, of the liquid to be supplied, is thus added in equation (7) . By assuming a desired gamma y, the required c_pEGR may be determined, so that a corresponding substance amount of liquid for supply may be determined with the use of equation 7, where the liquid is calculated, and where such substance amount may then be converted into mass for supply by

multiplying with the molar mass. This amount of liquid may then be injected into the combustion chamber. The method shown may be arranged to be implemented for e.g. each crank angle degree, or with another applicable interval, for the duration of the liquid injection, so that the injected amount may be corrected during the o goi g injection.

For example, a desired gamma γ curve may be stored in the vehicle's control system, where such curve represents the development for gamma y as a function of the crank angle during the combustion cycle desired, so that control is carried out towards this curve. This curve may e.g. consist of a maximum level for gamma y, realistically achievable during the combustion cycle with the given load and prevailing speed, and may advantageously be determined in advance. This may e.g. be achieved with

applicable calculations and/or measurements for the engine type, wherein such data may be stored in the control system's memory with different curves as a function of e.g. engine speed and load.

At e.g. practical determination of applicable set point values for gamma y, measurement may be carried out in a test cell, where water (or another liquid) may be supplied in increasing amounts for an operating point for the combustion engine, wherein the amount of water supplied may be increased until the efficiency no longer improves, or until the amount of injected water gives rise to negative consequences with respect, to the combustion engine, for example by washing away oil film on cylinder walls, etc. as described below. Such tests may be carried out for several load/engine speed

conditions, and for different EGR recirculations. Thus, a somewhat optimal liquid, quantity may be determined for

different operating points of the combustion engine. By simultaneously saving parameters such as EGR recirculation, cylinder pressure, etc,, the supplied amount of water/liquid may then be used to calculate a resulting gamma γ, so that a representation of the optimal gamma y may be obtained. This determination may be carried out with crank angle resolution, in order thus to obtain a representation of e.g. the type displayed in Fig. 4 (see below), which may then be used, as a target in control. This mapping may be carried out for the entire combustion cycle, but often it is sufficient if the mapping is carried out for the crank angle interval where liquid, is injected. Performing mappings of this type is generally familiar to a person skilled in the art. For example, similar mapping is carried out by SCR catalysts for the determination of an applicable amount of additive to be supplied in different operating conditions . The mapping may be carried out for some applicable number of load/engine speed combinations, so that values for other load/engine speed combinations may be

obtained with e.g. interpolation .

According to one embodiment , the control is carried out on a cycle-by-cycle basis. Gamma may be estimated during a first combustion cycle, where liquid first is supplied during a subsequent second combustion cycle, wherein the supply may be carried out before/during/after the combustion during said subsequent second combustion cycle, according to the above . Actual parameters, such as actually measured cylinder pressure for a combustion cycle where supply of liquid has been carried out, or has not yet been carried out, may thus be used to determine the applicable amount for a subsequent combustion cycle, wherein the liquid for example may be supplied before the combustion during said subsequent combustion cycle. A new estimation may then be carried out, wherein the amount of liquid may again be adjusted based on such estimation for an additional subsequent third combustion cycle, and wherein thus the supply of liquid may be controlled on a cycle-by-cycle basis .

According to one embodiment, the injection of some applicable amount of liquid is carried out based on the determined gamma, where such amount may be determined in advance.

According to the above, gamma y may be prepared to represent a somewhat optimal efficiency. Generally, maximising gamma y is desirable., since the combustion engine's efficiency depends on gamma γ, approximately according to: η _¾; i _f where r represents the compression ratio. Thus, an increase of gamma y will result in an increase (i.e. an improvement) in efficiency.

Fig. 4 s ows a schematic example of the variation of gamma y from around TDC during a combustion cycle.

With reference to Fig. 3, in step 309, injection of liquid is then carried out, so that the method continues to step 310 in order to determine whether a new estimation of gamma y should be carried out, in which case the method reverts to step 305 for a new pressure determination and a new estimation of gamma y. This may continue until e.g. the combustion cycle ends and the exhaust valves are opened, or until it is no longer desirable, for some other reason, to inject liquid, such as e.g. because of prevailing temperature or for another reason, so that the method reverts to step 301 while waiting for injection during the subsequent combustion cycle.

Thus, the supply of liquid may be controlled continuously- based on estimations of γ, where thus the estimation of gamma Y may be arranged to be carried out continuously during the remaining combustion cycle, so that, the liquid may be injected with the objective to control gamma y towards a desired value. The present invention thus entails an efficient manner of controlling the combustion in a combustion engine.

The injection of liquid has, on the one hand, a cooling effect due to the energy consumed in the evaporation of the liquid. Additionally, a dissociation effect, arises when gaseous water molecules are split into hydrogen and oxygen, respectively, where energy is consumed for the molecule split.

Specific heat capacity, and thus gamma y, may thus be

controlled by adding liquid to the corabustion chamber, in the present example water, impacting specific heat capacity.

Obviously, in case of control of the type mentioned above, just like in all other model-based control, the model of the combustion used for the control may not be entirely consistent with actual circumstances . For example, it is not certain that assumed chemical conditions, such as the exact composition of the fuel and e.g. the size of the EGR recirculation, coincide exactly with actual conditions. Still, a marked improvement of the combustion efficiency is, however, obtained with the use of the invention, and. such differences may also, as and when needed, r completely or at least partly be compensated by estimating the actual result in a customary manner, through e.g. the use of pressure sensor signals, so that the

applicable correction factor/filtration may, if needed, be applied in a customary way in control, to correct the

calculated amount of liquid for injection and thus compensate for errors in the calculation model. Through the use of e.g. the cyli der pressure sensor, a very accurate representation of the cylinder pressure is usually obtained, so that a good analysis of the actual combustion process may thus be carried out .

Injection of liquid may according to one embodiment be carried out using the following calculation: c_{p nial vaaen} (X)— Cp f) * (1— -vattetihcilt) - c_p ^_5rH20() * vaieriialt (8) , where c_{0 f(fr Η20}(Γ) is prior art and is available tabulated. a liquid other than water is supplied., the specific heat capacity may be available tabulated for such liquid, or th< specific heat capacity may be determined in a similar manm as described for c _EGR above, through knowledge about the composition of the additive. Gamma y may then be determined as:

(9) ,-.

'vmed vattesx -pnied vatten

In total, a decrease of the temperature in the combustion chamber thus arises, which increases gamma v" according to the above equations, which in turn increases the combustion engine ¹ s efficiency .

By using the present invention, actual differences from a somewhat desired "optimal" combustion may e.g. be compensated through the use of injection of liquid. For example, fuel injectors may be worn, over time, so that injected, fuel amounts may not be consistent with the desired fuel amount, with deviations from desired/expected combustion as a consequence.

Further, e.g. t e heat value or other features of t e fuel actually being used may differ from the fuel which is used at the calculation of the applicable amount for injection, which e.g. may be made available during the combustion engine's manufacturing process. The fuel's composition may also vary seasonally, e.g. in countries with temperature differences between winter and summer. Thus, the same amount of fuel may give rise to different results depending on t e f el that, actually being used, even if the injected amount is the same.

The present, i vention may be used, to compensate such effects by controlling gamma γ, and thus obtaining a more

advantageous/desired combustion.

Further, the injection of liquid may with great probability occur at the same time as the combustion in the combustion chamber is ongoing. In case the combustion is ongoing- at the same time as liquid is injected, consideration must, be had to the combustion's impact on gamma γ. This may e.g. be taken into consideration by adding the temperature increase that the combustion gives rise to, so that the impact of the

temperature increase on. gamma y, caused, by the combustion, is regarded, at the calculation, of C_P and. C_v , respectively, Generally, the temperature is higher in the part of the combustion chamber where the combustion is ongoing, and the combustion chamber may be considered to consist of two zones, where combustion takes place in one zone, with a high

temperature in this zone as a consequence, while no

combustion, with a lower resulting temperature, takes place in the other zone.

In total at each moment a mean temperature in the combustion chamber is thus obtained, falling below the combustion's temperature where combustion is ongoing. In. order to be able to carry out. a desirable determination of the combustion's temperature, information about the heat release during

combustion is also required.

This may be determined in various ways, and according to one embodiment of the present invention, pressure signals from the pressure sensor 206 inay be used, to calculate the neat release at combustion.

The heat release at. combustion may be expressed as: r 1

dQ = pdV +Vdp ■HT

;/^■■■· 1 r-i

Where dQ is released heat, p, V is determined according^" to the above and where dV constitutes the volume change of the combustion chamber, ν(φ) , i.e. the combustion chamber's volume as a function of the crank angle may be tabulated, as set out above, in the control system's memory or be calculated in an applicable

dV

manner, whereby also may be determined. dp constitutes the pressure change in the combustion chamber, determined with the pressure se sor 206.

<i :,_: represents the neat released during combustion, which may be determined in a manner that well described, in the prior art technology by e.g. Woschni. Here, regard may also be had to blackbody radiation in the combustion chamber in a known manner .

Further, in the international patent application

PCT/SE2014/050493 entitled "METHOD AND SYSTEM FOR CONTROL OF AN INTERNAL COMBUSTION ENGINE" is a description of a method for estimating released, heat during an ongoing combustion. The method described in this application may be applied according to the present invention. Further, the method shown in said application may be simplified, as no estimation of the P pressure is required according to the present embodiment , and pressure signals from the pressure sensor 206 may be used during an ongoing combustion cycle.

According to the present example , however, the heat release may be estimated according to equation (11) through the use of signals f om the pressure sensor 206,

The pressure change p as a function of crank angle degree φ in a cylinder (combustion chamber) for a combustion cycle may, according to the above, be obtained through the use of sensor signals from the pressure sensor 206, Further, with the use of a determined pressure, the temperature for the part of the combustion chamber where no combustion occurs may be estimated with the help of an estimated pressure and b using equation (12), where the temperature for the part of the combustion chamber where no combustion takes place is expressed as:

, where Τ_Λ=0 may constitute the corresponding combustion air temperature for e.g. the point in time/crank angle position where the valves are closed following supply of combustion air, according to the above, or a constitute a temperature that has been determined with the general gas law according to the above, at a point in time/crank angle position before the combustion has been started.

Further, n, n÷l, etc. constitute consecutive points in time or crank angle positions.

K ------ v where thus also K may be determined according to what is specified for γ above. By using equation (12) (or t e general gas law, before the combustion has started) the temperature for the part of the combustion chamber where no combustion takes place may be determined, this temperature, however, being impacted by ongoing combustion through the effect of the heat release on the pressure, which is reflected in the signals emitted by the pressure sensor, which in turn impacts the temperature according to equation (12). When a combustion then takes place, the heat release will give rise to a

temperature increase in the part(s) of the combustion, chamber where combustion is taking place. This temperature increase, which is added to the temperature determined according to equation (12) in order to obtain the combustion temperature, may be calculated based on the correlation: dQ = mC_pdT (13)

, where dQ constitutes heat release, which may be determined as above. m consists of burned mass (i.e. fuel + air + EGR comprised in the combustion) , which is also determined as set out above, , i.e. specific heat capacity, which may also be calculated as set out above. dT constitutes the temperature increase obtained from the combustion, with a given burned mass and with a given C„ value .

By using equation (13), dT and therefore ΔΤ may thus be determined, so that the increase generated by the combustion at each point in time/crank angle position may be added to the unburned zone's temperature, provided by equation (12), to obtain the combustion temperature. This temperature may then be used for the calculation of specific heat capacity according to the above, and. so the calculations inay t us be updated as the combustion proceeds.

According to one embodiment, no injection of liquid is carried out unless the combustion chamber's mean temperature exceeds some applicable temperature T_lli;;, where this may thus be obtained through the general gas law according to the above, and. which is also described in the international patent application PCT/SE2014/050491, which describes in detail how the mean temperature in a combustion chamber may be estimated through the use of e.g. the pressure in. the combustion chamber that may be obtained with the pressure sensor 206.

According to the method shown in said application, an

estimation for the future time is carried out, where e.g. the pressure is estimated, for the next part, of the combustion cycle. Such estimation may also be applied in the present invention, so that the estimation thus constitutes a

prediction, in order to by way of estimation predict the applicable amount, of liquid, for injection by estimating the pressure, wherein gamma γ may also be estimated, and thus predicted, for the next part of the combustion cycle. This also means that gamma y may be estimated for different

possible liquid injection alternatives before the injection actually takes place, so that an injection alternative that is expected to best fulfil the desired result may then be

selected, wherein, gamma y may be calculated according to the above equations and. estimated pressure development, i.e. the pressure change is also estimated. This is also exemplified in detail in said application, as well as in the previously mentioned international patent application PCT/SE2014/050493, which describes how released heat may be estimated before combustion occurs, and wherein the pressure is also estimated. As the combustion cycle proceeds, gamma γ may then be estimated again tor the next part, of the combustion cycle, based on the actually prevailing pressure when the estimation is carried out, so that a new injection may be determined based on the estimated gamma y, wherein the estimation for different alternatives may again be carried out. The liquid injection alternatives may e.g. consist of different

combinations of liquid amounts, timing for injection and duration of injection.

Thus, gamma γ may be estimated for an upcoming part of the combustion cycle, wherein gamma γ for the combustion cycle may also be estimated, for different, injection alternatives, so that the injection alternatives may be evaluated and one injection alternative may be selected. According to one embodiment of the invention, the injection is carried out at least partly during the combustion's compression step and thus entirely, or at. least partly, before the combustion. Thus, gamma y may, according to the above equations, be predicted by way of estimation for the entire combustion process for e.g. different amounts of liquid injected before the combustion, wherein the entire combustion is thus estimated., and wherein the estimation of the effect of liquid supplied, due to impact on a specific heat capacity, is taken into consideration.

Injection of an applicable liquid amount may then be carried out. based on the result, of the estimation. Gamma may thus be estimated for the entire next combustion and for several injection alternatives, where the injection alternatives may e.g. be selected based on how well the gamma curve for each injection alternative follows the desired gamma curve.

In connection with the supply of liquid to the combustion, according to the present invention, there are additional aspects to be considered. For example, according to the above, an EGR recirculation of a part of the exhausts that are formed during combustion is normally applied. The EGR recirculation generally has a positive (reducing) impact on e.g. NO_x

formation. The supply of liquid according to the present invention will entail an altered exhaust stream composition compared to a. case when liquid is not supplied. For example, accordinq to the above, the liquid consists partly of water, so that a greater fraction of water than normally present is likely occur in the resulting exhaust stream. This means that a regulation of t e EGR recirculation, based on supply of liquid, may be required. For example, the EGR recirculation may be required to be reduced because of a relatively higher water content in the exhaust stream, which gives a better effect with respect to the NO_x reduction, but with a risk that an undesirably high water content, may be obtained in the combustion chamber if the EGR recirculation becomes too high in relation to the water content.

The control of the EGR recirculation may be carried out in any suitable manner, where e.g. the EGR recirculation's impact on the specific heat capacity, according to the above, may be taken into consideration and the EG recirculation may e.g. be controlled based on these calculations. Generally, control of the EGR recirculation is slow (in the range of seconds) compared to the control carried out, according to the present invention, where calculations are carried, out during the ongoing combustion cycle and where calculation may be carried out in e.g. one hundredth of a second, thousandth of a second or an even shorter time.

Further, at the supply of liquid to the combustion chamber there are additional aspects to be considered. The pressure in a. combustion chamber may rise to relatively high pressures, such as maximum pressures in the range of 200-300 bar.

Normally, the fuel injection is carried out with substantially higher pressure than the combustion chamber pressure, e.g. at. 1,500-2,500 bar, so that changes in the combustion chamber's pressure become substantially negligible in relation to the high fuel injection pressure. This means that the injected amount of fuel may be determined with good accuracy. The use of high pressures is, however, usually associated with high costs, which is why it may be desirable to carry out the injection of liquid at substantially lower pressures, e.g. at a pressure in the same range as the prevailing combustion chamber pressure. This in turn means that, due to the

combustion chamber's back pressure, for a certain opening time of the injection nozzle for injection of liquid, different amounts may be supplied for one and the same opening time, depending on the prevailing combustion chamber pressure. Thus, the liquid's injection time may be arranged to be controlled based on the prevailing combustion chamber pressure, where this may e.g. be determined with the use of the pressure sensor 206.

Thus, at prevailing higher combustion chamber pressures a longer opening time may be used, compared to when the

prevailing combustion chamber pressure is lower, wherein, obviously, the prevailing combustion chamber pressure will depend on the crank angle position at which, injection of liquid occurs. Further, the liquid supply may require that certain protection aspects/measures may need to be considered. For example, there may be restrictions with respect to at which point during the combustion cycle the injection of liquid should occur for other reasons. For example, it may be desirable that the piston at a maximum may be located a certain number of crank. angle degrees from the top dead, centre when injection takes place, so that not too great a part of the cylinder wall is revealed during t e injection, with a risk, of a wall nit and the oil film being washed away as a consequence, and thus an associated risk of unwanted wear.

Further, the supply of liquid may e.g. be arranged to be shut off if the vehicle's speed drops below some determined speed, or if the vehicle comes to a standstill, or if for another reason there is a risk that the combustion engine will shortly be shut off. In such situations, it may be desirable e.g. that the occurrence of water in the combustion engine system is reduced before the combustion engine is shut down, in order to avoid water-associated damage. According to one embodiment of the invention, the supply of liquid, may be arranged to be shut off if the vehicle's speed drops below some applicable speed, and the vehicle's ambient temperature drops below e.g. zero degrees Celsius, with the objective to avoid that water- remains in the system after the combustion engine has been shut down with a freezing risk as a consequence.

According to one embodiment , gamma is estimated, for a

combustion cycle, so that the applicable liquid injection is determined based on such estimation, where the injection of liquid is then carried out during- one or several subsequent combustion cycles. The injection may e.g. occur before and/or during the combustion during the subsequent combustion cycle. This method may e.g. be applied when the conditions for several consecutive combustion cycles are substantially the same .

The invention has been exemplified above in. a manner where a pressure sensor 206 is used to determine a pressure in the combustion chamber, and with the help of which the temperature and specific eat capacity as set out above may be estimated. One alternative to using pressure sensors may instead consist of the use of one (or several) other sensors, e.g. high- resolution ion current sensors, knock sensors or strain gauges, where the pressure in the combustion chamber may be modelled with the use of sensor signals from such sensors. It is also possible to combine different types of sensors, e.g. in order to obtain a more reliable estimation of the pressure in the combustion chamber, and/or to use other applicable sensors, where the sensor signals are converted into

corresponding pressures for use i control, as set out above. The method according to the invention for the control of the combustion engine may also be combined with sensor signals from other sensor systems, where the resolution of the crank angle level is not available, such as another pressure

transmitter, NO_x sensors, NH3 sensors, PM sensors, oxygen sensors and/or temperature transmitters etc., the input signals of which may e.g. be used, as input parameters in the estimation of e.g. expected pressure/temperature, by wholly or partly using of computer-driven models instead of models of the type described above .

Additionally, the present invention has been exemplified above in relation to vehicles. The invention is, however, also applicable to any vessels/processes where control of specific heat capacity as set out above is applicable, such as

watercrafts or aircrafts with combustion processes as per the above.

It should also be noted that the system may be modified according to various embodiments of the method according to the invention (and vice versa) and that the present invention is in no way limited to the above described embodiments of the method according to the invention, but pertains to and

comprises all embodiments in the protection scope of the enclosed independent claims. For example, the invention is applicable for injection of any liquid into t e combustion engine's combustion chamber, as long as this liquid at least partly, or primarily, contains water.

Claims

3 C<X..

1. Method for the control of a combustion engine (101),

wherein said, combustion engine (101) comprises at least one combustion chamber (201) and elements (202) for the supply of fuel to said combustion chamber (201), wherein combustion in said combustion chamber (201) occurs in combustion cycles, wherein the method is characterised in :

- estimating, during a first part of a first combustion cycle, a first measure of a specific heat capacity for said first, combustion cycle,

- determining, based on said first measure, a first amount of a first liquid for supply to said combustion chamber (201), and

- supplying to said combustion, chamber (201) said first amount. of sa id first 1 iquid .

2. Method according to claim 1, further comprising:

- to determine, with the use of a first sensor element (206), a first parameter value representing a quantity with respect to the combustion in said combustion chamber (201), and

- to determine said first measure of a specific heat capacity based on said first parameter value.

3. Method according to claim 1 or 2, wherein said, first

liquid consists of a liquid mainly containing water.

4. Method according to any one of claims 1-3, wherein said first liquid consists of water.

5. Method according to any one of claims 1-4, further

comprising to add said first amount of liquid to said combustion chamber (201) during a subsequent part of said first combustion cycle, after said, first part of said first combustion cycle.

6. Method according to any one of claims 1-5, further

comprising :

- to determine a desired specific heat capacity for sard subsequent part of said first combustion cycle,

- to compare the desired specific heat capacity with said estimated first measure of specific heat capacity, and

- based on said comparison, to determine said first amount of said first liquid.

7. Method according to claim 6, wherein said desired

specific heat capacity is stored in the control system for control of said combustion engine, as dependent on one or several from the group: crank angle position, combustion engine load, combustion engine speed,

8. Method according to claim 6 or 7, further comprising:

- to carry out several estimations of specific heat capacity during said first combustion cycle, and

- to control the supply of said first liquid during said first combustion cycle, based on said several estimations of specific heat capacity.

9. Method according to any one of claims 6-8, further

comprising to carry out the supply of liquid at several points in time during said first combustion cycle.

10. Method according to any one of the previous claims,

wherein said specific heat capacity constitutes a ratio between isobar heat capacity C_P and isochoric heat capacity C_v .

11, Method according to any one of the previous claims, wherein said specific heat capacity consists of the neat capacity ratio gamma or a similar ratio.

12, Method according to any one of the previous claims,

wherein said specific heat capacity is estimated for a crank angle position, which at its earliest constitutes a crank angle position at a maximum of 20 crank angle degrees prior to a top dead centre (TDC) .

13, Method according to any one of the previous claims,

wherein exhausts are recirculated to said combustion, further comprising, at the determination of said specific heat capacity, to estimate a first specific heat capacity for air and a second specific heat capacity for exhausts recirculated, to the combustion (EGR) , wherein said specific heat capacity is determined based, on a weighting of said first and second specific heat capacities.

1.4, Method, according to any one of the previous claims, also comprising :

to supply said first liquid at a first point in time, wherein supply of said first liquid at said first point in time is such that, evaporation of said first liquid occurs substantially subsequently to a compression phase of said first combustion cycle.

15. Method according to any one of the previous claims,

further comprising:

to supply said first liquid at a. first point in time during said first combustion cycle, wherein supply of said first liquid at said first point in time is such that said liquid at least partly is supplied during a compression phase of said first combustion, cycle.

16, Method according to any one of the previous claims, further comprising:

to supply said first liquid at a first point in time during said first combustion cycle, wherein supply of said, first liquid at said first point in time is such that said liquid at least partly is supplied before the combustion is initiated during said first combustion cycle .

17. Method according to any one of the previous claims, also comprising:

- at said determination of said first amount of said, first liquid for supply to said combustion chamber (201), to estimate an expected specific heat capacity for at least two alternatives for supply of liquid during said subsequent part of said combustion, cycle, wherein said alternative for supply of liquid, comprises alternatives with respect to at least one of the following: amount of liquid, point in time for supply, liquid pressure at supply, and duration, of supply.

18. Method according to any one of the previous claims,

wherein said specific heat capacity constitutes an.

estimation of an expected specific heat, capacity for said subsequent part of said first combustion cycle.

19. Met.h od a ccord ing to c1aim. 18 , further compri s ing to

estimate said expected specific heat capacity for said subsequent part of said first combustion cycle, through an estimation of the pressure change in said combustion chamber, during said, subsequent, part of said, first combustion cycle.

20 , Method according to c1aim 1 , herein said pressure change is estimated based on an estimated heat release during combustion during said first combustion cycle.

21, Method according to any one of the previous claims, also comp isincj :

- evaluating at least one first alternative and one second alternative for supply of liquid during said subsequent part of said first combustion cycle, wherein, of said first and second alternatives for supply of liquid the one is selected, which to the greatest extent is expected to result in a desired specific heat

capacity .

22. Method according to any one of the previous claims,

wherein supply of liquid, is carried out at least on two occasions during said subsequent part of said combustion cycle, wherein said second supply is determined after said first supply of liquid has been completed.

23. Method according to any one of the previous claims,

further comprising that regard is had to said supply of said first liquid at the estimation of specific heat capacity after the supply of liquid has been completed.

24. Method according to any one of the previous claims, also comprising to estimate said first measure of a specific heat capacity for sard first combustion cycle, based on a prevailing pressure in said combustion chamber (201) .

25. Method according to any one of the previous claims, also comprising :

- to estimate said first measure of specific heat

capacity, at least partly based on an estimated

combustion temperature.

26, Method according to claim 25, also comprising to estimate said combustion temperature as a sum of an estimation of a combustion caused by a temperature increase in relation to a first temperature, and an. estimation of said first temperature, wherein said first temperature constitutes an estimated temperature for unburned gas in said

combustion chamber.

27. Method according to any one of the previous claims, also comprising to supply said first liquid to a subsequent combustion cycle, after a said first combustion.

28. Method according to any one of the previous claims, also comprising to determine the amount of liquid for

injection individually for each cylinder.

29. Method according to any one of the previous claims,

wherein said control is carried out for a number of consecutive combustion, cycles,

30. Method according to any one of the previous claims,

wherein said liquid constitutes an additive for reduction of a substance resulting- during said combustion.

31. Method according to any one of the previous claims,

wherein said liquid constitutes an additive for reduction of nitrogen oxides resulting during said combustion in said corabustion chamber .

32, Method according to any one of the previous claims,

wherein said first measure of a specific heat capacity for said first, combustion cycle constitutes a measure of specific heat capacity for the gas composition in said combustion chamber.

33. Computer program comprising a program code which, when said program code is executed in a computer, achieves that said computer carries out the method according to any one of claims 1-32.

34. Computer program product, comprising a. computer readable medium and a computer program according to claim 33, said computer program being comprised in said computer

readable mediu ,

35. System for the control of a combustion engine (101),

wherein said combustion engine (101) comprises at least one combustion chamber (201) and. elements (202) for the supply of fuel to said combustion chamber (201), wherein combustion in said combustion chamber (201) occurs in combustion cycles, wherein the method is characterised in that the system comprises:

- elements (115) arranged to estimate, during a first part of a first combustion cycle, a first measure of a specific eat capacity for said first combustion cycle,

- elements (115) arranged to determine, based on. said first, measure, a first amount, of a first, liquid for supply to said combustion chamber (201), and

- elements (115, 210) arranged to supply said first amount of said, first liquid to said combustion, chamber (201) .

36. System according to claim 35, characterised in that said combustion engine comprises elements for the supply of liquid to said combustion chamber, independently of fuel supply to sard combustion chamber.

.

37. System according to claim 35 or 36, characterised in that said combustion engine consists of one out of the group: a vehicle engine, a marine engine, an industrial engine.

38. Vehicle (100), characterised in that it comprises a system according to any one of claims 35-37.