DK177566B1

DK177566B1 - An internal combustion engine with control of fuel gas injection pressure

Info

Publication number: DK177566B1
Application number: DKPA201270381A
Authority: DK
Inventors: Jens Rane Baungaard
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2012-06-29
Filing date: 2012-06-29
Publication date: 2013-10-21
Also published as: CN103511104A; JP2014051968A; JP2016186308A; KR101393320B1; KR20140002498A; CN103511104B; JP2015057548A; JP6334596B2

Abstract

An internal combustion engine, such as a two-stroke crosshead Diesel engine, comprising a fuel gas supply system and cylinders provided with fuel gas injectors for injecting fuel gas directly into combustion chambers in the cylinders, and at least one engine control unit controlling the amount of fuel gas injected into the combustion chambers according to an applied fuel index for obtaining a desired engine speed at a given engine bad, where the fuel index defines an amount of fuel gas to be injected into the cylinders per injection, and the amount of fuel gas injected is controlled by adjusting the duration of a fuel gas injection period. A sensor arrangement is provided for measuring the engine bad during operation, and the at least one engine control unit controls the injection pressure of fuel gas into the combustion chambers in response to changes in the energy density of the fuel gas, so that the applied fuel index corresponds to the reference fuel index.

Description

DK 177566 B1

The present invention relates to an internal combustion engine, such as a two-stroke crosshead Diesel engine, comprising cylinders provided with fuel gas injectors for injecting fuel gas directly into combustion chambers in the cylinders, and at least one engine control unit controlling the amount of 5 fuel gas injected into the combustion chambers according to an applied fuel index for obtaining a desired engine speed at a given engine load, where the fuel index defines an amount of fuel gas to be injected into the cylinders per injection, and the amount of fuel gas is controlled by adjusting the duration of fuel gas injection period.

10 There is an increasing interest in lowering carbon dioxide, nitric oxide and sulphur emissions from the operation of internal combustion engines and hence alternative fuel alternatives to the conventional fuel oil has been investigated. Operation of large two-stroke diesel engines such as a MAN Diesel 12K80MC-GI-S has shown that operation with fuel gas as primary fuel may 15 be both safe, reliable and environmentally desirable as to emissions compared to conventional fuel oil. As regards large two-stroke diesel engines for the maritime market, engines using fuel gas are becoming increasingly interesting, especially for liquid natural gas carriers (LNG carriers), wherein boil-off gas from the gas tanks must be handled during transportation.

20 Hence it is desirable to use natural gas and/or boil-off gas from the gas tanks of LNG carriers for operation of such engines. However, the calorific value of fuel gas from a gas tank of a LNG carrier may vary over time, e.g. because the boil-off gas also comprises e.g. nitrogen, which reduces the energy density of the fuel gas provided to the cylinders. Likewise, variations of 25 the temperature of the fuel gas provided to the cylinders result in a variation in the energy density of the fuel gas injected into the combustion chambers of the cylinders.

When the energy density of the fuel gas injected into the cylinders differ from the energy density of the reference fuel gas, which is the basis for 30 a manufacturing reference adjustment of the engine and for determining a reference fuel index of the engine, i.e. the amount of fuel to be injected into the cylinders at a given load to obtain a desired engine speed, it is necessary to adjust the applied fuel index in order to maintain the engine speed. Variations in the energy density of the fuel gas are traditionally experienced as a 35 change in the applied fuel index from the reference fuel index at the actual 2 DK 177566 B1 engine load.

If for instance the energy density of the fuel gas is lower than the reference fuel gas, the amount of energy injected per time unit would be insufficient to maintain the engine speed and the engine speed would decrease.

5 However, this is compensated by the electronic control unit as the fuel index is increased and the amount of energy injected into the cylinders is increased so that the engine speed is at the desired level, i.e. the duration of the fuel gas injection period is increased.

However, this approach for compensating for variations in the energy 10 density of the fuel gas and achieving the desired engine speed results in a lower efficiency, because the maximum combustion pressure in the combustion chamber is lower than at the optimum operating point. Likewise, if the energy density of the fuel gas is higher than the reference gas, the maximum combustion pressure will be higher than what the engine is designed for, 15 which will result in increased wear and potential damage of the engine.

Hence variations in the calorific value of the fuel gas and the temperature of the fuel gas both affect the energy density and the amount of energy injected into the cylinders per time unit.

EP 1 546 532 discloses a system for operating a multiple fuel engine 20 which runs on a combination of fuel oil and fuel gas. An electronic control unit is connected to an engine system, and controls the amounts of each of the multiple fuels to be delivered to the engine based on operating characteristics of the engine system such as the fuel gas temperature and the fuel gas pressure.

25 Furthermore GB 1 325 349 discloses an internal combustion engine of the Diesel comprising a fuel gas supply system provided with fuel gas injectors for injecting fuel gas into combustion chamber of the engine. The fuel gas system has a pressure line that extends from the compressor to fuel gas injection valves in the engine, for injecting fuel gas into combustion chamber 30 of the engine. An engine control unit controls the amount of fuel gas injected into the combustion chambers for obtaining a desired engine speed at a given engine load. The amount of fuel gas injected is controlled by adjusting the duration of a fuel gas injection period. A sensor arrangement is provided for measuring the engine load during operation and the engine control unit will 35 control the engine speed at a given engine load. GB 1 325 349 also describes 3 DK 177566 B1 how the engine control unit controls the injection pressure of fuel gas into the combustion chamber in response to variation in calorific value of the fuel gas.

According to the present invention it is a desire to optimize the efficiency of an internal combustion engine when operated on fuel gas with vary-5 ing energy density.

With a view to this the internal combustion engine according to the present invention is characterized in that a sensor arrangement is provided for measuring the engine load during operation, that based on a reference fuel index determined from the measured engine load compared with an ap-10 plied fuel index determined by the at least one engine control unit in order to obtain the desired engine speed at a given engine load, the at least one engine control unit controls the injection pressure of fuel gas into the combustion chambers in response to changes in the energy density of the fuel gas, so that the applied fuel index corresponds to the reference fuel index.

15 The electronic control unit can on basis of readings from the sensor arrangement determine the measured engine load and a corresponding reference fuel index and compare it with the applied fuel index calculated by the engine control unit. If there is a difference between the reference fuel index and the applied fuel index, the fuel gas injection pressure is adjusted so that 20 the amount of energy injected per time unit is constant even with variations in the calorific value of the fuel gas and/or the temperature of the fuel gas.

Fast engine load disturbances e.g. due to waves acting on a ship with a marine engine according to the invention or power variations such as fast energy density variations of the fuel gas causing speed variations from 25 the desired speed, is compensated by a quick adjustment of the amount of energy injected into the cylinders per injection by adjusting the duration of the fuel injection period. By adjusting the fuel injection pressure it is possible to compensate for slow changes over time of the calorific value of the fuel gas and/or changes of the temperature of the fuel gas and maintaining the 30 same heat release and efficiency as if the properties of the injected fuel gas corresponded to the reference fuel gas. This furthermore results in a more efficient timing of the time critical combustions process with respect to for instance timing of injection, and the timing of opening and closing the exhaust valve, than by adjusting the duration of the fuel injection period.

35 Besides from the evident benefits from reduced fuel consumption 4 DK 177566 B1 and emission combustion gasses, an adjusted and balanced engine potentially delivers large savings in maintenance costs and reduces the risk of damage to the engine.

In a preferred embodiment that allows for a more efficient operation 5 of the engine, the at least one engine control unit controls the injection pressure of fuel gas into the combustion chambers in response to changes in the calorific value and/or the temperature of the fuel gas.

In a practically simple embodiment the measured engine load is determined from sensor arrangement measurements of the shaft torque and 10 shaft rotational speed.

In an alternative embodiment the measured engine load is determined from sensor arrangement measurements of the combustion pressure during the combustion cycles and the rotational speed of the shaft.

This allows for an especially advantageous embodiment according to 15 the invention, where the fuel gas injection pressure is adjusted in combination with adjustment of the injection timing and the timing of opening and closing of the exhaust valve in dependence of the crankshaft position in order to obtain an optimal fuel consumption and combustion gas emission.

According to a reliable implementation of the invention the cylinders 20 are provided with fuel oil injectors injecting fuel oil directly into the combustions chambers in the cylinder and a fuel oil supply system.

According to a reliable implementation of the invention the fuel gas supply system is a common rail fuel gas supply system.

In a practically preferred embodiment the temperature of the fuel 25 gas provided to the cylinders is in the range of 10° to 70 ° Celsius. This prevents condensation on the gas supply piping.

In a preferred embodiment at 100 % engine load the engine speed is in the range from 45 rpm to 250 rpm. Low speed engines are typically very large powered engines where it really matters to operate the engine effi-30 ciently in terms of combustion pressure.

In a practically preferred embodiment a gas supply system providing fuel gas to the cylinders is connected to a liquid natural gas tank of a liquid natural gas carrier.

Examples of the present invention and embodiments thereof are in 35 the following described in more detail with reference to the highly schematic 5 DK 177566 B1 drawing, in which

Fig. 1 is a general view of an engine according to the present invention,

Fig. 2 is an example of an engine with a combined fuel oil and fuel 5 gas operating mode according to the invention.

An internal combustion engine 1 according to a preferred embodiment of the present invention may be a two-stroke crosshead diesel engine as illustrated in Fig. 1. Such an engine 1 can e.g. be of the make MAN Diesel and the type MC or ME, or of the make Wårtsilå of the type Sulzer RT-flex or 10 Sulzer RTA, or of the make Mitsubishi Heavy Industries. An engine of this type is a large engine typically used as a main engine in a ship or as a stationary engine in a power plant. The cylinders can e.g. have a bore in the range from 25 cm to 120 cm, and the engine can e.g. have a power in the range from 3000 kW to 120.000 kW. The engine speed is typically in the 15 range from 40 rpm to 250 rpm. The compression ignition internal combustion engines according to the present invention are typically capable of using heavy fuel oil as primary fuel.

The engine 1 of Fig. 1 has a plurality of cylinders with a cylinder liner 2 mounted in a cylinder section 3 of an engine frame 4. An exhaust valve 20 housing 5 is mounted in a cylinder cover 6 and an exhaust gas duct 7 extends from the individual cylinder to an exhaust gas receiver 8 common to several or all cylinders. In the exhaust gas receiver pressure variations caused by the exhaust gas pulses emitted from the exhaust gas ducts are equalized to a more even pressure, and one or more turbochargers 9 receive 25 exhaust gas from the exhaust gas receiver 8 and deliver compressed air to a scavenge air system comprising at scavenge air receiver 10 which, like the exhaust gas receiver, is an elongated pressure vessel.

In the individual cylinder a piston is mounted on a piston rod that is connected with a crank pin on a crankshaft via a crosshead and a connecting 30 rod (not illustrated). A fuel injector injects the fuel into a combustion chamber. When the injected fuel is fuel oil it auto-ignites because of the high temperature in the air above the piston. The high temperature is present because the piston has compressed the inlet air during the upward compression stroke.

35 It is preferred that the present invention is implemented in a marine 6 DK 177566 B1 diesel engine with a dual fuel supply system, and in the following the invention is described by such example, but of course the invention may be implemented as a single fuel system. The engine in the present example is an electronically control engine, which electronic control of both oil and gas in-5 jection, ensuring that the fuel injection and combustion is optimized. Further it is based on a high pressure gas injection principle with pilot fuel oil injection for igniting the fuel gas combustion. With this principle the diesel combustion process can be fully utilized and thereby the same high thermal efficiency as for fuel oil combustion can be obtained. In Fig. 2 cylinder section 3 10 is illustrated with only a single cylinder 11, but the engine has a plurality of cylinders such as from 4 to 16 cylinders. As schematically shown in Fig. 2 the internal combustion engine 1 comprises a fuel oil supply system 23 and a fuel gas supply system 19 providing a fuel oil injection system 20 and fuel gas injection system 30 with fuel oil and fuel gas to be provided into the combus-15 tion chambers of the cylinders 11. In the present example the fuel oil injection system 20 and the fuel gas injection system 30 controls injection of fuel oil and fuel gas into the combustion chambers of the cylinders 11, respectively. The general principle of the fuel injection systems 20, 30 is that each cylinder 11 is associated with a cylinder control unit 12 controlling one or 20 more fuel dosing devices 15, 16 such as fuel pumps or valves connected to fuel injectors 13, 14 in the cylinder cover 6. The number of injectors 13, 14 per cylinder depends on the power of the cylinder 11. In a preferred embodiment each cylinder comprises at least a fuel oil injector 13 and a fuel gas injector 14. In smaller engines a single injector per fuel type may be suffi-25 cient to inject the amount of fuel required for one combustion process, whereas in larger, more powerful engines two or three injectors for each fuel type may be required. When several injectors are provided per cylinder 11, there may be one fuel dosing device 15, 16 per injector 13, 14. The cylinder control unit 12 of the fuel injection system 20, 30 is controlled by an engine 30 control unit 17 in communication with the bridge of a vessel.

It is preferred that the fuel gas supply system 19 is connected to a liquid natural gas (LNG) tank 18 of a LNG carrier vessel operated at sea. The LNG tank of an LNG carrier vessel is kept at low temperatures, but is inevitably heated as external heat from the seawater and atmosphere is transferred 35 through the insulation of tanks. By the intrusion of the external heat, a por- 7 DK 177566 B1 tion of the LNG is gasified, i.e. boiled off, and the tank pressure gradually increases. In order to keep the tank pressure at an acceptable level a reliquefaction system (not shown) may be used to reliquefy boil-offgas. Alternatively, or in combination with the reliquefaction system, a boil-off gas compressor 5 may provide high-pressure boil-off gas when such is ordered by the fuel gas injection system 30. At the cylinders a fuel gas dosing device 16 controlled by the cylinder control unit 12 effect the timing and opening of the fuel gas injector 14. The fuel gas is preferably provided to the fuel gas injection system by a double-walled gas supply piping 26 of the common rail design, where a 10 valve of the fuel gas injector 14 is controlled by an auxiliary control oil system. This, in principle, consists of a hydraulic control oil system and an electronic gas injection valve, supplying high-pressure control oil to the gas injector 14, thereby controlling the timing and opening of a gas valve of the gas injector 14. An efficient gas injection is obtained when the gas delivery pres-15 sure is between 150 to 400 bar depending on the engine load, and the fuel gas has a temperature between 30° Celsius and 60° Celsius, preferably about 45° Celsius. A buffer tank 22 is used for storage of boil-off gas before provided to the fuel gas injection system 30 by the fuel gas supply system 19.

The amount of inevitable boil-off gas in an LNG tank of a LNG carrier is nor-20 mally not sufficient as the only fuel for the operation of the internal combustion engine of the LNG carrier, but the amount of boil-off gas may advantageously be used in combination with fuel oil in an internal combustion engine according to the invention. The operation of the fuel gas injection system 30 is insensitive to the gas composition as well as the variation in the gas com-25 position. Hence, also liquefied petroleum gas (LPG) that normally consists of higher hydrocarbons like propane and butane may like LNG apply as fuel gas without changing the engine's performance in terms of speed, thermal efficiency and power output, while maintaining the same rating as for fuel oil.

In the fuel oil injection system 20 the fuel oil dosing device 15 may 30 be a fuel pump, and in that case the fuel oil supply system 23 needs only deliver fuel oil from a fuel oil tank 21 to the fuel dosing device at a relatively low feeding pressure in a fuel feeding pipe 24, such as a pressure in the range from 2 bar to 15 bar. Alternatively, the fuel oil dosing device 15 may be a valve or a valve in connection with a metering device, and the fuel feed-35 ing pipe is then a high-pressure pipe in which the fuel is at a pressure higher 8 DK 177566 B1 than the injection pressure, such as a feeding pressure in the range of 500 bar to 1500 bar. Such a fuel oil supply system 23 is called a common-rail system. In either case, the fuel oil dosing device 15 is connected to fuel feeding pipe 24 by a branch conduit with a valve that is maintained in open position 5 during normal engine operation. Fuel oil dosing device 15 is connected to fuel oil injectors 13 via high-pressure fuel oil conduits. A return conduit leads from the fuel oil injectors to a fuel oil return line (not shown). The fuel oil provided to the cylinders is typically heavy fuel oil or marine diesel oil.

An internal combustion engine 1 according to the invention may be 10 provided by installing a fuel gas supply system 19 and a fuel gas injection system 30 on an existing engine with a fuel oil supply system as described above. The injection control can be either with one cylinder control unit or with independent cylinder control units 12a, 12b, which control the amount of fuel oil and the fuel gas provided into the combustion chambers of the cylin-15 ders 11, respectively. Likewise, both the fuel oil injection system 20 and the fuel gas injection system 30 can be either controlled from a engine control unit 17 or separate in independent engine control units 17a, 17b. When operating an internal combustion engine according to the invention, the engine regulation of fuel injection is either with the fuel oil injection system 20 or the 20 fuel gas injection system 30. Generally, the engine control unit 17 receives an engine speed signal and other engine operating parameters from a sensor arrangement 40, and controls the amount and rate of fuel to be provided into the combustion chambers of the cylinders 11, which is also known as the engine's governor control. The internal combustion engine according to the 25 invention may be operated in a fuel oil operating mode, a fuel gas operating mode and a combined fuel oil and fuel gas operating mode. The operating modes may be ordered from the bridge of a ship, except for safety reasons in case of e.g. a gas leak, the engine is automatically immediately switched to the fuel oil operating mode.

30 The combined fuel oil and fuel gas operating mode may be implemented by automatically alternating between the fuel oil operation mode and the fuel gas operating mode. Switching between fuel oil operating mode and fuel gas operating mode may be commanded by an engine mode select function 25 connected to the fuel oil injection system 20 and the fuel 35 gas injection system 30, and preferably the engine switch functionality is part 9 DK 177566 B1 of the fuel gas supply system 19, hence the switching is controlled by the engine control unit 17b dedicated to the fuel gas injection system 30. In the combined fuel oil and fuel gas operating mode the engine mode select function 25 determines if the combustion in the internal combustion engine is 5 initiated with the fuel oil injection system 20 or the fuel gas injection system 30, i.e. the engine mode select function 25 switches the governor control function of the engine control unit 17 between using the fuel oil injection system 20 or the fuel gas injection system 30.

In the fuel gas operating mode the fuel gas injection and the timing 10 of the combustion process is controlled by the fuel gas injection system 30.

This is done according to a predetermined reference fuel index, i.e. a fuel gas index specifying a fuel gas injection length and a fuel gas injection pressure required to operate the engine optimally at a given engine load. Before taken into operation the engine is tested at different loads along the propeller curve 15 to determine the optimum reference fuel gas injection length and fuel gas injection pressure at different loads. Hence, when the engine control unit 17, 17b makes a look-up in the engine maps for finding e.g. the correct timing of fuel gas injection, timing of opening and closing of the exhaust valve and the hydraulic pressure, it also finds both an ordered fuel gas injection length and 20 an ordered fuel gas injection pressure required to operate the engine at a desired engine load.

When the engine is operated in the fuel gas mode, the governor control of the engine control unit 17, 17b controls the amount of fuel gas to be injected by calculating the fuel index for obtaining a desired engine speed at 25 a given engine load. Hence changes in the engine load will make the engine speed differ from a desired engine speed and therefore the applied fuel index is adjusted so that the desired engine speed is achieved. If for instance the calorific value of the fuel gas is lower than the calorific value of the reference gas less energy is injected into the cylinder during the fuel gas injection pe-30 riod. This will result in a reduced engine speed, which is measured by a sensor arrangement 40 in communication with the engine control units 17, 17b.

In order to obtain the desired engine speed the engine control unit 17, 17b increases the applied fuel index so that the fuel gas injection period is increased and thereby the amount of injected fuel gas is increased. The same 35 principle for maintaining the desired engine speed is used by the engine con- 10 DK 177566 B1 trol unit 17a of the fuel oil injection system, and is a very efficient and fast control of sudden changes in the engine load. However, in the fuel gas operating mode the desired engine speed is achieved with a lower maximum pressure in the combustion chamber and therefore with a lower efficiency 5 than what the engine is designed for when using the reference gas. When the calorific value of the fuel gas is higher than the reference gas, the maximum combustion pressure in the combustion chamber is higher than what the engine is designed for, and wear on engine parts is increased and the engine may be damaged.

10 Assuming a constant pressure of the fuel gas provided to the cylin ders, a lower fuel gas temperature compared to the temperature of the reference fuel gas will result in a maximum combustion pressure higher than what the engine is designed for, because the energy density of the fuel gas is then higher than the reference fuel gas. Hence variations in the calorific value and 15 the temperature of the fuel gas provided to the cylinders has the same effect on the combustion process, and such variations are experienced by the engine control unit as changes in the engine load and the fuel index is accordingly adjusted by the engine control unit 17, 17b.

Therefore, when the fuel index is adjusted in a fast regulation by ad-20 justing the fuel injection period in response to changes of the energy density of the fuel gas, the applied fuel index used by the engine control unit 17, 17b will differ over time from the reference fuel index corresponding to the actual engine load. The actual engine load and thereby the reference fuel index may for instance be determined by the engine control unit 17, 17b on basis of the 25 engine speed and measurements of the mean cylinder combustion pressure or the torque of the crankshaft received from the sensor arrangement 40.

The engine control unit 17, 17b compare the applied fuel index with the reference fuel index and adjust the fuel gas injection pressure so that the applied fuel index corresponds to the reference fuel index. Hence the engine 30 control unit 17, 17b controls the injection pressure of fuel gas by ordering an adjusted fuel gas pressure from the fuel gas supply system 19 so that the amount of energy injected into the cylinders per time unit is kept constant, e.g. at the same level as stored in a map in the engine control unit 17, 17b under the manufacturing reference adjustment of the engine. Since the ad-35 justed fuel gas injection pressure and the corresponding adjustment of the 11 DK 177566 B1 amount of energy injected per time unit results in a change in the engine power, the governor control of the engine control unit 17, 17b will adjust the applied fuel index to keep the engine power and thereby the engine speed constant resulting in an applied fuel index, which corresponds to the refer-5 ence fuel index.

Therefore a decreasing calorific value of the fuel gas results in an increased fuel gas injection pressure, whereas an increasing calorific value of the fuel gas results in a decreased fuel gas injection pressure. Likewise, a lower temperature of the fuel gas with respect to the reference gas will in-10 crease the energy density of the fuel gas and the fuel gas injection pressure ordered from the fuel gas supply system 19 is reduced by engine control unit 17b, whereas a higher temperature of the fuel gas with respect to the reference gas will decrease the energy density of the fuel gas, and the fuel gas injection pressure ordered from the fuel gas supply system 19 by the engine 15 control unit 17b is increased.

Claims

12 DK 177566 B112 DK 177566 B1

1. Forbrændingsmotor (1), såsom en totakts krydshoved-dieselmotor omfattende et brædnselsgasforsyningssystem (19) og cylindre (11) med 5 brændselsgasinjektorer (14) til injicering af brændselsgas direkte ind i forbrændingskamrene i cylindrene (11), og i det mindste én motorstyreenhed (17), der styrer mængden af brændselsgas, som injiceres ind i forbrændingskamrene, i overensstemmelse med et anvendt brændselsindeks for at opnå en ønsket motorhastighed ved en given motorlast, hvor brændselsindekset 10 definerer en brændselsgasmængde, der skal injiceres ind i cylindrene (11) per injection, og den injicerede brændselsgasmængde styres ved justering af varigheden af en brændselsgasinjiceringsperiode, kendetegnet ved, at der er tilvejebragt et følerarrangement til måling af motorlasten under drift, og at den i det mindste ene motorstyreenhed (17) for at opnå den ønskede 15 motorhastighed ved en given motorlast, styrer injektionstrykket for brændselsgas ind i forbrændingskamrene som reaktion på ændringer i energitæthe-den af brændselsgassen baseret på et referencebrændselsindeks, der bestemmes ud fra den målte motorlast sammenlignet med et anvendt brændselsindeks, som bestemmes af den i det mindste ene motorstyreenhed (17), 20 således at det anvendte brændselsindeks svarer til referencebrændselsindekset.An internal combustion engine (1), such as a two-stroke cross-head diesel engine comprising a fuel gas supply system (19) and cylinders (11) with 5 fuel gas injectors (14) for injecting fuel gas directly into the combustion chambers of the cylinders (11), and at least one engine control unit (17) controlling the amount of fuel gas injected into the combustion chambers in accordance with an applied fuel index to obtain a desired engine speed at a given engine load, wherein the fuel index 10 defines a fuel gas quantity to be injected into the cylinders (11) per and the injected fuel gas quantity is controlled by adjusting the duration of a fuel gas injection period, characterized in that a sensor arrangement is provided for measuring the engine load during operation and that the at least one engine control unit (17) is obtained at the desired engine speed at a given engine load, controls fuel injection pressure into combustion the chambers in response to changes in the energy density of the fuel gas based on a reference fuel index determined from the measured engine load compared to an spent fuel index determined by the at least one engine control unit (17), 20 such that the fuel index used corresponds to reference fuel index.

2. Forbrændingsmotor (1) ifølge krav 1, kendetegnet ved, at den i det mindste ene motorstyreenhed (17) styrer injektionstrykket for brændselsgas ind i forbrændingskamrene som reaktion på ændringer i 25 brændværdien og/eller temperaturen af brændslet.Internal combustion engine (1) according to claim 1, characterized in that the at least one engine control unit (17) controls the injection pressure of fuel gas into the combustion chambers in response to changes in the fuel value and / or the temperature of the fuel.

3. Forbrændingsmotor (1) ifølge krav 1 eller 2, kendetegnet ved, at den målte motorlast bestemmes ud fra følerarrangementets (40) målinger af forbrændingstrykket under forbrændingscyklerne og omdrejningshastigheden af en aksel.Internal combustion engine (1) according to claim 1 or 2, characterized in that the measured motor load is determined from the combustion pressure (40) measurements of the combustion pressure during the combustion cycles and the speed of rotation of a shaft.

4. Forbrændingsmotor (1) ifølge krav 1 eller 2, kendetegnet ved, at den målte motorlast bestemmes ud fra følerarrangementets (40) målinger af et akseldrejningsmoment og akselomdrejningshastighed.Internal combustion engine (1) according to claim 1 or 2, characterized in that the measured motor load is determined from the measurements of the sensor arrangement (40) of a shaft torque and shaft speed.

5. Forbrændingsmotor (1) ifølge krav 1 til 4, kendetegnet ved, at brændselsgasinjektionstrykket justeres i kombination med justering 35 af timingen af injektionen og timingen af åbningen og lukningen af en ud- 13 DK 177566 B1 stødsventil i afhængighed af en krumtapakselposition for at opnå et optimal brændselsforbrug og forbrændingsgasemission.Internal combustion engine (1) according to claims 1 to 4, characterized in that the fuel gas injection pressure is adjusted in combination with the adjustment of the timing of the injection and the timing of the opening and closing of an exhaust valve in dependence of a crankshaft position to achieve an optimal fuel consumption and combustion gas emission.

6. Forbrændingsmotor (1) ifølge et hvilket som helst af de foregående krav, kendetegnet ved, at cylinderene (11) er forsynet med 5 brændselsolieinjektorer (13), der injicerer brændselsolie direkte ind i forbrændingskamrene i cylindrene, og et brændselsolieforsyningssystem.An internal combustion engine (1) according to any one of the preceding claims, characterized in that the cylinders (11) are provided with 5 fuel oil injectors (13) which inject fuel oil directly into the combustion chambers of the cylinders and a fuel oil supply system.

7. Forbrændingsmotor (1) ifølge et hvilket som helst af de foregående krav, kendetegnet ved, at brændselsgasforsyningssystemet er et common rail brændselsgasforsyningssystem.Combustion engine (1) according to any one of the preceding claims, characterized in that the fuel gas supply system is a common rail fuel gas supply system.

8. Forbrændingsmotor (1) ifølge et hvilket som helst af de foregåen de krav, kendetegnet ved, at temperaturen af den brændselsgas, der leveres til cylindrene, er i intervallet 10° til 70° celsius.Internal combustion engine (1) according to any one of the preceding claims, characterized in that the temperature of the fuel gas supplied to the cylinders is in the range 10 ° to 70 ° C.

9. Forbrændingsmotor (1) ifølge et hvilket som helst af de foregående krav, kendetegnet ved, at ved 100 % motorlast er motorhastighe- 15 den i intervallet 45 o/min til 250 o/min.Combustion engine (1) according to any one of the preceding claims, characterized in that at 100% engine load, the engine speed is in the range of 45 rpm to 250 rpm.

10. Forbrændingsmotor (1) ifølge et hvilket som helst af de foregående krav, kendetegnet ved, at et gasforsyningssystem, der leverer brændselsgas til cylindrene (11), er forbundet til en tank (18) for flydende naturgas på en tanker for flydende naturgas. 20Combustion engine (1) according to any one of the preceding claims, characterized in that a gas supply system supplying fuel gas to the cylinders (11) is connected to a liquid natural gas tank (18) on a liquid natural gas tank. 20