CN113356984B

CN113356984B - Internal combustion engine and method for determining specific emission thereof

Info

Publication number: CN113356984B
Application number: CN202110252131.9A
Authority: CN
Inventors: 戴维·拉松; 安杰洛·拉·塞塔
Original assignee: Mannone Solutions Mannone Solutions Germany Branch
Current assignee: Mannone Solutions Mannone Solutions Germany Branch
Priority date: 2020-03-06
Filing date: 2021-03-08
Publication date: 2023-03-24
Anticipated expiration: 2041-03-08
Also published as: JP2021139367A; CN113356984A; DK180561B1; JP6938800B2; DK202070149A1; KR102279489B1

Abstract

An internal combustion engine is provided that operates on a given fuel and produces exhaust gas during operation by combustion of the given fuel with intake air. The engine includes an electronic control unit, a sensor configured to detect a concentration of a first exhaust gas component in the exhaust gas, and a sensor configured to detect a concentration of a reference gas in the exhaust gas. The reference gas is oxygen or carbon dioxide. The electronic control unit is configured to determine a difference in reference gas concentration between the inlet air and the outlet gas, and to determine a specific exhaust amount of the first outlet gas component based on the detected concentration of the first outlet gas component and the determined difference in reference gas concentration between the inlet air and the outlet gas. A method for determining specific emissions of exhaust gas constituents of an internal combustion engine is also provided.

Description

Internal combustion engine and method for determining specific emission thereof

Technical Field

The present disclosure relates to internal combustion engines operated to combust a given fuel with air to produce exhaust gases, in particular large two-stroke uniflow scavenged internal combustion engines with crossheads.

Background

Large two-stroke turbine-boosted uniflow-scavenged internal combustion engines with crossheads are used, for example, to propel large ocean-going vessels or as prime movers for power plants. Not only because of their large size, these two-stroke diesel engines are structurally different from any other internal combustion engine.

These large two-stroke turbo-boosted uniflow scavenging internal combustion engines are increasingly subject to stricter emissions regulations. The art of meeting these emission regulations is rapidly evolving, such as by changing to cleaner fuels, improved fuel injection systems, and by adding exhaust gas treatment systems including, for example, selective catalytic reduction, to name a few. Emission regulations for these engines define emission levels to be specific, i.e., the emission level is limited to the maximum mass produced in the exhaust gas per kilowatt-hour delivered at the engine shaft [ g/kWh ]. Therefore, these emission limits are also referred to as braking specific limits.

In practice, this limitation is implemented in the form of a total dosing cycle discharge limitation (g/kWh). Such restrictions are for example enforced by the International Maritime Organization (IMO). An example of the composition of the exhaust gas that is restricted in this way is nitrogen oxide (NOx).

Measuring the NOx concentration in the exhaust gases of a large two-stroke internal combustion engine, for example operating as a prime mover, on a marine vessel is relatively simple, for example in Parts Per Million (PPM). However, converting such measured NOx concentrations in exhaust gases to specific values in g/kWh is a daunting task when the engine is not on a test stand. In practice, therefore, large two-stroke internal combustion engines are tested for emissions on a test bench with the engine connected to a hydraulic brake (water brake: hydraulic brake dynamometer, hydraulic dynamometer). Torque and speed readings from the hydraulic brake provide accurate information about the power delivered on the engine shaft. Such information is not available to engines used as prime movers in marine vessels.

Thus, current large two-stroke engines are certified in a shop test that proves compliance with NOx regulations once. The marine engine is compliant if the marine engine can demonstrate that neither the critical "NOx constituents" nor the NOx affecting engine tuning have been modified. The model is well-adapted to the engine that has been tuned once and the tuning remains accurate.

The NOx regulation by IMO Tier III requires NOx reduction technology that makes NOx emissions significantly lower than what is possible using engine-only tuning. It remains to be determined whether these NOx reduction systems have proven compliance only once in a plant test, or whether they are based on continuous monitoring and/or closed loop control of continuously measured NOx emissions.

However, there is no simple official method to measure specific NOx emissions during operation. The inability to determine whether an operating engine meets legal requirements for a particular emission is a problem, as engine manufacturers will wish to optimize engine operation, and in particular will wish to optimize exhaust gas treatment systems to ensure compliance with legal limits. However, it is not feasible to limit legal restrictions to specific emissions and to measure during operation to provide only the emissions as concentrations in the exhaust gas.

Another complicating factor is that exhaust gas treatment systems, such as NOx reduction in selected catalytic reduction processes, need to admit a dose of reductant (e.g., urea) into the exhaust gas. Currently, this is done in a feed forward manner, which may result in significant deviations from the optimum level of reductant tolerated, due to e.g. different locations of installation of the reductant pump and different conduits and resulting different flows of reductant. It would therefore be an advantage if the efficiency of a selected catalytic reduction process could be monitored on an operating engine.

JPH10131789 discloses an Otto cycle engine that uses an oxygen sensor and a NOx sensor for controlling the air-fuel ratio.

Disclosure of Invention

It is an object of the present invention to provide a system that overcomes or at least reduces the above problems.

The foregoing and other objects are achieved by embodiments of the present invention. Further embodiments are apparent from the description and drawings of the invention.

According to a first aspect, there is provided an internal combustion engine configured to operate on a given fuel and to produce exhaust gas during operation by combustion of the given fuel with intake air,

the engine includes:

-an electronic control unit for controlling the operation of the electronic control unit,

a sensor configured to detect a concentration of a first exhaust gas component in the exhaust gas,

a sensor configured to detect a concentration of a reference gas in the exhaust gas, the reference gas being oxygen or carbon dioxide,

the electronic control unit is configured to:

-determining a difference between the reference gas concentration between the inlet air and the outlet gas,

-determining the specific exhaust amount of the first exhaust gas component on the basis of the detected concentration of the first exhaust gas component and on the basis of the determined difference in reference gas concentration between the inlet air and the exhaust gas.

By measuring the concentration of the first exhaust gas component in the exhaust gas, and by determining the difference between the reference gas concentrations between the inlet air and the exhaust gas, and correlating this information with the type of fuel used and with the (instantaneous) fuel efficiency of the engine, an accurate estimate of the amount of emissions per kwh of the first exhaust gas component produced by the engine can be obtained. This enables the calculation of a specific emission of the first exhaust gas component without knowing the exhaust flow rate or the complete exhaust composition.

This is possible from the insight that the amount of oxygen reduction (or the amount of carbon dioxide increase) is proportional to the energy consumed. For many fuels, the oxygen consumption per fuel heating unit is almost the same, but the engine is preferably configured to take into account the properties of the actual fuel used in the engine. The calculation of the type of fuel used is more sensitive to the increase in carbon dioxide and the actual compensation factor for the fuel type needs to be determined if carbon dioxide is used as reference gas.

Thus, knowing the fuel properties and knowing the oxygen reduction (or carbon dioxide increase) allows an accurate estimate of the energy consumed to be calculated. The electronic control unit also uses the energy efficiency of the engine as a factor in the calculation in order to accurately calculate the energy produced. Heretofore, in one embodiment, the electronic control unit is provided with a look-up table, algorithm, or computer model of the engine to determine the energy efficiency of the engine under transient operating conditions.

According to a possible embodiment of the first aspect, the electronic control unit is configured to determine the reference gas concentration in the incoming air as a function of the humidity of the incoming air.

According to a possible embodiment of the first aspect, the electronic control unit is configured to determine an instantaneous fuel efficiency of the engine, and wherein the electronic control unit is configured to apply the determined fuel efficiency as a factor in determining the specific emission amount of the first exhaust gas constituent.

According to a possible embodiment of the first aspect, wherein the electronic control unit is preferably provided with a look-up table and/or an algorithm and/or with a computer model of the engine to determine the instantaneous fuel efficiency based on the instantaneous operating conditions.

According to a possible embodiment of the first aspect, the electronic control unit is configured to apply a fuel factor associated with the given fuel when determining the specific emission amount of the first exhaust gas constituent

According to a possible embodiment of the first aspect, the electronic control unit is configured to determine the specific emission amount of the first exhaust gas component by dividing the detected concentration of the first exhaust gas component in the exhaust gas by the product of the determined difference between the reference gas concentrations between the inlet air and the exhaust gas and the adjustment factor.

According to a possible embodiment of the first aspect, the adjustment factor comprises an instantaneous fuel efficiency of the engine determined by the electronic control unit.

According to a possible embodiment of the first aspect, the adjustment factor comprises a fuel factor associated with the given fuel.

According to a possible embodiment of the first aspect, the electronic control unit is configured to determine the specific emission amount of the first exhaust gas component by dividing the detected concentration of the first exhaust gas component in the exhaust gas by the determined product of the difference between the reference gas concentration between the inlet air and the exhaust gas and the instantaneous fuel efficiency of the engine determined by the electronic control unit and the fuel factor associated with the given fuel.

According to a possible embodiment of the first aspect, the first exhaust gas composition is one of: CO, CO2, HC, CH4, NOx, SOx, NH3, PM, PN, or BC.

According to a possible embodiment of the first aspect, the first exhaust gas constituent is NOx, the engine is configured to operate under control of an electronic control unit (50), and the electronic control unit is configured to control operation of the engine in dependence on the determined specific NOx emission.

According to a possible embodiment of the first aspect, the first exhaust gas constituent is NOx, the engine comprising a NOx treatment system configured to operate under control of the electronic control unit, and the electronic control unit being configured to control operation of the NOx treatment system in dependence on the determined specific NOx emission.

According to a possible embodiment of the first aspect, the NOx treatment system is configured to apply a reducing agent to the exhaust gas, and wherein the amount of reducing agent applied to the exhaust gas is controlled by the electronic control unit (50) in dependence on the determined specific NOx emission.

According to a second aspect, there is provided a method for determining a specific emission amount of a first exhaust gas constituent of an internal combustion engine, the method comprising:

-detecting a concentration of a first exhaust gas component in the exhaust gas,

-detecting the concentration of a reference gas in the exhaust gas, the reference gas being oxygen or carbon dioxide,

According to a possible embodiment of the second aspect, the method comprises determining the reference gas concentration in the inlet air in dependence on the humidity of the inlet air.

According to a possible embodiment of the second aspect, the method comprises determining an instantaneous fuel efficiency of the engine, and applying the determined fuel efficiency as a factor in determining the specific emission amount of the first exhaust gas constituent.

According to a possible embodiment of the second aspect, the method comprises applying a look-up table and/or an algorithm and/or a computer model of the engine when determining said instantaneous fuel efficiency based on the instantaneous operating conditions.

According to a possible embodiment of the second aspect, the method comprises applying a fuel factor associated with a given fuel in determining the specific emission of the first exhaust gas constituent

According to a possible embodiment of the second aspect, the method comprises determining the specific emission of the first exhaust gas component by dividing the detected concentration of the first exhaust gas component in the exhaust gas by the product of the determined difference between the reference gas concentration between the inlet air and the exhaust gas and the adjustment factor.

According to a possible embodiment of the second aspect, the adjustment factor comprises an instantaneous fuel efficiency of the engine determined by the electronic control unit.

According to a possible embodiment of the second aspect, the adjustment factor comprises a fuel factor associated with the given fuel.

According to a possible embodiment of the second aspect, the method comprises determining the specific emission of the first exhaust gas constituent by dividing the detected concentration of the first exhaust gas constituent in the exhaust gas by the product of the determined reference gas concentration difference between the inlet air and the exhaust gas and the instantaneous fuel efficiency of the engine determined by the electronic control unit and the fuel factor associated with the given fuel.

According to a possible embodiment of the second aspect, the first exhaust gas composition is one of: CO, CO2, HC, CH4, NOx, SOx, NH3, PM, PN, or BC.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

In the following detailed part of the disclosure, the invention will be explained in more detail with reference to exemplary embodiments shown in the drawings, in which:

figure 1 is a high angle front view of a large two-stroke diesel engine according to an exemplary embodiment,

figure 2 is a high angle side view of the large two-stroke engine of figure 1,

FIG. 3 is a diagrammatic schematic view of a large two-stroke engine according to FIG. 1, showing a system for determining a specific emission of the engine, an

FIG. 4 is a block diagram illustrating an electronic control unit and algorithm for determining specific emissions from the engine in the system.

Detailed Description

In the following detailed description, the internal combustion engine will be described in exemplary embodiments with reference to a large two-stroke, low-speed turbo-boosted internal combustion engine having a crosshead.

Fig. 1 and 2 are high perspective views of a large low speed turbo-boosted two-stroke internal combustion engine with a crankshaft 8 and a crosshead 9. The engine may be operated by diesel (compression ignition) or Otto cycle (timed ignition).

Fig. 3 shows a diagrammatic representation of the large low speed turbo-boosted two-stroke internal combustion engine of fig. 1 and 2 and its intake and exhaust systems. In this exemplary embodiment, the engine has six cylinders in series. Large low speed turbo-charged two-stroke diesel engines typically have four to fourteen cylinders in series, carried by a cylinder frame 23 carried by the engine mount 11. The engine may for example be used as a main engine in a marine vessel or as a stationary engine for operating a generator in a power plant. The total output of the engine may be, for example, in the range of 1,000 to 110,000kw.

In this exemplary embodiment, the engine is a two-stroke single-flow type compression ignition engine, having a scavenging port 18 at the lower region of the cylinder liner 1 and a central exhaust valve 4 at the top of the cylinder liner 1. The scavenging air is led from the scavenging air receiver 2 to the scavenging port 18 of each cylinder liner 1. The piston 10 in the cylinder liner 1 compresses scavenging air, and fuel is injected through the fuel injection valve 31 in the cylinder head 22, and then burned and exhaust gas is generated.

When the exhaust valve 4 is opened, the exhaust gas flows through the exhaust pipe associated with the cylinder liner 1 into the exhaust gas receiver 3 and up through the first exhaust conduit 19 to the turbine 6 of the turbo-booster 5, from where it flows away, through the second exhaust conduit via the economizer 20 to the outlet 21 and into the atmosphere. The turbine 6 drives a compressor 7 by means of a shaft, which is supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging air conduit 13 leading to the scavenging air receiver 2. The scavenging air in the duct 13 passes through an intercooler 14 for cooling the scavenging air.

When the compressor 7 of the turbo booster 5 does not deliver sufficient pressure for the scavenging air receiver 2, i.e. in low or partial load conditions of the engine, the cooled scavenging air is delivered via an auxiliary blower 16 driven by an electric machine 17. At higher engine loads, the turbo-booster compressor 7 delivers enough compressed scavenging air, and then the auxiliary blowers 16 are bypassed via the check valves 15.

The engine is operated using a given fuel, such as, for example, marine diesel, heavy fuel oil, (liquefied) natural gas, coal gas, biogas, methanol, ethanol, ethane, landfill gas, methane, ethylene or (liquefied) petroleum gas (non-exhaustive list), which is supplied by the fuel supply system 35.

The fuel supply system 35 includes the required pump/blower and fuel injection valve 31, and is controlled by the electronic control unit 50 via, for example, signal lines. The electronic control unit 50 receives engine operating parameters such as crankshaft speed and position, for example, as received by a crankshaft position sensor 39, and humidity of the air in the engine compartment, for example, as received by a humidity sensor 33, also connected to the electronic control unit 50, for example, by a signal line. This is a non-exhaustive list of operating parameters and the electronic control unit 50 may well receive other engine operating parameters such as, for example, scavenging air temperature and pressure, exhaust gas temperature and pressure, compression pressure, as is well known in the art.

A sensor 40 is arranged in the exhaust stack, which sensor is configured to detect the NOx concentration in the exhaust gas as a first component, for example in parts per million units. In one embodiment, sensor 40 is a commercially available NOx sensor.

In the exhaust stack there is also arranged a further sensor 41 configured to detect the concentration of the reference gas in the exhaust gas, in parts per million. The reference gas may be oxygen or carbon dioxide. In the present embodiment, oxygen will be used as a main example of the reference gas.

In the present embodiment, the

sensors

40 and 41 are shown in the second exhaust conduit, i.e. on the low pressure side of the turbo-booster (downstream of the turbine 6), but it should be understood that the

sensors

40, 41 may also be arranged on the high pressure side of the turbo-booster, i.e. upstream of the turbine 6.

Furthermore, the detection need not be performed in situ, and it should be understood that a sample may be taken from the exhaust gas and analyzed at another location.

A single sensor may be capable of sensing both the oxygen concentration in the exhaust gas and the NOx concentration in the exhaust gas, and thus, the sensor 40 and the sensor 41 may be formed of one single physical sensor.

In one embodiment (not shown), another sensor is provided that is configured to detect the presence of a second component of the exhaust gas. Note that neither the first exhaust gas component nor the second exhaust gas component can be oxygen, because oxygen is not considered to be a component of the exhaust gas that is to be determined as a specific amount of exhaust.

The signal from the sensor 40 that detects the NOx concentration in the exhaust gas and the signal from the sensor 41 that detects the concentration of the reference gas (oxygen or carbon dioxide) in the exhaust gas are transmitted to the electronic control unit 50 through signal lines, for example.

An exhaust gas treatment system 30, for example including an SCR reactor, may be provided on the high pressure side of the turbo booster 5 or on the low pressure side of the turbo booster 5. In the present embodiment, the exhaust gas treatment system is shown on the high pressure side of the turbo booster 5, but it should be understood that the SCR reactor may also be arranged at the low pressure side of the turbo booster 5. The SCR reactor is provided with a flow of a reactant, such as for example urea. The amount of reactant added to the exhaust gas in the SCR reactor is controlled by the electronic control unit 50.

Similarly, the engine control system (electronic control unit 50) in an embodiment applies specific NOx feedback control of EGR, water in fuel, direct water injection, low NOx fuel, humid air and/or engine performance regulation.

Fig. 4 shows an algorithm used by the electronic control unit 50 to determine the specific emission amount of the exhaust gas component of the engine.

The electronic control unit 50 is configured to determine the difference in oxygen concentration between the inlet air and the outlet gas. The signal from the humidity sensor 33 allows the electronic control unit 50 to determine the humidity of the air in the engine room and estimate the oxygen concentration of the air in the engine room, i.e., the oxygen concentration in the intake air, by an algorithm. The algorithm reflects the functional relationship between the oxygen content and the humidity of the ambient air. The oxygen content in the dry air was 20.95%. In one embodiment, the algorithm determines that the inlet air oxygen concentration [ mol% ] is equal to:

20.95X (100/(100 + inlet air molar humidity [ mol% ]))

The electronic control unit 50 is also configured to determine the specific NOx emission amount from the detected concentration of NOx in the exhaust gas and from the determined difference in oxygen concentration between the intake air and the exhaust gas.

In an embodiment, the electronic control unit 50 is configured to determine the instantaneous fuel efficiency of the engine and to apply the determined fuel efficiency as a factor in determining the specific amount of emission of an exhaust gas component, such as, for example, NOx. In order to determine the instantaneous fuel efficiency, the electronic control unit 50 is provided with look-up tables and/or algorithms and/or with a computer model of the engine, and the instantaneous fuel efficiency is determined or simulated according to the instantaneous operating conditions.

In one embodiment, the electronic control unit 50 is configured to apply a fuel factor associated with the fuel when used to determine a specific amount of NOx emissions.

The fuel factor reflects the heat release of a particular fuel using each mass unit of oxygen. This factor is also known in the art as the Thornton factor. Many fuels with fuel factors of about 12.8MJ/kg oxygen consumption, such as diesel, heavy fuel oil, methane, methanol, ethane, ethanol, propane and butane, are used in large two-stroke internal combustion engines. Thus, the fuel factor value may be used regardless of which of the fuels listed above is used to power the engine.

If carbon dioxide is used as the reference gas, this needs to be reflected in the fuel factor. When determining the heat release based on the CO2 increase between the inlet air and the exhaust gas, the fuel factor is different. The fuel factor associated with CO2 is sensitive to the type of fuel used and will need to be adjusted according to the particular fuel used.

The electronic control unit 50 is configured to determine the specific NOx emission amount by dividing the detected NOx concentration by the product of the determined difference in oxygen concentration between the intake air and the exhaust gas and the adjustment factor. The adjustment factor takes into account the type of fuel used and the fuel efficiency of the engine in order to achieve an accurate estimate of the energy delivered at the crankshaft of the engine. As such, the adjustment factors include the instantaneous fuel efficiency of the engine as determined by the electronic control unit 50 and the fuel factor associated with the fuel used to run the engine.

Specifically, as shown in FIG. 4, the algorithm determines the specific NOx emission by dividing the detected NOx concentration by the product of the determined difference in oxygen concentration between the intake air and the exhaust gas and the instantaneous fuel efficiency of the engine determined by the algorithm and the fuel factor associated with the fuel used to run the engine. The algorithm returns the specific NOx emissions in g/kWh.

In one embodiment, the algorithm uses a corrected O2 concentration, where the inlet oxygen content is corrected for the difference in moles in the exhaust gas and air. In one embodiment, this is accomplished by introducing a second fuel constant that reflects the stoichiometric molar ratio between the exhaust gas and the inlet air. Then, based on the actually measured exhaust oxygen concentration, the actual correction amount is instantaneously calculated by the algorithm by linear interpolation between the stoichiometric ratio and pure air. However, it should be understood that the corrected O2 concentration may be determined in other ways well known to those skilled in the art.

In one embodiment, the algorithm uses the following equation:

specific NOx [ g/kWh ] = measured NOx [ ppm ]/(fuel factor engine efficiency corrected O2 concentration difference [% ])

In another embodiment, the algorithm uses the following equation:

specific NOx [ g/kWh ] = measured NOx [ ppm ]/(fuel factor engine efficiency corrected O2 consumption [% ])

O2 consumption [% ] "is the percentage reduction in O2 concentration. It is applied as a percentage O2 concentration reduction, or as a% O2 concentration reduction or O2 concentration difference, which may be a maximum of 20.95% (when all O2 is consumed).

In one embodiment, the fuel factor, or another correction factor, also takes into account the conversion from exhaust mass flow to molarity used in this embodiment.

The above embodiments have described the use of oxygen as the reference gas. However, it is to be understood that carbon dioxide may be used equally as a reference gas. When using carbon dioxide as a reference counter, the increase in carbon dioxide between the inlet air and the exhaust gas should be determined, rather than the decrease in oxygen content between the inlet air and the exhaust gas.

In one embodiment, the electronic control unit 50 is configured to control the operation of the engine based on the determined specific NOx emission. This may include, for example, controlling the timing of fuel injection, exhaust valve timing, and operation of the exhaust gas treatment system 30 based on the specific NOx emissions determined, preferably to stay within legal limits. For NOx treatment systems, the control involves controlling the amount of reductant applied to the exhaust gas for selective catalytic reduction based on the specific NOx emissions determined.

The embodiments have been described above with reference to the first exhaust gas constituent being NOx. However, it should be understood that the exhaust gas constituents may be any constituents present in the exhaust gas, such as, for example: carbon monoxide (CO), carbon dioxide (CO 2), hydrocarbons (HC), methane (CH 4), oxides of sulfur (SOx) (SO 2+ SO 3), ammonia NH3, particulate Matter (PM), particle Number (PN), or carbon Black (BC), the above being a non-exhaustive list.

Further, as described above, the second exhaust gas component may also be measured and the specific discharge amount for the second exhaust gas component may be determined simultaneously with the specific discharge amount of the first exhaust gas component. The second exhaust gas component may be any of the exhaust gas components listed above.

The different aspects and embodiments have been described in connection with different embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor, control unit or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

Claims

1. An internal combustion engine configured to operate on a given fuel and to produce exhaust gas during operation by combustion of the given fuel with intake air,

the engine includes:

an electronic control unit (50) for controlling the operation of the motor,

a sensor (40) configured to detect a concentration of a first exhaust gas constituent in the exhaust gas,

a sensor (41) configured to detect a concentration of a reference gas in the exhaust gas, the reference gas being oxygen or carbon dioxide,

characterized in that said electronic control unit (50) is configured to:

determining a difference in reference gas concentration between the inlet air and the outlet gas, and,

determining a specific emission of the first exhaust gas constituent based on the detected concentration of the first exhaust gas constituent and based on the determined difference in reference gas concentration between the inlet air and the exhaust gas.

2. An engine according to claim 1, wherein the electronic control unit (50) is configured to determine a reference gas concentration in the inlet air as a function of the humidity of the inlet air.

3. An engine according to claim 1 or 2, wherein the electronic control unit (50) is configured to determine an instantaneous fuel efficiency of the engine, and wherein the electronic control unit (50) is configured to apply the determined fuel efficiency as a factor in determining the specific emission of the first exhaust gas constituent.

4. An engine according to claim 3, wherein the electronic control unit (50) is provided with a look-up table and/or algorithm and/or with a computer model of the engine to determine the instantaneous fuel efficiency based on instantaneous operating conditions.

5. The engine according to claim 1 or 2,

the electronic control unit (50) is configured to apply a fuel factor associated with the given fuel in determining a specific emission of the first exhaust gas constituent.

6. An engine according to claim 1 or 2, wherein the electronic control unit (50) is configured to determine the specific emission amount of the first exhaust gas component by dividing the detected concentration of the first exhaust gas component in the exhaust gas by the determined product of the difference between the reference gas concentrations between the inlet air and the exhaust gas and an adjustment factor.

7. The engine of claim 6, wherein said adjustment factor comprises an instantaneous fuel efficiency of said engine as determined by said electronic control unit.

8. The engine of claim 6, wherein the adjustment factor comprises a fuel factor associated with the given fuel.

9. An engine according to claim 1 or 2, wherein the electronic control unit (50) is configured to determine the specific emission of the first exhaust gas constituent by dividing the detected concentration of the first exhaust gas constituent in the exhaust gas by the determined product of the reference gas concentration difference between the inlet air and the exhaust gas and the instantaneous fuel efficiency of the engine determined by the electronic control unit (50) and the fuel factor associated with a given fuel.

10. An engine according to claim 1 or 2, wherein the first exhaust gas constituent is one of: CO, CO2, HC, CH4, NOx, SOx, NH3, PM, PN, or BC.

11. An engine according to claim 1 or 2, wherein the first exhaust gas constituent is NOx, the engine is configured to operate under the control of the electronic control unit (50), and the electronic control unit (50) is configured to control the operation of the engine in dependence on the determined specific NOx emission.

12. An engine according to claim 1 or 2, wherein the first exhaust gas constituent is NOx, the engine comprises a NOx treatment system (30) configured to operate under the control of the electronic control unit (50), and the electronic control unit (50) is configured to control the operation of the NOx treatment system (30) in dependence on the determined specific NOx emission.

13. An engine according to claim 12, wherein the NOx treatment system (30) is configured to apply a reducing agent to the exhaust gas, and wherein the amount of reducing agent applied to the exhaust gas is controlled by the electronic control unit (50) in dependence on the determined specific NOx emission.

14. A method for determining a specific emission amount of a first exhaust gas constituent of an exhaust gas producing internal combustion engine, the method comprising:

detecting a concentration of a first exhaust gas component in the exhaust gas,

detecting a concentration of a reference gas in the exhaust gas, the reference gas being oxygen or carbon dioxide,

it is characterized in that the preparation method is characterized in that,

determining a difference in reference gas concentration between the inlet air and the outlet gas,

15. The method of claim 14, comprising: determining a reference gas concentration in the intake air based on the humidity of the intake air.

16. The method according to claim 14 or 15, comprising: determining an instantaneous fuel efficiency of the engine, and applying the determined fuel efficiency as a factor in determining the specific emission amount of the first exhaust gas constituent.

17. The method of claim 16, comprising: applying a look-up table and/or algorithm and/or a computer model of the engine when determining the instantaneous fuel efficiency based on instantaneous operating conditions.

18. A method according to claim 14 or 15, wherein the engine is operated using a given fuel, the method comprising applying a fuel factor associated with the given fuel in determining the specific emission of the first exhaust gas constituent.

19. The method according to claim 14 or 15, comprising: determining a specific emission amount of the first exhaust gas constituent by dividing the detected concentration of the first exhaust gas constituent in the exhaust gas by the product of the determined reference gas concentration difference between the inlet air and the exhaust gas and an adjustment factor.

20. The method of claim 19, wherein the engine includes an electronic control unit, and the adjustment factor includes an instantaneous fuel efficiency of the engine determined by the electronic control unit.

21. The method of claim 19, wherein the engine is operated using a given fuel, and the adjustment factor comprises a fuel factor associated with the given fuel.

22. A method according to claim 14 or 15, wherein the engine comprises an electronic control unit and is operated using a given fuel, the method comprising: determining a specific emission of the first exhaust gas constituent by dividing the detected concentration of the first exhaust gas constituent in the exhaust gas by the product of the determined reference gas concentration difference between the intake air and the exhaust gas and the instantaneous fuel efficiency of the engine determined by the electronic control unit and the fuel factor associated with the given fuel.

23. The method of claim 14 or 15, wherein the first exhaust gas constituent is one of: CO, CO2, HC, CH4, NOx, SOx, NH3, PM, PN, or BC.