METHOD FOR DETERMINING FUEL QUALITY

Description

[0001] The invention relates to a method for determining fuel quality. The fuel is supplied in gaseous form to an internal combustion engine and stored in a pressure vessel in at least partially liquefied form. The fuel is, in particular, LNG or another liquefied gas which, due to its vapor pressure and boiling curve, requires the pressure vessel used for storing the fuel to be vented after a certain downtime.

[0002] LNG ( "liquefied natural gas ") , Liquefied methane gas or natural gas is now seen as an alternative to diesel fuel in the field of motor vehicles (e.g. cars, trucks, but also shipping, etc.).

[0003] LNG is stored as a cryogenic, liquefied gas in insulated tanks and storage containers (pressure vessels). When a vehicle is stationary, no LNG or vaporized methane is consumed, so the pressure in the vehicle's pressure vessel rises. Shortly before the maximum permissible pressure is reached, the pressure vessel is released to the atmosphere via at least one safety valve. This causes the pressure vessel to lose its contents and the vehicle to lose its remaining range.

[0004] LNG, in particular, does not always have the same composition. The contents of CH4, CO2, N2, and H2, as well as higher hydrocarbons such as C2H6, C2H4, C3H8, and higher hydrocarbons up to hexane, as different components of the fuel, can vary. Internal combustion engines that burn LNG rely on the high knock resistance of CH4 (the property of a fuel or a component of a fuel not to ignite prematurely, e.g., in a gasoline engine only due to compression). Knowing the composition of a fuel is particularly important for the operation of an internal combustion engine.

[0005] DE 10 2005 009 823 A1 discloses a system for monitoring a compressed gas stored in a pressure vessel.

[0006] From DE 10 2007 022 610 A1 a compressed gas storage system with an integrated pressure relief device is known.

[0007] DE 10 2012 024 717 A1 is directed to a vehicle with a liquid gas tank and an overpressure relief line.

[0008] DE 601 31 484 T2 describes a fuel system in which the integrity of a fuel vapor recovery system is monitored via on-board diagnostics.

[0009] A monitoring system for a pressure vessel is known from DE 602 08 563 T2.

[0010] From KR 2011 0062638 A, a fuel tank arrangement is known in which the proportion of fuel discharged from a pressure vessel is measured via a safety device and thus the quality of the residual fuel in the pressure vessel is determined.

[0011] The object of the present invention is to at least partially solve the problems cited with reference to the prior art. In particular, a method for determining fuel quality is to be proposed so that safe operation of the internal combustion engine can be ensured.

[0012] A method having the features according to patent claim 1 contributes to the solution of these objects. Advantageous further developments are the subject of the dependent patent claims.

[0013] A method for determining the fuel quality of a fuel is proposed. The fuel is supplied in gaseous form to an internal combustion engine, wherein the fuel is an at least partially liquefied fuel stored in a pressure vessel. When a limit pressure is reached, the pressure vessel is (regularly) released to the environment via a safety device (e.g., a safety valve or similar) by removing a gaseous component of the fuel from the pressure vessel. The method comprises at least the following step: a) Determining the fuel quality of the fuel stored in the pressure vessel, taking into account at least one remaining discharge of a gaseous component of the fuel via the safety device, wherein a forecast regarding a quantity of the gaseous component of the fuel to be discharged via the safety device at a future point in time is taken into account.

[0014] The fuel is LNG or another liquid gas fuel. The fuel is stored in a pressurized container and fed into an internal combustion engine for combustion. The internal combustion engine can, for example, be installed in a motor vehicle to power the vehicle.

[0015] The process can be used in particular in a motor vehicle or in a facility for storing liquefied gases. When storing a fuel, e.g., LNG in motor vehicles, higher proportions of more easily volatile fuel components can be discharged via the safety device (pressure relief valve, safety valve), which can change the composition of the fuel remaining in the pressure vessel. Due to its material properties, CH4, in particular, can be the first to evaporate from the mixture of various fuel components, or can evaporate in higher proportions, thereby contributing to the pressure buildup in a gas phase in a pressure vessel.

[0016] During the cyclical depressurization of the pressure vessel or the fuel, this component, e.g., CH4, may be disproportionately released into the atmosphere. This increases the concentration or proportion of the other components, and in particular the other hydrocarbons, in the remaining liquid fuel (or fuel mixture). In particular, this can change the material properties of the fuel, particularly with regard to knock resistance. However, a decrease in knock resistance can lead to the well-known problems with fuel combustion and requires appropriate countermeasures, such as adjusting the injection quantity.

[0017] Using the proposed method, it is now possible, in particular, to determine the changed composition of the fuel intended for combustion in the internal combustion engine and to adjust the parameters influencing combustion accordingly. In particular, the fuel quality is determined before an internal combustion engine is started up and before the fuel is combusted.

[0018] In particular, this allows for a predictive determination of fuel quality. This allows a motor vehicle user to be informed, for example, directly at the vehicle or via telemetry, that the fuel quality is no longer sufficient for the proper operation of the internal combustion engine or, in particular, that the internal combustion engine should no longer be operated. This can prevent, in particular, damage to the motor vehicle due to insufficient fuel quality, e.g., after the vehicle has been idle for an extended period.

[0019] Telemetrically (or telemetrically transmitted) means in particular that information (fuel quality, etc. or data sets) is transmitted to a spatially separate receiving point (e.g. via radio) (e.g. to the motor vehicle or to a mobile phone, a computer, etc.).

[0020] Data records can be determined, for example, in a control unit on the pressure vessel or in the motor vehicle and at least displayed, collected and recorded or even evaluated at the receiving point.

[0021] Fuel quality is preferably taken into account during the operation of an internal combustion engine. In particular, the parameters influencing combustion are modified or adjusted taking fuel quality into account (e.g., injection quantity, injection timing, ignition timing, mixture formation, compression, etc.).

[0022] Preferably, at least a knock resistance of the fuel is determined for the fuel quality.

[0023] In particular, taking fuel quality into account, the internal combustion engine is prevented from being started.

[0024] In particular, for step a), a fuel quality determined on the basis of a combustion process in the internal combustion engine is taken into account.

[0025] In particular, at least one of the following parameters (of the fuel or the internal combustion engine, e.g., a fuel-dependent property of the internal combustion engine) is determined based on a combustion process (or several combustion processes): energy content of the fuel; methane number of the fuel; power of the internal combustion engine; hydrogen to carbon ratio (e.g., determined by air mass measurement and lambda sensor); exhaust gas composition (CO2 and / or O2 content). These data can be used, in particular, to verify or calibrate the fuel quality determined in step a).

[0026] Furthermore, for step a), information regarding the fuel introduced into the pressure vessel can be taken into account. This information can be entered manually or transmitted telemetrically (e.g., to a control unit). The information can include at least one of the following fuel parameters: methane number, energy content, methane content, etc. In particular, the information can be transmitted during a refueling process of the pressure vessel.

[0027] In particular, the actual or presumed, determined, or verified composition of the fuel can be taken into account in the process. This knowledge of the composition enables a more accurate prediction of the evaporation behavior as well as the resulting gas phase pressure and the amount of fuel (or methane, i.e., CH4) released via the safety device.

[0028] The actual composition can be determined by the vehicle itself, for example, using a device for determining the current fuel composition in the pressure vessel itself or in fuel-carrying components. Furthermore, the determination can be made by evaluating the combustion behavior of the fuel in the internal combustion engine or by transmitting the fuel quality from a refueling station with known fuel qualities. The fuel quality can also be entered manually. A combination of the above options may be advantageous, particularly for plausibility checks.

[0029] In particular, a fuel or its composition is determined. Based on the determined composition, a model can be considered that describes the evaporation or composition of the vapor. In particular, the fuel or its composition can be determined using sensors, such as mass flow meters or measurements and / or pressure and temperature-compensated flow measurements.

[0030] In particular, for step a) at least one of the following environmental conditions is taken into account: a climatic environmental condition (humidity, air temperature, air pressure, predicted change in the ambient condition, etc.) of the pressure vessel, a geographical environmental condition (location, e.g. ferry, parking garage, tunnel, residential area, etc.; altitude in relation to sea level, solar radiation, etc.; country or state; predicted change in the ambient condition, e.g. as a result of the movement of the motor vehicle, possibly taking into account a navigation system, etc.) of the pressure vessel, a legal regulation existing at the location of the pressure vessel, an environmental condition of the pressure vessel determined by a sensor system of the pressure vessel or the motor vehicle (camera, radar, ultrasound) (taking into account living beings, buildings, enclosed spaces, etc. in the vicinity of the motor vehicle).

[0031] Furthermore, according to the invention, for step a), a forecast regarding the quantity of gaseous components of the fuel to be discharged via the safety device at a future point in time is taken into account.

[0032] When predicting the amount of fuel to be released via the safety device at a future point in time, it is particularly important to consider the fact that, for example, the pressure vessel must be released at a specific point in time. The prediction is used to predict (predict) the fuel quality (remaining in the pressure vessel) at a future point in time or to determine the development of the fuel quality of the fuel remaining in the pressure vessel over time.

[0033] In particular, by taking one or more environmental conditions into account, it can be ensured that the fuel quality can be determined or predicted with greater accuracy. Regarding the prognosis, reference is made to the subsequently published DE 10 2018 209 423.3. The methods explained therein for determining the point in time at which a pressure in the pressure vessel reaches a pressure limit (first limit pressure) can be applied in this case.

[0034] In particular, for step a) at least one of the following parameters can be taken into account: temperature in the pressure vessel, pressure in the pressure vessel, refuelling quantity or fill level of the pressure vessel.

[0035] A motor vehicle is further proposed, at least having an internal combustion engine operable with a gaseous fuel and a pressure vessel for storing the at least partially liquefied fuel (LNG or other liquid gas fuel), as well as a control unit configured to carry out the described method. The pressure vessel has a safety device for releasing the pressure from the pressure vessel to the environment. The control unit is designed to carry out the method or carries out the method. The internal combustion engine can be started up by the control unit, and its operation can be controlled by the control unit. Furthermore, the method can also be carried out by a computer or by a processor of a control unit.

[0036] Accordingly, a data processing system (in particular a control unit or part thereof) is also proposed, which comprises a processor which is adapted / configured to carry out the method or part of the steps of the proposed method.

[0037] A computer-readable storage medium may be provided which comprises instructions which, when executed by a computer / processor, cause the computer / processor to carry out the method or at least some of the steps of the proposed method.

[0038] The statements regarding the method are particularly transferable to the motor vehicle, the system, the storage medium or the computer-implemented method and vice versa.

[0039] In particular, the method also enables a user of the motor vehicle to be informed about a fuel quality, a change in the fuel quality, a (possibly only expected) limited use of the motor vehicle or a warning regarding the commissioning of the internal combustion engine.

[0040] The method can also be used outside of motor vehicles, for example to monitor pressure vessels or systems for storing liquid gases.

[0041] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily dictate any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment.

[0042] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, it should be noted that the figures, and in particular the proportions shown, are only schematic. They show: Fig. 1: a motor vehicle; Fig. 2: a first diagram; and Fig. 3: a second diagram.

[0043] Fig. 1 shows a motor vehicle 6 with an internal combustion engine 2 operable with a gaseous fuel 1 and a pressure vessel 3 for storing the at least partially liquefied fuel 1, as well as a control unit 7 configured to carry out the described method. The pressure vessel 3 has a safety device 4 for depressurizing the pressure vessel 3 to an environment 5.

[0044] Fig. 2 shows a first diagram. It depicts a first sequence of the method. In the pressure vessel 3, the fuel quality of the fuel 1 stored therein can be determined based on several parameters. These parameters include, for example, a first temperature 8 and a first pressure 9 of an environment 5, the detection of a refueling quantity 10, the detection of a fill level 11, a second pressure 12, and a second temperature 13 within the pressure vessel 3, as well as the detection of a quantity dispensed via the safety device 4 and, if applicable, the fuel quality of the gaseous fuel 1.

[0045] The internal combustion engine 2 can be monitored with respect to the parameters power 14, fuel consumption 15, and intake air flow 16. Furthermore, the knock resistance 17 of the combustion processes can be checked.

[0046] Furthermore, the parameters of the exhaust gas 18 can be checked, e.g. by measuring the CO2 concentration 18, the O2 concentration 19 and (if derived therefrom) by determining the hydrogen / carbon ratio 20.

[0047] The described parameters can be evaluated via the control unit 7.

[0048] Fig. 3 shows a second diagram. It illustrates a second sequence of the procedure.

[0049] In the pressure vessel 3, the quantity and, if applicable, fuel quality of the gaseous fuel 1 delivered via the safety device 4 (boil-off detection 27) are determined, taking into account the second pressure 12 and second temperature 13 within the pressure vessel 3 as well as the fill level 11. Furthermore, an indication 23 regarding the fuel 1 introduced into the pressure vessel 3, e.g., from a refueling system, is taken into account. Based on this, new properties 22 or the new composition of the fuel 1 are determined.

[0050] Based on these new properties 22, a knock resistance 17 is determined. This knock resistance 17 is taken into account for the operation or commissioning of the internal combustion engine 2. Based on the knock resistance 17, a decision 24 regarding the operation of the internal combustion engine 2 is therefore made.

[0051] Using the internal combustion engine 2 put into operation, the parameters energy content 25, methane number 26, power 14 and hydrogen / carbon ratio 21 can be determined, which can be used for further determination or verification / plausibility / calibration of the fuel quality or the properties 22 of the fuel 1.

[0052] The findings obtained can then be further used in connection with the parameters recorded in pressure vessel 3. List of reference symbols

[0053] 1Fuel 2Internal combustion engine 3Pressure vessel 4Safety device 5Environment 6Motor vehicle 7Control unit 8First temperature 9First pressure 10Fuel quantity 11Fill level 12Second pressure 13Second temperature 14Power 15Consumption 16Intake air quantity 17Knock resistance 18Exhaust gas 19CO2 concentration 20O2 concentration 21Hydrogen / carbon ratio 22New property 23Information 24Decision 25Energy content 26Methane number 27Boil-off

Claims

1. Method for predicting a fuel quality of a fuel (1), which is supplied in gaseous form to an internal combustion engine (2), at a future time or determining the development of the fuel quality of the fuel (1) remaining in a pressure vessel (3) over time, wherein the fuel (1) is an at least partially liquefied fuel (1) stored in the pressure vessel (3), wherein, when a limit pressure is reached, the pressure vessel (3) is depressurized to an environment (5) via a safety device (4) by way of a gaseous component of the fuel (1) being removed from the pressure vessel (3); wherein the method comprises at least the following step: (a) determining the fuel quality of the fuel (1) stored in the pressure vessel (3), taking into account at least one ongoing discharge of a gaseous component of the fuel (1) via the safety device (4), wherein a forecast relating to a quantity of the gaseous component of the fuel (1) to be discharged via the safety device (4) at a future time is taken into account.

2. Method according to Claim 1, wherein the fuel quality is determined before commissioning an internal combustion engine (2) and before carrying out a combustion process on the fuel (1).

3. Method according to either of the preceding claims, wherein the fuel quality is taken into account during operation of an internal combustion engine (2).

4. Method according to any of the preceding claims, wherein a knock resistance of the fuel (1) is determined for the fuel quality.

5. Method according to any of the preceding claims, wherein commissioning of the internal combustion engine (2) is prevented taking into account the fuel quality.

6. Method according to any of the preceding claims, wherein a fuel quality determined on the basis of a combustion process in the internal combustion engine (2) is taken into account for step a).

7. Method according to any of the preceding claims, wherein an indication relating to the fuel (1) introduced into the pressure vessel (3) is taken into account for step a).

8. Method according to any of the preceding claims, wherein at least one of the following environmental conditions is taken into account for step a): • a climatic environmental condition of the pressure vessel (3), • a geographical environmental condition of the pressure vessel (3), • a legal requirement applicable at the site of the pressure vessel (3), • an environmental condition of the pressure vessel (3) determined by a sensor system of the pressure vessel (3).

9. Motor vehicle (6), at least comprising an internal combustion engine (2) which can be operated with a gaseous fuel (1) and a pressure vessel (3) for storing the at least partially liquefied fuel (1), wherein the pressure vessel (3) has a safety device (4) for depressurizing the pressure vessel (3) to an environment (5), and a control unit (7), which is designed for carrying out a method according to any of the preceding claims; wherein the internal combustion engine (2) can be commissioned by the control unit (7) and operation of the internal combustion engine can be controlled by the control unit (7).