DETERMINING FUEL PROPERTIES AND THEIR INFLUENCE ON EXHAUST EMISSIONS DURING THE OPERATION OF AN ENGINE

Description

[0001] Alternative and synthetic fuels, such as fatty acid methyl esters (FAME), vegetable oil, liquefied biomass (biomass-to-liquid (BTL)), liquefied gases (gas-to-liquid (GTL)), etc., are gaining increasing importance. However, they differ significantly in their material properties, such as density, viscosity, calorific value, heat capacity, aromatic content, oxygen content, hydrogen content, carbon content, inorganic impurities (alkali metals, alkaline earth metals), phosphorus content, sulfur content, storage stability, boiling point, and speed of sound, etc., from the standardized and approved fuels used for engine design and approval, or required by law.

[0002] This means that when internal combustion engines are operated with these non-standard fuels, emissions, exhaust temperatures, maximum engine power, and peak cylinder pressures may change.

[0003] The altered exhaust emissions may lead to exceedances of legally prescribed limits. For example, the use of FAME increases NOx emissions while decreasing particulate emissions.

[0004] If exhaust gas temperatures drop due to a different calorific value or ignition delay, the activation temperatures of catalytic converters may no longer be reached, or may occur less frequently, resulting in a deterioration of emissions. Conversely, an increase in exhaust gas temperatures can lead to thermal damage to the catalytic converters.

[0005] At the same time, the use of "biofuels" leads to an accelerated chemical deactivation of the catalysts for exhaust gas aftertreatment due to the increased input of alkali and alkaline earth metals, phosphorus and sulfur.

[0006] Since the fuel system and the engine oil circuit are usually not hermetically sealed, this leads to a mixing of fuel and engine oil. The use of non-approved fuel therefore results in an uncontrollable change in the properties of the engine oil, which in turn can damage the engine.

[0007] In order to recognize this and be able to react if necessary, it would be useful to determine the fuel properties during operation.

[0008] German patent DE 103 46 314 A1 describes a sensor of this type that can be used to determine the viscosity of fuel. For this purpose, the fuel is set into vibration by an actuator, and these vibrations are detected by a pressure sensor. The viscosity can then be determined by evaluating the pressure profile. The disadvantage of this method is the requirement for an actuator, which increases costs and maintenance.

[0009] German patent applications DE 101 52 236 A1, DE 102 17 376 A1, and DE 102 17 379 A1 describe methods for determining fuel properties from the fuel's vapor pressure. This involves measuring the vapor pressure in the fuel tank and / or the fuel system. For this to work, it is essential that the engine is not drawing any fuel from the fuel system; that is, the engine must be switched off. Therefore, this method is not applicable to engines where switching off is not possible, such as those used in generators, combined heat and power plants, compressors, etc. Furthermore, determining the vapor pressure requires isolating the volume in which the pressure measurement is taken from the surrounding environment, or even creating a slight vacuum within this volume. This necessitates the use of shut-off valves and / or vacuum pumps, resulting in high costs and correspondingly high maintenance requirements.

[0010] German patent DE 100 15 162 A1 describes a method in which the combustion noise is detected and the quality of the injection, i.e., the injection start or the injection rate, is determined from it. The disadvantage of this method is that the combustion noise cannot be used to determine the type of fuel used, as it is additionally influenced by several other factors, such as the tolerances, degree of contamination, or wear of the injector nozzle, the injection pump, the intake valves, the exhaust valves, the exhaust turbocharger, etc.Since combustion noise is highly dependent on the energy released, this method, due to the typically volumetric addition of fuel to the combustion chamber, only allows for the determination of the volumetric heating value, the start of injection, or the injection rate with sufficient accuracy. Determining viscosity or compressibility is not possible, and consequently, no definitive statements about the fuel used can be made. Rather, the method primarily serves to improve engine smoothness.

[0011] In DE 199 55 796 B4, fuels are differentiated by measuring the acceleration of the crankshaft with angle resolution, and thus the energy released. Analogous to patent DE 100 15 162 A1, this method only allows the determination of the volumetric calorific value with sufficient accuracy; determining viscosity or compressibility is not possible, meaning that unambiguous statements about the fuel used are not possible here either. Rather, this method also primarily serves to improve engine smoothness.

[0012] German patent DE 40 19 083 A1 describes a method in which fuel quality is determined using a lambda or fuel quality sensor and the engine parameters are changed accordingly. The disadvantage of these sensors is that they are very sensitive and expensive.

[0013] Furthermore, the methods described in WO 2005 / 021952 A1 and WO 2008 / 007128 A1 deal with determining fuel quality or fuel type through vibration analysis. This involves coupling a vibration into the fuel and then recording and subsequently analyzing its vibration behavior using appropriate vibration sensors. Based on the result of the vibration analysis, a conclusion is drawn about the fuel quality or fuel type. It is further proposed that injection timing and / or injection quantities be varied depending on the determined fuel quality or the deviation from a fuel reference quality. However, this approach is not suitable for responding to critical deviations of raw exhaust emissions from a target raw exhaust emission level.

[0014] Document EP 1 775 584 A2 relates to a method and a device for assessing the quality of the fuel currently being burned in an internal combustion engine. It is proposed that a fuel-specific factor k be determined using a sensor that, for example, records the combustion chamber pressure and / or a lambda value, and an algorithm. In a further embodiment, the operating parameters (injection quantity, injection start, injection end, injection pattern, exhaust gas recirculation rate, etc.) are corrected using the factor k.

[0015] Furthermore, DE 103 27 978 A1 discloses a fuel-powered drive system with an internal combustion engine for a motor vehicle, including a computing device for determining the fuel quality, and a method for determining the fuel quality. Such a drive system can include an exhaust system downstream of the internal combustion engine for discharging an exhaust mixture of at least two exhaust gases produced by the combustion of a fuel. The exhaust system includes an exhaust gas sensor arrangement for measuring the quantity of at least one exhaust gas discharged by means of the exhaust system, and the computing device is configured to determine the fuel quality as a function of the quantity of at least one exhaust gas.

[0016] Ultimately, EP 2 037 112 A1 relates to a fuel discrimination system that distinguishes whether the fuel supplied to a machine is normal fuel or not, and performs an appropriate control action based on the discrimination result. For this purpose, a fuel quality detection device measures the quality of the supplied fuel at a predetermined time. A data generation device generates measurement data based on the measurement result, the remaining fuel quantity, and the ambient temperature. Based on the analysis of the measured data, a data analysis device limits engine power, issues a warning to the user, and adjusts the user's assessment.

[0017] Furthermore, the sensors are usually used to improve the smoothness of the engine's running and / or its starting behavior; an adjustment of emissions is not described, nor is the influence of non-approved fuel on the engine oil properties.

[0018] Based on this, the invention aims to determine the fuel properties in order to optimize the effectiveness of the exhaust aftertreatment system and to protect it. This objective is achieved according to the characterizing part of claim 1.

[0019] The core of the invention lies in using pressure fluctuations in the fuel system, which occur during discontinuous fuel delivery and / or withdrawal, to determine the type of fuel being used and / or the exhaust emissions. These pressure fluctuations are influenced by the density, viscosity, speed of sound, and compressibility of the fuel being used. If these fluctuations are recorded using a pressure sensor and evaluated in an electronic control unit, a very simple and inexpensive method for differentiating between different fuels is available. Using this information, it is possible to determine the exhaust emissions resulting from the currently used fuel.

[0020] If the unauthorized fuel leads to a permanent and irreversible change in emissions, it is possible to estimate these changes using the identified type of fuel used and the operating time.

[0021] The frequencies of the oscillation, including higher-order frequencies, their maxima, the pressure rise and / or the pressure drop can be used as evaluation parameters. For simple frequency analysis, it is advisable to perform a Fourier transform, particularly a discrete and / or fast Fourier transform, on the measured pressure signal.

[0022] If the fuel delivery system is already equipped with a sensor on the high-pressure side, this can be used to monitor the pressure profile. This is the case, for example, with accumulator injection systems such as the common rail system, where the fuel is pumped into a pressure accumulator, the so-called rail, at a specific pressure and then supplied to the combustion chamber via injectors, which are usually individually controlled. To ensure optimal system performance and prevent damage from excessively high fuel pressures, the pressure on the high-pressure side is measured and regulated.

[0023] Since viscosity depends on the temperature of the medium, it makes sense to determine the temperature of the fuel using a temperature sensor.

[0024] When fuel is pumped to the injection pressure, friction in the fuel pump and the compression work performed cause the fuel temperature to rise. Since this temperature increase depends on the fuel's heat capacity, it can be used to further refine the determination of the fuel type. For this purpose, the fuel temperature is measured on both the low-pressure and high-pressure sides of the pump, and the heat capacity is then calculated from the temperature difference and the delivered fuel volume or mass flow rate.

[0025] To determine the temperature on the low-pressure side, the ambient temperature or the temperature in the fuel tank can also be used as a first approximation.

[0026] If the fuel type and / or a deviation from the standard has been detected, this information can be stored in an electronic control unit and, if necessary, read out at a later time.

[0027] Since the manufacturer's warranty is usually limited to the fact that the internal combustion engine is operated with approved fuel, this function can serve as proof of correct refueling.

[0028] It is also possible to display the fuel type and / or information about the use of unauthorized fuel using an optical display unit.

[0029] If a deviation in exhaust emissions is detected due to the use of non-reference fuel, it is possible to adjust these emissions to match those of standard fuel by varying the engine's operating parameters and / or the aftertreatment system. For example, by changing engine parameters such as injection timing and / or injection pressure and / or the intervals and / or durations of split injections and / or the exhaust gas recirculation rate and / or the fuel / air ratio, the emissions can be brought back into line with the level of standard fuel.

[0030] When using an aftertreatment system to comply with emissions regulations, the control parameters for emissions compliance can also be adjusted accordingly. For example, in SCR systems (selective catalytic reduction of nitrogen oxides), the amount of reducing agent supplied can be varied. With NOx storage catalysts and particulate filters, it is possible to change the ratio between storage and regeneration.

[0031] Modifying engine and aftertreatment parameters is also conceivable, for example, by changing the exhaust gas temperature and / or mass through engine-side adjustments such as injection timing, injection quantity, injection intervals, exhaust gas recirculation rate, etc. Since the temperature and the mass of exhaust gas passed through the aftertreatment system are closely related to the desired conversion rates, this results in a change in the conversion capacity of the aftertreatment system.

[0032] Furthermore, it is conceivable to infer long-term changes in exhaust emissions from the duration and / or the cumulative quantity of non-approved fuel. This can be caused, for example, by increased coking of the injectors and / or accelerated chemical deactivation of the aftertreatment system. Due to this irreversible damage, the subsequent use of approved fuel usually does not result in emissions levels comparable to those before the use of the non-approved fuel.

[0033] Here too, countermeasures can be taken by changing the operating parameters of the engine and / or the aftertreatment system.

[0034] Operating the engine with non-approved fuel may necessitate shortening service intervals, such as oil change intervals or the replacement and cleaning intervals for injectors, compressors, coolers, etc., as otherwise long-term changes in emissions will occur. Determining these modified service intervals and displaying them to the operator represents another application of the procedure.

[0035] To further explain the control processes mentioned above, some processes are illustrated below using block diagrams. Figures 1 to 5 described. It is assumed that the described control processes are embedded in higher-level control routines, which are executed with the help of an electronic motor control system, which is usually present in modern engines for motor control.

[0036] The block diagram according to Fig. 1 (No embodiment of the present invention) shows a process for determining the use of an unauthorized fuel and storing the relevant information for later retrieval.

[0037] After the control sequence is initiated, pressure profiles in the fuel system are recorded at predetermined times using one or more pressure sensors. These times are chosen so that the pressure profiles provide information about the type of fuel in the system. In the next step, the recorded pressure profile is processed using an analytical method, such as a Fourier transform, so that the information can be easily compared with characteristic stored data of an approved reference fuel. This comparison takes place in the next step. Depending on the comparison result, if the recorded information matches the stored data, the control sequence is terminated. If there is a discrepancy, however, information is stored indicating that an unapproved fuel is being used.In parallel, it is conceivable to record the time at which the mismatch was detected, since corresponding engine control systems typically include a time recording device that can be queried to determine the time. After the data has been recorded, the control sequence is also terminated.

[0038] By querying the stored values, it is possible at a later time to determine the fact that an unauthorized fuel was used and, if applicable, the duration of its use.

[0039] As a variation of the example described above, it is possible to directly display the fact that an unauthorized fuel is being used, for example to inform or alert an operator. A corresponding control sequence is shown. Fig. 2 The first three control steps are identical to those shown in the block diagram. Figure 1As described, reference is made to the relevant sections of the description. The control process terminates if the acquired information matches the stored information. If there is a discrepancy, a message is displayed indicating that an unauthorized fuel is being used. This message can be visual, audible, and / or tactile and will remain active as long as unauthorized fuel is present in the fuel system.

[0040] Naturally, a combination of the control sequences according to the block diagrams is also possible. Figure 1 and 2 It is conceivable that in this case the control step for storing the information that no approved fuel is being used and the control step for displaying this fact are executed in parallel or sequentially.

[0041] As described above, the use of an unauthorized fuel can lead to a reduction in the required service intervals, for example, for a motor vehicle. To counter this risk, the block diagram below states... Fig. 3 The possibility, after determining that an unauthorized fuel is being used, to calculate the reduction of the service interval in a corresponding control step and to display the calculated new service interval in a further control step. The control steps for determining that an unauthorized fuel is being used are identical to the corresponding ones in conjunction with the block diagram according to Figure 1 The described control steps are so self-explanatory that a further description is unnecessary.

[0042] Naturally, the control sequence can be illustrated according to the block diagram. Figure 3with the control sequences according to the block diagrams according to the Figure 1 and / or combine 2.

[0043] Furthermore, as mentioned above, using a non-approved fuel in an engine may necessitate adjusting the engine's and / or exhaust aftertreatment system's operating parameters by changing the settings, for example, to comply with permissible engine emissions. A corresponding control sequence is shown in the block diagram according to... Fig. 4 (not an embodiment of the present invention) shown.

[0044] In this example as well, the first step is to determine whether the measured pressure profile corresponds to the pressure profile of the reference fuel. The control steps to be performed for this purpose are identical to those corresponding to the block diagram according to... Figure 1 As described, reference is therefore made to the relevant sections of the description. Figure 1If it is determined that the measured pressure profile does not correspond to the pressure profile of the reference fuel, a further control step uses stored settings and / or activatable control loops to reduce pollutant emissions to an acceptable level. The corresponding control mechanisms are described in detail in the technical literature, so no further explanation is necessary. Engine operating parameters that can be used to minimize pollutants include, among others, the injection timing, the injection quantity, the injection intervals, the exhaust gas recirculation rate, the exhaust gas temperature, the exhaust gas mass, etc.

[0045] Since a limited number of usable fuels are usually available on the market, the operating parameters of the internal combustion engine or the exhaust aftertreatment system of the internal combustion engine can also be adjusted according to the example in the block diagram. Fig. 5 (not an embodiment of the present invention). The control sequence shown there is identical in the first steps up to the query of whether the detected pressure curve corresponds to the pressure curve of the reference fuel to that shown in conjunction with the block diagram according to Figure 1 described, so that here too the corresponding description can be found, for example, after Figure 1If the aforementioned query reveals that the determined pressure profile does not match the pressure profile of the reference fuel, a further comparison is made with stored pressure profiles corresponding to known fuels. If a match is found, the relevant operating parameters for the engine and, if applicable, the exhaust aftertreatment system are read from a memory and used to control the engine and exhaust aftertreatment system, thus enabling fuel-specific adjustment of the engine and exhaust aftertreatment parameters.

[0046] Naturally, the control sequences can be represented according to the block diagrams as per the Figures 4 and 5 combine, which also results in pollutant minimization in the case of an unknown fuel, as in the example above. Figure 4 However, this does not represent an embodiment of the present invention.

[0047] Furthermore, the control processes can be described as follows: Figure 4 and 5 or a combination thereof with the control processes according to the Figures 1 to 3 combining them in any way possible, however this does not constitute an embodiment of the present invention.

Claims

1. Method for determining the deviation of the quality of a fuel from a reference quality and the resulting change in exhaust gas emissions by analysing pressure waves in the fuel system, wherein - the internal combustion engine is or is equipped with discontinuous fuel delivery and / or fuel extraction, - during operation, the pressure oscillations forming in the fuel system are detected with the aid of at least one sensor, - the deviation from a fuel reference quality is determined by analysing this pressure curve in an electronic control unit, characterised in that - deviations of the raw emissions of the internal combustion engine from the raw emissions when using the reference fuel and / or influences on the changed behaviour of an aftertreatment system downstream of the internal combustion engine compared to operation with reference fuel are determined from the deviation from a fuel reference quality, and - when determining a deviation from the reference fuel quality: a) a service interval is changed and the changed service interval is displayed, wherein preferably, the service interval is an oil change interval or a change and cleaning interval of injection nozzles, compressors, coolers; and / or b) information about the use of a fuel that differs from the reference fuel is displayed, whereby preferably, the display is visual and / or audible and / or tactile and remains as long as the fuel that differs from the reference fuel is in the fuel system.

2. Method according to one of the preceding claims, characterised in that the duration of the deviation from the fuel quality and / or its frequency and / or its first and / or last occurrence is stored in an electronic control unit.

3. Method according to claim 2, characterised in that this stored information is used to infer the degree of chemical and / or thermal deactivation of the aftertreatment system and / or a long-term change in emissions.

4. Method according to one of the preceding claims, characterised in that the fuel type is determined by analysing this pressure curve in an electronic control unit.

5. Method according to claim 4, characterised in that the fuel type is stored in an electronic control unit.

6. Method according to one of the preceding claims, characterised in that a change in operating parameters of the internal combustion engine is carried out, wherein the operating parameters of the internal combustion engine are changed as a function of the information obtained from the pressure oscillations such that the emissions are at least approximated to those when using the reference fuel.

7. Method according to claim 6, characterised in that the emissions when using a non-reference fuel are adapted to the emissions when using the reference fuel by changing the injection pressure and / or the injection timing and / or the number of injections of the fuel per injection process and / or the exhaust gas recirculation rate and / or the fuel / air ratio and / or the valve timing.

8. Method according to one of the preceding claims, characterised in that the at least one sensor is arranged on the high-pressure side of the fuel delivery device, the sensor signal also serving as a reference variable for controlling the fuel pressure on the high-pressure side.

9. Method according to one of the preceding claims, characterised in that the fuel temperature is additionally determined with the aid of at least one further sensor and is used to determine the deviation of the quality of a fuel from a reference quality and / or the fuel type.

10. Method according to one of the preceding claims, characterised in that the temperature difference between the low-pressure side and the high-pressure side of the fuel delivery device is determined with the aid of sensors and is used to determine the deviation of the quality of a fuel from a reference quality and / or the fuel type.

11. Method according to one of the preceding claims, characterised in that the information obtained from the pressure oscillations is stored.

12. Method according to one of the preceding claims, characterised in that the pressure curve for the analysis in an electronic control unit is subjected to a Fourier transform and / or a discrete Fourier transform and / or a fast Fourier transform.