METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE, AND INTERNAL COMBUSTION ENGINE

Abstract

A method for operating an internal combustion engine, having of the following steps: operating the internal combustion engine with a gas fuel; detecting a lambda value in the exhaust gas of the internal combustion engine; determining at least one variable from the detected lambda value, characterizing the quality of the gaseous fuel; and controlling the internal combustion engine based on the at least one variable

Claims

1-10. (canceled)

11. A method for operating an internal combustion engine, comprising the steps of: operating the internal combustion engine with a gaseous fuel; detecting a lambda value in exhaust gas of the internal combustion engine; determining at least one characteristic value, which is characteristic for a quality of the gaseous fuel, from the detected lambda value; and controlling the internal combustion engine based on the at least one characteristic value.

12. The method according to claim 11, including operating the internal combustion engine in a dual-substance mode with the gaseous fuel and a liquid fuel, wherein a ratio masses of gaseous fuel fed to a combustion chamber to liquid fuel is at least 1:4.

13. The method according to claim 12, wherein the ratio is at least 1:1.

14. The method according to claim 13, wherein the ratio is at least 7:3.

15. The method according to claim 14, wherein the ratio is at least 8:2.

16. The method according to claim 15, wherein the ratio is at most 9:1.

17. The method according to claim 11, including determining at least one parameter selected from a group consisting of a stoichiometric air requirement, a density, a heating value, an inert gas portion, and an H/C ratio of the gaseous fuel as the characteristic value.

18. The method according to claim 11, including determining the characteristic value by a characteristic value regulator, wherein a lambda value calculated by the characteristic value regulator from the characteristic value is regulated by variation of the characteristic value to the detected lambda value.

19. The method according to claim 11, including determining the characteristic value by calculating a second numerical value for the characteristic value from a value, which is dependent on or derived from a first numerical value for the characteristic value, for a parameter of the internal combustion engine and the detected lambda value, wherein the method is carried out iteratively.

20. The method according to claim 11, including determining at least one correction variable for correcting a measured value, which determines the detected lambda value, from the characteristic value, and correcting the measured value based the correction variable, and wherein the detected lambda value is obtained from the corrected measured value.

21. The method according to claim 11, including using the at least one characteristic value for controlling a quantity of gaseous fuel to be metered.

22. An internal combustion engine, comprising: at least one combustion chamber; a controllable feed device for a gaseous fuel in the at least one combustion chamber; an exhaust gas train connected to the at least one combustion chamber; a lambda sensor arranged in the exhaust gas train; and a control device configured to detect a lambda value in the exhaust gas of the internal combustion engine for determining at least one characteristic value that is characteristic for a quality of the gaseous fuel, from the detected lambda value, and for controlling the internal combustion engine based on the at least one characteristic value, wherein the control device is configured to carry out the method according to claim 11.

23. The internal combustion engine according to claim 22, wherein the lambda sensor is a broadband lambda sensor.

24. The internal combustion, engine according to claim 22, further comprising a metering device for metering liquid fuel into the at least one combustion chamber.

Description

[0042] The invention is explained in greater detail in the following with reference to the drawing. In the drawing

[0043] FIG. 1 shows a schematic representation of one exemplary embodiment of an internal combustion engine;

[0044] FIG. 2 shows a schematic detailed representation of one first embodiment of the method;

[0045] FIG. 3 shows a schematic detailed representation of one second embodiment of the method, and

[0046] FIG. 4 shows one further detailed representation of the method.

[0047] FIG. 1 shows a schematic representation of one exemplary embodiment of an internal combustion engine 1 comprising a controllable feed device 3 which is configured for—indirectly—feeding a gaseous fuel into a combustion chamber 5 of the internal combustion engine 1. Connected to the combustion chamber 5 is an exhaust gas train 7, wherein a lambda sensor 9, in particular a broadband lambda sensor 11 in this case, is situated in the exhaust gas train 7. In addition, a control device 13 is provided, which is configured for detecting a lambda value in the exhaust gas of the internal combustion engine 1, and for determining, from the detected lambda value, at least one characteristic value which is characteristic for a quality of the gaseous fuel. The control device 13 is also configured for controlling the internal combustion engine 1 on the basis of the at least one characteristic value.

[0048] For this purpose, the control device 13 is operatively connected to the lambda probe 9, in particular, and to the feed device 3.

[0049] The internal combustion engine 1 is also configured for operation in a dual-substance mode, wherein the gaseous fuel as well as a liquid fuel can be fed to the combustion chamber 5. For this purpose, the internal combustion engine 1 comprises a metering device 15, in particular an injector 17, by means of which the liquid fuel can be metered directly into the combustion chamber 5.

[0050] The internal combustion engine 1 is preferably designed as a piston engine, in particular as a four-stroke engine, wherein a piston 19 is displaceably situated in the combustion chamber 5 in a manner known per se. Preferably, the internal combustion engine 1 comprises a plurality of combustion chambers 5 and pistons 19, which are displaceably situated therein, wherein one metering device 15 for the cylinder-specific injection of liquid fuel is preferably assigned to each combustion chamber 5. Likewise, a piston 19 is separately assigned to each combustion chamber 5, of course.

[0051] In the exemplary embodiment represented here, the feed device 3 comprises a venturi mixer 21 which is situated upstream from a compressor 23 in a charge air line 25. Combustion air can be fed into the venturi mixer 21 via the charge air line 25.

[0052] Gaseous fuel can be fed to the venturi mixer 21 via a gas supply line 27, wherein situated in the gas supply line 27 is a gas valve 29 which is operatively connected to the control device 13 and, therefore, can be controlled thereby. The gas valve 29 is preferably designed as a so-called TecJet, wherein said valve is controlled by the control device 13—preferably via a CAN bus—with a gaseous-fuel volumetric flow rate to be set, wherein the gas valve 29 automatically determines a gaseous fuel pressure prevailing upstream from the gas valve 29, a temperature of the gaseous fuel, and a differential pressure dropping across the gas valve 29, and sets a suitable valve position in order to implement the volumetric flow rate of the gaseous fuel—which was previously determined and was specified by the control device 13—through the gas valve 29. For this purpose, additionally preferably, a density determined as the characteristic value or from the characteristic value is fed, as the parameter for the control, to the gas valve 29.

[0053] In one preferred exemplary embodiment of the internal combustion engine 1, the compressor 23 is designed as a supercharger. In another exemplary embodiment of the internal combustion engine 1, it is possible that the compressor 23 is designed as a compressor of an exhaust gas turbocharger which can be driven by a turbine which is not represented in FIG. 1 and which is situated in the exhaust gas train 7.

[0054] The feed device 3 is preferably provided upstream from a proportioning of the combustion air/gaseous fuel mixture generated by the venturi mixer 21 to the individual combustion chambers 5, therefore jointly for all combustion chambers 5. In another exemplary embodiment, it is possible that a combustion chamber-specific gas feed device 3 is provided, either in the form of a cylinder-specific manifold injection, or in the form of an injection directly into the individual combustion chambers 5, in particular with the aid of gas injectors provided for this purpose. In this case, it is also possible that the internal combustion engine 1 does not comprise a compressor.

[0055] The control device 13 is preferably designed as an engine control unit (ECU) of the internal combustion engine 1.

[0056] The control device 13 is operatively connected to a charge pressure sensor 31 and a charge air temperature sensor 33 in order to detect a quantity of combustion air fed to the combustion chamber 5, in particular a volume of combustion air fed to the combustion chamber 5. In the exemplary embodiment represented here, said charge pressure sensor and charge air temperature sensor are situated downstream from the compressor 23 and, in particular, downstream from the venturi mixer 21. Since the internal combustion engine 1 is preferably operated with a lean mixture having an excess quantity of combustion air, it is possible, despite the gaseous fuel present at this point in the charge air line 25, to determine a sufficiently precise value for the quantity of combustion air fed to the combustion chamber 5 with the aid of the sensors 31, 33.

[0057] The control device 13 is also operatively connected to the metering device 15, in order to be able to control a quantity of liquid fuel fed to the combustion chamber 5.

[0058] In addition, a speed sensor 35 is also provided, to which the control device 13 is operatively connected in order to detect a speed of the internal combustion engine 1.

[0059] The charge air line 25 is fluidically connected to the combustion chamber 5 via at least one inlet valve 37, wherein the exhaust gas train 7 is fluidically connected to the combustion chamber 5 via at least one outlet valve 39.

[0060] Given that the control device 13 is configured for determining, from the lambda value detected by means of the lambda sensor 9, a characteristic value which is characteristic for the quality of the gaseous fuel, it is always possible to control the gas valve 29 in such a way that a suitable quantity of gaseous fuel is fed to the combustion chamber 5 with consideration for the quality of the gaseous fuel, on the one hand, and, on the other hand, with consideration for the present operating point of the internal combustion engine. There is no need, in this case, for either a complex chemical analysis of the gaseous fuel which is used, or a cylinder pressure indication or a temperature measurement in the combustion chamber 5 in order to determine the combustion properties of the gaseous fuel.

[0061] FIG. 2 shows a schematic detailed representation of one first embodiment of the method. In this case, the characteristic value 41, which, in this embodiment is, in fact, the stoichiometric air requirement 43 of the gaseous fuel, is determined by means of a characteristic value regulator 45. For this purpose, a lambda value 47 calculated on the basis of the characteristic value is compared with the lambda value 49 detected by means of the lambda sensor 9, wherein the characteristic value regulator 45 varies the characteristic value 41 in such a way that the calculated lambda value 47 is regulated to the detected lambda value 49. A deviation between the calculated lambda value and the detected lambda value 49 is therefore minimized by the characteristic value regulator 45 by adjusting the characteristic value 41. In this way, a characteristic value 41 which characterizes the quality of the gaseous fuel which is actually used, in this case the stoichiometric air requirement 43 thereof, in particular, is obtained.

[0062] This regulating method is preferably carried out continuously and permanently. In this case, the regulation is initialized, upon a start of the method, initially with a characteristic value 41 which corresponds to a high or the highest expected, realistic quality of the gaseous fuel, in this case, i.e., a high or the highest expected stoichiometric air requirement 43. It is therefore assumed that a gaseous fuel of the highest possible quality is used, which results in the quantity of gaseous fuel ultimately fed to the combustion chamber 5 initially being too low, but definitely not too great, and so the combustion chamber 5 is protected against an introduction of an undesirably high quantity of energy and, therefore, the internal combustion engine 1 is protected against damage. Due to the characteristic value regulator 45, the characteristic value 41 is then adapted, in the subsequent course of the method, to the actual value for the gaseous fuel which is actually used.

[0063] Within the scope of the method, at least one further characteristic variable for the gaseous fuel is determined from the stoichiometric air requirement 43 determined by means of the characteristic value regulator 45, in particular is calculated and/or preferably read from a map or a characteristic curve, in particular, in the exemplary embodiment represented here, a density 51, a heating value 53, an inert gas portion 55, and an H/C ratio 56 of the gaseous fuel. The characteristic values which are characteristic for the gaseous fuel and which are determined in this way can all be combined as gas properties 57.

[0064] Within the scope of the embodiment represented here, the detected lambda value 49 is determined in the following way: The lambda sensor 9 transmits, to the control device 13, a measured value 59 which determines the lambda value, in this case, specifically an oxygen concentration in the exhaust gas of the internal combustion engine 1. The detected lambda value 49 is calculated in a lambda value calculation step 61, preferably by the control device 13, wherein the calculation is based at least on one correction variable 63, by means of which the measured value 59 is corrected, in this case, specifically two correction variables 63, specifically a—preferably average—H/C ratio 56 of the gaseous fuel and an inert gas correction value 67. In this case, it is possible that the H/C ratio 65 and the inert gas correction value 67—in particular as average values for different gaseous fuels—are assumed. Alternatively, it is possible that at least one of the two correction variables 63 is determined from the stoichiometric air requirement 43. In particular, it is possible that the inert gas portion 55 is used as the inert gas correction value 67, or that the inert gas portion 55 determined from the stoichiometric air requirement 43 is utilized for calculating the inert gas correction value 67. It is also possible that the H/C ratio 56 determined from the stoichiometric air requirement 43 is used as the correction variable 63. Alternatively or additionally, the measured value 59 is also corrected with the exhaust gas pressure measured at the location of the lambda sensor 9, for the detection of which the internal combustion engine 1 preferably comprises an exhaust gas sensor which is situated in the direct vicinity of the lambda sensor 9 and is preferably operatively connected to the control device 13.

[0065] It is also apparent that also incorporated into the calculation of the lambda value 47 calculated from the characteristic value 41 are a liquid-fuel mass 69 fed to the combustion chamber 5, a gaseous-fuel quantity 71 fed to the combustion chamber 5, in particular a gaseous-fuel mass or a gaseous-fuel volume, and a combustion-air quantity 73 fed to the combustion chamber 5, in particular a combustion-air mass or a combustion-air volume. In addition, it is possible that a charging behavior of the internal combustion engine 1 and the stoichiometric air requirement of the liquid fuel are incorporated into the calculation of the calculated lambda value 47.

[0066] FIG. 3 shows a detailed representation, which is similar to FIG. 2, of a second embodiment of the method. Identical and functionally identical elements are provided with identical reference numbers, and therefore reference is made in this regard to the description provided above. In contrast to the first embodiment according to FIG. 2, in this case, the characteristic value 41, specifically the stoichiometric air requirement 43 of the gaseous fuel, is calculated by means of a characteristic value calculating step 75 by calculating, from the present value of the characteristic value 41, a value 77 for a parameter of the internal combustion engine 1 and, from the detected lambda value 49, a new value for the characteristic value 41. This procedure is carried out iteratively. Specifically, it is apparent here that a gaseous-fuel volume 79, which results from the control of the gas valve 29 and is fed to the combustion chamber 5 in the previous iteration step, is utilized as the value 77 for the parameter of the internal combustion engine 1, wherein the density 51 derived from the stoichiometric air requirement 43 is utilized for a correct metering, wherein a new value for the stoichiometric air requirement 43 is calculated, by means of the characteristic value calculation step 75, from the gaseous-fuel volume 79 and further variables 81, which are combined in this case, and from the detected lambda value 49. The variables 81 are preferably a mass of liquid fuel fed to the combustion chamber 5 and a volume of combustion air fed to the combustion chamber 5. In this case, the stoichiometric air requirement 43 is calculated in the characteristic value calculation step 75, preferably according to the following formula:

[00001]$\begin{array}{cc}{L}_{\mathrm{St}.Math.\stackrel{\mathrm{.Math.}}{o}.Math.\mathrm{Gas}}=\frac{V_L-{\lambda }_A.Math.\frac{m_{\mathrm{Fl}}}{{\rho }_L}.Math.L_{\mathrm{St}.Math.\stackrel{\mathrm{.Math.}}{o}.Math.\mathrm{Fl}}}{{\lambda }_A.Math.V_{\mathrm{Gas}}},& \left(1\right)\end{array}$

wherein L.sub.StöGas is the stoichiometric air requirement of the gaseous fuel, L.sub.StöFl is the stoichiometric air requirement of the liquid fuel, m.sub.Fl is the mass of liquid fuel fed to the combustion chamber 5, ρ.sub.L is the density of the combustion air fed to the combustion chamber 5, V.sub.Gas is the volume of gaseous fuel fed to the combustion chamber 5, V.sub.L is the volume of combustion air fed to the combustion chamber 5, and λ.sub.A is the lambda value detected in the exhaust gas train 7.

[0067] In FIG. 3, it is also indicated that the inert gas portion 55 determined from the stoichiometric air requirement 43 is used for calculating the inert gas correction value 67 or is used as the inert gas correction value 67.

[0068] FIG. 4 shows a further schematic detailed representation of one embodiment of the method. Identical and functionally identical elements are provided with identical reference numbers, and therefore reference is made in this regard to the description provided above. On the basis of FIG. 4, it is apparent that the gas properties 57 determined according to one of the above-described embodiments of the method, in particular the characteristic value 41, are used for controlling a quantity of gaseous fuel to be metered. For this purpose, said properties are fed to a gaseous fuel lambda value control 83, by means of which the gas valve 29 is controlled. The gaseous fuel lambda value control ultimately determines the quantity of gaseous fuel fed to the combustion chamber 5 by means of a suitable control of the gas valve 29. Also incorporated into the gaseous fuel lambda value control 83 are a gaseous fuel lambda value setpoint value 85 and further parameters 87 which characterize a quantity of combustion air fed to the combustion chamber 5. In the exemplary embodiment represented here, said further parameters are, in particular, the charge pressure and the charge air temperature and, preferably, the speed of the internal combustion engine 1, the air requirement for the combustion chamber 5, the number of combustion chambers 5, the displacement of the internal combustion engine 1, and/or at least one further relevant variable.

[0069] On the basis of the gaseous fuel lambda setpoint value 85 and the parameter 87, the gaseous fuel lambda value control 83 calculates, with consideration for the gas properties 57, a quantity of gaseous fuel to be metered, in particular a desirable setpoint volumetric flow rate for the gaseous fuel, by means of which the gas valve 29 is controlled. In this case, it is obvious that the quantity of gas to be introduced into the combustion chamber 5 in order to achieve the gaseous fuel lambda setpoint value 85 depends on the quality of the gaseous fuel and, highly particularly, on its stoichiometric air requirement 43. In addition, the gaseous fuel lambda value control 83 calculates the gaseous-fuel quantity 71 fed to the combustion chamber 5, in particular a gaseous-fuel volume or a gaseous-fuel mass, which is utilized in a torque determination element 91 in order to determine a torque 93 of the internal combustion engine 1. In addition, a liquid-fuel mass 95 fed to the combustion chamber 5 is incorporated into the torque determination element 91. On the basis of the liquid-fuel mass 95 and the gaseous-fuel quantity 71, the torque determination element 91 calculates the present torque 93 of the internal combustion engine 1.

[0070] The liquid-fuel mass 95 is calculated by means of a speed regulating element 97 which has, as the input variable, the speed 99 of the internal combustion engine 1 detected by means of the speed sensor 35.

[0071] The speed 99 and the torque 93 are also input variables of a gaseous fuel lambda setpoint value map 101, in which values for the gaseous fuel lambda setpoint value 85 are stored as a function of the torque 93 and the speed 99, and from which the gaseous fuel lambda setpoint value 85 is read.

[0072] In all, with respect to the specifically represented exemplary embodiment, the following is apparent: The speed 99 of the internal combustion engine 1 is regulated by means of a variation of the liquid-fuel mass 95 fed to the combustion chamber 5. A speed regulation which is typical for diesels therefore takes place, which can be carried out in real time, i.e., very rapidly and very simply and precisely. If a higher load is requested of the internal combustion engine 1, for example, the speed 99 tends to decrease. In this case, the liquid-fuel mass 95 is increased by means of the speed regulating element 97, whereby the torque 93 of the internal combustion engine 1 increases, and therefore the speed 99 can be held constant. The increase in the torque 93 is registered by the torque determination element 91. Due to the higher torque 93, a changed gaseous fuel lambda setpoint value 85 is read from the gaseous fuel lambda setpoint map 101, preferably a lower gaseous fuel lambda setpoint value, which results in the gas valve 29 being controlled, by the gaseous fuel lambda value control 83, to meter a greater quantity of gaseous fuel. Therefore, the gaseous-fuel quantity 71 fed to the combustion chamber 5 also increases. This, in turn, results in another increase in the torque 93, which tends to result in an increase in the speed 99. Said increase in speed is detected by the speed regulating element 97, however, which can therefore reduce the liquid-fuel mass 95 fed to the combustion chamber 5. If the internal combustion engine 1 has a load drop, a reduction in the liquid-fuel mass 95 therefore takes place first, followed by a reduction of the gaseous-fuel quantity 71.

[0073] In all, a very rapid, diesel-typical speed and/or power regulation of the internal combustion engine 1 can therefore take place, wherein, on the other hand, the substitution rate can be adjusted in an individualized manner for different operating or load points of the internal combustion engine 1 by means of the gaseous fuel lambda setpoint value map 101. In addition, the substitution rate can be held at least approximately constant, preferably constant at a given load point independently of, or at least essentially independently of a quality of the gaseous fuel which is used.

[0074] In this case, a transient monitoring device, which is not represented in FIG. 4, monitors to ensure that an excessive liquid-fuel mass 95 is not introduced into the combustion chamber 5 by means of the speed regulating element 97.

[0075] It is also apparent that the liquid-fuel mass 95 in the preferred exemplary embodiment represented here is not incorporated, as an input variable, into the gaseous fuel lambda value control 83. This is not required, because a resultant effect on the total lambda value of the internal combustion engine 1 and, therefore, indirectly on the gaseous fuel lambda value assigned to the gaseous fuel, can be depicted by means of a suitable data input into the gaseous fuel lambda setpoint value map 101. Alternatively, it is also possible, however, that the liquid-fuel mass 95 is incorporated as an additional input parameter into the gaseous fuel lambda value control 83.

[0076] Due to the control represented in FIG. 4, the internal combustion engine 1 has a greater transient capability than a charge-regulated gasoline engine. Rather, a diesel-typical power and/or torque regulation, along with the associated high transient capability, is possible. In particular, it is possible to readily retrofit a diesel engine for the operation within the scope of the method represented here.

[0077] In one preferred embodiment of the method, the speed 99 is also incorporated, as an input variable, into the torque determination element 91. In this case, the speed can be utilized, in particular, for determining an instantaneous engine efficiency for the internal combustion engine 1.

[0078] Given that, within the scope of the method proposed herein, the gas properties 57, in particular the stoichiometric air requirement 43 of the gaseous fuel, can be determined in a very simple and, simultaneously, reliable way, it is also possible—without carrying out a gas analysis or cylinder-internal measurement in advance—to reliably operate the internal combustion engine 1 even with greatly varying gas qualities. The method is preferably carried out continuously and permanently during operation of the internal combustion engine 1, in particular because the gas quality of the gaseous fuel can also change during the operation of the internal combustion engine 1. It is also possible within the scope of the method to hold a substitution rate for the liquid fuel, in particular a diesel substitution rate, approximately constant, independently of a quality of the gaseous fuel which is used. In addition, due to the knowledge of the quality of the gaseous fuel, it is possible at all, for the first time, to correctly determine the power of the internal combustion engine 1. In this case, complex measurement technology can be dispensed with, which results in cost savings. The engine torque and the gaseous fuel lambda value—i.e., in particular, the lambda value of the gaseous fuel before the introduction of the mixture of gaseous fuel and combustion air into the combustion chamber 5—can be determined sufficiently well, and therefore a stable engine running of the internal combustion engine 1 can be achieved despite an initially unknown gas composition.