JP2004239132A - Multifuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely perform reduction treatment to a catalyst while preventing the catalyst from causing damage or the like and achieve to make fuel consumption low as well as pollution. <P>SOLUTION: A multifuel engine 1 which can use by switching CNG with gasoline or reversely is provided with an exhaust manifold 11 into which engine exhaust is introduced and a catalyst apparatus 14 connected to the exhaust manifold. The multifuel engine 1 is operated by employing the gasoline suitable for NOx reduction treatment among various fuels when performing the reduction treatment of NOx component stored to absorb by means of NOx absorptive storage reduction catalyst of the catalyst apparatus 14. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-fuel engine capable of switching and using a plurality of fuels including a gas fuel and a liquid fuel, and an operation method thereof.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a multi-fuel engine that can switch and use a plurality of types of fuels including a gas fuel such as compressed natural gas (CNG) and a liquid fuel such as gasoline. As a fuel supply device applied to this type of engine, for example, a fuel supply device described in Patent Document 1 is known. Also, there is known an engine in which at least one of a plurality of cylinders is operated using a gaseous fuel such as natural gas, and the remaining cylinders are operated using a liquid fuel such as light oil (for example, See Patent Document 2.). In this engine, exhaust gas from a cylinder operated using liquid fuel and exhaust gas discharged from a cylinder operated using gas fuel and passing through a three-way catalyst are guided to a NOx reduction catalyst. As a result, the NOx component in the exhaust gas is reduced in the NOx reduction catalyst using ammonia obtained by the reaction of the exhaust gas from the cylinder driven by the gaseous fuel in the three-way catalyst with the reducing agent.
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-110665 [Patent Document 2]
Japanese Patent Application Laid-Open No. 9-4441
[Problems to be solved by the invention]
By the way, in recent years, from the viewpoint of low fuel consumption and high output of engines, so-called lean-burn engines capable of operating in lean combustion have been widely used. In addition, it has been required that the lean burn operation can be performed. Here, when the lean burn operation is performed in the multi-fuel engine, it is difficult to sufficiently remove the NOx component in the engine exhaust by the three-way catalyst. Therefore, in this case, for example, it becomes necessary to cause the NOx storage catalyst to store the NOx component generated due to lean combustion and to reduce the NOx component stored in the catalyst at a predetermined timing. However, it has been pointed out that a multi-fuel engine operated in a lean burn operation cannot obtain a sufficient reduction performance or causes thermal damage to a catalyst.
[0005]
Therefore, an object of the present invention is to provide a multi-fuel engine capable of reliably performing a reduction treatment on a catalyst while preventing damage to the catalyst and achieving low fuel consumption and low pollution, and an operation method thereof. I do.
[0006]
[Means for Solving the Problems]
A multi-fuel engine according to the present invention is a multi-fuel engine capable of switching and using a plurality of types of fuel, comprising: an exhaust path into which engine exhaust is introduced; and a catalyst provided in the exhaust path, and a reduction process for the catalyst. Is performed using a fuel suitable for the reduction process among a plurality of types of fuels.
[0007]
The multi-fuel engine can be used by switching a plurality of fuels including gaseous fuel such as CNG and liquid fuel such as gasoline. In addition, a catalyst for treating the NOx component in the engine exhaust gas that increases during the lean burn operation is provided in the exhaust passage of the multifuel engine. In this multi-fuel engine, for the reduction processing on the catalyst, only the fuel suitable for the reduction processing on the catalyst (reduction of the NOx component) among the plurality of types of fuel is used. Thus, the catalyst can be prevented from being damaged due to misfiring, etc., and the catalyst can be satisfactorily reduced without consuming more fuel than necessary. Thus, low fuel consumption and low pollution can be easily achieved.
[0008]
In this case, gasoline is included in the plurality of types of fuel, and it is preferable that the multi-fuel engine be operated using gasoline when performing the reduction process on the catalyst.
[0009]
As described above, by performing the reduction process on the catalyst by the rich operation using gasoline or the like, the thermal damage of the catalyst due to the rich misfire that tends to occur when the reduction process is performed using the gaseous fuel such as CNG can be reliably performed. Can be prevented, and a reduction in the reduction processing performance can be suppressed. Further, by using only gasoline for the reduction treatment of the catalyst, it is possible to perform a good reduction treatment without consuming more fuel than necessary.
[0010]
Furthermore, it is preferable that the multi-fuel engine of the present invention be operated in a rich spike manner using a fuel suitable for the reduction process when performing the reduction process on the catalyst.
[0011]
Further, the multi-fuel engine of the present invention has an integrating means for integrating the usage of each of the plurality of types of fuel, and a timing for executing the reduction process based on the usage of each of the plurality of types of fuel obtained by the integrating means. Is preferably further provided.
[0012]
In general, various fuels applied to multi-fuel engines contain a considerable amount of sulfur components that poison the catalyst and deteriorate its performance. Depending on the state of poisoning of the catalyst by the sulfur component, reduction of the catalyst is performed. It is necessary to shorten the processing interval. Further, the content of the sulfur component varies depending on the fuel, and particularly, the content of a liquid fuel such as gasoline is large. For this reason, the poisoning state of the catalyst due to the sulfur component changes according to the amount of use of each of the plurality of types of fuels. Therefore, the frequency of performing the reduction process also needs to be changed according to the amount of use of each of the types of fuels. There is.
[0013]
On the other hand, if the amount of use of each of the plurality of types of fuel is integrated and the execution timing of the reduction process is determined based on the obtained amount of use of each of the plurality of types of fuel as in this configuration, the reduction process can be performed. Since the interval is prevented from being shortened more than necessary, it is possible to minimize the execution of the reduction process. As a result, it is possible to effectively suppress the deterioration of fuel efficiency due to the reduction treatment on the catalyst.
[0014]
Further, the catalyst is a NOx storage catalyst, and the reduction timing determination means estimates the poisoning state of the NOx storage catalyst by the sulfur component from the usage amounts of the plurality of types of fuels obtained by the integration means, and estimates the estimated NOx. It is preferable to determine the timing for executing the reduction process based on the poisoning state of the storage catalyst.
[0015]
Further, the plurality of types of fuels include a gaseous fuel, and preferably further includes a gaseous fuel supply path for supplying the gaseous fuel, and sulfur component removing means provided in the gaseous fuel supply path.
[0016]
Generally, the content of a sulfur component in a gaseous fuel such as CNG is relatively small, and the sulfur component can be relatively easily removed. Therefore, if a sulfur component removing means is provided in the gaseous fuel supply path as in this configuration, the sulfur component in the gaseous fuel is removed on the upstream side of the catalyst. Poisoning of the catalyst can be prevented. As a result, the interval of the reduction process for the catalyst can be further lengthened, and deterioration in fuel efficiency due to the reduction process can be extremely effectively suppressed.
[0017]
In this case, it is preferable to further include a unit that determines whether it is time to replace the sulfur component removing unit based on the usage amount of the gaseous fuel.
[0018]
If such a configuration is adopted, the sulfur component removing means can be replaced at an appropriate timing. As a result, it is possible to reliably prevent a situation in which the sulfur component in the gaseous fuel passes through the sulfur component removal means and reaches the catalyst, so that the catalyst is poisoned by the sulfur component in the gaseous fuel. It is possible to surely prevent it.
[0019]
Another multi-fuel engine according to the present invention is a multi-fuel engine that can switch and use a plurality of types of fuel including at least gaseous fuel, wherein a gaseous fuel supply path for supplying gaseous fuel and a gaseous fuel supply path are provided. And a provided sulfur component removing means.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a multifuel engine and a method of operating the same according to the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a schematic configuration diagram showing a multi-fuel engine according to the present invention. A multi-fuel engine 1 shown in FIG. 1 includes a gas fuel (hydrocarbon gas fuel having 4 or less carbon atoms) such as compressed natural gas (CNG) and propane gas (LPG), and a liquid fuel such as gasoline. It is a so-called bi-fuel engine that can be used by switching fuels. In the multi-fuel engine 1, gaseous fuel or liquid fuel is directly injected into each combustion chamber CR of a plurality of cylinders (only one cylinder is shown in FIG. 1), and the air-fuel mixture burns in each combustion chamber CR. As a result, the power is obtained from the output shaft S.
[0022]
The multi-fuel engine 1 of the present embodiment is, for example, for selectively switching between CNG, which is a gaseous fuel, and gasoline, which is a liquid fuel, to use as fuel. Each has a plurality of gas injectors 3 and gasoline injectors 4 arranged. The gas injector 3 is connected to a gas cylinder 7 for storing CNG via a gas supply pipe (gas fuel supply path) 5 and directly injects CNG as fuel into the corresponding combustion chamber CR. The gasoline injector 4 is connected to a gasoline tank 8 for storing gasoline via a gasoline supply pipe 6, and directly injects gasoline as fuel into a corresponding combustion chamber CR. Here, the multi-fuel engine 1 is described as a so-called direct injection engine, but is not limited to this, and it goes without saying that the present invention can also be applied to an intake pipe injection type engine.
[0023]
An intake port of each combustion chamber CR is connected to an intake manifold 10 connected to an air cleaner 9, and an exhaust port of each combustion chamber CR is connected to an exhaust manifold (exhaust passage) 11. An intake valve Vi for opening and closing an intake port and an exhaust valve Ve for opening and closing an exhaust port are provided for each cylinder in the cylinder head of the multi-fuel engine 1. Further, a plurality of spark plugs 12 are arranged on the cylinder head of the multi-fuel engine 1 so as to face each combustion chamber CR.
[0024]
Further, the piston 2 of the multi-fuel engine 1 is configured as a so-called deep dish top surface type, and a concave portion 2a is formed on an upper surface thereof. In the multi-fuel engine 1, CNG or gasoline is directly injected from the gas injector 3 or the gasoline injector 4 toward the recess 2a of each piston 2 in a state where a large amount of air is sucked into each combustion chamber CR. Thereby, a layer of a mixture of fuel and air is formed (stratified) in the vicinity of the ignition plug 12 in a state separated from the surrounding air layer. As a result, in the multi-fuel engine 1, it is possible to execute a stable lean burn operation using an extremely lean air-fuel mixture.
[0025]
On the other hand, when the stratified lean burn operation is performed as described above, the NOx component in the exhaust gas of the multi-fuel engine 1 increases. For this reason, the exhaust manifold 11 of the engine 1 is connected to a catalyst device 14 including a NOx storage reduction catalyst. The NOx component in the exhaust gas from each combustion chamber CR is stored by the NOx storage reduction catalyst of the catalyst device 14, and the NOx component stored in the catalyst is reduced by the catalyst device 14 at a predetermined timing. Reduced by processing.
[0026]
Further, the multi-fuel engine 1 includes an ECU 15 functioning as control means. The ECU 15 includes a CPU, a ROM, a RAM, an input / output port, and a storage device, all of which are not shown. The input / output ports of the ECU 15 are connected to the gas injector 3 and the gasoline injector 4, the spark plug 12, and various sensors (not shown). The ECU 15 uses various maps and the like stored in the storage device, and based on the detection values of the various sensors and the like, the operation timing of the gas injector 3 or the gasoline injector 4, the fuel injection amount from the gas injector 3 or the gasoline injector 4. Further, it controls the opening / closing operation of each intake valve Vi and each exhaust valve Ve.
[0027]
Next, the operation of the multi-fuel engine 1 will be described with reference to FIGS.
[0028]
As shown in FIG. 2, when the engine 1 is started, the ECU 15 determines whether or not to execute the lean burn operation based on the throttle opening, the detection value of the rotation speed sensor, the detection value of other sensors, and the like. A determination is made (S10). If the ECU 15 determines in S10 that the lean burn operation should not be performed, the ECU 15 determines which of the gaseous fuel and the liquid fuel is to be used according to a predetermined condition, and then performs stoichiometric combustion under the ideal air-fuel ratio. The operation is executed (S12).
[0029]
On the other hand, when the ECU 15 determines that the lean burn operation should be performed in S10, the ECU 15 determines which of the gas fuel (CNG) and the liquid fuel (gasoline) should be used to perform the lean burn operation. (S14). In the present embodiment, in the process of S14, basically CNG is preferentially selected as fuel. That is, the ECU 15 determines the remaining amount of CNG in the gas cylinder 7 from the indicated value of the fuel gauge (not shown) provided in the gas cylinder 7 in S14, and when CNG remains in the gas cylinder 7, Select CNG as fuel.
[0030]
When CNG is selected as fuel in S14, the ECU 15 controls each gas injector 3 and each spark plug 12 and the like so that the lean combustion operation of the engine 1 using CNG is performed (S16). On the other hand, when gasoline is selected as fuel in S14, the ECU 15 controls each gasoline injector 4 and each spark plug 12 and the like so that the lean burn operation of the engine 1 using gasoline is performed (S18).
[0031]
In this way, when the stratified lean burn operation of the engine 1 is executed in S16 or S18, exhaust gas containing a relatively large amount of NOx component is discharged from the exhaust port of each combustion chamber CR. The exhaust gas from each combustion chamber CR is guided to the catalyst device 14 via the exhaust manifold 11, and the NOx component in the exhaust gas is stored by the NOx storage reduction catalyst of the catalyst device 14. Therefore, in the multi-fuel engine 1, it becomes necessary to reduce the NOx component stored in the NOx storage reduction catalyst. For this reason, after the processing in S16 or S18, the ECU 15 needs to execute the reduction processing for the catalyst device 14, that is, whether or not it is necessary to reduce the NOx component stored in the NOx storage reduction catalyst of the catalyst device 14. Is determined (S20).
[0032]
Here, gasoline and CNG used in the multifuel engine 1 contain a sulfur component that poisons the NOx storage reduction catalyst of the catalyst device 14 and deteriorates its performance. Therefore, it is necessary to shorten the interval of the reduction process (reduction of the NOx component) for the catalyst device 14 according to the poisoning state of the catalyst by the sulfur component. Further, the content of the sulfur component differs depending on the fuel, and the content of the sulfur component in CNG is about 6 ppm, whereas the content of the sulfur component in liquid fuel such as gasoline is large. In this case, it is about 50 ppm. Therefore, the poisoning state of the NOx storage reduction catalyst due to the sulfur component changes according to the usage amount of each fuel, and the frequency of performing the reduction process also needs to be changed according to the usage amounts of CNG and gasoline. .
[0033]
In view of these points, the ECU 15 of the multi-fuel engine 1 executes the processing shown in FIG. 3 for the determination processing in S20 independently of the series of processing shown in FIG. 2 and the like. . That is, during operation of the multi-fuel engine 1, the ECU 15 determines which of CNG (gas fuel) and gasoline (liquid fuel) is being used (in this embodiment, CNG (gas fuel) is used). Is determined (S30).
[0034]
If the ECU 15 determines in step S30 that CNG is being used as fuel, the ECU 15 calculates (integrates) the total CNG usage Qgas based on the indicated value of the fuel gauge of the gas cylinder 7 and the like, The calculated usage amount Qgas is stored in a predetermined storage area (S32). If it is determined in S30 that CNG is not used as fuel (gasoline is used as fuel), the ECU 15 determines the value of the fuel gauge of the gasoline tank 8 based on the indicated value of the fuel gauge. The total gasoline usage Qliquid is calculated (integrated), and the calculated usage Qliquid is stored in a predetermined storage area (S34).
[0035]
When the CNG usage amount Qgas or the gasoline usage amount Qliquid is obtained in S32 or S34, the ECU 15 estimates the amount of fuel corresponding to sulfur poisoning for estimating the poisoning state of the NOx storage reduction catalyst of the catalyst device 14 due to the sulfur component. Q is calculated (S36). Here, the sulfur-poisoning-equivalent fuel amount Q is determined in consideration of the difference in the sulfur content between CNG (gas fuel) and gasoline (liquid fuel).
Q = α × Qgas + Qliquid (where α <1)
Is calculated as Thus, by appropriately setting the coefficient α, even if switching between CNG and gasoline is performed at an arbitrary timing, it is possible to accurately estimate the poisoning state of the NOx storage reduction catalyst due to the sulfur component. It becomes possible.
[0036]
After calculating the sulfur-poisoning-equivalent fuel amount Q in S36, the ECU 15 further calculates a NOx reduction interval Ti which is an execution interval of the reduction process (reduction of the NOx component) for the catalyst device 14 (S38). Here, as can be seen from FIG. 4, the NOx reduction interval Ti decreases substantially in proportion to the sulfur poisoning equivalent fuel amount Q obtained in S36. Therefore, assuming that the proportional coefficient is a (where a> 0) and the NOx reduction interval determined when there is no catalyst poisoning due to the sulfur component is T0, the NOx reduction interval Ti is
Ti = T0−a × Q
Is calculated as
[0037]
The ECU 15 stores the NOx reduction interval Ti thus calculated in a predetermined storage area. The series of processes from S30 to S38 described above is repeatedly executed by the ECU 15 while the multi-fuel engine 1 is operating, and the value of the NOx reduction interval Ti is updated as needed according to CNG and gasoline usage. Will be done.
[0038]
Now, returning to FIG. 2, the determination process in S20 will be described. In S20, the ECU 15 reads out the NOx reduction interval Ti stored in the predetermined storage area, and based on the read NOx reduction interval Ti, At this time, it is determined whether or not the NOx reduction processing for the catalyst device 14 should be executed. If the ECU 15 determines in S20 that the NOx reduction process should be performed on the catalyst device 14, regardless of whether the fuel used up to that time is CNG or gasoline, In order to reduce the NOx component, a rich spike operation of the engine 1 using gasoline is executed (S22). That is, in S22, the ECU 15 controls each gasoline injector 4 such that the inside of each combustion chamber CR temporarily and rapidly changes from a fuel-lean state (lean state) to a fuel-rich state (rich state). .
[0039]
As described above, by performing a rich spike operation using gasoline, which is a fuel suitable for NOx reduction processing, as compared with CNG (gas fuel) among a plurality of types of fuels (CNG and gasoline), for example, CNG or the like It is possible to reliably prevent thermal damage to the NOx storage reduction catalyst due to rich misfire, which is likely to occur when performing NOx reduction processing using gaseous fuel, and also to suppress reduction in reduction processing performance. . In addition, by using only gasoline for the reduction treatment, as a result, the catalyst can be favorably reduced without consuming more fuel than necessary. As a result, according to the multi-fuel engine 1, it is possible to easily achieve low fuel consumption and low pollution.
[0040]
Further, in the multi-fuel engine 1, the amounts of use of each of the plurality of types of fuels (CNG and gasoline) are integrated, and the fuel amount Q equivalent to sulfur poisoning is obtained based on the amount of use of each of the plurality of types of fuel. The execution timing of the reduction process for the catalyst device 14 is determined based on the NOx reduction interval Ti determined using the poison equivalent fuel amount Q. Therefore, the interval Ti of the reduction process for the catalyst device 14 is prevented from being shortened more than necessary, and the execution of the NOx reduction process can be minimized. Can be effectively suppressed.
[0041]
In the multi-fuel engine 1, after the processes in S12 and S22 in FIG. 2 and when it is determined that it is not time to execute the NOx reduction process in S20, the processes in S10 to S22 described above are performed again. This is executed by the ECU 15.
[0042]
FIG. 5 is a flowchart for explaining another example of the procedure for determining the execution timing of the reduction process for the catalyst device.
[0043]
When executing a series of processes shown in FIG. 5, a gas supply pipe (gas fuel supply) for supplying gaseous fuel (CNG) from gas cylinder 7 to gas injector 3 as shown by a two-dot chain line in FIG. A sulfur component adsorbing material 16 (sulfur component removing means) containing activated carbon, zeolite, or the like is incorporated in the middle of the route 5.
[0044]
Here, a hydrocarbon gas fuel having 4 or less carbon atoms does not originally contain a sulfur component, and is added to a gas fuel such as CNG as an odorant for discriminating a gas leak or the like. It only contains relatively small amounts of sulfur compounds (eg mercaptans). Then, the sulfur component contained in CNG or the like can be easily removed by using an adsorbent made of activated carbon, zeolite, or the like. Therefore, if the sulfur component adsorbent 16 is provided in the middle of the gas supply pipe 5, the sulfur component in CNG is removed on the upstream side of the catalyst device 14, so that the NOx storage reduction by the sulfur component in CNG is performed. Poisoning of the catalyst can be very reliably prevented.
[0045]
Then, when the sulfur component adsorbent 16 is used, as shown in FIG. 5, the ECU 15 determines whether or not gasoline (liquid fuel) is used during operation of the multi-fuel engine 1 (S50). ). Further, only when it is determined in S50 that gasoline is being used as fuel, the ECU 15 integrates the total gasoline usage Qliquid based on the indicated value of the fuel gauge of the gasoline tank 8 and the like, The calculated usage amount Qliquid is stored in a predetermined storage area (S52).
[0046]
After the process in S52, and when it is determined in S50 that gasoline is not used as fuel (CNG is used as fuel), the ECU 15 determines in S54 the amount of fuel equivalent to sulfur poisoning Q = Qliquid, and in S56, the NOx reduction interval Ti is calculated as Ti = T0−a × Q. As a result, the poisoning of the NOx storage reduction catalyst by the sulfur component in CNG (gas fuel) is estimated to be zero, and accordingly, the interval Ti of the reduction process of the catalyst device 14 for the NOx storage reduction catalyst is lengthened. This makes it possible to extremely effectively suppress deterioration in fuel efficiency due to the reduction process.
[0047]
Also, as shown in FIG. 6, even when the sulfur component adsorbent 16 is provided in the middle of the gas supply pipe 5, the usage amount Qgas of CNG (gas fuel) is integrated in the same manner as in the example of FIG. Then (S32), the ECU 15 may be configured to determine whether it is time to replace the sulfur component adsorbent 16 based on the calculated CNG usage amount Qgas. In this case, the ECU 15 compares the gas fuel usage amount Qgas calculated in S32 with a predetermined threshold in S40, and determines that the gas fuel usage amount Qgas exceeds the threshold value. Then, an indicator mounted on a dashboard or the like of a vehicle or the like to which the multi-fuel engine 1 is applied is turned on (S42).
[0048]
If such a configuration is adopted, the sulfur component adsorbent 16 can be replaced at an appropriate timing. As a result, it is possible to reliably prevent a situation in which the sulfur component in the gaseous fuel (CNG) passes through the sulfur component adsorbent 16 and reaches the catalyst device 14, so that the NOx storage reduction by the sulfur component in the gaseous fuel is performed. It is possible to reliably prevent the catalyst from being poisoned. In the example shown in FIG. 6, the processes in S40 and S42 are performed after the process in S38, but the present invention is not limited to this. That is, the processes in S40 and S42 can be executed at an arbitrary timing, such as immediately after the step of calculating Qgas in S32.
[0049]
【The invention's effect】
As described above, according to the present invention, it is possible to reliably perform a reduction process on a catalyst while preventing damage to the catalyst and the like, and to achieve low fuel consumption and low pollution.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a multi-fuel engine according to the present invention.
FIG. 2 is a flowchart illustrating the operation of the multifuel engine of FIG. 1;
FIG. 3 is a flowchart illustrating a procedure for determining an execution timing of a reduction process for a catalyst device.
FIG. 4 is a graph showing a relationship between a sulfur poisoning equivalent fuel amount and a NOx reduction interval.
FIG. 5 is a flowchart for explaining another example of the procedure for determining the execution timing of the reduction process for the catalyst device.
FIG. 6 is a flowchart for explaining still another example of the procedure for determining the execution timing of the reduction process for the catalyst device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Multi-fuel engine 2 Piston 2a Recess 3 Gas injector 4 Gasoline injector 5 Gas supply pipe 11 Exhaust manifold 12 Spark plug 14 Catalyst device 15 ECU
16 Sulfur component adsorbent CR combustion chamber

Claims (8)

In a multi-fuel engine that can switch and use multiple types of fuel,
An exhaust passage into which engine exhaust is introduced,
A catalyst provided in the exhaust path,
A multi-fuel engine, wherein when performing the reduction process on the catalyst, the multi-fuel engine is operated using a fuel suitable for the reduction process among the plurality of types of fuels. 2. The multi-fuel engine according to claim 1, wherein the plurality of types of fuel include gasoline, and the plurality of types of fuel are operated using gasoline when performing the reduction process on the catalyst. 3. 3. The multi-fuel engine according to claim 1, wherein when performing the reduction process on the catalyst, a rich spike operation is performed using a fuel suitable for the reduction process. 4. Integrating means for integrating the usage of each of the plurality of fuels;
4. The method according to claim 1, further comprising: a reduction timing determination unit configured to determine a timing at which the reduction process is performed based on the usage amount of each of the plurality of types of fuel obtained by the integration unit. 5. A multi-fuel engine as described in Crab. The catalyst is a NOx storage catalyst, and the reduction timing determination means estimates the poisoning state of the NOx storage catalyst by the sulfur component from the usage amount of each of the plurality of types of fuel obtained by the integration means, and estimates The multifuel engine according to any one of claims 1 to 4, wherein a timing at which the reduction process is performed is determined based on the poisoned state of the NOx storage catalyst. The plurality of types of fuels include a gaseous fuel, and further include a gaseous fuel supply path for supplying the gaseous fuel, and sulfur component removing means provided in the gaseous fuel supply path. The multi-fuel engine according to any one of claims 1 to 5, wherein The multi-fuel engine according to claim 6, further comprising: means for determining whether it is time to replace the sulfur component removing means based on the usage amount of the gaseous fuel. In a multi-fuel engine that can switch and use a plurality of fuels including at least gaseous fuel,
A gaseous fuel supply path for supplying the gaseous fuel,
A multi-fuel engine, comprising: a sulfur component removing unit provided in the gaseous fuel supply path.

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