JP4310729B2 - Multi-fuel engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-fuel engine capable of switching and using a plurality of types of fuel including gaseous fuel and liquid fuel, and an operation method thereof.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a multi-fuel engine that can switch and use a plurality of types of fuel including gas fuel such as compressed natural gas (CNG) and liquid fuel such as gasoline is known. As a fuel supply device applied to this type of engine, for example, the one described in Patent Document 1 is known. An engine in which at least one cylinder among a plurality of cylinders is operated using a gaseous fuel such as natural gas while the remaining cylinders are operated using a liquid fuel such as light oil is also known (for example, (See Patent Document 2). In this engine, exhaust from a cylinder operated using liquid fuel and exhaust after passing through a three-way catalyst after being exhausted from a cylinder operated using gaseous fuel are led to a NOx reduction catalyst. As a result, the NOx component in the exhaust gas is reduced by using, as the reducing agent, ammonia obtained by the exhaust gas from the cylinder operated by the gaseous fuel reacting in the three-way catalyst in the NOx reduction catalyst.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-110665 [Patent Document 2]
Japanese Patent 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 an engine, an engine capable of so-called lean combustion operation has been popularized, and the same applies to a multi-fuel engine that can be used by switching between plural kinds of fuels. In addition, it has been demanded that the lean combustion operation can be performed. Here, when the lean combustion operation is executed in the multifuel 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 is necessary to cause the NOx storage catalyst to store the NOx component generated by the lean combustion, and to reduce the NOx component stored in the catalyst at a predetermined timing. However, with respect to a multifuel engine that is operated with lean combustion, problems have been pointed out that sufficient reduction performance cannot be obtained or the catalyst is thermally damaged.
[0005]
Therefore, the present invention aims to provide a multi-fuel engine that can reliably reduce the catalyst while preventing the damage of the catalyst and the like, and achieve low fuel consumption and low pollution, and an operation method thereof. To do.
[0006]
[Means for Solving the Problems]
The multi-fuel engine according to the present invention is a multi-fuel engine capable of switching and using a plurality of types of fuels, and includes 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 reduction treatment among a plurality of types of fuels.
[0007]
This multi-fuel engine can be used by switching a plurality of types of fuel including gas fuel such as CNG and liquid fuel such as gasoline. In addition, a catalyst for treating NOx components in the engine exhaust that increase during lean combustion operation is installed in the exhaust passage of the multifuel engine. In this multi-fuel engine, only a fuel suitable for the reduction process (reduction of NOx components) among the plurality of types of fuels is used for the reduction process for the catalyst. As a result, the catalyst can be prevented from being damaged due to misfire, and the reduction process for the catalyst can be performed satisfactorily without consuming more fuel than necessary, and fuel consumption and 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 is operated using gasoline when performing the reduction process on the catalyst.
[0009]
In this way, by performing the reduction process on the catalyst by a rich operation using gasoline or the like, for example, the thermal damage of the catalyst due to the rich misfire that tends to occur when the reduction process is performed using a gaseous fuel such as CNG is ensured. Can be prevented, and the reduction in reduction performance can be suppressed. Further, by using only gasoline for the reduction process for the catalyst, it is possible to execute a good reduction process without consuming more fuel than necessary.
[0010]
Furthermore, the multi-fuel engine of the present invention is preferably operated in a rich spike operation using a fuel suitable for the reduction process when the reduction process is performed on the catalyst.
[0011]
In the multi-fuel engine of the present invention, an integration means for integrating the usage amounts of each of the plurality of types of fuel, and a timing for executing the reduction process based on the usage amounts of each of the plurality of types of fuel obtained by the integration means. It is preferable that a reduction timing determining means for determining
[0012]
In general, various fuels applied to multi-fuel engines contain a considerable amount of sulfur components that poison the catalyst and degrade its performance. Depending on the poisoning state of the catalyst by the sulfur component, reduction to the catalyst is possible. It is necessary to shorten the processing interval. Further, the content of the sulfur component varies depending on the fuel, and in particular, the content of liquid fuel such as gasoline is large. For this reason, since the poisoning state by the sulfur component of the catalyst changes according to the amount of each of the plurality of types of fuel used, the frequency of performing the reduction treatment also needs to be changed according to the amount of each of the types of fuel used. There is.
[0013]
On the other hand, if the usage amount of each of the plurality of types of fuel is integrated and the execution timing of the reduction processing is determined based on the obtained usage amount of each of the plurality of types of fuel as in this configuration, the reduction processing is performed. Since the interval is prevented from being shortened more than necessary, it is possible to minimize the implementation of the reduction process. Thereby, the fuel consumption deterioration accompanying the reduction process with respect to a catalyst can be suppressed effectively.
[0014]
The catalyst is a NOx storage catalyst, and the reduction timing determination means estimates the poisoning state due to the sulfur component of the NOx storage catalyst from the amount of each of the plurality of types of fuel 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 gaseous fuel, and it is preferable to further include a gaseous fuel supply path for supplying the gaseous fuel and a sulfur component removing means provided in the gaseous fuel supply path.
[0016]
In general, the content of a sulfur component in a gaseous fuel such as CNG is relatively small, and the sulfur component can be removed relatively easily. Therefore, if the sulfur component removing means is provided in the gaseous fuel supply path as in such a configuration, the sulfur component in the gaseous fuel is removed upstream from the catalyst, so that it depends on the sulfur component in the gaseous fuel. Catalyst poisoning can be prevented. Thereby, it becomes possible to further lengthen the interval of the reduction process with respect to the catalyst, and it is possible to extremely effectively suppress the deterioration in fuel consumption accompanying the reduction process.
[0017]
In this case, it is preferable to further include means for determining whether it is time to replace the sulfur component removing means based on the amount of gaseous fuel used.
[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 the sulfur component in the gaseous fuel from passing through the sulfur component removing means and reaching the catalyst, so that the catalyst is poisoned by the sulfur component in the gaseous fuel. It becomes possible to prevent it reliably.
[0019]
Another multi-fuel engine according to the present invention is a multi-fuel engine in which a plurality of types of fuel including at least a gaseous fuel can be switched and used. In the multi-fuel engine, a gaseous fuel supply path for supplying gaseous fuel, and a gaseous fuel supply path And a sulfur component removing means provided.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a multi-fuel engine and an operation method thereof according to the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a schematic diagram showing a multi-fuel engine according to the present invention. A multi-fuel engine 1 shown in FIG. 1 includes a plurality of types including gaseous fuel (hydrocarbon gas fuel having 4 or less carbon atoms) such as compressed natural gas (CNG) and propane gas (LPG), and liquid fuel such as gasoline. This is a so-called bi-fuel engine that can be used by switching the fuel. 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 of reciprocating the piston 2, power is obtained from the output shaft S.
[0022]
The multifuel engine 1 of the present embodiment uses, for example, CNG that is a gaseous fuel and gasoline that is a liquid fuel by selectively switching them as fuel, and is used as a cylinder head so as to face each combustion chamber CR. A plurality of gas injectors 3 and gasoline injectors 4 are provided. The gas injector 3 is connected to a gas cylinder 7 that stores CNG via a gas supply pipe (gaseous fuel supply path) 5 and directly injects CNG as fuel into the corresponding combustion chamber CR. The gasoline injector 4 is connected via a gasoline supply pipe 6 to a gasoline tank 8 that stores gasoline, and directly injects gasoline as fuel into the corresponding combustion chamber CR. Here, the multi-fuel engine 1 is described as a so-called direct injection engine. However, the present invention is not limited to this, and it goes without saying that the present invention can be applied to an intake pipe injection type engine.
[0023]
The intake port of each combustion chamber CR is connected to an intake manifold 10 connected to the air cleaner 9, and the exhaust port of each combustion chamber CR is connected to an exhaust manifold (exhaust passage) 11. The cylinder head of the multifuel engine 1 is provided with an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port for each cylinder. Furthermore, a plurality of spark plugs 12 are arranged in the cylinder head of the multifuel engine 1 so as to face the combustion chambers CR.
[0024]
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 the 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 2 a of each piston 2 in a state where a large amount of air is sucked into each combustion chamber CR. As a result, a layer of a mixture of fuel and air is formed (stratified) in the vicinity of the spark plug 12 while being separated from the surrounding air layer. As a result, the multifuel engine 1 can execute a stable lean combustion operation using an extremely lean air-fuel mixture.
[0025]
On the other hand, when the stratified lean combustion operation is executed in this way, the NOx component in the exhaust of the multifuel 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 from each combustion chamber CR is occluded by the NOx occlusion / reduction catalyst of the catalyst device 14, and the NOx component occluded in the catalyst is reduced with respect to the catalyst device 14 at a predetermined timing. Reduced by processing.
[0026]
The multifuel engine 1 includes an ECU 15 that functions as a control means. The ECU 15 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. The input / output port of the ECU 15 is connected to the above-described gas injector 3, gasoline injector 4, 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 detection values of various sensors, the operation timing of the gas injector 3 or the gasoline injector 4 and the fuel injection amount from the gas injector 3 or the gasoline injector 4 Furthermore, the opening / closing operation of each intake valve Vi and each exhaust valve Ve is controlled.
[0027]
Next, the operation of the above-described 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 combustion operation based on the throttle opening, the detection value of the rotation speed sensor, the detection value of other sensors, and the like. Determine (S10). When the ECU 15 determines that the lean combustion operation should not be executed in S10, the ECU 15 determines which one of the gaseous fuel and the liquid fuel to use in accordance with a predetermined condition, and then performs the 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 combustion operation should be executed in S10, the ECU 15 determines which of the gaseous fuel (CNG) and the liquid fuel (gasoline) is used as the fuel to execute the lean combustion operation. (S14). In the present embodiment, basically, CNG is preferentially selected as the fuel in the process of S14. That is, in S14, the ECU 15 obtains the remaining amount of CNG in the gas cylinder 7 from the indication value of the remaining amount meter (not shown) provided in the gas cylinder 7, and when CNG remains in the gas cylinder 7, Select CNG as fuel.
[0030]
When CNG is selected as the fuel in S14, the ECU 15 controls each gas injector 3, each spark plug 12, and the like so that the lean combustion operation of the engine 1 using CNG is executed (S16). On the other hand, when gasoline is selected as fuel in S14, the ECU 15 controls each gasoline injector 4, each spark plug 12, and the like so that the lean combustion operation of the engine 1 using gasoline is executed (S18).
[0031]
In this way, when the stratified lean combustion operation of the engine 1 is executed in S16 or S18, exhaust containing a relatively large amount of NOx component is exhausted from the exhaust port of each combustion chamber CR. Exhaust gas from each combustion chamber CR is guided to the catalyst device 14 via the exhaust manifold 11, and NOx components in the exhaust gas are occluded by the NOx storage reduction catalyst of the catalyst device 14. Therefore, in the multifuel engine 1, it is necessary to reduce the NOx component stored in the NOx storage reduction catalyst. Therefore, the ECU 15 needs to perform a reduction process on the catalyst device 14 after the process in S16 or S18, that is, whether or not the NOx component stored in the NOx storage reduction catalyst of the catalyst device 14 needs to be reduced. Is determined (S20).
[0032]
Here, the 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 degrades its performance. Therefore, it is necessary to shorten the interval of the reduction process (NOx component reduction) for the catalyst device 14 in accordance with the poisoning state of the catalyst by the sulfur component. In addition, the content of the sulfur component varies depending on the fuel. The content concentration of the sulfur component in CNG is about 6 ppm, whereas the content concentration of the sulfur component in liquid fuel such as gasoline is large. In this case, it is about 50 ppm. Therefore, since the poisoning state of the NOx storage reduction catalyst due to the sulfur component changes according to the amount of each fuel used, the frequency of performing the reduction process must also be changed according to the amounts of CNG and gasoline used. .
[0033]
In view of these points, the ECU 15 of the multi-fuel engine 1 performs the process shown in FIG. 3 independently of the series of processes shown in FIG. 2 for the determination process in S20. . That is, the ECU 15 determines which fuel is used between CNG (gas fuel) and gasoline (liquid fuel) during operation of the multi-fuel engine 1 (in this embodiment, CNG (gas fuel) is used. (S30).
[0034]
If the ECU 15 determines in S30 that CNG is being used as fuel, the ECU 15 calculates (integrates) the total usage amount Qgas of CNG based on the indicated value of the remaining amount indicator of the gas cylinder 7 and the like. The calculated usage amount Qgas is stored in a predetermined storage area (S32). In S30, when it is determined that CNG is not used as fuel (gasoline is used as fuel), the ECU 15 determines, based on the indicator value of the fuel gauge of the gasoline tank 8, and the like. The total used amount Qliquid of gasoline is calculated (integrated), and the calculated used amount Q liquid is stored in a predetermined storage area (S34).
[0035]
When the ECU 15 obtains the CNG usage amount Qgas or the gasoline usage amount Qliquid in S32 or S34, the sulfur poisoning equivalent fuel amount for estimating the poisoning state due to the sulfur component of the NOx storage reduction catalyst of the catalyst device 14 is obtained. Q is calculated (S36). Here, the sulfur poisoning equivalent fuel amount Q takes into account the difference in 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, it is possible to accurately estimate the poisoning state of the NOx occlusion reduction catalyst due to the sulfur component even when switching between CNG and gasoline is performed at an arbitrary timing. 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 that is an execution interval of the reduction process (NOx component reduction) 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, when the proportional coefficient is a (where a> 0), and the NOx reduction interval determined when it is assumed that there is no catalyst poisoning by 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 calculated in this way in a predetermined storage area. The series of processes from S30 to S38 described above are 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 the amounts of CNG and gasoline used. It will be done.
[0038]
Now, referring back to FIG. 2, the determination process in S20 will be described. In S20, the ECU 15 reads the NOx reduction interval Ti stored in the predetermined storage area, and based on the read NOx reduction interval Ti, It is determined whether or not the NOx reduction process for the catalyst device 14 should be executed at the time. If the ECU 15 determines in S20 that the NOx reduction process for the catalyst device 14 should be executed, regardless of whether the fuel used so far is CNG or gasoline, In order to reduce the NOx component, the rich spike operation of the engine 1 using gasoline is executed (S22). That is, in S22, the ECU 15 controls each gasoline injector 4 so that the inside of each combustion chamber CR temporarily and rapidly changes from a fuel-lean state (lean state) to a fuel-excess state (rich state). .
[0039]
In this way, by performing rich spike operation using gasoline, which is a fuel suitable for NOx reduction treatment, compared to CNG (gaseous fuel) among a plurality of types of fuel (CNG and gasoline), for example, CNG or the like It is possible to reliably prevent thermal damage of the NOx storage reduction catalyst due to rich misfire that tends to occur when performing NOx reduction treatment using gaseous fuel, and to suppress reduction in reduction treatment performance. . Further, by using only gasoline for the reduction treatment, as a result, it is possible to reduce the catalyst satisfactorily without consuming more fuel than necessary. As a result, according to the multifuel engine 1, it is possible to easily achieve low fuel consumption and low pollution.
[0040]
Further, in the multi-fuel engine 1, the use amounts of the plurality of types of fuels (CNG and gasoline) are integrated, and the sulfur poisoning equivalent fuel amount Q is obtained based on the use amounts of the plurality of types of fuels. Based on the NOx reduction interval Ti determined using the poison-equivalent fuel amount Q, the execution timing of the reduction process for the catalyst device 14 is determined. Accordingly, it is possible to prevent the interval Ti of the reduction process for the catalyst device 14 from being unnecessarily shortened, and it is possible to minimize the execution of the NOx reduction process. 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 the timing to execute the NOx reduction process in S20, the processes in S10 to S22 described above are performed again. It 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 the series of processes shown in FIG. 5 is executed, a gas supply pipe (gaseous fuel supply) for supplying gaseous fuel (CNG) from the gas cylinder 7 to the gas injector 3 as shown by a two-dot chain line in FIG. Road) A sulfur component adsorbent 16 (sulfur component removing means) containing activated carbon, zeolite or the like is incorporated in the middle of 5.
[0044]
Here, the hydrocarbon gas fuel having 4 or less carbon atoms does not originally contain a sulfur component, and is added to the gas fuel such as CNG as an odorant for discriminating gas leakage or the like. Only relatively small amounts of sulfur compounds (eg mercaptans) are included. And the sulfur component contained in CNG etc. can be easily removed using the adsorbent which consists of activated carbon, zeolite, etc. 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 upstream from the catalyst device 14, and therefore NOx occlusion reduction by the sulfur component in CNG. The poisoning of the catalyst can be extremely 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 multifuel engine 1 (S50). ). Further, only when it is determined in S50 that gasoline is being used as fuel, the ECU 15 integrates the total amount Qliquid of gasoline based on the indication value of the fuel gauge of the gasoline tank 8, etc. The calculated usage amount Qliquid is stored in a predetermined storage area (S52).
[0046]
After the processing of S52 and when it is determined that gasoline is not used as fuel (CNG is used as fuel) in S50, the ECU 15 determines the sulfur poisoning-equivalent fuel amount Q to be Q in S54. = 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 due to the sulfur component in CNG (gaseous fuel) is estimated to be zero, so the interval Ti of the reduction process for the NOx storage reduction catalyst of the catalyst device 14 is increased accordingly. This makes it possible to suppress the deterioration of fuel consumption associated with the reduction process very effectively.
[0047]
Further, 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 (gaseous fuel) is integrated as in the example of FIG. However, 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 Qgas. In this case, the ECU 15 compares the usage amount Qgas of the gaseous fuel calculated in S32 with a predetermined threshold value in S40 and determines that the usage amount Qgas of the gaseous fuel 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 structure is employ | adopted, it will become possible to replace the sulfur component adsorbent 16 at an appropriate timing. As a result, it is possible to reliably prevent the sulfur component in the gaseous fuel (CNG) from passing through the sulfur component adsorbent 16 and reaching the catalyst device 14, so that the NOx occlusion reduction is performed by the sulfur component in the gaseous fuel. 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 executed 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 any timing, such as immediately after the Qgas calculation step 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 the 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 diagram showing a multi-fuel engine according to the present invention.
FIG. 2 is a flowchart for explaining the operation of the multi-fuel engine of FIG. 1;
FIG. 3 is a flowchart for explaining a procedure for determining execution timing of a reduction process for a catalyst device;
FIG. 4 is a graph showing the relationship between the sulfur poisoning equivalent fuel amount and the 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 Multifuel engine 2 Piston 2a Recess 3 Gas injector 4 Gasoline injector 5 Gas supply pipe 11 Exhaust manifold 12 Spark plug 14 Catalytic device 15 ECU
16 Sulfur component adsorbent CR Combustion chamber

Claims (8)

In a multi-fuel engine that can be used by switching multiple types of fuel,
An exhaust passage through which engine exhaust is introduced;
A catalyst provided in the exhaust passage ;
Integrating means for integrating the usage of each of the plurality of types of fuel;
Reduction timing determining means for determining a timing for executing a reduction process on the catalyst based on the usage amount of each of the plurality of types of fuel obtained by the integrating means ,
The determined by the reduction timing determining means, on the basis of the timing of executing the reduction process, a multi-fuel engine, characterized and Turkey to execute the reduction process for the catalyst. 2. The multi-fuel engine according to claim 1, 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. 3. The multi-fuel engine according to claim 1, wherein the plurality of types of fuel includes gasoline, and is operated using gasoline when performing a reduction process on the catalyst. 4. In performing the reduction processing for the catalyst, the multi-fuel engine according to any one of claims 1 to 3, characterized in that it is the rich spike operation using the fuel suitable for the reduction treatment.   The catalyst is a NOx storage catalyst, and the reduction timing determination means estimates the poisoning state due to the sulfur component of the NOx storage catalyst 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 for executing the reduction process is determined based on a poisoning state of the NOx storage catalyst.   The plurality of types of fuel includes gaseous fuel, and further includes a gaseous fuel supply path for supplying the gaseous fuel, and a sulfur component removing unit provided in the gaseous fuel supply path. A multi-fuel engine according to any one of claims 1 to 5.   The multifuel engine according to claim 6, further comprising means for determining whether it is time to replace the sulfur component removing means based on the amount of the gaseous fuel used. In a multi-fuel engine that can switch and use a plurality of types of fuel including at least gaseous fuel,
A gaseous fuel supply path for supplying the gaseous fuel;
Sulfur component removing means provided in the gaseous fuel supply path ;
An exhaust passage through which engine exhaust is introduced;
A catalyst provided in the exhaust passage;
Integrating means for integrating the amount of liquid fuel used in the plurality of types of fuel;
Reduction timing determination means for determining a timing for executing a reduction process on the catalyst based on the usage amount of the liquid fuel obtained by the integrating means ,
A multi-fuel engine that performs a reduction process on the catalyst based on a timing of executing the reduction process determined by the reduction timing determination unit.

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