Exhaust emission control device for hydrogen engine

Abstract

To provide an exhaust emission control device for a hydrogen engine that suppresses thermal deterioration of a catalyst.SOLUTION: An exhaust emission control device for a hydrogen engine includes: a catalyst provided in an exhaust passage; and an air-fuel ratio detection section provided upstream of the catalyst. The exhaust emission control device for the hydrogen engine further includes: a catalyst bed temperature detection section that detects a catalyst bed temperature; a first determination section that determines whether or not to execute catalyst temperature rise processing on the basis of the catalyst bed temperature detected by the catalyst bed temperature detection section; a hydrogen amount estimation section that estimates a hydrogen amount adsorbed to a surface of the catalyst when the first determination section determines execution of the catalyst temperature rise processing; a second determination section that determines whether or not to execute the catalyst temperature rise processing in accordance with the hydrogen amount estimated by the hydrogen amount estimation section; and a catalyst temperature rise section that executes the catalyst temperature rise processing when the second determination section determines that execution of the catalyst temperature rise processing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an exhaust purification device for a hydrogen engine. [Background technology]

[0002] Patent Document 1 below discloses an exhaust purification device for a hydrogen engine that maintains NOx purification performance regardless of catalyst temperature by changing the amount of hydrogen injected during the exhaust stroke depending on the catalyst temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-074448 Summary of the Invention [Problem to be solved by the invention]

[0004] Due to its small atomic weight, hydrogen can penetrate and adsorb not only on the surface of the catalyst but also deep within. When hydrogen is adsorbed deep within the catalyst, the amount of heat generated increases, causing local overheating and accelerating thermal degradation of the catalyst, such as sintering and structural destruction. The technology in Patent Document 1 adjusts the amount of hydrogen depending on the catalyst temperature, but does not take into account the amount of hydrogen adsorbed on the surface and deep within the catalyst, leaving room for improvement in terms of suppressing thermal degradation of the catalyst. [Means for solving the problem]

[0005] In order to solve the above problems, one embodiment of an exhaust purification device for a hydrogen engine is an exhaust purification device for a hydrogen engine comprising a catalyst provided in an exhaust passage and an air-fuel ratio detection unit provided upstream of the catalyst, and comprising: a catalyst bed temperature detection unit that detects a catalyst bed temperature; a first judgment unit that judges whether or not to perform a catalyst heating process based on the catalyst bed temperature detected by the catalyst bed temperature detection unit; a hydrogen amount estimation unit that estimates the amount of hydrogen adsorbed on the surface of the catalyst when the first judgment unit judges that the catalyst heating process should be performed; a second judgment unit that judges whether or not to perform a catalyst heating process based on the amount of hydrogen estimated by the hydrogen amount estimation unit; and a catalyst heating unit that executes the catalyst heating process when the second judgment unit judges that the catalyst heating process should be performed. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an exhaust purification device for a hydrogen engine that suppresses thermal degradation of a catalyst. [Brief explanation of the drawings]

[0007] [Figure 1] 10 is a time chart showing the time up to when the catalyst temperature increase process is executed. [Figure 2] 10 is a flowchart showing a process up to the execution of a catalyst temperature increase process. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Exhaust purification device for hydrogen engines)

[0009] As shown in FIG. 1, the exhaust gas purification device for a hydrogen engine of the present invention performs catalyst heating processing when the catalyst bed temperature is at a predetermined low temperature that requires catalyst heating processing, and the amount of hydrogen adsorbed on the catalyst surface reaches a predetermined threshold value or more.

[0010] Generally, the penetration of hydrogen into the deep layer of the catalyst is inhibited depending on the amount of hydrogen on the catalyst surface. In other words, if a large amount of hydrogen is adsorbed on the catalyst surface, the penetration of hydrogen into the deep layer of the catalyst can be prevented. In addition, high energy such as high temperature and high pressure is required for hydrogen to be adsorbed into the deep layer of the catalyst.

[0011] The exhaust gas purification device for a hydrogen engine of the present invention performs catalyst warming when the catalyst bed temperature is at a predetermined low level that requires catalyst warming, and only after the amount of hydrogen adsorbed on the catalyst surface reaches a predetermined threshold. This configuration allows a sufficient amount of hydrogen to be adsorbed on the catalyst surface before performing catalyst warming, and prevents hydrogen from adsorbing deep into the catalyst even when high energy is applied. This accordingly prevents thermal degradation due to localized catalyst overheating.

[0012] (Flowchart related to exhaust purification device) FIG. 2 is a diagram showing a flowchart up to the execution of catalyst temperature raising processing in an exhaust purification device for a hydrogen engine according to one embodiment.

[0013] <Step 1 (S1)> First, the catalyst bed temperature detection unit detects the catalyst bed temperature provided in the exhaust passage (S1, step 1). The catalyst bed temperature detection unit may be provided with a sensor that detects the catalyst bed temperature, or may estimate the catalyst temperature using a catalyst temperature estimation logic that uses the accumulated air amount value since the engine started, the exhaust gas sensor output, etc. The catalyst is not particularly limited, and examples thereof include those containing Pt, Pd, Rh, Cu, Ni, etc.

[0014] <Step 2 (S2)> Next, the first determination unit determines whether or not to execute catalyst temperature increase processing based on the catalyst bed temperature detected by the catalyst bed temperature detection unit. The catalyst bed temperature used as the determination criterion can be, for example, 300°C. That is, when the catalyst bed temperature is less than 300°C, the process proceeds to step 3 (S3) (Yes direction), and when the catalyst bed temperature is 300°C or higher, the catalyst temperature increase processing is not executed (No direction), and the process proceeds to normal operation.

[0015] <Step 3 (S3) and Step 4 (S4)> When the first determination unit determines that the catalyst temperature increase process should be performed, the hydrogen amount estimation unit measures the amount of hydrogen in the catalyst and the surface adsorption rate, and estimates the amount of hydrogen adsorbed on the catalyst surface based on these values ​​(step 3 (S3) and step 4 (S4)). The amount of hydrogen in the catalyst may be, for example, a sensor that measures the amount of hydrogen in the exhaust passage, or may be an estimated value based on the catalyst bed temperature, map values, etc. Here, the amount of hydrogen adsorbed on the catalyst surface can be estimated based on the following formula.

[0016]

number

[0017] <Step 5 (S5)> Next, a second determination unit determines whether or not to perform catalyst temperature increase processing based on the estimated hydrogen amount. The hydrogen amount used as the determination criterion is not particularly limited, and it is preferable to set a threshold value in advance based on the catalyst being used. That is, if the amount of hydrogen on the catalyst surface is equal to or greater than a predetermined threshold, the process may proceed to step 6 (S6) (Yes direction), and if the amount of hydrogen on the catalyst surface is less than the predetermined threshold, the catalyst temperature increase processing may not be performed (No direction), and the process may return to step 1 (S1) again.

[0018] The threshold value of the amount of hydrogen on the catalyst surface can be determined from the sensitivity of the amount of hydrogen inflow into the catalyst depth to the amount of hydrogen adsorbed on the catalyst surface. The threshold value is set appropriately depending on the catalyst type and structure used, and the amount of hydrogen inflow into the catalyst depth is set appropriately depending on the system requirements.

[0019] If the second determination unit determines in step 5 (S5) that the catalyst temperature increase process should not be performed, a mechanism for introducing hydrogen into the exhaust passage may be used to cause hydrogen to be adsorbed onto the catalyst surface. The mechanism for introducing hydrogen into the exhaust passage may, for example, be a hydrogen engine equipped with a hydrogen injector that supplies hydrogen, or a mechanism for providing a hydrogen injector in the exhaust passage to add hydrogen directly to the catalyst, or a combination of these. The hydrogen injector may be equipped with a mechanism for controlling the amount of hydrogen injected.

[0020] <Step 6 (S6)> When the second determination unit determines that the catalyst temperature increase process should be performed, the catalyst temperature increase processing unit executes the catalyst temperature increase process. The catalyst temperature increase processing unit may include, for example, a heater and a means for controlling the heater. The controlling means may include, for example, controlling the power supply to an external heater or releasing the engine load.

[0021] Steps 3 (S3) to 5 (S5) can also be replaced by an air-fuel ratio detector provided upstream of the catalyst. The air-fuel ratio detector detects the amount of rich gas, which is accumulated in the catalyst and has a large amount of unburned hydrogen, and executes catalyst temperature increase processing when the amount exceeds a predetermined threshold. For example, an A / F sensor can be used as the air-fuel ratio detector.

[0022] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Claims

[Claim 1] An exhaust purification device for a hydrogen engine, comprising: a catalyst provided in an exhaust passage; and an air-fuel ratio detection unit provided upstream of the catalyst, a catalyst bed temperature detection unit that detects a catalyst bed temperature; a first determination unit that determines whether or not to execute a catalyst temperature increase process based on the catalyst bed temperature detected by the catalyst bed temperature detection unit; a hydrogen amount estimation unit that estimates an amount of hydrogen adsorbed on a surface of the catalyst when the first determination unit determines that the catalyst temperature increase process should be performed; a second determination unit that determines whether or not to execute a catalyst temperature increase process in accordance with the amount of hydrogen estimated by the hydrogen amount estimation unit; a catalyst temperature increasing unit that executes the catalyst temperature increasing process when the second determination unit determines that the catalyst temperature increasing process is to be executed; An exhaust purification device for a hydrogen engine, comprising:

Images