JP2589531Y2 - Exhaust purification system for alcohol engine - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification system for an alcohol engine using methanol or ethanol as a fuel.

[0002]

2. Description of the Related Art In recent years, from the viewpoints of resource problems and pollution problems, alcohols such as methanol produced from natural gas and ethanol produced from biomass such as sugar cane are likely to be promising oil substitute fuels and low pollution fuels in the future. It is attracting attention as a candidate. The exhaust characteristics of an alcohol engine are NO, because the calorific value is small and the combustion temperature is relatively low.
_Although unburned alcohol has low photochemical reactivity and low ozone generation compared to HC discharged from gasoline and diesel engines, the amount of unburned alcohol emitted is low. There is a disadvantage that the amount is relatively large and the amount of aldehyde causing an off-odor is large.

Therefore, as an exhaust gas purifying device for reducing the emission of unburned alcohol and aldehyde, a plurality of catalysts are provided in an exhaust passage as proposed in, for example, Japanese Utility Model Laid-Open No. 4-27107. A device that opens and closes a valve provided in an exhaust passage in accordance with the engine speed to increase or decrease the number of catalysts through which exhaust gas passes to adjust the space velocity (gas flow rate per unit time / catalyst capacity) is known. Have been.

[0004]

According to the conventional exhaust gas purifying apparatus, the space velocity is reduced in a high engine speed range, the exhaust resistance is reduced, and the fuel consumption is prevented from deteriorating. Since the structure is such that a plurality of catalysts of the same type are combined and the number of catalysts that allow exhaust gas to pass through is adjusted, the capacity of each catalyst must be relatively large due to exhaust resistance, especially when idling. In a low-load, low-speed range, such as at times, the flow rate of exhaust gas is low and the space velocity cannot be sufficiently increased, so that there has been a problem that the amount of emission of unburned alcohol and aldehyde increases.

[0005] In view of the above problems, the present invention can increase the space velocity at low load and low rotation, such as during idling, to reduce the emission of unburned alcohol and aldehyde. In other cases, an object of the present invention is to provide an exhaust purification device for an alcohol engine that can reduce exhaust resistance and improve fuel efficiency by reducing the space velocity.

[0006]

According to a first aspect of the present invention, there is provided an exhaust purification system for an alcohol engine in which a first passage and a second passage are formed by branching an exhaust passage of the alcohol engine. the first catalyst and the volume V _M of the volume V _S
A second catalyst of (> V _S ) is provided, and a valve for opening and closing the second catalyst and a third catalyst of a capacity V _L (> V _M ) are provided in the second passage.
A controller is provided for opening and closing the valve based on a control map using the engine speed and the engine load as parameters.

In adjusting the relationship between the capacities of the respective catalysts, it is preferable that the diameter of the first catalyst be smaller than the diameters of the other catalysts. When the diameter of the catalyst is reduced, the cross-sectional area of the passage is reduced, and the flow rate of the exhaust gas can be increased. Therefore, the reaction time of the catalyst is significantly reduced, and the purification rate of unburned alcohol and aldehyde is extremely improved. It is an effective means.

[0008] As a control method using the control map,
According to the relationship between the engine speed and the engine load, for example, when the engine speed is low and the engine load is low, opening and closing the valve so as to exhaust the exhaust gas through the first catalyst having a small capacity increases the space velocity. Is preferred. Further, in performing this control, the engine rotation region and the engine load region may be respectively divided into a plurality of parts, and the opening and closing of the valve may be controlled stepwise according to a combination of the respective regions. Stepless control may be performed not only by controlling the opening and closing of the valve but also by adjusting the opening degree according to the engine load.

Further, in performing this control, in addition to the engine speed and the engine load described above, the temperature of the cooling water of the engine and the temperature of the exhaust gas in the exhaust passage are detected by a temperature sensor to finely match the operating conditions of the engine. It is more preferable to do so.

[0010]

[Operation] The exhaust gas purifying apparatus for an alcohol engine according to the present invention has the above-described configuration, and opens and closes the valve of the branched second passage according to the engine speed and the engine load, and selectively uses catalysts having different capacities. The space velocity will be appropriately adjusted to the operating conditions of the engine.

In particular, when the diameter of the first catalyst is made smaller than the diameter of the other catalysts, the valve is closed when the engine speed is low and the load is low, and the valve is opened otherwise. In the former case, the exhaust gas passes only through the first passage and the space velocity increases, whereas in the latter case, the exhaust gas mainly passes through the second passage and also passes through the first passage. Space velocity decreases.

[0012]

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings. The exhaust gas purifying apparatus 2 of the alcohol engine 1 shown in FIG. 1 branches the exhaust passage 3 into two branches in the middle. One of the first passages 4 is provided with a first catalyst (pre-catalyst) 5 having a capacity V _S and the first catalyst 5. Capacity V _M (>) with the same length as catalyst 5 but with a larger diameter
V _S ) of the second catalyst (main catalyst) 6
In the passage 7, a capacity V having the same diameter as the second catalyst 6 and twice the length thereof is provided.
_{An L} (> V _M ) third catalyst (main catalyst) 8 is provided.

As described above, the diameter of the first catalyst 5 is
The diameters of the catalyst 6 and the third catalyst 8 are set to be smaller than that of the catalyst 6 in order to reduce the cross-sectional area of the passage and increase the flow rate of the exhaust gas by reducing the diameter of the catalyst. When the flow rate of the exhaust gas increases, the reaction time of the catalyst can be shortened, and the purification rate of HC and aldehyde is improved.

A butterfly valve 9 is provided in the second passage 7 upstream of the third catalyst 8. The butterfly valve 9 opens and closes a solenoid valve 10 and is connected to an air cylinder 11 connected to an air tank 11. It is opened and closed by activating 12.
In the present embodiment, the butterfly valve 9 is set to be closed when the solenoid valve 10 is open, and the butterfly valve 9 is set to be opened when the solenoid valve 10 is closed.

The solenoid valve 10 is controlled by an output signal of a controller 13. The controller 13 has an engine speed N, detected by a speed sensor 14,
The engine load L detected by the load sensor 15, the cooling water temperature T _W detected by the water temperature sensor 16, and the exhaust temperature T _EXH detected by the temperature sensor 17 are input and controlled based on these parameters. .

Specifically, the control map shown in FIG. 2 is stored in the memory of the controller 13, and the opening and closing of the solenoid valve 10 is controlled according to the flowchart shown in FIG. It has become. That is, in the control map shown in FIG. 2, the engine speed range is conveniently divided into an idle speed N _I , a low speed N _L , a medium speed N _M , and a high speed (rated speed) N _H. the engine load region is divided between the low load L _L, medium load L _M, a high load (rated load) L _H.

From the idle speed N _I , the low speed N
_In the rotation range up to _L, when the engine load is equal to or less than the medium load L _M , and in the rotation range from low rotation N _L to high rotation N _H , the control region is A when the engine load is equal to or less than the low load L _L. In other cases, the control region is the B region. The control area determined based on the control map is a condition for controlling the opening and closing of the solenoid valve 10 and the butterfly valve 9 performed according to a flowchart described later.

Next, in performing control in accordance with the flowchart shown in FIG. 3, first, the engine speed N, the engine load L, the cooling water temperature T _W , and the exhaust temperature T _EXH are read, and the cooling water temperature T _W is set to a predetermined value (warm-up temperature). If it is higher than T _L , it is determined whether the control region selected according to the control map is the A region or the B region. In the case of the A region, since the engine load and the engine speed are relatively low, the electromagnetic valve Open 10 and
The butterfly valve 9 is closed, and the exhaust gas flows only through the first passage 4 in which the first catalyst 5 and the second catalyst 6 are arranged.

When the cooling water temperature T _W is higher than the warm-up temperature T _L and the control range is the B range, the engine load and the engine speed are relatively high, so the solenoid valve 10 is closed and the butterfly is closed. The valve 9 is opened and the second catalyst 8
Exhaust gas flows through the first passage 4 as well as the passage 7. In this case, since the exhaust resistance is different between the first passage 4 side and the second passage 7 side and the resistance on the second passage 7 side is small, the exhaust gas tends to flow more to the second passage 7 side. .

Furthermore, when the cooling water temperature T _W is less than the warm-up temperature T _L, and, when the exhaust gas temperature T _EXH predetermined value higher than (catalyst activation temperature) T _H closes the solenoid valve 10, the butterfly When the valve 9 is opened, the exhaust gas is caused to flow through the second passage 7 as well as the first passage 4, and conversely, when the cooling water temperature T _W is equal to or lower than the warm-up temperature _TL , and the exhaust temperature T _EXH is increased. if: catalyst activation temperature T _H, open the electromagnetic valve 10, closes the butterfly valve 9, flow exhaust gas only to the first passage 4.

In practicing the present invention, the first catalyst (pre-catalyst) 5 having a relatively high space velocity is used, which is based on the following knowledge. That is, when the diameter of the catalyst is D and the capacity is V as shown in FIG.
The relatively large diameter, large capacity catalyst of 44 mm and V = 2600 ml requires a relatively long reaction time due to the low space velocity as shown by the curve E, and the relatively large catalyst of D = 88 mm and V = 800 ml. A small-diameter, small-capacity catalyst requires a relatively short reaction time because of a large space velocity as shown by the curve F.

However, when a catalyst having a large space velocity is used as shown in FIG. 5, the exhaust resistance becomes larger than the limit which adversely affects the engine output and the fuel consumption as shown by a straight line F, so that the engine speed becomes higher. If it is within the range, there arises a problem that the output performance decreases and the fuel efficiency also deteriorates. Therefore, it is preferable to select and use catalysts having different capacities so that an appropriate space velocity can be obtained according to the operating conditions such as the engine speed and the engine load. When a small catalyst (main catalyst) and a catalyst having a relatively large space velocity (pre-catalyst) are combined, the effect of the pre-catalyst causes the curve E indicating the emission level before purification in FIG.
+ F is rapidly purified in a short reaction time, whereas when only a main catalyst having a relatively low space velocity is used without using a pre-catalyst, the reaction is It takes a long time and the purification action is not enough.

Generally, as shown in FIG. 7, the exhaust gas flow velocity distribution greatly varies depending on the engine speed. In an idling state, the exhaust gas flow velocity decreases and
There is a tendency for the gas to flow in the central part of the exhaust passage 3. Therefore, in order to improve the purification rate of HC and aldehyde in the idling state, it is necessary to shorten the reaction time of the catalyst. Therefore, the diameter of the catalyst is reduced and the flow rate of the exhaust gas is increased. It is effective.

For these reasons, catalysts having different space velocities, in other words, catalysts having different capacities are used in combination, and the catalyst to be used is selected in accordance with the operating conditions of the engine, thereby purifying exhaust gas and improving fuel efficiency. The best effect can be obtained from both sides.

[0025]

According to the invention, the exhaust purification device for an alcohol engine of the present invention branches off the exhaust passage of the alcohol engine to the first position.
A passage and a second passage are formed, a first catalyst having a capacity V _{S and} a second catalyst having a capacity V _M (> V _S ) are provided in the first passage, and a valve for opening and closing the second catalyst and a capacity V _L ( > V _M ), and a controller that opens and closes the valve based on a control map using the engine speed and the engine load as parameters is provided. Therefore, the following effects can be obtained.

According to the engine speed and the engine load,
Since the valves of the branched second passages can be opened and closed to selectively use catalysts having different capacities, the space velocity can be appropriately adjusted according to the operating conditions of the engine. Therefore,
In particular, when the engine is low in speed and load is low (when idling, etc.), the valve is closed, and in other cases, the valve is opened. In the former case, the space velocity increases,
The emission amount of unburned alcohol and aldehyde can be reduced, and in the latter case, exhaust resistance is reduced and fuel efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for purifying exhaust gas of an alcohol engine according to an embodiment of the present invention;

FIG. 2 is a control map of a controller used in the exhaust gas purification device for an alcohol engine in FIG. 1;

FIG. 3 is a flowchart of a controller used in the exhaust gas purification device for an alcohol engine in FIG. 1;

FIG. 4 is a characteristic diagram showing a difference in reaction time due to a difference in catalyst diameter and capacity.

FIG. 5 is a characteristic diagram showing a difference in exhaust resistance due to a difference in catalyst diameter and capacity.

FIG. 6 is a characteristic diagram showing the concentration of HC in exhaust gas depending on the presence or absence of a precatalyst.

FIG. 7 is a characteristic diagram showing a flow velocity distribution of exhaust gas.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Alcohol engine 2 Exhaust gas purifier 3 Exhaust passage 4 First passage 5 First catalyst 6 Second catalyst 7 Second passage 8 Third catalyst 9 Valve (butterfly valve) 13 Controller

Claims (1)

(57) [Scope of request for utility model registration] A first passage and a second passage are formed by branching an exhaust passage of an alcohol engine, and a first catalyst having a capacity V _{S and} a second catalyst having a capacity V _M (> V _S ) are formed in the first passage. Provided, second
Provided with a third catalyst passageway valve and capacity for opening and closing this to V _L (> V _M), the alcohol engine having a controller for opening and closing the valve based on a control map in which the engine speed and the engine load as parameters Exhaust purification equipment.