JPH068259Y2 - Nitrogen oxide removal mechanism of diesel engine - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a nitrogen oxide removing mechanism of a diesel engine,
More specifically, the present invention relates to a nitrogen oxide removing mechanism of a diesel engine that can effectively remove nitrogen oxides (NO _x ) from the exhaust gas of the diesel engine by a catalyst.

[Technical background of the invention]

Nitrogen oxides (hereinafter referred to as NO
_As a method of reducing the amount, the fuel injection timing of the conventional diesel engine is slightly delayed to burn the fuel (so-called timing retard).
Methods for preventing the generation of NO _x are known. That is, the N
Since a large amount of O _x is generated when the fuel burns at a high temperature, the timing retard is performed as described above to burn the fuel at a lower temperature and suppress the generation of NO _x .

However, according to this timing retard method, NO
_Although the generation of _x is suppressed, there is a drawback that not only the combustion efficiency is deteriorated but also black smoke is increased.

For removing NO _x as described above, a method of reducing and removing NO _x once generated by a catalyst as in a gasoline engine can be considered.

However, compared to a gasoline engine, a diesel engine is characterized by a large amount of residual oxygen in exhaust gas, and cannot be reduced using a reducing agent used in a gasoline engine, such as hydrocarbon or carbon monoxide. There was a flaw. That is, in a gasoline engine, air-fuel can be burned at a theoretical mixing ratio, and oxygen in exhaust gas is almost zero. However, in the case of a diesel engine, the air-fuel equivalent ratio is maintained even at full engine load. It is necessary to make the air about 1.3: 1 and excess,
For this reason, a considerable amount of residual oxygen is mixed in the exhaust gas. Therefore, even if a normal reducing agent, for example, a reducing agent such as hydrogen or carbon monoxide is added to the exhaust gas in the presence of a catalyst, it will react with oxygen first and cannot reduce NO _x . For this reason, the method of removing the exhaust gas of the diesel engine by a catalytic reaction has not been put into practical use at present.

Recently, as a method for removing NO _{x in} combustion gas for thermal power generation, a method has been developed for reducing NO _{x in} combustion gas rich in oxygen in the presence of a catalyst using NH ₃ as a reducing agent. There is.

However, NO _{x in} the exhaust gas of diesel engines
This technology cannot be used as is for the reduction of. That is, in the thermal power generation, in order to reduce the combustion gas in a steady state, the temperature of the combustion gas is almost constant, but in the case of a diesel engine, the temperature of the exhaust gas significantly changes depending on the engine load, Since thermal power generation is in a steady state, the amount of NO _x is almost constant, but in the case of a diesel engine, the amount of NO _x changes depending on the engine load. The NH ₃ is toxic and has a strong irritating odor. for, strictly control the amount of NH ₃ corresponding to the amount of nO _x, that NH ₃ is required to avoid remaining in the exhaust gas, in the case of automobiles, the operation range is wide and a reducing agent Since NH ₃ must be installed separately, it is necessary to reduce NO _x in the entire operating range and reduce the consumption of NH ₃ as much as possible to enable long-term reduction, etc. Because there is.

In order to achieve such various conditions, the present inventor made various inventions and filed patent applications and utility model registration applications (for example, Japanese Patent Application No. 62-31149).

[Purpose of device]

The present invention further embodies the above-mentioned series of inventions and inventions, and particularly provides a mechanism for controlling the temperature of the exhaust gas brought into contact with the TiO ₂ -based catalyst.

That is, using NH ₃ as a reducing agent, and the mechanism for reducing and removing the NO _x in the diesel engine using a catalyst, given that the activation temperature of the TiO ₂ catalyst is 200 to 500 ° C., the exhaust gas temperature It is an object to provide a mechanism for cooling the exhaust gas when the temperature is high.

[Constitution of device]

Therefore, the nitrogen oxide removing mechanism of the diesel engine according to the present invention has a supercharger driven by the engine, adds NH ₃ to the exhaust passage, and exhausts the exhaust gas containing the NH ₃ to the downstream of the turbine. A nitrogen oxide removing mechanism for reducing and removing the NO _x by contacting a provided TiO ₂ based catalyst, wherein a bypass passage connected to an exhaust passage upstream of the catalyst is provided in an intake passage of the supercharger. And a valve that can be opened and closed is provided in the air supply passage so that a part of the supply air can be supplied to the exhaust passage.

Further, the nitrogen oxide removing mechanism of the diesel engine according to the present invention is particularly applied to the engine with the turbocharger, and the turbine provided in the exhaust passage rotates the compressor provided in the air supply passage to supercharge. With such a turbocharger, and adding NH ₃ to the exhaust passage, the exhaust gas containing the NH ₃ is brought into contact with a TiO ₂ -based catalyst provided downstream of the turbine to reduce and remove the NO _x. In the nitrogen oxide removing mechanism, a bypass passage connected to an exhaust passage upstream of the catalyst and downstream of the turbine is formed in the supply passage downstream of the compressor, and an openable valve is provided in the supply passage. In addition, a part of the supply air can be supplied to the exhaust passage.

〔Example〕

FIG. 1 is a schematic view of an embodiment of the present invention. As is apparent from the drawing, the nitrogen oxide removing mechanism of the diesel engine according to the present invention is provided with a catalyst 3 in the exhaust passage 2 of the engine 1. The exhaust gas exhausted from the engine 1 passes through the catalyst 3 and is released into the atmosphere. NH ₃ which is a reducing agent for removing NO _x of the exhaust gas is connected to an NH ₃ tank 5 via a flow rate adjusting valve 4 so that a predetermined amount of NH ₃ can be supplied to the exhaust passage 2 upstream of the catalyst 3. .

The engine 1 in this invention has a turbocharger 6. As is well known, the turbocharger 6 includes a turbine 61 provided in the exhaust passage 2 of the engine 1 and the turbine 61.
The compressor 62 is coaxially connected to the air supply introduction pipe 11 and the air supply passage 8 and is rotated by the exhaust gas. Air and air are compressed and supercharged to the engine 1 through the air supply passage 8.

In the air supply passage 8 downstream of such a turbocharger 6,
In the present invention, a bypass passage 7 is provided that is connected upstream of the catalyst 3 and downstream of the turbine 61. An electromagnetic valve 9 is provided in the bypass path 7, for example,
The opening degree of the solenoid valve 9, that is, the amount of air supplied to the exhaust gas can be controlled according to the temperature of the exhaust gas or the supply air pressure of the supply passage 8, that is, the boost pressure.

The opening of the solenoid valve 9 is controlled by the computer 10, for example. The computer 10 can control the opening degree of the solenoid valve 9 based on the signals of engine speed and engine load. That is, the temperature of the exhaust gas exhausted from the engine 1 due to the engine speed and the engine load can be estimated experimentally, and therefore a map using the engine load and the engine speed as a function is prepared and The opening degree of the solenoid valve 9 may be controlled to keep the exhaust gas at a predetermined temperature.

Further, by measuring the boost pressure, it is possible to experimentally estimate the temperature of the exhaust gas exhausted from the engine 1. Therefore, the boost pressure is measured, and the computer 10
You may make it control by the map previously input into. Further, the temperature of the exhaust gas may be measured and fed back.

In the present invention, a TiO ₂ -based catalyst is used as a catalyst for causing the above-mentioned catalytic reaction, and NO _x is reduced by the following reaction and removed as nitrogen.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (a) 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (b) For example, catalysts such as Pt and Pd also cause the above reaction. The catalyst is characterized by having good activity at a relatively low temperature of 200 to 300 ° C. However, at such low temperatures, the amount of NO _{x in} the exhaust gas is limited (when fuel burns at relatively low temperatures, NO _x
The amount of _x generated is small), and it is not necessary to reduce and remove NO _x .

Therefore, in the present invention, a TiO ₂ -based catalyst that is inexpensive and active at a relatively high temperature is used.

Such a TiO ₂ catalyst has activity at a relatively high temperature of 200 to 500 ° C.

The nitrogen oxide removing mechanism according to the present invention operates as follows.

The exhaust gas discharged from the engine 1 rotates the turbine 61, and the compressor 62 supplies the supply air to the engine 1.
After supercharging, the catalyst reaches the catalyst 3 through the exhaust passage 2. An NH ₃ tank 5 is provided upstream of the catalyst 3 via a flow rate adjusting valve 4 for adding NH ₃ to the exhaust gas. The flow rate adjusting valve 4 is controlled by, for example, a computer 10 so that NH ₃ can be added according to the amount of the exhaust gas.

When the exhaust gas temperature is 500 ° C. or lower, it is not necessary to cool the exhaust gas, so the solenoid valve 9 provided downstream of the compressor 62 in the air supply passage 8 is kept closed.

If the exhaust gas exceeds 500 ° C, the computer 10
Opens the solenoid valve 9 at a predetermined opening according to a map input in advance. The supply air is supplied to the upstream side of the catalyst 3 in the exhaust passage 2 through the bypass passage 7 and serves to cool the exhaust gas from the engine 1.

When the exhaust gas becomes high in temperature as described above, the engine 1 has a high load and a high rotation speed.
Also rotates at a high speed, but as described above, at the time of this high load and high rotation, a part of the supply air is bypassed from the supply passage 8 to the exhaust passage 2, so the cylinder of the engine 1 It is possible to prevent a situation in which excessive air enters the cylinder and the cylinder pressure becomes too high.

That is, in the present invention, for example, using a computer, as a means for detecting the exhaust gas temperature, a method of measuring the engine load and the number of revolutions and controlling by the map, or a method of detecting the boost pressure and controlling by the map By adopting the method and the method of measuring and feeding back the temperature of the exhaust gas, it is possible to prevent the pressure in the cylinder of the engine 1 from becoming too high and damage the engine, and it is possible to maintain the catalyst 3 at a predetermined activation temperature. Therefore, it is particularly preferable.

On the other hand, when the temperature of the exhaust gas is less than 200 ° C., the amount of NO _x has a relatively low concentration, so it may be released into the atmosphere without being brought into contact with the TiO ₂ -based catalyst.

In this embodiment, the solenoid valve is used and its opening is adjusted.However, when the supply pressure in the supply passage exceeds a predetermined value, the temperature of the exhaust gas is controlled by the valve that is opened. Obviously, it may be lowered.

For convenience of explanation, the present embodiment has been described by taking a turbocharger as an example of a supercharger, but any other supercharger mounted on an engine such as a roots blower can exert the present effect. It is a thing.

[Effect of device]

As described above, according to the method for removing nitrogen oxides of a diesel engine according to the present invention, by using TiO ₂ as a catalyst and NH ₃ as a reducing agent, exhaust gas of a diesel engine, which has been impossible in the past, can be obtained. There is an advantage that the nitrogen oxides therein can be satisfactorily removed. Furthermore, according to the present invention, a bypass passage is provided in the air supply passage downstream of the compressor of the turbocharger to allow a part of the air supply to be supplied upstream of the catalyst, so that the exhaust gas temperature can be controlled by the TiO ₂ system. Since it can be kept within the activation temperature of the catalyst, there is an advantage that the removal efficiency of NO _x becomes good.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an embodiment of a nitrogen oxide removing mechanism according to the present invention. 1 ... Engine, 2 ... Exhaust passage, 3 ... Catalyst, 5 ...
NH ₃ tank, 6 ... turbocharger, 61 ... turbine, 62 ... compressor, 7 ... bypass passage, 8 ... air supply passage, 9 ... solenoid valve, 10 ... computer.

Claims (2)

[Scope of utility model registration request] 1. A supercharger driven by an engine,
And a nitrogen oxide removing mechanism for reducing and removing the NO _x by adding NH ₃ to the exhaust passage and bringing the exhaust gas containing the NH ₃ into contact with a TiO ₂ -based catalyst provided downstream of the turbine, A bypass passage connected to an exhaust passage upstream of the catalyst is formed in the air supply passage of the supercharger, and an openable / closable valve is provided in the air supply passage so that part of the supply air is exhausted through the exhaust passage. A nitrogen oxide removal mechanism for diesel engines, which is characterized in that it can be supplied to 2. A turbine provided in the exhaust passage,
It has a turbocharger that rotates the compressor installed in the air supply passage to supercharge,
A nitrogen oxide removing mechanism for reducing and removing the NO _x by adding ₃ and bringing the exhaust gas containing the NH ₃ into contact with a TiO ₂ -based catalyst provided downstream of the turbine. A bypass passage is formed in the air passage, which is connected to the exhaust passage downstream of the turbine and upstream of the catalyst, and an openable / closable valve is provided in the air supply passage so that a part of the supply air is supplied to the exhaust passage. A nitrogen oxide removal mechanism for diesel engines characterized by being able to supply.