JPH0610129Y2 - Nisel 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, reforming a fuel and separating and storing hydrogen in the reformed gas. The present invention relates to a nitrogen oxide removing mechanism of a diesel engine that uses this hydrogen to reduce and remove nitrogen oxides in the presence of 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 NOx are known. That is, the N
Since a large amount of Ox is generated when the fuel burns at a high temperature, the timing retardation is performed as described above to burn the fuel at a lower temperature and suppress the generation of NOx.

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.

To remove NOx as described above, a method of reducing and removing NOx 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 the exhaust gas, and it is not possible to reduce using a reducing agent used in a gasoline engine, such as hydrogen or carbon monoxide. was there. That is, in a gasoline engine, air-fuel can be burned at a theoretical mixing ratio, and therefore oxygen in the exhaust gas becomes almost zero, but in a diesel engine, the mixing ratio of air-fuel is about 1.3: 1
(Volume mixing ratio) and air must be in excess, so even if a normal reducing agent such as hydrogen or carbon monoxide is added to the exhaust gas in the presence of a normal catalyst, Since it reacted with oxygen, NOx could not be reduced.

[Purpose of device]

The present invention has been made in view of the above points, and uses nitrogen formed by reforming a fuel as a reducing agent to reduce NOx in the presence of a special catalyst. The purpose is to provide.

[Constitution of device]

To achieve the above object, the nitrogen oxide removing mechanism of a diesel engine according to the present invention is modified by a reformer that reforms a part of fuel of a diesel engine to hydrogen and lower hydrocarbons, and the reformer. A hydrogen tank filled with a metal that selectively occludes hydrogen in the reformed reformed gas as a metal hydride; a means for introducing the hydrogen occluded in the hydrogen tank into an exhaust pipe; And a reduction catalyst capable of reducing the nitrogen oxides in the exhaust gas in the presence of oxygen.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a NOx removing mechanism for a diesel engine according to the present invention. As is apparent from FIG. 1, the NOx removing mechanism according to the present invention provides a fuel for a diesel engine 1. The fuel in the tank 2 is not only supplied to the injection pump of the diesel engine 1,
A part of it is supplied to the reformer 3. The reforming device 3 is a device for decomposing light oil as fuel and reforming it into lower hydrocarbons such as hydrogen and methane. In this embodiment, the light oil is reformed by the heat quantity of exhaust gas. It has become.

The reformed gas reformed by the reformer 3 is supplied to the hydrogen tank 5
Be led to. The hydrogen tank 5 is loaded with a metal that produces a metal hydrogen lower product by hydrogen, and the substance has a property of occluding hydrogen as a metal hydride. Occlude only hydrogen. As a result, hydrogen is separated and occluded from the reformed gas. That is, this metal undergoes a reversible reaction of MH (metal hydride) → M (metal) + H (hydrogen), occludes hydrogen at a low temperature (reaction proceeds to the left side of the above formula), and hydrogen at a high temperature. Is generated (the reaction proceeds to the right side in the above formula). Therefore, when it is desired to store hydrogen at a low temperature and generate hydrogen, the tank 5
Can be heated to generate hydrogen.

The hydrogen stored in the hydrogen tank 5 is introduced into the exhaust pipe 4 upstream of the catalytic converter 6. Then, the NOx in the exhaust gas is reduced and removed by the action of the water catalyst.

Conventional catalysts cannot be used to reduce NOx in the exhaust gas of such oxygen-rich diesel engines. That is, it is necessary to use a catalyst that selectively reduces NOx without oxidizing the reducing agent hydrogen, that is, a catalyst that reduces NOx in the presence of oxygen.
Examples of such a catalyst include Fe ₂ O ₃ and Cr ₂ O ₃ .

In this embodiment, a computer 7 is provided, and this computer 7 measures the NOx amount in the exhaust gas from the load of the diesel engine 1 and the like, and based on the above information, the hydrogen introduced from the hydrogen tank 5 to the exhaust pipe 4 is measured. It is designed to control the quantity.

With such a configuration, first, a part of the fuel in the fuel tank 2 for supplying the fuel to the diesel engine 1 is sent to the reformer 3. The fuel introduced into the reformer 3 is reformed by the heat of the exhaust gas of the diesel engine 1 and becomes a reformed gas composed of hydrogen and lower hydrocarbons. This reformed gas is introduced into the hydrogen tank 5. Since the hydrogen tank 5 is loaded with a metal capable of producing a metal hydride, only hydrogen in the reformed gas is selectively stored. On the other hand, lower hydrocarbons are exhausted without being stored.

NOx in the exhaust gas is measured based on information such as the load of the diesel engine 1 and the computer 7
Introduces a predetermined amount of hydrogen from the hydrogen tank 5 into the exhaust pipe 4.

Hydrogen in the hydrogen tank 5 is introduced from the upstream of the catalytic converter 6, and NOx is reduced and removed by the action of the catalyst loaded in the catalyst computer 6.

The amount of hydrogen mixed in the exhaust gas introduced into the catalytic converter 6 is preferably 0.3 to 0.8 mol of hydrogen added to 1 mol of NOx. NOx less than 0.3 mol
Of 30% or more may not be reduced, and on the other hand, if it exceeds 0.8 mol, a large amount of unreacted hydrogen may be discharged into the atmosphere and the hydrogen may be wasted. This hydrogen has the advantage that it can be precisely controlled because the hydrogen that has been stored in the hydrogen tank 5 is added. There is also an advantage that hydrogen can be added to the exhaust gas even when the engine 1 is started.

The temperature when introducing the exhaust gas into which hydrogen has been introduced into the catalytic converter 6 as described above is preferably 200 to 500 ° C. If it is lower than 200 ° C., the catalyst does not have sufficient activity, and if it exceeds 500 ° C., the quality of the catalyst may deteriorate and the activity of the catalyst may decrease.

The exhaust gas thus mixed with hydrogen is introduced into the catalytic converter 6, and NOx is reduced and removed by the above-mentioned catalyst loaded in the catalytic converter 6.

In this embodiment, the computer 7 measures NOx based on the load of the diesel engine 1 and the like.
It was only used to control the amount of hydrogen introduced based on the amount, but in addition to this, for example by connecting to a temperature sensor,
It is also possible to control the temperature of the exhaust gas introduced into the catalytic converter 6 based on the information of this temperature sensor, and control the reformer 3 to control the amount of hydrogen stored in the hydrogen tank 5. You may control.

[Effect of device]

As described above, according to the present invention, a part of fuel is reformed to generate hydrogen and lower hydrocarbons, and hydrogen in the reformed gas is selectively stored in the hydrogen tank. Is used to reduce and remove NOx under a special catalyst. Therefore, there is an advantage that NOx can be removed without delaying the fuel injection timing as in the conventional case.

Further, since the reformer produces the reducing gas from the fuel, there is also an advantage that it is not necessary to store the gas that reduces NOx.

Further, since the hydrogen tank is provided, NOx at the time of starting the diesel engine can be reduced and removed, and the amount of hydrogen added to the exhaust gas can be easily controlled, which is also extremely advantageous. is there.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a nitrogen oxide removing mechanism of a diesel engine according to the present invention. 1 ... Diesel engine, 2 ... Fuel tank, 3 ...
Reformer, 4 ... Exhaust pipe, 5 ... Hydrogen tank.

Claims (1)

[Scope of utility model registration request] 1. A reformer for reforming a part of fuel of a diesel engine into hydrogen and lower hydrocarbons, and hydrogen in the reformed gas reformed by the reformer for selectively selecting metallic hydrogen. Hydrogen tank filled with metal to be stored as a compound, means for introducing hydrogen stored in the hydrogen tank into the exhaust pipe, and reduction of nitrogen oxides in the exhaust gas mixed with hydrogen in the presence of oxygen And a reduction catalyst capable of removing nitrogen oxides in a diesel engine.