FI73297B - FOERFARANDE FOER MINSKANDE AV KVAEVEOXIDEMISSIONER FRAON EN FOERBRAENNINGSMOTORS AVGASER. - Google Patents

Description

1 73297

METHOD OF REDUCING NITROGEN OXIDE EMISSIONS FROM COMBUSTION ENGINES

The present invention relates to a method for reducing nitrogen oxide emissions from the exhaust gases of an internal combustion engine by means of water and exhaust gas recirculation introduced into the engine.

The use of internal combustion engines, such as diesel engines, has the disadvantage of harmful compounds containing exhaust gases 5. Of these, nitrogen oxides are the most dangerous and the most difficult to eliminate. The amount of nitrogen oxides generated is proportional to the temperature in the combustion chamber and the oxygen content of the explosive gas.

One known means of reducing nitrogen oxides is to lower the combustion temperature by adding water to the combustion engine. The addition of water can be carried out in various ways: according to DE-A-31 44 472, a separate water is injected directly into the fire chamber. In connection with the addition of water, it is also possible to use condensed water from the exhaust gases, which is passed in pieces by water spray, as the addition of water is carried out in an apparatus according to DE-A-28 51 232. The water to be added can be fed directly to the suction duct (DE-A-28 31 694) or the water is first decomposed into a finely divided form by feeding fresh: combustion air through a liquid volume and further to the suction duct (DE-A-26 01 456 and 26 33 639). The water fed to the combustion chamber can also first be evaporated by means of a heat exchanger, whereby the heating takes place by passing hot exhaust gases through a water vessel. The steam thus obtained is then led to the intake duct, while the exhaust gases are led to the outside air. Evaporation is disclosed, for example, in SE publication 428 587 and DE application publications 21 54 755 and 26 04 050.

25 The disadvantage of the above-mentioned methods of supplying water with fires is the expensive acquisition cost of the equipment needed to control the amount of water. In addition, their maintenance requires special care: which contributes to the formation of high operating costs.

Another known way to reduce the nitrogen oxide production of an internal combustion engine is to partially recirculate the exhaust gases. In known ways, such as 2 73297 in SE 404 068 and DE application 2 443 897, the exhaust gas is recycled back to the engine dry. The recirculated exhaust gas, which is preferably 20% of the amount of intake air, then acts as an inert gas and thus reduces the oxygen content of the gas 5 in the combustion chamber. The word also reduces the production of nitric oxide. The control of the recirculated exhaust gas is also difficult to control. In addition, the recirculated exhaust gases must preferably be cooled, for example to reduce the thermal load.

It is an object of the present invention to obviate the disadvantages of the prior art and to provide an improved and more reliable method for reducing nitrogen oxide emissions from the exhaust gases of an internal combustion engine, such as a diesel engine, by utilizing refrigerated exhaust gas recirculation in combination with exhaust water vapor. The essential features of the invention appear from the appended claim 1.

According to the invention, the exhaust gases from the engine are passed through a catalyst, preferably to reduce carbon monoxide and hydrocarbons, before passing the gas to a water scrubber. In the water scrubber, the exhaust gas is simultaneously washed and cooled. The cooled exhaust gas is returned to the intake duct of the internal combustion engine, moistened with the steam generated during the washing. The recirculated exhaust gas, which accounts for about 20% of the total exhaust volume, is mixed with the rest of the intake air flow by means of a mixing valve and a nozzle, which allow the mixture ratio to be kept constant regardless of the load and speed.

Using the method according to the invention, it is thus possible to recycle the exhaust gases, to cool the recirculated exhaust gas and to add water in pieces, and to control the amount of exhaust gas to be returned.

The invention will be described in more detail below with reference to the accompanying drawings, in which Figure 1 schematically shows a preferred embodiment of the invention, Figure 2 shows the advantage of the wet recycle according to the invention over dry recycle.

According to Figure 1, the exhaust gases from the internal combustion engine 1 are passed through the catalyst 2 to the water scrubber 3. In the water scrubber 3, the exhaust gases are cooled and washed. Most of the exhaust is removed through the exhaust pipe 4. The recirculated moist exhaust gas according to the invention is instead led through the return pipe 5 to the internal combustion engine suction system 10. The recirculated exhaust gas entering The mixture of recirculated exhaust gas and clean intake air thus obtained by the nozzle 7 is further led through the intake duct 10 of the internal combustion engine to the combustion chamber 9, from which the resulting exhaust gases pass on to the catalyst 2. A recirculation valve 6 maintained despite possible changes in load and speed.

In Fig. 2, where ΝΟχ denotes the sum of NO and 20 NO2, the wet exhaust gas recirculation method according to the invention is compared with the prior art dry recirculation when the recycled part is 20% of the total exhaust gas volume. The nitrogen oxide concentration curves plotted in Figure 2 are shown as a function of the average engine pressure. It can be seen from Figure 2 that when using the method according to the invention (curves A), the total amount of nitrogen oxides ΝΟχ is substantially reduced according to the so-called compared to the dry recycling method (curves B). The advantage of wet recirculation also becomes apparent when comparing the concentration curves A to curves C, which represent a prior art method in which water is introduced into an internal combustion engine but no exhaust gas recirculation is performed. According to curves A, the total amount of nitrogen oxides ΝΟχ decreases and the most dangerous component NOj of nitrogen oxides disappears almost completely from the exhaust gases by the method according to the invention as the average engine pressure increases.

Claims (3)

4,73297 1. Förfarande förminskning av kväveoxidemissioner i en förbränn-ingsmotors, som en dieselmotors avgaser genom recirkulation av vatten som skall mätäs account motorns brännrum ocg avgaser, kän nat -tecknat av att i en förbränningsmotor (1) bildade avgate (3) and with the aid of the water supply, with the aid of the recirculation of the recirculation motors (1) of the system (10) A method for reducing nitrogen oxide emissions from the exhaust gases of an internal combustion engine, such as a diesel engine, by means of water and exhaust gas recirculation to the combustion engine, characterized in that the exhaust gases generated in the internal combustion engine (1) are returning the combustion engine (1) to the intake system (10) so that the amount of exhaust gas to be returned is kept substantially constant with respect to the total amount of exhaust gas from the internal combustion engine (1). 2. A patent according to claim 1, which comprises a recirculation of the internal components of the rotary engine (1). Method according to Claim 1, characterized in that the recirculated exhaust gases comprise water supplied to the combustion chamber of the internal combustion engine (1). Method according to Claim 1 or 2, characterized in that the amount of exhaust gas to be returned is approximately 20% of the total amount of exhaust gas from the internal combustion engine (1). 3. A patent according to claim 1 or 2, which comprises a recirculating play of about 20% of the rotating motors (1) of the backbone.