DE2851675A1 - IC engine exhaust gas after burner - has one catalyst block contg. coarsely grained active material followed by spaced second block contg. finely grained material - Google Patents

Abstract

The IC exhaust gas afterburner is of the catalysing-and-bypassing type and is pref. bolted directly onto the exhaust manifold. Gas flows through radila holes in a central inlet pipe projecting into the casing into a header space and through an annular catalyser block. The butterfly-type bypass valve is further along the inlet pipe. Both catalysed and bypassed gas flows via a second chamber through a further, full width catalyser block before entering the exhaust pipe. Thickness of the first block is about 40mm, and the second block is 25mm thick. The blocks respectively contain coarse and fine-grained active material.

Description

Post-combustion device for the exhaust gases from internal combustion

machines are afterburning devices for the oxidation of CO and HC known and become as a result of the tightening of exhaust gas regulations for automobiles more and more necessary.

Since the emission tests start with a cold engine, it is important to that the afterburner starts up quickly. This is achieved by means of catalysts, those for CO afterburning at around 1500 C and for HC at around 3500 with the combustion kick off.

This catalytic material is used as a small-grain bulk material from 2 - 2.5 mm in size placed in chambers through which the exhaust gas must flow. There it is very tight for the purpose of good functioning, it offers resistance to the gas flow, which gets bigger the more gas has to flow through. This resistance brings a loss of engine power and an increase in fuel consumption of around 10%.

The invention is intended to eliminate these disadvantages without the effect in the afterburning deteriorates will.

Various patents already show a subdivision of afterburning into a catalytic part for cold start, warm-up and lower partial load range of the engine combined with an additional heat reactor for the middle to upper Partial load range of the engine.

In DE-PS 22 11 775, English patent 1,307,684, US-PS 3,744,249 and others are described devices that have a throttle valve in the central duct and in which catalytic annular chambers are arranged around the outside of the channel are.

In the partial load range, the exhaust gases go through openings in front of the throttle valve into the annular chambers, where the catalytic material flows through and is burned afterwards with very low CO and HC in the exhaust. With medium load to full load the throttle valve in the central channel opens and releases the majority of the gases Passage free. These should cause an afterburning reaction when flowing through with heat obtained, whereby mixture images and heat conductors are intended to promote this process.

It has been shown, however, that these gases can be oxidized so well how does not take place. The success is very low.

According to the invention, this deficiency is also intended to be remedied.

It is further taken into account that modern engines of the next few years Drive with little CO and HC in the exhaust gas and also a high oxygen content 3 - 6% contained in the exhaust gas, which means that additional air is fed into the post-combustion not applicable.

The afterburner shown in section in the drawing is preferred with the flange 18 screwed directly to the exhaust manifold of the engine from which the exhaust gases flow into the afterburning device 1 through the inlet 2. In the middle Gas duct 3, a throttle valve 4 is rotatably mounted on shaft 5. Around the central channel 3 is an annular channel 9 with an antechamber 8 and openings 7 arranged.

Downstream of the central and annular channel is an intermediate chamber 12 above arranged the entire width. This is followed by a second catalytic chamber 13, the top and bottom with perforated sheets 15 and 14 is completed. The annular chamber 9 is Finished with perforated sheets 10 and 11 at the top and bottom.

After the catalytic chamber 13 follows a conically narrowing one Space 16 to which the outlet pipe 17 is connected.

It has been shown that the flow path of the exhaust gases through the catalytic material should not exceed 40 mm. As for an engine from 75 HP is required for the post-oxidation, about 1.5 liters of catalyst would be the catalytic one Flow chambers become very wide or will - they will be very long if placed differently, for which in most cases there is no space in the engine compartment directly after the exhaust manifold is available. However, the afterburner must be installed close to the engine in order to do this it starts quickly with hot exhaust gases. This possibility is also made possible by the Invention ensures that the afterburner is small.

The mode of operation is as follows: At idle and part load up to approx 80 km / h - that's 11 to 15 hp - the throttle valve 4 is closed, and alk exhaust gases flow through the openings 7 into the antechamber 8. From there they go through the catalytic Material of the annular chamber 9 and exit into the intermediate chamber 12. You flow through further the second catalytic chamber 13 and then come via the space 16 into the Exit pipe 17.

Since only 0.3 liters of catalytic converter is required for 15 HP engine power, this is well accommodated in the annular chamber 9. You could go there with less Material get by as a further afterburning in the second catalytic Chamber 13 takes place.

From about 80 km / h the throttle valve 4 is opened, and the exhaust gases For the most part, they only flow through the middle channel 3, the intermediate chamber 12 and the second catalytic chamber 13 to the exit pipe 17.

Since the exhaust gases are very little when the engine is at operating temperature CO (approx. 0.1-0.2%) and little HC (approx. 50-100 ppm) in the range from 50 km / h to close to full load, there is only a little catalytic material and less Dwell time when flowing through is necessary. While the height of the first catalyst chamber 40 mm, it is only 25 mm for the second catalyst chamber. It will preferably There also coarser catalytic material taken, which means more free flow space arises. This chamber only contains about 0.25 liters of cat material.

Because this chamber is already after the start and in the lower load range oxidized gas receives what is very hot, it is heated itself before not oxidized gas from the central channel 3 flows through them. This is also hot because the engine is at operating temperature and in the range from medium to full load is located.

In addition, a partial gas comes out of the first already oxidized and hot Catalyst 9.

So it will be sufficient to have the wide chamber 13 with good heat conducting To fill metal material in order to achieve thermal oxidation. In this case the flow height of the chamber 13 is made slightly larger.

The switchover of the flap can be speed-dependent or speed-dependent on an electric thrust device that moves the lever of the shaft 5, made will.

Tests have shown that with the described in the invention Arrangement of the catalytic converters and this control of the gas flow during warm-up, Partial load and the rest of the load range you can manage with 0.55 liters of catalytic material and still the exhaust gas detoxification is complete.

Since precious metal for catalysts will become scarce and therefore more expensive, it is important to get by with less.

Despite this small afterburner, there is no loss of performance and no increase in consumption.

Due to its small diameter and its shortness, it can almost in all cases directly on the exhaust manifold in the engine compartment.

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Claims (7)

Claims 1. Device for afterburning exhaust gases in internal combustion engines with a catalyst for the oxidation of CO and HC in the upper load range a part of the exhaust gas is passed through a gas duct, bypassing a catalytic converter it will be noted that the catalytic converter and the gas duct a second catalyst is arranged downstream. 2. Apparatus according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the first catalyst as an annular chamber (9) around the middle gas channel (3) is arranged, while the second catalyst (13) after a gap (12) is arranged over the entire width of the afterburner (1). 3. Apparatus according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the flow path through the first catalytic converter (9) is greater than the one through the second catalyst. 4. Apparatus according to claim 1, d a d u r c h g e k e n n z e i c Note that the flow path (height) of the first catalyst is about 40 mm and the of the second catalyst (13) is approx. 25 mm. 5. Apparatus according to claim 1, d a d u r c h g e k e n n z e i c Note that in the first catalyst (9) fine-grained material and in the second catalyst (13) coarse-grained material is included. 6. The device according to claim 1, d a d u r c h g e k e n n z e i c Note that the second chamber (13) does not contain catalytic material is, but only good thermally conductive metals for thermal oxidation are filled will. 7. The device according to claim 1, d a d u r c h g e k e n n z e i c n e t that the flap (4) speed or speed dependent is controlled by means of an electric thruster so that it is idling as well as the lower partial load range is closed and in the middle to upper load range is opened.