DE2166191A1 - Catalytic exhaust gas afterburner - divided into several sections with the smallest preheated alone during cold start - Google Patents

Abstract

A catalytic afterburner for the exhaust gases of internal combustion engines is divided into a smaller and a bigger catalytic section, with separate inlets but a common manifold at the outlet. During the starting period, a flap valve keeps the inlet to the larger section closed. The smaller section quickly reaches its working temperature, and then the larger section via the common manifold, before the flap valve opens the access to both inlets. This utilizes the catalytic volume better than when a small unit is used just for starting and is then cut off. Purified exhaust gases are emitted very shortly after every cold start.

Description

Device for catalytic post-combustion of exhaust gases from internal combustion engines The invention relates to a device for catalytic post-combustion the exhaust gases from internal combustion engines using from several, in a common Housing arranged catalyst units and switching valves through which the Admission of the exhaust gases to the individual catalyst units is controllable.

During the catalytic combustion of the pollutants contained in the exhaust gases it prepares particular difficulties in the case of externally ignited internal combustion engines these Pollutants during the start-up phase when the internal combustion engine is still cold and in the interest of the ignitability of the fuel-air mixture with an excess is operated on fuel to effectively eliminate. This is due to that the catalyst in this operating phase is not yet sufficient for its effectiveness required temperature. The exhaust gas content is in this operating state -an carbon monoxide and hydrocarbons are particularly high, while the proportion of Nitrogen oxides is relatively low, which is otherwise by exhaust gas recirculation slightly lower into the intake duct and the resulting mixture dilution can. In the start-up phase, the most important thing is to do it as quickly as possible to achieve good combustion of carbon monoxide and hydrocarbons The goal is to be achieved by catalytic combustion provided that it succeeds to bring the catalytic converter quickly to its so-called light-off temperature the achievement of which it is only effective.

To quickly heat up the catalytic converter to its light-off temperature, from which this is effective can be achieved, for example, by the US patent 3 297 400 known, two catalysts arranged in a common housing in To switch in series. With thermostatically controlled flap valves it is possible the exhaust gases emerging from the internal combustion engine either through each a of the two catalysts and bypassing the other. It is provided that the front catalytic converter with regard to the incoming exhaust gases during the cold start phase to use the internal combustion engine. This catalyst is relative because of its Small volume on the one hand can be heated up quickly by the sensible heat of the exhaust gases and on the other hand develops early due to its high catalytic effectiveness Afterburning heat. That way it is ensured that very early after exhaust gas cleaning starts after a cold start.

As soon as the downstream catalytic converter is ready for normal operation Has prescribed temperature, the exhaust gas flow is diverted so that the first highly effective catalytic converter is bypassed and the exhaust gases exclusively the main catalytic converter apply. As a major disadvantage of this known exhaust gas cleaning system must it can be considered that after reaching the normal operating state of the internal combustion engine or the catalyst a catalyst unit is shut down and so to speak only is kept available for the next cold start start-up phase. Such a mode of operation is synonymous with poor utilization of the installed catalyst material and makes the system larger, especially given the limited space that is found in automobiles is available, is particularly important.

The invention has therefore set itself the task of a system to the catalytic purification of the exhaust gases, with space-saving construction and full utilization of the entire mass of the catalyst means that it becomes effective quickly the exhaust gas cleaning after a cold start. To solve this problem it is proposed according to the invention that the catalyst units share a common Have collecting space and that their separate vestibules by means of individual lines are connected to a distributor in which the switching valves for the control the access of the exhaust gases to the individual catalytic converter units is only released, after they have reached their minimum temperature.

The first catalytic converter unit is after the internal combustion engine has been cold started acted upon by the exhaust gases. Because of their low mass and high throughput This catalytic converter unit heats up very quickly to its light-off temperature in the presence of exhaust gases and takes effect. After flowing through the first catalytic converter unit, the exhaust gases emerge into the collecting space, from where the further catalyst units to be switched on later be heated. With the connection of the last, the exhaust line from the collecting area opposite catalyst unit is the total catalyst mass of exhaust gases applied and is used uniformly for exhaust gas cleaning. This requires the lowest possible for a certain throughput of exhaust gases through the catalytic converter Loading of the individual catalyst units, so that there is a risk of overheating is reduced.

Two embodiments of the invention are shown in the drawing and are described in more detail below.

The figures show: FIG. 1 a catalyst with two catalyst units in longitudinal section and Fig. 2 shows a catalyst with three catalyst units in longitudinal section.

In Fig. 1, an internal combustion engine 30 is indicated from which by the line 31 exhaust gases that are purified in the downstream catalytic converter will. In the line 31, a manifold 32 is installed, which is a thermally controlled Flap valve 33 has so that the line 31 in a secondary line 34 and a Main line 39 divides.

The container 35 containing a suitable catalyst mass, into the the two exhaust ducts 34 and 39 open, is divided by a partition 42 so that that two vestibules 40 and 41 arise and also the catalyst mass 36, 38 through the partition wall 42 is divided, while a common plenum 37 for the Exhaust extends under the two catalyst masses. This creates a catalyst with two levels.

The size of stage I is dimensioned so that those with etwn 900 to 10000C Amount of exhaust gas flowing in from channel 34 when passing through the catalyst mass 36 the first stage this smaller catalyst mass in the shortest Time brings to operating temperature and the size of stage II is such that together with stage I, it can process the total amount of exhaust gases.

When in the start-up phase of the internal combustion engine, the valve 33 is the main line 39 holds closed, the exhaust gases flow through the secondary line 34 into the anteroom 40 and from here penetrate exclusively the catalyst mass 36, which they heat up very quickly due to the heat they contain. When leaving the Catalyst mass 36, the exhaust gases enter the collecting space 37 and flow under it the catalyst mass 38 in the direction of the outlet line 43 and from there into the The atmosphere.

When flowing through the collecting space 37, they are still very hot Exhaust gases on a long way with the catalyst mass 38 in heat exchange, so that During this process, the catalyst mass 38 also quickly reaches the required operating temperature is brought.

As soon as the catalyst mass 38 also reaches its operating temperature has, the valve 33 opens the channel 39 and the exhaust gases can both through secondary line 34 into the vestibule 40 as well as through main line 39 and the vestibule 41 the entire Flow through catalyst mass 36, 38.

It is easy to see that the effects of what has been described are gradual Commissioning a catalytic converter with limited resources can be strengthened by one, as illustrated in Fig. 2, three- or multi-stage catalysts of the in Fig. 1 is used.

In Fig. 2, the exhaust gases from the internal combustion engine come through a line 51 into a distributor 52, from which lines 53, 54, 55 branch off. In the distributor 52 there are two thermally controlled valves 56, 57, which when the machine is cold in the start-up phase shut off the lines 54, 55 so that all exhaust gases through the Channel 53 enter the anteroom 58a of stage I and when passing through the catalyst mass 59 heat it up quickly and bring it to effect. The vestibules of levels II and III are denoted by 58b and 58c. Exiting from the catalyst mass 59, flow through the exhaust gases then enter the collecting space 60 and heat those located in stages II and III Catalyst masses 61, 62.

As soon as the catalyst mass 61 of stage II reaches its operating temperature has reached, the valve 56 opens the line 54 and stage II with the catalyst mass 61 takes part in the cleaning of the exhaust gases. In the same way then increases after a short time Time by opening the valve 57 also the stage III the operation.

Claims

Claims (3)

Claims P 21 66 191.6 1. Device for catalytic afterburning the exhaust gases from internal combustion engines with a catalytic converter, which consists of several in one common housing arranged catalytic converter units, and with switching valves, through which the access of the exhaust gases to the individual catalytic converter units can be controlled is, characterized in that the catalyst units (36 and 38; 59, 61 and 62) have a common collecting space (37 and 60) and that their mutually separate vestibules (40 and 41; 58a, 58b d 58c) by means of single lines (34 and 39; 53, 54 and 55) are connected to a distributor (32 and 52) in which the Switching valves +33; 56 and 57) for controlling the access of the exhaust gases to the individual Catalyst units are installed so that the access of the exhaust gases to the to be switched on Catalyst units (38; 61 and 62) crst is released after they reach their minimum temperature achieved. 2. Apparatus according to claim 1, characterized by such a control the switching valves (33; 56 and 57) that a first catalyst mass (36 and 59) in all operating states of exhaust gases from the internal combustion engine (30) are applied. 3. Apparatus according to claim 1 and 2, characterized in that the collecting space (37 and 60) of the catalyst units (36 and 38; 59, 61 and 62) cutting outlet lines (43) approximately in the area of the catalyst unit that was switched on last (38 and 62) is arranged. L e r s e i t e