DE3939921A1 - ARRANGEMENT FOR CATALYTICALLY CLEANING THE EXHAUST GAS FROM COMBUSTION ENGINES, IN PARTICULAR ACCORDING TO THE TWO-STOCK PRINCIPLE - Google Patents

Abstract

The invention relates to an arrangement for catalytic purification of the exhaust gases of internal combustion engines, especially two-stroke engines, consisting of a jacket tube (1) which is arranged in the exhaust path and in which there is installed a perforated inner tube (3) to form a narrow annular space (5) between the jacket tube and the inner tube. The inner tube (3) is occupied by a catalyst. <IMAGE>

Description

The invention relates to an arrangement for catalytic cleaning of exhaust gases from Internal combustion engines, especially two-stroke engines.

Internal combustion engines, especially after Two-stroke principle, require for the purpose of an inexpensive Sequence of the gas exchange processes (fresh gas filling Flushing and exhaust emission process) a certain Training the exhaust system. For that play next to one appropriate tuning of the silencer certain constructive measures in the area between the exhaust outlet of the engine and the silencer performance-related role. So z. B. in or immediately after the exhaust manifold reflective surfaces and / or expansion halls (so-called exhaust bulbs) provided to positively influence the gas dynamics.

Conventional catalytic emission control systems, such as Bulk bed or monolith catalysts, which mostly arranged in the area of the exhaust system near the engine have to be with vehicles Two-stroke engines due to the Exhaust gas back pressure and the disturbance of the gas dynamic Vibrations proven to reduce performance.

It can also cause blockages due to oil coal occur; this happens e.g. B. sometimes Monolith catalysts under certain Operating conditions of the engine. Conventional Monolith catalysts prove to be at all disadvantageous because such catalysts in engines with high emissions due to their very high Conversion potential on small volumes high Are exposed to exotherms and therefore the risk of thermal damage to the melting of the Catalyst exists. The object of the invention is to achieve this the basis, a more suitable for such engines to create catalytic emission control system. These Object is achieved by the one described in the claims Arrangement solved.

The arrangement according to the invention is according to the claims Also suitable for four-stroke engines, as with these too a fine tuning of the exhaust system is necessary is.

In the arrangement for exhaust gas purification according to the invention, the casing tube ( 1 ) can have any shape. The inner tube ( 3 ) is shaped accordingly in order to obtain an annular space ( 5 ) of approximately constant cross section. Tapered annular spaces are also part of the invention.

The annular space ( 5 ) takes up only a fraction of the volume of the casing tube ( 1 ) due to the dimensions provided. Annulus ( 5 ) and perforation increase the turbulence and thus the gas exchange in the catalyst area. This effect is reinforced in the basic configuration of the arrangement according to the invention by the annular gap which is open on both sides and which ensures a backflow of the catalytically coated inner tube. In some motor designs, an at least one-sided closure of the annular space at any point is expedient (claim 2).

With round holes as perforations they move Hole diameter of the inner tube from 0.75 to 10 mm, at a hole spacing of 1.0 to 15 mm. Are preferred Hole diameters from 1.5 to 6 mm and hole spacing from 2.0 to 7.5 mm (claim 7). The inner tube can over holes arranged regularly throughout the sheath have different diameters.

In addition to the round perforations, rectangular and Slotted perforations and any shape application find and their combination. Likewise, the Perforation size or number over the length of the Inner tube can be varied. If necessary, the Tubular body also made of expanded metal or coarse Wire mesh exist.

The relative free hole area (total hole area) is 5 to in the various embodiments 80%, preferably 20-60% (claim 8).

The perforations acting as turbulators in the Inner tube can according to claim 3 in their effect be reinforced.  

The inner tube can, if necessary, in particular manufacturing reasons, for 2 if necessary interconnected half shells (Claim 4). This can result in a division of the Annulus in two halves.

The geometric surface can be surrounded by a wire mesh, expanded metal or another perforated tube increased to increased To achieve conversion rates for the pollutants (Claim 5).

The arrangement according to the invention is suitable both as a main catalyst and as a starting catalyst for a downstream main catalyst ( 6 ) of any type (claim 6). When used as a starting catalytic converter, partial conversion of pollutants results in an increase in temperature, which makes it easier or even possible to start a main catalytic converter which may be connected in a cooler part of the exhaust system. If high pollutant concentrations occur and at the same time high exhaust gas temperatures, a partial conversion has a favorable effect in that it reduces the temperature load due to the exhaust gas cooling and protects the main catalytic converter from premature destruction or thermal deactivation. As the following exemplary embodiments show, the conversion rates of the arrangement according to the invention are surprisingly high when used as the main catalyst. Even when used as a main catalytic converter, current and future limit values can be met when used on two-wheelers.

As a catalyst, all of the usual Exhaust gas cleaning known from gasoline engines containing precious metals and / or non-precious metals Formulations are used.

Pt, Pd and / or Rh-containing ones are particularly suitable Precious metal catalysts on heat-resistant, oxidic carrier material (Al₂O₃, SiO₃ Aluminum silicates). For activation and improvement the thermal stability of the carrier material oxidic additives such as CeO₂, ZrO₂, Alkaline earth metal oxide and / or rare earth oxides be.

If necessary, before applying the oxidic A pretreatment by sandblasting, Flame spraying, aluminizing carried out to the Temperature resistance of the perforated tubular body and improve the adhesion of the coating.

example 1

A perforated, tapered pipe bend with Diameters of 30 mm or 55 mm, an elongated Pipe length of 345 mm, 2 mm hole diameter and 3.15 mm Hole spacing made of high temperature resistant steel 1.4841 is first annealed in air at 900 ° C for 3 h.  

Then the pipe bend is approx. 40% Dispersion of γ-Al₂O₃, (150 m² / g), cerium acetate and Zirconium acetate coated, dried at 120 ° C and at Calcined at 600 ° C for 2 h. The coating amount was 7.5 g Al₂O₃, 2 g CeO₂, 0.5 g ZrO₂ per part. Then the tube body with a solution of Pt (NH₃) ₄ (OH) ₂ and Rh (NO₃) ₃ (weight ratio Pr: Rh = 5: 1) impregnated, dried and in the forming gas (N₂: H₂ = 95: 5) reduced at 400 ° C. The The amount of precious metal loaded is 0.24 g / part.

Example 2

The catalyst according to Example 1 was according to the experimental setup in Fig . I tested. The annular gap between the inner tube outer diameter and the inner tube diameter was 1 mm. A two-wheel motorcycle with an air-cooled two-stroke single-cylinder engine with a displacement of 148 cm³ served as the test vehicle. The performance of the two-wheeler was 14 KW at a nominal speed of 8100 min ^-1 . An oil / petrol mixture of 1:50 was used.

The vehicle was tested on a roller dynamometer according to the Measure test specification ECE R40. The Exhaust gas temperatures at the catalyst inlet varied in Test cycle of 250-650 ° C. The exhaust gas analysis was carried out according to the CVS principle.  

The following emission values were determined:

The conversion types were 68% for CO and 56% for (HC + NO _x ).

By using this specially designed catalytic converter, it is possible to fall below the Swiss limit values applicable from October 1, 1990 (CO = 8.0 g / km, HC + NO _x = 3.1 g / km), without causing any comes strong impairment of the gas dynamic processes, which lead to a decrease in performance of the two-stroke engine.

Example 3

A conical tube made of heat-resistant steel 1.4828 with a sheet thickness of 1 mm and a diameter of 39 mm or 61 mm and a length of 150 mm, the one Slot perforation (1.5 mm hole width × 6 mm hole length, Web width 1.3 mm) is by flame spraying with a firmly adhering, rough oxide layer Al₂O₃ base occupied. The pretreated metal pipe is made into a 42% suspension La₂O₃-stabilized γ-Al₂O₃ (130 m² / g) and cerium oxide submerged, excess coating material through Blow out, dried and 2 h at 500 ° C annealed. After the coating was on the  Tube 3.9 g Al₂O₃, 0.2 g La₂O₃ and 1.0 g CeO₂. Then the catalyst precursor was with a nitric acid solution of Pt (NH₃) ₂ (NO₂) ₂ and Pd (NO₃) ₂ (Weight ratio Pt: Pd = 2: 1) impregnated, dried and calcined at 300 ° C in air. The The amount of noble metal was 125 mg / part.

Example 4

The catalyst according to Example 3 was tested according to the experimental setup in Fig. II. The annular gap between the inner tube outer diameter and the inner tube diameter was 1.5 mm on average. A two-wheel motorcycle with an air-cooled two-stroke single-cylinder engine with a displacement of 134 cm³ served as the test vehicle. The engine output was 12 kW at a rated speed of 8100 min ^-1 . An oil / petrol mixture of 1:30 was used.

The vehicle was tested on a roller dynamometer according to the Measure test specification ECE R40. The exhaust gas temperature at the catalyst inlet was 150-420 ° C. The Exhaust gas analysis was carried out according to the CVS principle. The following Emission values were determined:

The conversion types were therefore 53% for CO, 41% for HC and 13% for NO _x .

By using this specially designed catalyst, it is possible to comply with the limit values applicable in Austria from September 30, 1991 (CO = 8 g / km, HC = 7.5 g / km, NO _x = 0.1 g / km) Adhere to two-stroke motorcycles.

Example 5

A monolithic metal support with a diameter of 60 mm, 75 mm in length and a cell density of 31 cells / cm² is made by immersion in an aqueous suspension γ-Al₂O₃, cerium acetate and zirconium acetate and Excess coating material by blowing away. After drying at 120 ° C and calcining at 700 ° C for one hour is 25 g of Al₂O₃, 5 g CeO₂, and 1 g ZrO₂ on the carrier. The The catalyst precursor is then mixed with a solution impregnated by Pt (NH₃) ₄ (OH) ₂ and Rh (NO₃) ₃ and at 300 ° C dried. After coating there were 0.36 g precious metal in the weight ratio Pt: Rh = 5: 1 on the catalyst.

Example 6

The catalysts according to Examples 3 and 5 are integrated into the exhaust of a two-stroke motorcycle according to Fig. III. The tests are carried out in accordance with Example 4.

The following emission values were measured:

In comparison to Example 4, the results are clear increased conversion types of 84% for CO and 86% for HC, with almost the same nitrogen oxide emissions. A Such a concept is therefore particularly suitable if future, stricter limit values have to be met.

If the catalyst according to Example 5 is used alone with an arrangement according to Fig. III, the high conversion types cannot be achieved since the temperature level is too low without a conical pre-catalyst.

Installing the catalytic converter according to Example 5 closer to the engine in the area of the pre-catalytic converter ( Fig. III) would lead to a disruption of the gas dynamic processes and thus to unacceptable performance losses and is therefore not indicated.

Claims (8)

1. Arrangement for the catalytic cleaning of the exhaust gases of internal combustion engines, in particular of two-stroke engines, characterized by a casing pipe ( 1 ), which optionally forms a section of the exhaust pipe or an expansion space arranged in the exhaust pipe, one arranged inside the casing pipe and at a distance therefrom, with which Shape of the casing pipe, possibly corresponding and perforated inner pipe ( 3 ) coated on one or both sides with an exhaust gas purification catalyst ( 2 ), the distance between the casing pipe and the inner pipe being formed by at least one web ( 4 ) connected to both pipes, forming an annular space ( 5 ) can be interrupted by lugs or beads in the inner tube, is produced and in an area given by the ratio between the inner tube diameter and the inner tube outer diameter; from 1.01 to 1.20. 2. Arrangement according to claim 1, characterized in that the annular space ( 5 ) is closed at least on one side at any point, preferably by widening the inner tube ends or by welding or soldering. 3. Arrangement according to claim 1 or 2, characterized, that the perforation as deep drawn and / or downward bulges are present. 4. Arrangement according to claims 1 to 3, characterized in that the inner tube ( 3 ) consists of two, optionally interconnected half-shells. 5. Arrangement according to claims 1 to 4, characterized, that the inner tube is also flush with one catalyst-coated wire mesh, expanded metal or another perforated tube is surrounded. 6. Arrangement according to claims 1 to 5, characterized in that it is connected as a pre-catalyst before an optionally monolithic main catalyst ( 6 ). 7. Arrangement according to claims 1 to 6, characterized, that the perforations with a round hole Hole diameters from 0.75 to 10, preferably 1.5 up to 6 mm.   8. Arrangement according to claims 1 to 7, characterized, that the total perforated area is 5 to 80, preferably 20 is up to 60%.