EP1625288A1 - Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst - Google Patents

Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst

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Publication number
EP1625288A1
EP1625288A1 EP04731886A EP04731886A EP1625288A1 EP 1625288 A1 EP1625288 A1 EP 1625288A1 EP 04731886 A EP04731886 A EP 04731886A EP 04731886 A EP04731886 A EP 04731886A EP 1625288 A1 EP1625288 A1 EP 1625288A1
Authority
EP
European Patent Office
Prior art keywords
exhaust gas
temperature
catalyst
engine
diesel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04731886A
Other languages
German (de)
French (fr)
Inventor
Jürgen GIESHOFF
Egbert Lox
Ulrich Neuhausen
Marcus Pfeifer
Thomas Kreuzer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Umicore AG and Co KG
Original Assignee
Umicore AG and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Umicore AG and Co KG filed Critical Umicore AG and Co KG
Publication of EP1625288A1 publication Critical patent/EP1625288A1/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/024—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus
    • F02D41/0245—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus by increasing temperature of the exhaust gas leaving the engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
    • F01N3/2013—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using electric or magnetic heating means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F01N2430/08—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by modifying ignition or injection timing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F01N2430/08—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by modifying ignition or injection timing
    • F01N2430/085—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by modifying ignition or injection timing at least a part of the injection taking place during expansion or exhaust stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B3/00—Engines characterised by air compression and subsequent fuel addition
    • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F02B37/12—Control of the pumps
    • F02B37/24—Control of the pumps by using pumps or turbines with adjustable guide vanes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • F02D41/405—Multiple injections with post injections
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Abstract

The invention relates to a method and an apparatus for purifying the exhaust gas of a modern diesel engine (1) by means of a diesel oxidation catalyst (3). In the low load range, such diesel engines (1) have an exhaust gas temperature which can be below the light-off temperature of the oxidation catalyst (3). This results in unsatisfactory pollutant conversion during phases when the diesel engine (1) is operated at low loads and in fouling of the catalyst. The method of the invention solves the problem by, inter alia, increasing the catalyst temperature to at least a minimum temperature which ensures satisfactory pollutant conversion during phases when the engine (1) is operated at low load and a low exhaust gas temperature which is lower than the minimum temperature.

Description

Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst
The present invention relates to a method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst.
The main pollutants from diesel engines are, apart from the very small amounts of hydrocarbons (HC) and carbon monoxide (CO), nitrogen oxides (NOx) and soot particles (PM). The soot particles are composed of a constituent which is soluble in organic solvents and a constituent which is insoluble. The soluble part comprises a large number of different hydrocarbons which are condensed or adsorbed or absorbed on the particle core. The insoluble component comprises sulfur trioxide or sulfate, carbon, abraded metal (for example iron and nickel) and small amounts of other oxides formed from additives in lubricating oil and in the fuel (for example zinc, calcium, phosphorus). Sulfur trioxide is formed by oxidation of sulfur dioxide over the catalyst as a function of temperature, noble metal loading and exhaust gas flow. A particular characteristic of diesel engines is the high oxygen content of the exhaust gas. While the exhaust gas of stoichiometrically operated gasoline engines contains only about 0.7% by volume of oxygen, the exhaust gas of diesel engines can contain from 6 to 15% by volume of oxygen.
The ratio of the various pollutants in the diesel exhaust gas to one another depends on the type of diesel engine and its mode of operation. In principle, what has been said above applies both to stationary diesel engines and to diesel engines in motor vehicles for light and heavy duties.
The permissible emissions of diesel engines are subjected to upper limits imposed by legislation. To adhere to these limits, various concepts are employed depending on the type of d esel engine and its mode of operation.
In the case of relatively low power diesel engines in passenger cars, it is frequently sufficient to pass the exhaust gas over a diesel oxidation catalyst which burns the emitted hydrocarbons, carbon monoxide and also part of the soluble organic compounds adsorbed on the soot particles. The oxidation function of diesel oxidation catalysts is designed so that although they oxidize the organic compounds and carbon monoxide, they do not convert the nitrogen oxides and sulfur dioxide into more highly oxidized species. Together with the remaining proportion of the particles, the nitrogen oxides and sulfur oxide leave the catalyst virtually unchanged. A typical representative of such catalysts is described in DE 3940758 Al (US 5,157,007).
The conversion of pollutants by means of such catalysts is strongly dependent on the temperature. In the case of carbon monoxide and hydrocarbons, the conversion of the pollutants increases with increasing exhaust gas temperature. The temperature at which a prescribed percentage, usually 50%, of a pollutant is reacted is referred to as the light- off temperature of the catalyst for the conversion of this pollutant. It is an important parameter for describing the catalytic activity of the catalyst.
The amounts of exhaust gas, the exhaust gas composition and the exhaust gas temperature are established as a function of the mode of operation of the vehicle and thus the engine revolutions and the load. The development of diesel engines has, as a result of optimization of combustion, led to a decrease in the exhaust gas temperatures. The exhaust gas temperature of modern diesel engines is, for example, now only 100-200°C in the low load range. Only at full load does the exhaust gas temperature rise to above 300°C.
The low exhaust gas temperatures represent a great problem in exhaust gas purification, since they are sometimes below the light-off temperatures of the catalyst. Thus, if the exhaust gas temperature of the diesel engine during operation drops below the light-off temperature of the catalyst because of momentary low load conditions, the catalyst "extinguishes", i.e. the pollutants present in the exhaust gas are no longer converted by the catalyst and are thus emitted into the environment. Only when the load on the engine increases again does the exhaust gas temperature exceed the light-off temperature of the catalyst and pollutant conversion recommences. Such operating conditions occur particularly in the case of diesel passenger cars in city traffic and contribute significantly to the remaining emissions of road traffic.
A further problem caused by the low exhaust gas temperatures is fouling of the catalyst. As a result of the low exhaust gas temperatures, unburnt hydrocarbons, volatile organic compounds and particles deposit on the catalytically active coating and reduce its catalytic activity. Furthermore, there is a risk of combustible components deposited on the catalyst burning suddenly with liberation of large quantities of heat when the exhaust gas temperature rises above the respective ignition temperature of these components in the case of chance operation at high load. The consequence of this can be thermal damage to the catalytic activity of the catalyst. These problems can partly be countered by the catalyst being located as close as possible to the engine, but for space reasons this is frequently not possible. Furthermore, the light-off temperature of the catalyst can be reduced by increasing the loading with noble metal. Noble metal loadings of more than 100 gram per liter of catalyst volume are no rarity here and are associated with correspondingly high costs.
It is an object of the present invention to alleviate the above-described disadvantages (unsatisfactory pollutant conversion at low load of the diesel engine; fouling of the catalyst; high noble metal loadings) by providing a suitable method of purifying the exhaust gas.
This object is achieved by a method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst, where the diesel engine has a raw emission of hydrocarbons and carbon monoxide and the exhaust gas has an exhaust gas temperature and the catalyst has a catalyst temperature. In the method, during phases when the engine is operated at low load and a low exhaust gas temperature which is lower than a minimum temperature, the catalyst temperature is increased to at least this minimum temperature.
The catalyst is heated by the exhaust gas. Its temperature at the inlet therefore follows, to a degree determined by its thermal inertia, the temperature of the incoming exhaust gas. The conversion of pollutants over the catalyst liberates heat which heats both the catalyst and the exhaust gas.
As already stated above, a great problem in the purification of exhaust gas from diesel engines is that the exhaust gas temperature at low load can drop below the light-off temperatures of the catalyst for the oxidation of carbon monoxide and hydrocarbons, which in the case of modern diesel oxidation catalysts are in the range from 100 to 200°C.
According to the method of the invention, the pollutant conversion over the catalyst over a driving cycle can be significantly improved when the catalyst temperature during phases of operation at low load, i.e. during phases of operation with an exhaust gas temperature below the light-off temperature of the catalyst, is increased by means of measures yet to be discussed to at least the minimum temperature, with this minimum temperature being chosen so as to be equal to or greater than the light-off temperature for the oxidation of carbon monoxide in order to ensure satisfactory conversion of carbon monoxide. The minimum temperature is preferably selected so as to be from 10 to 30°C higher than the light-off temperature. In the case of conventional oxidation catalysts, the minimum temperature is preferably in the range from 150 to 180°C.
The method proposed ensures that the oxidation catalyst is operated at above the light- off temperature for the conversion of the pollutants during the total period of operation of the diesel engine (with the exception of the cold start phase), which leads to a reduction in the pollutant emission over the driving cycle.
At the same time, the method prevents fouling of the catalyst, i.e. the deposition of large amounts of hydrocarbons on the catalyst without being reacted as a result of an excessively low exhaust gas temperature is prevented. Rather, application of the method results in continuous combustion of the hydrocarbons. High temperature peaks in the event of sudden combustion of hydrocarbons accumulated on the catalyst can therefore not occur.
In addition, the method allows the noble metal loading of the catalyst to be reduced significantly. While the prior art has attempted to give the oxidation catalyst a low light- off temperature by means of high noble metal loadings, the present method increases the temperature of the catalyst to its light-off temperature. The noble metal loading is therefore no longer determined by the required pollutant conversion but can largely be optimized in accordance with economic aspects.
Various strategies are proposed for increasing the temperature of the catalyst:
In a first embodiment of the invention, the catalyst temperature is increased by increasing the exhaust gas temperature to the predetermined minimum temperature before the exhaust gas enters the oxidation catalyst. The exhaust gas temperature is preferably increased to at least 10°C above and in particular at least 20°C above the light-off temperature for the pollutants.
The exhaust gas temperature can be increased by post-injection of fuel into the cylinders of the diesel engine, by setting late combustion on the engine or by means of multistage combustion. In general, the exhaust gas temperature of a diesel engine can be increased by the tuning of the engine and thus the efficiency of the engine being made worse.
Modern diesel engines are equipped with an electronic engine control system. In normal operation, the engine control system ensures that the diesel engine is optimally tuned, i.e. is operated at optimum efficiency. This leads to correspondingly low exhaust gas temperatures. The transition from normal operation of the engine to operation with an increased exhaust gas temperature can be induced by the electronic engine control system. The performance characteristics of the engine are usually stored in the memory of the electronic engine control system. At any operating point of the engine defined by engine revolutions and load, i.e. torque, the exhaust gas temperature can be determined in advance. Thus, those operating points at which the exhaust gas temperature is below the light-off temperature of the oxidation catalyst are known. The control program of the engine control system can thus recognize the commencement of phases of operation at low load (low exhaust gas temperature) from the operating data of the engine and can increase the exhaust gas temperature to at least the minimum temperature during these phases of operation by means of one of the abovementioned measures. On changing to phases of operation with a sufficiently high exhaust gas temperature, these measures are reversed again.
As an alternative, commencement of phases of operation with a low exhaust gas temperature can also be detected directly by measuring the exhaust gas temperature upstream of the catalyst. For this purpose, a temperature sensor is installed in the exhaust gas line upstream of the catalyst and its output signal is fed to the engine control system.
A slightly increased fuel consumption is accepted in order to increase the exhaust gas temperature. However, this additional consumption is small since the exhaust gas temperature only has to be increased slightly to achieve a significantly increased pollutant conversion above the light-off temperature of the catalyst.
In a second embodiment of the invention, the temperature of the oxidation catalyst can be increased at low load by electric heating of the catalyst. This ensures that the catalyst remains active even during these phases of operation.
The invention will now be explained in more detail with the aid of figures 1 and 4. In the figures:
Figure 1 shows a diesel engine with an exhaust gas system containing an oxidation catalyst which is suitable for the method of purifying the exhaust gas
Figure 2 shows by way of example the exhaust gas temperature versus time during operation of a diesel engine Figure 3 shows the real exhaust gas temperature versus time for a vehicle having a 2.01 diesel engine during an NEDC (NEDC = New European Driving Cycle) and also the temperature curve corrected according to the invention
Figure 4 shows the calculated CO and HC emissions of the diesel vehicle downstream of a diesel oxidation catalyst for the temperature curve of figure 3 and for 3 temperature curves altered according to the invention.
Figure 1 shows a diesel engine (1) with an exhaust gas line (2). A short distance downstream of the diesel engine, a diesel oxidation catalyst (3) has been installed in the exhaust gas line. (4) denotes a silencer. (5) denotes the electronic engine control system of the diesel engine. Measurement signals giving information about the state of operation of the engine are transmitted to the engine control system and control signals are transmitted in the opposite direction to the engine via data lines (6). (7) denotes a temperature sensor for determining the temperature of the exhaust gas before it enters the oxidation catalyst (3). The temperature sensor (7) is connected to the engine control system via the line (8).
Figure 2 schematically shows the temperature curve (10) for the exhaust gas upstream of the oxidation catalyst during a driving cycle with changing load. The limit line (30) indicates the light-off temperature of the catalyst for the oxidation of hydrocarbons. As can be seen from the graph, the exhaust gas temperature drops below the light-off temperature of the catalyst during phases when the engine is operated at low load. During these phases of operation, the catalyst "extinguishes". It is no longer able to convert the pollutants. According to the invention, the exhaust gas temperature is increased to a temperature (minimum temperature) equal to or above the light-off temperature during the time interval Δt of these phases of operation by means of suitable measures on the engine. The temperature is preferably increased to a value which is ΔT = 10 to 30°C above the light-off temperature.
To increase the temperature by late combustion, the combustion peak is shifted from 7° after the UDP (upper dead point) onward to a later point in time (for example, 14° after the UDP). This is done with exhaust valves still closed. Combustion then continues until after opening of the exhaust valves, which effects an increase in the exhaust gas temperatures. In the case of multistage combustion, injection of the fuel is carried out in a plurality of stages. If there are only three stages, these are referred to as pre-injection, main injection and post-injection. This procedure, too, can increase the exhaust gas temperature.
Further measures on the engine for increasing the exhaust gas temperature are conceivable, for example opening the turbine blades of the turbocharger. The charging pressure decreases and the efficiency therefore drops. This in turn leads to an increase in the exhaust gas temperature, since more fuel has to be burnt for the same power. EGR (exhaust gas recirculation) can also be used to influence the exhaust gas temperature.
The life of a diesel oxidation catalyst can be significantly increased by means of the proposed method. However, the method is not restricted to application to diesel oxidation catalysts. Rather, it can be used for all catalysts which have been proposed for purification of exhaust gas from diesel engines and have an oxidation function. They can be, for example, SCR catalysts, hydrolysis catalysts, HC-deNOx catalysts or four- way catalysts.
SCR (Selective Catalytic Reduction) catalysts are described, for example, in the European patent publications EP 0376025 Bl (US 5,116,586) and EP 0 385 164 Bl (US 5,198,403). According to EP 0376025 Bl, catalysts based on acid-resistant zeolites, which may have been exchanged with the metals iron, copper, cerium and molybdenum, can be used for selective catalytic reduction. On the other hand, EP 0 385 164 Bl describes catalysts for selective catalytic reduction which comprise mainly titanium oxide in admixture with various other oxides. According to this patent, the reduction catalysts comprise titanium oxide and at least one oxide of tungsten, silicon, boron, aluminum, phosphorus, zirconium, barium, yttrium, lanthanum and cerium and, as additional components, at least one oxide of vanadium, niobium, molybdenum, iron and copper. These additional components in particular give the catalyst good reducing properties in oxygen-containing exhaust gases.
Hydrolysis catalysts are usually oxides which have solid state acid properties and comprise titanium dioxide, aluminum oxide, silicon dioxide or mixed phases thereof and compounds made up of these oxides as matrix oxide, with the acid properties being increased by addition of oxides of pentavalent and hexavalent elements, e.g. SO3 and WO3, as stabilizers and to increase the activity. In DE 4203 807 A1, mixtures of aluminum oxide with titanium oxide, silicon dioxide, zirconium dioxide and/or H-zeolites in a weight ratio of aluminum oxide to the other oxides of from 90:10 to 10:90 are said to be suitable active components of a hydrolysis catalyst.
An HC-deNOx catalyst is a catalyst which is able to convert nitrogen oxides in the presence of unburnt hydrocarbons present in the exhaust gas into nitrogen, water and carbon dioxide in the lean exhaust gas of an internal combustion engine. A catalyst suitable for this purpose is described, for example, in DE 196 14540 Al (US 5,928,981). It comprises at least one platinum group metal, preferably platinum, as catalytically active component deposited on a high surface area aluminum silicate as support material. In addition, the catalyst further comprises various zeolites which, owing to their acidic surface properties, are able to crack long-chain, organic molecules which are adsorbed on soot particles. This catalyst is also referred to as a four- way catalyst because it can not only convert carbon monoxide, hydrocarbons and nitrogen oxides but also reduce the amount of soot particles as fourth component.
Example
Modeling calculations for the pollutant conversion in the NEDC test were carried out on a real drive system comprising a diesel engine having a capacity of 2.2 liters and provided with a dual flow exhaust gas purification unit having two oxidation catalysts.
In the NEDC (New European Driving Cycle) test, the pollutant conversion is determined for set-down driving conditions including both an inner city component and a country component. The total test time is about 1200 seconds. The distance covered is 11.4 km.
The diesel engine has a raw emission in the NEDC test of 1.5 g km of carbon monoxide and 0.32 g km of hydrocarbons. The oxidation catalysts in this drive system are two honeycomb catalysts each having a volume of 1.1 1, a cell density of 62 cm"2 (400 cpsi) and a platinum loading of 3.18 g/1 (90 g/ft3).
The above-described diesel engine gives the curve of exhaust gas temperature versus driving time shown in figure 3 during the NEDC over a total distance of 11.4 km. The first 800 seconds of this test cycle simulate inner city traffic after a cold start.
In the modeling calculations, the carbon monoxide and hydrocarbon emissions were calculated for four different cases. In the first case, it was assumed that the exhaust gas is passed over the catalyst without any additional measures. In the other cases, it was assumed that the exhaust gas temperature is prevented from dropping below a minimum temperature of 150°C, 160°C or 170°C between about 180 seconds and 800 seconds by means of appropriate engine measures or external heating.
Figure 4 shows that ensuring an exhaust gas temperature of at least 170°C during the inner city part of the NEDC test enables the carbon monoxide emission to be reduced from 8.3 to 6.5 g per test, i.e. by about 22%. The HC emission in this case is reduced from 1.3 to 1.2 g per test.

Claims

Claims
1. A method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst, where the diesel engine has a raw emission of hydrocarbons and carbon monoxide and the exhaust gas has an exhaust gas temperature and the catalyst has a catalyst temperature, during phases when the engine is operated at low load and a low exhaust gas temperature which is lower than a minimum temperature, the catalyst temperature is increased to at least this minimum temperature.
2. The method as claimed in claim 1, wherein the minimum temperature is selected from the range from 150 to 180°C.
3. The method as claimed in claim 1 or 2, wherein the catalyst temperature is increased by increasing the exhaust gas temperature to at least the minimum temperature before the exhaust gas enters the oxidation catalyst.
4. The method as claimed in claim 3, wherein the exhaust gas temperature is increased by post-injection of fuel into the cylinders of the diesel engine, by setting late combustion on the engine or by means of multistage combustion.
5. The method as claimed in claim 1 or 2, wherein the temperature of the oxidation catalyst is increased to at least the minimum temperature by means of electric heating.
6. An apparatus for purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst, in particular for implementing a method as claimed in any of the preceding claims, where the diesel engine has a raw emission of hydrocarbons and carbon monoxide and the exhaust gas has an exhaust gas temperature and the catalyst has a catalyst temperature, wherein a facility for increasing the catalyst temperature to at least a minimum temperature during phases when the engine is operated at low load and a low exhaust gas temperature which is lower than the minimum temperature.
EP04731886A 2003-05-22 2004-05-10 Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst Withdrawn EP1625288A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE10323245A DE10323245A1 (en) 2003-05-22 2003-05-22 Process for cleaning the exhaust gas of a diesel engine using a diesel oxidation catalytic converter
PCT/EP2004/004977 WO2004104389A1 (en) 2003-05-22 2004-05-10 Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst

Publications (1)

Publication Number Publication Date
EP1625288A1 true EP1625288A1 (en) 2006-02-15

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EP04731886A Withdrawn EP1625288A1 (en) 2003-05-22 2004-05-10 Method of purifying the exhaust gas of a diesel engine by means of a diesel oxidation catalyst

Country Status (4)

Country Link
EP (1) EP1625288A1 (en)
JP (1) JP2007501356A (en)
DE (1) DE10323245A1 (en)
WO (1) WO2004104389A1 (en)

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