US20100175370A1

US20100175370A1 - Device and method for regenerating particulate filters, use of a medium for regenerating particulate filters, and refill pack comprising said with the medium

Info

Publication number: US20100175370A1
Application number: US12/594,184
Authority: US
Inventors: Rainer Bunge
Original assignee: HOCHSCHULE RAPPERSWIL
Current assignee: HOCHSCHULE RAPPERSWIL
Priority date: 2007-04-25
Filing date: 2008-04-18
Publication date: 2010-07-15
Also published as: WO2008131573A1; JP2010524669A; EP2140115A1

Abstract

The invention relates to the use of a combustion fuel that differs from diesel or diesel cleavage products, in particular monoethylene glycol and/or methanol, for enriching exhaust gas in front of a particulate filter (19) of a diesel engine (11), in order to heat the exhaust gas by means of a catalytic oxidation of this combustion fuel to a temperature sufficient for a regeneration of the particulate filter (19). It also relates to the device that permits this use and to this end comprises a combustion fuel tank (25) and a combustion fuel line (27) connected to an exhaust gas train (17) of a diesel engine (11), the combustion fuel tank (25) of which is not the diesel tank (15) of the diesel engine. Furthermore, the invention can also comprise the diesel engine (11) and the tank (15) thereof, as well as the exhaust gas train (17) with the particulate filter (19). The concept common to all of these aspects of the invention is expressed in the method that is characterized by the steps that a combustion fuel, in particular methanol and/or ethylene glycol is added to the exhaust gas of a diesel engine (11) in front of its particulate filter (19), so that it in a gaseous state oxidizes on the catalyst surface (21) and thereby heats the exhaust gas to a temperature at which the regeneration of the particulate filter can be carried out. Due to the combustion fuel tank (25) separate from the propellant fuel tank (15), a combustion fuel can be used for this purpose which reacts with the catalyst (21) at exhaust temperatures too low for diesel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT/CH2008/000176 filed on Apr. 18, 2008 and to EP07405127 filed on Apr. 25, 2007, the entirety of each of which is incorporated by this reference.

FIELD OF THE INVENTION

The invention relates to the regeneration of a particulate filter, or a method therefor, the use of a medium and a device for the regeneration of the particulate filter.

STATE OF THE ART

Particulate filters are installed in diesel vehicles and units with diesel engines. Particulate filters of this type can clog. The counterpressure in the exhaust gas system thus becomes greater. In the case of a substantially increased pressure in the exhaust system, the engine ultimately stops and can no longer be started.
In order to avoid this, particulate filters must be regenerated. For the regeneration of the particulate filter, the soot particles deposited therein must be burned. There are essentially two possibilities for a regeneration of this type. With both regeneration alternatives, a minimum operating temperature is necessary.
With a first method of achieving a regeneration, the filter cake composed of soot is oxidized to CO2 by means of NO2. The NO2 is oxidized by means of an oxidation catalyst from the NO contained in the exhaust gas and the residual oxygen contained in the exhaust gas. An oxidation catalyst of this type is predominantly coated with platinum, but also contains portions of palladium.
The oxidation catalyst is therefore arranged in the exhaust gas flow as a component and arranged upstream of the particulate filter. Particulate filters of this type are referred to as “continuously generating.” Namely from an exhaust gas temperature of approx. 180° C., NO2 is continuously formed, which reacts with the soot in the particulate filter. The regeneration of the particulate filter is thereby dependent on the operating temperature. It takes place from temperatures of approx. 220° C., but increases exponentially with the increase in the operating temperature in the particulate filter. However, in the temperature ranges relevant in practice, the NO2 production increases with the temperature increase in an essentially linear manner.
An increased discharge of the strong oxidizing agent and irritant gas NO2, however, is not desirable. With these continuously regenerating particulate filters, the production of NO2 must therefore be coordinated as precisely as possible with the quantity of soot accumulating. The NO2 discharge is reduced by a reduction in the platinum doping of the catalysts. However, since different quantities of soot accumulate depending on the operating method of the diesel engine, and the temperature-dependent conversion of the NO2 with the soot to CO2 and NO is low at low temperatures, there is a risk of the particulate filter clogging with high soot accumulation and at low operating temperatures, in particular if this falls below 220° C. The conflict of objectives with continuously regenerating particulate filters is therefore that on the one hand as much NO2 as possible must be produced in order to achieve a regeneration of the filter even at low exhaust gas temperatures, on the other hand an excess of NO2 must be avoided for reasons of environmental protection.
A second method of achieving the regeneration of the particulate filter is referred to as thermal. The filter cake is thermally burned off from time to time. To this end, as a rule it is heated to a temperature of 600° C. At this temperature the soot burns off independently. Through a catalytic coating of the particulate filter, the ignition temperature of the soot can be reduced from 660° C. to 450° C. Another method for reducing the ignition temperature is to add an additive to the diesel. This additive is usually based on iron compounds. It reaches through the engine into the exhaust gas and is thus deposited in the particulate filter together with the soot. This mixture of soot and additive of the filter cake deposited in the particulate filter has a lower ignition temperature than soot without additive, namely approx. 450° C.
The filter cake built up in the particulate filter is periodically burned off with the thermal regeneration, usually dependent on the counterpressure in the exhaust system. To this end, the filter cake is ignited and then burns off independently as a rule.
There are four possibilities for igniting the filter cake

- Ignition with an electric heater
- Ignition through intervention in the operating conditions of the engine so that the exhaust gas temperature is increased. This can be achieved, for example, through manipulation of the combustion air supply (e.g., closing a throttle valve in the air intake nozzle).
- Ignition through the combustion of fuel in open flame. To this end, a fuel-operated burner is installed in the exhaust gas flow.
- Ignition through catalytic combustion of fuel.

In the catalytic combustion, the fuel is either directly injected into the exhaust gas flow or it is discharged from the engine through manipulation of the engine control of unburned fuel. In both cases the exhaust gas flow enriched with fuel is guided via a catalytically coated surface, so that the fuel is oxidized catalytically (i.e., namelessly) and thus leads to heating of the exhaust gas. The injection of the fuel has the disadvantage with diesel engines that, because of its high boiling point, diesel has to be atomized very finely via a compressed-air nozzle. To this end, a compressed air supply must therefore be established. Practice shows that the injection nozzle arranged at the end of a supplying pipe is easily clogged by a carbonization of the diesel, which requires special precautions to avoid this carbonization.
Catalysts used for thermal regeneration as a rule contain more palladium and less platinum than the catalysts used for continuous regeneration. The NO2 production on the catalyst is thus suppressed. The catalyst used for catalytic combustion of the fuel can be arranged upstream of the particulate filter as a component. However, it can also be mixed to the diesel or the exhaust gas as an additive, so that it is deposited on the filter cake. Furthermore, the particulate filter itself can be coated with a catalyst layer.
With the catalysts commercially available today this thermal type of regeneration requires exhaust gas temperatures before the catalyst of more than 200 degrees, so that at least half of the injected diesel is catalytically oxidized. The main constituents of the diesel fuel are chiefly alkane, cycloalkane and aromatic hydrocarbons with approx. 9 to 22 carbon atoms per molecule and a boiling range between 150° C. and 390° C. The evaporation temperature of diesel is reduced to below the nominal boiling temperature through an atomization to very small droplets. Nevertheless, only a few of the diesel constituents volatize at exhaust gas temperatures below 200° C. Although with some catalysts, at least in mint condition, the light-off temperature can be reduced to 180° C., the combustion of diesel is then so incomplete that a cloud of unburned diesel is discharged from the exhaust (“blue smoke”), which is considered unacceptable in practical use. So many constituents of the diesel are brought into a reactive condition that it can be used in practice for regeneration of particulate filters only at temperatures above 200° C. in the catalyst through the heat formed there.
There are attempts to further reduce the reaction temperature of the catalyst through enrichment of the exhaust gas with cleavage products from the diesel. However, this requires technically very complex apparatus to crack the diesel into above all shorter-chain alkanes with lower boiling points (“reformer”). This approach is not currently market-ready and it is questionable whether an approach of this type for “on-board” diesel cracking will be practically feasible at all.
To sum up, at exhaust gas temperatures below 200 degrees Celsius no system for the regeneration of particulate filters through the catalytic oxidation of a fuel is known, which was not provided through the technically very complex cracking of diesel.
The necessity for the regeneration of particulate filters at low exhaust gas temperatures is intensified, when, for example, for reasons of space the filter has to be installed at a large distance from the engine. In order to reduce temperature losses in the exhaust gas, in a case of this type the long exhaust pipes between the engine and the catalyst must be expensively insulated.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a solution which makes it possible to achieve a regeneration of particulate filters at low exhaust gas temperatures of, for example, less than 200° C. More specifically, the present invention provides a retrofittable device with which this method can also be used with already existing vehicles and units equipped with particulate filters, without intervention in the electric engine control being necessary.
The advantages of the present invention are attained with the invention through the features of the independent claims.
With a method for the regeneration of a particulate filter of a diesel-driven internal combustion engine, the invention has in common with the prior art the steps that the exhaust gas is enriched at a feed point upstream of the particulate filter with a catalytically oxidizable medium at exhaust gas temperature too low for the regeneration, and through catalytic oxidation of the medium is heated to a temperature sufficient for the regeneration of the particulate filter. Whereas with the prior art this medium is the fuel, in particular diesel, or in tests also diesel cleavage products were used, according to the invention the exhaust gas is enriched with a fuel that differs from diesel and the cleavage products thereof.
While the prior art derives the diesel fuel from the diesel tank already present and adds it to the exhaust gas, the invention requires a second tank for the fuel. This has the disadvantage that two media have to be refueled. However, it has the advantage that a fuel of this type can be selected from a large range of combustible substances.
According to this measure according to the invention the range of possible fuels extends from gases, such as hydrogen, propane or butane, to organic liquids, such as kerosene, gasoline or constituents thereof and cleavage products, to less widespread fuels. Fuels are advantageously chosen which are volatile at temperatures below 200 degrees, or oxidize on the catalyst at lower temperatures than diesel. It is particularly advantageous with NO2-regenerating particulate filters if the fuel oxidation is as far as possible not in competition with the NO2 production.
It has been shown that advantageous fuels are to be found among alcohols. Many alcohols have volatilization temperatures below 200° C. and can therefore be introduced into the exhaust gas flow without complex pneumatic atomization. Furthermore, they evaporate free from residue, so that there is no danger of carbonization, and at least some react at exhaust gas temperatures from 150° C. with the known catalyst surfaces. (Mono) ethylene glycol, for example, degrades from 165° C. and thereby releases among other things glycolaldehyde, glyoxal, acetaldehyde, methane, formaldehyde, carbon monoxide and hydrogen. The less toxic propylene glycol has a boiling point of 187° C. Methanol (methyl alcohol) even has a boiling point of 65 degrees Celsius.
Alcohols are standard commercial products in gas station shops, so that no new distribution channels need to be created to sell the fuel to be used according to the invention.
With the fuel, that is, e.g., through an atomization of methanol into the exhaust gas system and the catalytic oxidation thereof, the exhaust gas temperature is directly heated to the temperature necessary for regeneration. This is expedient with vehicles and units without diesel injection in the exhaust gas system.
In particular with vehicles and units with a diesel injection in the exhaust gas system, the exhaust gas is advantageously heated by means of the additional fuel only to a temperature at which the diesel can be catalytically oxidized, e.g., to 240° C. Subsequently, the reaction temperature necessary for regeneration can be achieved by enrichment of the exhaust gas with diesel in the conventional manner. This has the advantage that only small amounts of fuel are required to start the regeneration process, but the diesel present in larger quantities can be used for maintaining the expedient temperature for regeneration.
The exhaust gas can be enriched with the fuel and the diesel. The enrichment can be carried out consecutively or simultaneously with a mixture of fuel and diesel.
The method according to the invention is suitable for oxidation catalysts in general, but in particular for the commercially available catalysts coated with platinum and/or palladium. It is therefore not specifically suitable for regeneration by means of NO2, nor exclusively suitable for thermal regeneration.
Advantageous alcohols are methanol (methyl alcohol, CH₃OH) and monoethylene glycol (MEG, ethylene glycol, ethane-1,2-diol, C₂H₆O₂). In particulate filters with nitric oxide regeneration, these two alcohols exhibit a surprising effect in that they do not seem to impede NO2 production at all. However, other fuels appear to load the catalyst in competition to the NO2 production.
In exhaust gas purification systems that manage without installed catalyst surfaces or in which the catalytic surface is present in the particulate filter and in large part is covered by the soot, a catalytically oxidizing additive can be added. This can be added to the combustion fuel or to the propellant. In any case, it is to serve as a catalyst in the exhaust gas/combustion fuel mixture.
As a rule, however, a catalyst installed in the exhaust gas system between the feed point and the particulate filter is used for the catalytic oxidization of the combustion fuel. Most filter bowls contain a catalyst component upstream of the particulate filter component.
The enrichment of the exhaust gas with combustion fuel can be carried out by measures in front of or in the internal combustion engine. The enrichment of the exhaust gas is carried out between the internal combustion engine and the particulate filter. In particular for retrofitting kits, this is the suitable location for the injection of combustion fuel into the exhaust gas system. It is independent of the operating mode of the engine, so there does not need to be an intervention into the control thereof.
The use according to the invention of a catalytically oxidizable medium for enriching the exhaust gas of an internal combustion engine in order to heat the exhaust gas through catalytic oxidation of the medium to an exhaust gas temperature sufficient for the regeneration of the particulate filter, is characterized in that the medium contains in essential parts a combustion fuel different from diesel, the fuel of the internal combustion engine and the cleavage products thereof, which different combustion fuel is catalytically oxidizable at a lower temperature than diesel.
In principle, gases can also be used as a combustion fuel. For reasons of easier handling, it i the combustion fuel is a liquid. Liquids can also be considered here which split into oxidizable gases when heated. To carry out our invention organic liquids are considered as combustion fuels, above all alcohols.
The combustion fuel can thus be an alcohol or a mixture containing at least 40% alcohol. It can be methyl alcohol or a mixture containing at least 10% methyl alcohol. Advantageously compared to other combustion fuels, it can likewise contain monoethylene glycol or a mixture containing at least 10% monoethylene glycol. Furthermore advantageously compared to other combustion fuels, it can be propylene glycol or a mixture containing at least 10% propylene glycol. Glycols are cost-effective, frostproof, have a high flash point and are toxicologically relatively harmless. Furthermore, they are water-soluble and can be safely handled in this condition. They are therefore particularly suitable as a combustion fuel. Further advantageous combustion fuels are glycerins, in particular in methanol-containing glycerin solutions, which accumulate as waste substances in the production of biodiesel and therefore are particularly cost-effective.
The advantageous selection of combustion fuels can also be described through the condition that the volatilization temperature of the combustion fuel is lower than the volatilization temperature of essential constituents of diesel, in particular less than 250 degrees Celsius. Volatilization temperature means the decomposition temperature (as in the case of monoethylene glycol) as well as the boiling temperature (as in the case of methanol), at which the combustion fuel becomes volatile. This has the advantage that regeneration can be carried out at temperatures at which diesel is not yet volatile to a great extent.
The selection of the combustion fuels can also be restricted by the feature that the volatilization temperature of the combustion fuel is lower than the minimum exhaust gas temperature necessary for a catalytic reaction of diesel, in particular less than 200 degrees Celsius, less than 190 degrees Celsius, or less than 180° C. This selection has the advantage that the combustion fuel already evaporates when no reaction is yet expected between diesel and catalyst.
Surprisingly, the combustion fuel can be mixed with water, or used in aqueous solution. This makes it easy to handle. A mixture of methyl alcohol and water, for example, is not dangerous and can be merchandised in plastic bags. The content of water can be relatively large, without this having a substantial effect on the heat development in the catalyst.
A device according to the invention comprising a fuel tank and a fuel line is used, for example, as an emergency regenerator device or regeneration starting device on a device that has a diesel engine, a diesel tank for the diesel fuel, an exhaust system and a particulate filter in the exhaust system. Unlike a windshield washer system, which also meets the structural features listed above, with a use according to the invention of the device, the fuel line is arranged upstream of the particulate filter opening into the exhaust gas system, so that the exhaust gas can be enriched with a combustion fuel from the combustion fuel tank before the particulate filter. The device is used when only insufficient temperatures are present in the exhaust gas system for a regeneration of the particulate filter, but regeneration is necessary.
According to the invention a device that has an internal combustion engine, a diesel tank for accommodating a diesel fuel for the engine, and a diesel line from the diesel tank to the internal combustion engine, and in which adjoining the internal combustion engine an exhaust gas system and catalytic surfaces arranged therein and a particulate filter are present, is equipped with a device of this type. This added device characterizes the known system of the internal combustion engine according to the invention. It comprises a combustion fuel tank, separate from the diesel tank, for accommodating a fuel different from diesel and the cleavage products thereof, a combustion fuel line opening into the exhaust gas system from the combustion fuel tank to a feed point in the exhaust gas system, which feed point lies upstream of the particulate filter and the catalytic surfaces, conveyance means for conveying the combustion fuel into the exhaust gas system and a circuit for activating the conveyance means. The following can be present as conveyance means: an excess pressure in the combustion fuel tank in combination with a valve, a pump or a pressure source that presses a gas, in particular air or CO2 into the combustion fuel tank, a liquid pump for the combustion fuel in the combustion fuel line or in the combustion fuel tank, respectively optionally in combination with a valve in the combustion fuel line.
For the sake of simple assembly and handling, a liquid pump in the combustion fuel line for pumping the fuel through the combustion fuel line is used. A likewise simple manner of conveying combustion fuel is carried out by means of a self-priming injection nozzle in the exhaust gas flow (steel pipe or Venturi).
The device can be directly connected to a control or a display device of the device having the internal combustion engine, which control controls the regeneration of the particulate filter, and which display device displays the necessity of regenerating the particulate filter. An emergency regeneration can be triggered, for example, by this display device or by the signal activating the display device. The device can also be equipped with its own sensor for monitoring the pressure and/or temperature conditions in the exhaust gas system, which sensor gives the switch signal for activating the combustion fuel supply to the exhaust gas system that starts the regeneration.
In narrow terms, the invention lies on the one hand in the use of glycol (monoethylene glycol and/or propylene glycol) and/or methanol for exhaust gas enrichment before a particulate filter of a diesel engine, in order to heat the exhaust gas by means of a catalytic oxidization of this combustion fuel to a temperature sufficient for a regeneration of the particulate filter. It therefore comprises commercial packages of a combustion fuel for filling combustion fuel tanks of a regeneration device. A refill package of this type is advantageously characterized by a content of at least 60% of a mixture of methanol and at least one glycol. Expediently the refill package contains at least 20% methanol and at least 30% water.
The invention lies on the other hand in the device that permits this use and to this end comprises a combustion fuel tank and a combustion fuel line attached to an exhaust gas system of a diesel engine, the combustion fuel tank of which is not the diesel tank of the diesel engine, and the combustion fuel line of which is to be arranged opening into the exhaust gas system. In a form comprising the engine and the particulate filter, the invention therefore also includes the diesel engine and the tank thereof, as well as the exhaust gas system with the particulate filter.
The concept common to all of these aspects of the invention is expressed in the method that a combustion fuel, in particular methanol and/or a glycol (monoethylene glycol and/or propylene glycol) is added to the exhaust gas of a diesel engine in front of its particulate filter, so that the combustion fuel in a gaseous state oxidizes on the catalyst surface and thereby heats the exhaust gas to a temperature at which the regeneration of the particulate filter can be carried out. Due to the combustion fuel tank separate from the propellant fuel tank, a combustion fuel can be used for this purpose which reacts with the catalyst at exhaust temperatures too low for diesel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail based on specific test arrangements and based on the use of different selected combustion fuels. They show:

FIG. 1 diagrammatically illustrates a truck with an engine and exhaust gas system, diesel tank and combustion fuel tank for heating the exhaust gas.

FIG. 2 is a diagrammatic representation of a first test arrangement, blocking out the diesel tank and internal combustion engine.

FIG. 3 is a diagrammatic representation of a second test arrangement, blocking out the internal combustion engine.

FIG. 4 is a diagrammatic representation of a third test arrangement, blocking out the internal combustion engine.

FIG. 5 is a diagram of the temperature increase by ΔT of an exhaust gas with temperature T via a first diesel oxidation catalyst (manufacturer: HJS) without injection (base line) and with injection of different media.

FIG. 6 is a corresponding diagram of the NO2 concentration without and with injection of different media.

FIG. 7 is a diagram of the pressure and temperature development in the exhaust gas before and during the regeneration of the oxidation catalyst according to FIG. 1 by means of monoethylene glycol.

FIG. 8 is a diagram of the temperature increase over the oxidation catalyst against the exhaust gas temperature before the oxidation catalyst and the composition of the injected medium water and glycol.

FIG. 9 is a diagram of the temperature increase over the oxidation catalyst against the exhaust gas temperature before the oxidation catalyst and the composition of the injected medium of water and glycerin.

FIG. 10 is a container with a combustion fuel for regenerating particulate filters.

FIG. 11 is a diagram of the temperature increase by ΔT of an exhaust gas with temperature T over a second diesel oxidation catalyst (manufacturer: Peugeot) without (base line) and with injection of different media.

FIG. 12 is a corresponding diagram of the NO2 concentration without and with injection of various media.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The truck shown diagrammatically in FIG. 1 has a diesel engine 11, to which diesel fuel is fed from a diesel tank 15 with a diesel pump 13. The diesel combusts leanly with the compressed air in the cylinders of the engine 11 with power and heat output and forming soot. The exhaust gases from this combustion flow into the exhaust gas system 17 and finally reach the particulate filter 19. The soot particles are trapped and filtered out of the exhaust gas with the particulate filter 19. Through the increase of soot particles in the particulate filter 19, the resistance thereof increases. From a limit resistance, the exhaust gas pressure in the exhaust gas system 17 becomes too high, so that the internal combustion engine 11 shuts down.
The particulate filter must therefore be freed of the trapped soot by a regeneration, before the engine 11 no longer runs efficiently or even shuts down.
An oxidation catalyst 21 is arranged upstream of the particulate filter 19 shown in FIG. 1 in order to achieve a regeneration. As a rule, the catalyst 21 and the particulate filter 19 are arranged in a common muffler. This can be referred to as a whole as a particulate filter. In order to ensure clear terminology, the muffler together with the particulate filter 19 and the catalyst 21 is referred to in this document as filter bowl 23. When the temperature of the exhaust gas before the oxidation catalyst 21 is sufficient, NO contained in the exhaust gas together with the residual oxygen in the exhaust gas is converted to NO2 on the surface of the catalyst 21. This NO2 is an aggressive oxidant that is able to oxidize the soot in the particulate filter 19 to CO2. This reaction also takes place at low temperatures from 250 to 300 degrees, but increases substantially with increasing temperature. When there is a balance between soot production in the combustion and the NO2 production in the catalyst 21, this regeneration of the particulate filter is continuously guaranteed from a certain temperature of the exhaust gas.
However, for a safe regeneration a certain excess of NO2 must be produced. This NO2 excess leaves the exhaust gas system as environmentally harmful irritant gas, which should be avoided. More recent filter bowls 23 are therefore dimensioned such that the excess of NO2 on average is very low, which means that a regeneration of the particulate filter necessary on average takes place only at temperatures from 250 to 450 degrees. Under certain driving conditions, the regeneration performance is therefore below average, in others, above average. In the case of a longer lasting below average regeneration performance, the particulate filter must therefore increasingly clog.
The NO2 production is also dependent on the exhaust gas temperature. With exhaust gas temperatures below 220 degrees before the catalyst, the effectiveness thereof is restricted or even suppressed. The filter cake therefore increases at low exhaust gas temperatures, even if sufficient NO and O2 are contained in the exhaust gas to produce an excess of NO2. This is the main reason why particulate filters clog.
In order now to be able to install filter bowls 23 in the exhaust gas system of an internal combustion engine, which filter bowls produce only a low NO2 excess, it is necessary also to be able to carry out regeneration when the continuous regeneration is insufficient over longer periods of time. If the filter cake becomes too thick, a regeneration is therefore forced. This has occurred so far, e.g., by injecting diesel into the exhaust gas system or pushing unburned diesel through the engine 11. Under the condition that the exhaust gas in front of the catalyst is over 200 degrees, this diesel then combusts catalytically on the catalyst and increases the exhaust gas temperature to approx. 450 degrees, so that the exhaust gas is hot enough that the catalyst can produce sufficient NO2 and a regeneration of the particulate filter is quickly achieved.
However, a minimum exhaust gas temperature of 200 degrees is also necessary for this catalytic combustion of diesel. At lower temperatures the combustion of the unburned diesel is not guaranteed. However, without catalytic combustion, the enrichment of the exhaust gas with diesel ensures only that an increased discharge of hydrocarbons is generated. The exhaust gas temperature does not rise and the particulate filter is not regenerated.
In order now to nevertheless achieve a regeneration of the particulate filter at exhaust gas temperatures below 200 degrees, it is proposed according to the invention to enrich the exhaust gas with a medium that differs from diesel. To this end, a combustion fuel tank 25 separate from the diesel tank is necessary. This combustion fuel tank has its own combustion fuel line 27, which opens into the exhaust gas system, and a combustion fuel pump 29.
The combustion fuel can now be selected such that it already reacts catalytically with the residual oxygen in the exhaust gas at lower temperatures than diesel, and therefore increases the exhaust gas temperature. This increase of the exhaust gas temperature should be driven to at least a temperature that renders possible a catalytic oxidation of the diesel and therefore an effective enrichment of the exhaust gas with diesel.
A device for the regeneration of the particulate filter therefore comprises a combustion fuel tank 25 separate from the diesel tank 15, a combustion fuel line 27 and, for example, a pump as conveyance means 29. In order for the function of this device to be automated, a control 31 indicated in FIG. 1 is present. This control indicates, e.g., with a warning light 33, that the particulate filter 23 must be regenerated. To this end a sensor is arranged in the filter bowl 23, e.g., a counterpressure measuring device, the signal of which is evaluated by the control. Based on a signal from this control 31, the regeneration can now be initiated with the aid of the combustion fuel. For example, the combustion fuel pump 29 can be activated simultaneously or with a time delay with the illumination of the warning light 33.
FIG. 2 shows only a section from the device described above, namely the combustion fuel tank 25, the combustion fuel line 27 with combustion fuel pump 29, and the filter bowl 23 with the oxidation catalyst 21 and the particulate filter 19.
An alcohol is poured into the combustion fuel tank 25. This is sprayed with the nozzle 35 into the exhaust gas for emergency regeneration. The sprayed alcohol volatilizes quickly in the exhaust gas, even if it is only 190 degrees, for example. Even at these low temperatures (from 150° C.) it reacts on the catalyst surface with the residual oxygen while emitting heat, so that the exhaust gas, depending on the added quantity of alcohol, is heated by 100 to 300 degrees. A representation of the pressure development in the exhaust gas and the temperature after the oxidation catalyst is shown in FIG. 7 and discussed below. These measurements were made based on a device according to FIG. 2, wherein monoethylene glycol was used to heat the exhaust gas.
FIG. 3 shows an exemplary embodiment, which is suitable for injecting combustion fuel and propellant fuel. The pump 29, depending on the position of the valves 35 and 35′, presses combustion fuel, diesel or combustion fuel and diesel into the chamber in front of the catalyst component 21. A control 31 operates the valves 35, 35′ and regulates the proportions of diesel and combustion fuel for the enrichment of the exhaust gas 37. A temperature sensor between the catalyst 21 and particulate filter 19 supplies the necessary information for this purpose.
FIG. 4 shows an embodiment variant that is suitable for retrofitting existing vehicles and units with particulate filters that can heat the exhaust gas with diesel. The separate combustion fuel tank in this case can be an aftermarket part or an existing container with a suitable fuel. An already existing combustion fuel container of this type is the cooling-water tank, if sufficient antifreeze agent is contained therein. Another is the tank of the windshield washer system, as long as a washer fluid with sufficiently high alcohol content is present therein. The injection of combustion fuel and propellant fuel into the exhaust gas 37 can be carried out independently of one another.
The measurements shown in FIGS. 5 through 9 come from a test arrangement with a Euro 3 industrial diesel engine (1.91 TDI from VW with turbocharger, direct injection and exhaust gas recirculation) and a commercially available continuously regenerating particulate filter system from HJS (platinum-doped oxidation catalyst). Different fuels were injected into the exhaust gas system. The injection was carried out according to the device shown in FIG. 2, inside the filter bowl 23, upstream of the catalyst 21. The respective injection quantity was selected such that with complete combustion an increase in temperature of approx. 100° C. was achieved. The exhaust gas temperatures were adjusted via the speed of the engine and load (power brakes).
The effects of different organic liquids on the temperature increase (FIG. 5) and on the NO2 production (FIG. 6) over a commercially available platinum catalyst can be seen from FIGS. 5 and 6. It is astonishing thereby that the two alcohols methanol and monoethylene glycol already trigger a considerable increase in both temperature and NO2 production at 180° C. The light-off temperatures for monoethylene glycol (MEG), methanol and propylene glycol were at 180° C. In the case of methanol and MEG a complete conversion was already established at 190 degrees. With respect to the temperature development, methanol and monoethylene glycol are about equally effective. As can be seen in FIG. 6, methanol is used with continuously regenerating systems, because the NO2 regeneration already rises at temperatures approx. 20° C. cooler, compared to monoethylene glyclol.
It is likewise remarkable that the NO2 production with the use of ethanol, 2-propanol and cyclohexanon does not increase parallel to the temperature development. Compared to the increase in the NO2 production depending on the temperature without the injection of combustion fuels (base line), the increase with the injection of these combustion fuels is much flatter. This is attributed among other things to a competition between the oxidation of the combustion fuel and the oxidation of the NO on the catalyst.
It is also assumed that certain oxidation products of the longer chain alcohols, in particular acetic acid and corresponding aldehydes, are responsible for the inactivation of the catalyst with respect to the NO/NO2 conversion.
For comparison, diesel propellant fuel was also injected. A temperature increase on the catalyst used does not start until above 220° C. (FIG. 5). However, the NO2 production is thereby largely suppressed (FIG. 6).
The tests with methanol, monoethylene glycol, ethanol and diesel were also carried out on a different filter bowl (manufacturer Peugeot). This filter bowl contains a presumably highly platinum-doped catalyst, which produces NO2 and a downstream particulate filter, which likewise is doped with a catalyst, presumably above all palladium. This filter is commercially available for automobiles from Peugeot, in which a fuel additive is used. The filter cake formed by the additive and the soot is ignited in these vehicles, in that the engine control is manipulated such that unburned diesel is discharged. This oxidizes on the catalyst and on the catalytically doped particulate filter exothermally. We used the filter bowl from Peugeot without modifications, but the engine was not driven with the fuel with additive, but with diesel. Instead of intervening in the engine control, in order to guide unburned diesel from the engine into the filter bowl, in our tests a combustion fuel was introduced into the exhaust gas flow. In these tests the light-off temperatures for the oxidation of the propellant fuels or combustion fuels was about 30-40 degrees lower, but in qualitative terms a very similar picture resulted as with the first catalyst (HJS). In turn, only methanol and monoethylene glycol were already able to produce a temperature increase at very low temperatures (FIG. 11), without thereby suppressing the NO2 production (FIG. 12).
The regeneration of the particulate filter (from HJS) used in the above tests was also tested. The pressure pattern shown in FIG. 7 shows an increase in pressure during 5¾ hours in the exhaust gas system 37 according to FIG. 2 to 140 millibar. The temperature of the exhaust gas after the catalyst 21 during this time is around 200 degrees Celsius. At “start” monoethylene glyclol (8.5 g/kg exhaust gas) is injected (nozzle 35). Through the evaporation of this combustion fuel the pressure rises by 12 mbar. The evaporated MEG reacts with the oxygen in the exhaust gas 37 due to the catalytic surface of the catalyst component 21 (FIG. 2) and therefore releases heat. Due to the now increased temperature behind the catalyst of approx. 350° C., the regeneration of the particulate filter begins and the pressure is constantly reduced due to the reduction in soot. With the injection of more combustion fuel, a higher temperature and a quicker reduction in soot is achieved. For quicker regeneration of the particulate filter in practice temperatures of over 450 degrees are desirable. At the end of the injection at “stop” the exhaust gas pressure drops rapidly to a pressure of less than 100 mbar and begins to rise again. The new increase is the result of the fact that after the end of the injection of the monoethylene glycol the temperature suddenly falls to a level below 220 degrees, so that no NO2 is produced and for two reasons (temperature too low and lack of NO2) no regeneration occurs any longer. Through the injection of MEG, the NO2 concentration in the exhaust gas was increased from 60 ppm to 115 ppm, whereby sufficient NO2 was available for the soot combustion.
To clarify whether the disadvantage of the invention, namely the necessity of a media tank separate from the propellant fuel tank, the content of which media tank can be injected into the exhaust gas flow as combustion fuel, can be mitigated through the use of liquids already carried with motor vehicles, attempts were made to use the existing containers of a vehicle and to enrich the media contained therein for enriching the exhaust gas with a catalytically oxidizable combustion fuel. In principle the coolant system with the coolant flowing therein are available, the glycol concentration of which is typically about 50 to 60%. The windshield washer fluid in the corresponding container is also available. Windshield washer fluids are generally composed 50/50% of water and an alcohol or an alcohol mixture.
FIG. 8 therefore shows the effect of glycol 100% to the aqueous solution of glycol with a glycol content of only 50% on the temperature increase over the catalyst. In the case of the aqueous solutions, the temperature increase as expected decreases with increasing water content, since the water absorbs evaporation energy. In the measurements shown, the water content was corrected and the dosage adjusted such that with each test the same quantity of alcohol was injected. Surprisingly slight losses in the temperature increase were recorded.
Corresponding results are also shown in FIG. 9 regarding aqueous solutions of glycerin with a glycerin content of 75% and 50% respectively. The same picture is shown here, that namely the temperature increase is sufficient, even with the use of an aqueous solution, to render possible a regeneration.
This insight has two aspects. On the one hand, coolant fluid or windshield washer fluid can be used to enrich the exhaust gas with a catalytically oxidizable medium in order to increase the exhaust gas temperature to a temperature sufficient for the regeneration of the particulate filter. These liquids can be removed from the existing containers.
The second aspect is that evidently even an aqueous solution of an easily flammable alcohol, e.g., methyl alcohol, can be used. This is harmless in terms of sales and handling. It can be poured into combustion fuel tanks specially provided for the regeneration of particulate filters and does not require any special safety precautions, in contrast to a gas container, for example.
An alternative embodiment of the invention is the use of the combustion fuel to “ignite” a filter cake of soot, which is present in the mixture with a catalyst added by means of a propellant fuel additive. This is an alternative to the known methods for the electric ignition of filter cakes of this type or ignition by means of manipulation of the engine control for the purpose of the short-term exhaust gas temperature increase. In another variant, the exhaust gas enriched with the combustion fuel is converted on an oxidation catalyst arranged in front of the particulate filter and in this manner heats the exhaust gas above the ignition temperature of the filter cake.
Depending on the selection of the propellant fuel additive, instead of a catalyst element arranged in the exhaust gas flow, the catalyst present in the soot filter cake itself can be used to oxidize the added combustion fuel (e.g., platinum). Another variant lies in using a conventional ferriferous propellant fuel additive in order to dope the soot deposited in the particle filter with iron and thus to reduce the ignition temperature of the filter cake. To initiate the regeneration, a platinum additive is first added to the propellant fuel instead of the iron additive, so that a platinum layer forms on the surface of the filter cake. Then the combustion fuel necessary for regeneration is injected, which reacts directly on the soot surface with the platinum catalyst and thus causes the ignition of the filter cake.
A device to be retailed for installation in a vehicle or a unit with diesel engine and particulate filter therefore comprises a combustion fuel tank for, e.g., an aqueous alcohol solution, a line and a pump, as well as a nozzle for injecting the combustion fuel in the exhaust gas system. In the case of aftermarket parts, the line can be provided with a cuff, with which an exhaust pipe can be surrounded. The arrangement of the line with the nozzle in the exhaust pipe is therefore very simple. In addition, an electric line is required between the pump motor and a switch. The switch can also be manually operated.
FIG. 10 finally shows a canister that contains a combustion fuel that is provided for the regeneration of particulate filters. The combustion fuel can be, for example, an 80% aqueous solution of alcohol. The alcohol content can comprise various components, in particular a main component of methanol for an early increase in the NO2 and optionally a lower content of monoethylene glycol. A canister of this type is available in gas station shops through existing distribution channels.
The solution according to the invention renders possible primarily an emergency regeneration, but can also be used for regular regeneration. An emergency regeneration is not triggered more often than with every other regeneration cycle, such as not more often than with every fifth regeneration cycle. It is triggered only when with the given operating conditions of the lean engine, the regular regeneration cannot take place and a regeneration is necessary for the further operation of the engine.

Claims

1. A method for regenerating a particulate filter of a diesel engine, comprising:

enriching an exhaust gas when the exhaust gas temperature is below a predetermined temperature, the exhaust gas enriched at a feed point upstream of a particulate filter with a catalytically oxidizable medium; and

heating the exhaust gas through catalytic oxidation of the catalytically oxidizable medium to an exhaust gas temperature sufficient for a regeneration of the particulate filter, the exhaust gas enriched with a combustion fuel that differs from a propellant fuel and cleavage products thereof, the combustion fuel oxidizing on the catalytically oxidizable medium at a temperature that is lower than a propellant fuel temperature.

2. The method of claim 1, further comprising heating the exhaust gas enriched with the combustion fuel to a first temperature, at which the combustion fuel can be catalytically oxidized, and simultaneously or subsequently enriching the exhaust gas with the propellant fuel.

3. A method of using a catalytically oxidizable medium for enrichment of an exhaust gas of a lean-burn engine, comprising: providing a catalytically oxidizable medium for heating an exhaust gas through catalytic oxidation of the medium to an exhaust gas temperature sufficient for the regeneration of a particulate filter; and

providing a combustion fuel that differs from a propellant fuel of the lean-burn engine and the cleavage products thereof, the combustion fuel being catalytically oxidizable at a lower temperature than the propellant fuel.

4. The method of claim 3, wherein providing the combustion fuel further comprises providing a combustion fuel that is or contains an organic liquid.

5. The method of claim 4, wherein providing the combustion fuel further comprises providing a combustion fuel that is an alcohol or a mixture containing at least 40% alcohol.

6. The method of claim 4, wherein providing the combustion fuel further comprises providing a combustion fuel that is methyl alcohol or a mixture containing at least 10% methyl alcohol.

7. The method of claim 4, wherein providing the combustion fuel further comprises providing a combustion fuel that is at least one of a glycol, a monoethylene glycol, a propylene glycol, or a mixture containing at least 10% glycol.

8. The method of claim 3, wherein providing the combustion fuel further comprises providing a combustion fuel that has a volatilization temperature that is lower than an average volatilization temperature of the propellant fuel.

9. The method of claim 8, further comprising providing a combustion fuel wherein the volatilization temperature is below a minimum exhaust gas temperature necessary for a catalytic reaction of the propellant fuel.

10. The method of claim 3, wherein providing the combustion fuel further comprises providing a combustion fuel that is dissolved in water.

11. A device for regenerating a particulate filter, comprising:

a combustion fuel tank;

a combustion fuel line coupled to the combustion fuel tank;

a conveyance device for conveying a combustion fuel from the combustion fuel tank through the combustion fuel line

a lean burn engine,

a propellant fuel tank for supplying propellant fuel to said lean burn engine,

an exhaust gas system coupled to said lean burn engine, and

a particulate filter in the exhaust gas system, the combustion fuel line arranged upstream of the particulate filter opening into the exhaust gas system, so that exhaust gas can be enriched with a combustion fuel from the combustion fuel tank prior to entering the particulate filter.

12. A device for regenerating a particulate filter, comprising:

a lean burn engine,

a first fuel tank for supplying a first fuel to the lean burn engine,

a first fuel line from the first fuel tank to the lean-burn engine,

an exhaust gas system coupled to the lean burn engine,

at least one catalytic surface and a particulate filter coupled to the exhaust gas system,

a second fuel tank (25), separate from the first fuel tank, for accommodating a second fuel different from the first fuel and the cleavage products thereof,

a second fuel line opening into the exhaust gas system from the second fuel tank (25) to a feed point in the exhaust gas system, that is upstream of the particulate filter and the at least one catalytic surface, and

a conveyance device for conveying the second fuel into the exhaust gas system and a circuit for activating the conveyance device.

13. The device of claim 12, further comprising a sensor for monitoring at least one of pressure and temperature in the exhaust gas system and for activating the circuit.

14. The device of claim 12, further comprising a warning device connected to the circuit to indicate a necessity of a regeneration of the particulate filter.

15. The device of claim 12, further comprising a refill package containing the second fuel that is comprised of an alcohol.