U.S. patent application number 12/594184 was filed with the patent office on 2010-07-15 for device and method for regenerating particulate filters, use of a medium for regenerating particulate filters, and refill pack comprising said with the medium.
This patent application is currently assigned to HOCHSCHULE RAPPERSWIL. Invention is credited to Rainer Bunge.
Application Number | 20100175370 12/594184 |
Document ID | / |
Family ID | 39672134 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100175370 |
Kind Code |
A1 |
Bunge; Rainer |
July 15, 2010 |
DEVICE AND METHOD FOR REGENERATING PARTICULATE FILTERS, USE OF A
MEDIUM FOR REGENERATING PARTICULATE FILTERS, AND REFILL PACK
COMPRISING SAID WITH THE MEDIUM
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.
Inventors: |
Bunge; Rainer; (Zurich,
CH) |
Correspondence
Address: |
MORRISS OBRYANT COMPAGNI, P.C.
734 EAST 200 SOUTH
SALT LAKE CITY
UT
84102
US
|
Assignee: |
HOCHSCHULE RAPPERSWIL
Rapperswil
CH
|
Family ID: |
39672134 |
Appl. No.: |
12/594184 |
Filed: |
April 18, 2008 |
PCT Filed: |
April 18, 2008 |
PCT NO: |
PCT/CH2008/000176 |
371 Date: |
February 8, 2010 |
Current U.S.
Class: |
60/277 ; 60/295;
60/297; 60/303 |
Current CPC
Class: |
F01N 3/025 20130101;
F01N 3/106 20130101; F01N 3/029 20130101; F01N 2610/04 20130101;
Y02T 10/47 20130101; Y02T 10/40 20130101; F01N 2610/1406 20130101;
F01N 2610/05 20130101; F01N 3/035 20130101; F01N 3/103 20130101;
F01N 9/002 20130101; F01N 3/0253 20130101; F01N 3/206 20130101;
F01N 2610/03 20130101; F01N 13/0097 20140603 |
Class at
Publication: |
60/277 ; 60/295;
60/297; 60/303 |
International
Class: |
F01N 11/00 20060101
F01N011/00; F01N 3/023 20060101 F01N003/023; F01N 3/035 20060101
F01N003/035; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2007 |
EP |
EP07405127 |
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] 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
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.degree. 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.degree. 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.
[0007] 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.degree. 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.
[0008] 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.degree. 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.degree. C. to 450.degree. 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.degree. C.
[0009] 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.
[0010] There are four possibilities for igniting the filter cake
[0011] Ignition with an electric heater [0012] 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). [0013] Ignition
through the combustion of fuel in open flame. To this end, a
fuel-operated burner is installed in the exhaust gas flow. [0014]
Ignition through catalytic combustion of fuel.
[0015] 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.
[0016] 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.
[0017] 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.degree. C. and 390.degree. 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.degree. C. Although with some
catalysts, at least in mint condition, the light-off temperature
can be reduced to 180.degree. 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.degree. C. in the catalyst through the heat formed there.
[0018] 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.
[0019] 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.
[0020] 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
[0021] 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.degree. 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.
[0022] The advantages of the present invention are attained with
the invention through the features of the independent claims.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] It has been shown that advantageous fuels are to be found
among alcohols. Many alcohols have volatilization temperatures
below 200.degree. 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.degree. C. with the known catalyst surfaces.
(Mono) ethylene glycol, for example, degrades from 165.degree. 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.degree.
C. Methanol (methyl alcohol) even has a boiling point of 65 degrees
Celsius.
[0027] 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.
[0028] 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.
[0029] 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.degree. 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.
[0030] 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.
[0031] 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.
[0032] Advantageous alcohols are methanol (methyl alcohol,
CH.sub.3OH) and monoethylene glycol (MEG, ethylene glycol,
ethane-1,2-diol, C.sub.2H.sub.6O.sub.2). 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.degree. C. This selection has the advantage that the
combustion fuel already evaporates when no reaction is yet expected
between diesel and catalyst.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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).
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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
[0049] The invention is described in more detail based on specific
test arrangements and based on the use of different selected
combustion fuels. They show:
[0050] FIG. 1 diagrammatically illustrates a truck with an engine
and exhaust gas system, diesel tank and combustion fuel tank for
heating the exhaust gas.
[0051] FIG. 2 is a diagrammatic representation of a first test
arrangement, blocking out the diesel tank and internal combustion
engine.
[0052] FIG. 3 is a diagrammatic representation of a second test
arrangement, blocking out the internal combustion engine.
[0053] FIG. 4 is a diagrammatic representation of a third test
arrangement, blocking out the internal combustion engine.
[0054] FIG. 5 is a diagram of the temperature increase by .DELTA.T
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.
[0055] FIG. 6 is a corresponding diagram of the NO2 concentration
without and with injection of different media.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] FIG. 10 is a container with a combustion fuel for
regenerating particulate filters.
[0060] FIG. 11 is a diagram of the temperature increase by .DELTA.T
of an exhaust gas with temperature T over a second diesel oxidation
catalyst (manufacturer: Peugeot) without (base line) and with
injection of different media.
[0061] FIG. 12 is a corresponding diagram of the NO2 concentration
without and with injection of various media.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.degree. 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.
[0074] 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.
[0075] 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.
[0076] 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.degree. C. was achieved. The exhaust gas temperatures were
adjusted via the speed of the engine and load (power brakes).
[0077] 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.degree. C. The light-off
temperatures for monoethylene glycol (MEG), methanol and propylene
glycol were at 180.degree. 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.degree. C. cooler, compared to monoethylene glyclol.
[0078] 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.
[0079] 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.
[0080] For comparison, diesel propellant fuel was also injected. A
temperature increase on the catalyst used does not start until
above 220.degree. C. (FIG. 5). However, the NO2 production is
thereby largely suppressed (FIG. 6).
[0081] 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).
[0082] The regeneration of the particulate filter (from HJS) used
in the above tests was also tested. The pressure pattern shown in
FIG. 7shows an increase in pressure during 53/4 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.degree. 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
* * * * *