U.S. patent application number 11/577616 was filed with the patent office on 2008-02-07 for condenser in a turbo-compressor system and method for operating one such system.
This patent application is currently assigned to BEHR GmbH & Co. KG. Invention is credited to Jochen Eitel, Gerhard Frankle, Peter Geskes, Rainer Lutz, Rolf Muller, Eberhard Pantow.
Application Number | 20080028757 11/577616 |
Document ID | / |
Family ID | 35717711 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080028757 |
Kind Code |
A1 |
Eitel; Jochen ; et
al. |
February 7, 2008 |
Condenser in a Turbo-Compressor System and Method for Operating One
Such System
Abstract
The invention relates to an system, especially a
turbo-compressor system pertaining to a motor vehicle comprising an
internal combustion engine with exhaust gas recirculation. Said
system comprises an exhaust gas cooler (2) and a charge air cooler
(1) for cooling recirculate exhaust gases and/or charge air, a
compressor (V) for compressing the charge air, and at least on
condenser (3).
Inventors: |
Eitel; Jochen; (Bissingen,
DE) ; Frankle; Gerhard; (Remshalden, DE) ;
Geskes; Peter; (Ostfildern, DE) ; Lutz; Rainer;
(Steinheim, DE) ; Muller; Rolf; (Ludwigsburg,
DE) ; Pantow; Eberhard; (Moglingen, DE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BEHR GmbH & Co. KG
Mauserstrasse 3,
Stuttgart
DE
70469
|
Family ID: |
35717711 |
Appl. No.: |
11/577616 |
Filed: |
October 18, 2005 |
PCT Filed: |
October 18, 2005 |
PCT NO: |
PCT/EP05/11188 |
371 Date: |
June 25, 2007 |
Current U.S.
Class: |
60/311 ; 60/274;
60/280; 60/310 |
Current CPC
Class: |
Y02T 10/146 20130101;
F02M 26/15 20160201; F02M 26/06 20160201; F02M 26/24 20160201; F02M
26/35 20160201; F02M 26/05 20160201; F02B 37/00 20130101; F01N
2250/06 20130101; F02M 35/022 20130101; F02B 29/0468 20130101; Y02T
10/12 20130101; F02B 29/0443 20130101; F02M 26/28 20160201; F01N
3/033 20130101; F02M 26/22 20160201; F01N 3/021 20130101; F01N
13/009 20140601; Y02T 10/20 20130101 |
Class at
Publication: |
060/311 ;
060/274; 060/310; 060/280 |
International
Class: |
F01N 3/037 20060101
F01N003/037; F01N 3/00 20060101 F01N003/00; F01N 5/04 20060101
F01N005/04; F01N 3/04 20060101 F01N003/04; F01N 3/02 20060101
F01N003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2004 |
DE |
10 2004 051 922.6 |
May 20, 2005 |
DE |
10 2005 023 957.9 |
Claims
1. An arrangement, in particular a turbocharger arrangement of a
motor vehicle having an internal combustion engine, with exhaust
gas recirculation, wherein the arrangement has an exhaust gas
cooler and a charge air cooler for cooling recirculated exhaust gas
and/or charge air and, a compressor for compressing the charge air,
characterized in that the arrangement has at least one condensate
separator.
2. The arrangement as claimed in claim 1, wherein the condensate
separator is a centrifugal separator or cyclone separator.
3. The arrangement as claimed in claim 1, wherein the condensate
separator has a turbulence generator which causes the exhaust gas
stream or the charge air stream to rotate so that at least some of
the condensate droplets are deposited on the wall.
4. The arrangement as claimed in claim 3, wherein an annular duct
with an outflow opening for the condensate is arranged downstream
of the turbulence generator.
5. The arrangement as claimed in claim 1, wherein the condensate
separator is a filter.
6. The arrangement as claimed in claim 1, wherein multi-stage
condensate separation is provided.
7. The arrangement as claimed in claim 1, wherein a collector
vessel is arranged at the condensate outlet.
8. The arrangement as claimed in claim 1, wherein a valve is
provided for throttling the exhaust gas stream or the charge air
stream.
9. The arrangement as claimed in claim 1, wherein a pump is
provided for sucking in the collected condensate.
10. The arrangement as claimed in claim 1, wherein the condensate
separator is arranged directly downstream of the cooler, in
particular the exhaust gas cooler.
11. The arrangement as claimed in claim 1, wherein the condensate
separator is arranged in a region in which the temperature of the
exhaust gas stream or of the charge air stream reaches or drops
below the dew point.
12. The arrangement as claimed in claim 1, wherein the condensate
separator is coupled or permanently connected to the shaft of the
compressor.
13. The arrangement as claimed in claim 12, wherein the condensate
separator has an expeller element or centrifuge element which is
arranged on the shaft in a rotationally fixed fashion or formed by
a region of the shaft.
14. The arrangement as claimed in claim 13, wherein the expeller
element or centrifuge element is arranged upstream of the impeller
wheel of the compressor in the normal direction of flow of the
charge air and deflects the charge air stream by at least
90.degree., preferably by two times 180.degree..
15. The arrangement as claimed in claim 12, wherein the condensate
separator is arranged in the compressor housing and/or is designed
so as to be integrated into the compressor housing.
16. The arrangement as claimed in claim 1 wherein the arrangement
has a thermal condensate disposal means.
17. The arrangement as claimed in claim 16, wherein the thermal
condensate disposal means is of multi-stage design.
18. The arrangement as claimed in claim 16, wherein the thermal
condensate disposal means is connected to a plurality of condensate
separators via lines.
19. A method for operating a turbocharger, in particular of a motor
vehicle, having an internal combustion engine in which exhaust gas
is recirculated and fed to the charge air, wherein the exhaust gas
or charge air is deflected or directed through a filter in a region
in which the exhaust gas or the charge air is at a temperature
which corresponds to the dew point or drops below it.
20. The method as claimed in claim 19, wherein the exhaust gas
stream which flows essentially in a straight direction or the air
stream is deflected in a region directly downstream of a cooler, in
particular an exhaust gas cooler, or is directed through the
filter.
21. The method as claimed in claim 20, wherein a speed component is
applied to the in the tangential direction so that a rotational
movement is superimposed on the longitudinal movement.
22. The method as claimed in claim 19, wherein the average
tangential speed component is at least as large as the average
speed component in the longitudinal direction.
23. The method as claimed in claim 19, wherein the average
tangential speed component is at least twice as large as the
average speed component in the longitudinal direction.
24. The method as claimed in claim 19, wherein the condensate which
collects at an expeller element or centrifuge element is thrown
outwards by means of centrifugal force.
25. The method as claimed in claim 19, wherein the condensate is
evaporated by means of a thermal condensate disposal means, the
acids contained in the condensate are converted and the vapor which
is produced and/or the gases are fed again to the exhaust gas
stream.
Description
[0001] The invention relates to a turbocharger arrangement and a
method for operating a turbocharger according to the preamble of
claim 1 and claim 19, respectively.
[0002] In order to reduce the emissions of particles and nitrogen
oxides in diesel engines it is known to recirculate exhaust gas,
both high-pressure exhaust gas recirculation and low-pressure
exhaust gas recirculation being possible. In this context, the
exhaust gas stream is cooled to temperatures of approximately
150.degree. C. to 200.degree. C. and mixed into the intake air. At
these temperatures of the cooled intake air, a partial stream of
the engine coolant is generally used as a cooling medium in the
exhaust gas cooler but it is also known to use other coolants. The
exhaust gas recirculation becomes more effective as the gas outlet
temperatures at the exhaust gas cooler are reduced.
[0003] In the high-pressure exhaust gas recirculation, exhaust gas
is usually extracted upstream of the turbine and fed to the charge
air downstream of the charge air cooler. The recirculated exhaust
gas is cooled by means of the hot engine coolant so that owing to
the high temperatures an exhaust gas condensate is usually not
produced. The high-pressure exhaust gas recirculation brings about
a significant reduction in the nitrogen oxide emission but is
associated with a simultaneous rise in the emission of particles.
The emission of particles or fine dust can be reduced by means of
particle filters.
[0004] During the low-pressure exhaust gas recirculation the
exhaust gas is extracted from the exhaust gas stream downstream of
the turbine, preferably downstream of a particle filter, cooled and
fed to the compressor on the inlet side. Owing to the greater
degree of cooling of the recirculated exhaust gas, a further
reduction in the emission of nitrogen oxides is possible but owing
to the high degree of cooling of the recirculated exhaust gas
condensate forms which is highly acidic, essentially due to the
nitric acid HNO.sub.3 formed, so that corrosion occurs. If
condensate vapor is fed to the compressor, it can additionally
damage the compressor because its high rotational speed
(approximately 120 000 to 150 000 rpm).
[0005] In utility vehicles, in addition to the recirculation of
exhaust gas in order to reduce the emission of nitrogen oxide, the
SCR method (Selective Catalytic Reduction) is also known, in which
method ammonia is produced either from ammonium carbamate or
aqueous urea solution, and said ammonia catalytically converts the
nitrogen oxide generated by the engine into the innocuous
components nitrogen and water. However, this method has the
disadvantage that an additional operating substance has to be
carried in the vehicle.
[0006] Taking this prior art as a starting point, the object of the
invention is to make available an improved turbocharger arrangement
and a method for operating a turbocharger with which the risk of
corrosion is as low as possible. The object is achieved by means of
a turbocharger arrangement and a method having the features of
claim 1 and of claim 19. Advantageous refinements are the subject
matter of the subclaims.
[0007] In the text which follows, charge air is to be understood as
referring to both the intake air and to the intake air mixed with
the recirculated exhaust gas.
[0008] According to the invention, a turbocharger arrangement, in
particular of a motor vehicle having an internal combustion engine,
is provided with exhaust gas recirculation, the arrangement having
an exhaust gas cooler and a charge air cooler for cooling
recirculated exhaust gas and/or charge air and a compressor for
compressing the charge air and a condensate separator. By means of
the condensate separator, the corrosive component of the exhaust
gas which is located in the condensate which forms when the
temperature reaches and drops below the dew point temperature, can
be removed from the exhaust gas stream or the charge air stream and
it can be ensured that condensate which promotes possibly occurring
corrosion of the components does not collect in the following
region or only does so to a minimum degree. The condensate
separator is preferably arranged here directly downstream of the
cooler for cooling the recirculated exhaust gas and/or or
downstream of the charge air cooler and/or directly upstream of the
charge air compressor.
[0009] The condensate separator can preferably be a centrifugal
separator or cyclone separator. Alternatively it is also possible
to use another turbulence generator which conveys outward
condensate droplets located in an air stream so that said droplets
can be carried away. Any other identically acting devices are also
possible.
[0010] In addition, it is possible to use a filter, for example
composed of stainless steel mesh or plastic mesh or nonwoven which
serves as a condensate separator.
[0011] In all cases the separation of condensate can take place in
multiple stages in order to increase the efficiency. At the same
time it is also possible to combine different condensate separators
with one another as desired.
[0012] In order to be able to carry the condensate out of a
collector vessel or the like, a valve is preferably provided for
throttling the exhaust gas stream or the charge air stream so that
the pressure level can be raised and the condensate can be carried
away without additional resources. Alternatively it is also
possible to use resources such as, for example, a pump or some
other arrangement which permits a limited pressure increase in the
collector vessel.
[0013] A nonreturn valve which permits the condensate to flow out
but prevents condensate and/or air from flowing back from the
outside can be provided at the condensate outflow.
[0014] In addition, the condensate outflow can have such a
discharge gradient that the force due to weight acting on the
condensate corresponds at least to the intake pressure so that the
condensate can be prevented from being sucked back.
[0015] The condensate separator is preferably arranged directly
downstream of the cooler, in particular preferably directly
downstream of the exhaust gas cooler. An arrangement downstream of
the charge air cooler is also appropriate. In order to protect the
compressor against damage by condensate droplets, an arrangement
directly upstream of the compressor is also appropriate. In this
context is it possible to use the shaft of the compressor
advantageously as a drive or as part of a centrifugal
separator.
[0016] The condensate separator must additionally be arranged in a
region in which condensate droplets are present. This is usually
the case in a region in which the temperature of the exhaust gas
stream or of the charge air stream reaches or drops below the dew
point (taking into account the other parameters such as, in
particular, pressure and chemical composition).
[0017] The exhaust gas or the charge air are deflected, in
particular have a speed component applied to them in the tangential
direction in a region in which the exhaust gas or the charge air
has a temperature which corresponds to the dew point or drops below
it, with the result that a rotational movement is preferably
superimposed on the longitudinal movement but it may also be
sufficient to deflect the air stream. As a result of the speed
component in the tangential direction, the condensate droplets
which form are moved outwards and can be deposited on the wall,
where they collect, and can be conveyed onward and carried away.
The average tangential speed component in the region of the
separation of the condensate is at least as large as the average
speed component in the longitudinal direction, preferably at least
twice as large.
[0018] The condensate separator is preferably coupled or
permanently connected to the shaft of the compressor so that a high
rotational speed is possible with a small degree of structural
complexity and without an additional drive.
[0019] The condensate separator preferably has an expeller element
or centrifuge element which is arranged on the shaft in a
rotationally fixed fashion or formed by a region of the shaft. This
element which also rotates is preferably fabricated from a
lightweight metal or a lightweight alloy such as aluminum, titanium
or magnesium, or from a plastic. Alternatively or additionally it
can exhibit a surface coating, preferably an oxale layer, which
protects it against corrosion. The element is preferably designed
in terms of flow dynamics in such a way that despite the deflection
no eddies are generated. In addition, it is minimized in terms of
its mass in order to avoid mass inertia forces.
[0020] The expeller element or centrifuge element is preferably
arranged upstream of the impeller wheel of the compressor in the
normal direction of flow of the charge air and preferably deflects
the charge air stream by at least 90.degree., preferably by two
times 180.degree.. In particular, a Z-like deflection through two
times approximately 180.degree. brings about very good separation
of the condensate drops, with some of the condensate drops becoming
deposited on the body and being thrown from there against the inner
duct wall or housing wall owing to the centrifugal force. In the
process, the kinetic energy of the condensate drops can be used to
carry the condensate away from the interior.
[0021] The condensate separator is preferably arranged in the
compressor housing and/or designed so as to be integrated into the
compressor housing. At the same time, the compressor housing
preferably has bore holes for the condensate outlet.
[0022] The arrangement preferably has a thermal condensate disposal
means which permits the condensate to be detoxified so that the
acids contained in the condensate, in particular the nitric acid,
the sulfuric acid and the sulfurous acid are converted into their
innocuous gases and water. These can subsequently be added to the
exhaust gas and discharged into the surroundings via the
exhaust.
[0023] The thermal condensate disposal means is preferably of
multi-stage design, in particular in three stages. In this context,
the heat exchanger which is heated by exhaust gas for heating the
condensate is provided as the first stage. A thermal reactor which
preferably comprises a PTC heating element and powers down
automatically if no condensate occurs is preferably provided as a
second stage. A further thermal reactor for residual heating is
preferably provided as a third stage, in particular in the form of
an electric heating element which heats the evaporated condensate
to 350 to 450.degree. C. so that the nitric acid vapor is converted
into its innocuous components of nitrogen, water and oxygen.
Installations for increasing the surface are preferably provided,
in particular in the thermal reactor of the third stage, so that
the chemical process sequence can be optimized. A thermal
condensate disposal means can be provided for each condensate
separator, but a common condensate disposal means is preferably
provided for a plurality of condensate separators.
[0024] The heating means of the thermal condensate disposal means
can preferably be operated in a clocked fashion at low operating
temperatures (122.degree. C.) which bring about the formation of
NO.sub.2, in order to permit, for example, load-dependent metering
of the NO.sub.2 so that the NO.sub.x limiting values are complied
with.
[0025] Likewise, an additional blower can be provided which ensures
compliance with the MAK values, irrespective of the functioning of
the condensate disposal means.
[0026] Lines which have an automatic delivery effect owing to
capillary forces and/or their arrangement are preferably provided
between the condensate separator and condensate disposal means so
that pumps can be dispersed with.
[0027] Turbocharger arrangements are explained below in detail by
means of a plurality of exemplary embodiments and with reference to
the drawing, in which:
[0028] FIG. 1 is a schematic basic view of a device for cooling
exhaust gas such as can be used in a turbocharger arrangement
according to the invention,
[0029] FIG. 2 is a schematic view of a first exemplary
embodiment,
[0030] FIG. 3 is a schematic view of a second exemplary
embodiment,
[0031] FIG. 4 is a schematic view of a third exemplary
embodiment,
[0032] FIG. 5 is a schematic view of a fourth exemplary
embodiment,
[0033] FIG. 6 is a schematic view of a fifth exemplary
embodiment,
[0034] FIG. 7 is a schematic illustration of a turbocharger
arrangement with high-pressure exhaust gas recirculation,
[0035] FIG. 8 is a schematic illustration of a turbocharger
arrangement with low-pressure exhaust gas recirculation,
[0036] FIG. 9 is a schematic view of a seventh exemplary embodiment
with a first variant of a centrifugal separator,
[0037] FIG. 10 is a schematic view of an eighth exemplary
embodiment with a second variant of a centrifugal separator,
[0038] FIG. 11 is a schematic illustration of a turbocharger
arrangement with low-pressure exhaust gas recirculation with
two-stage cooling of the recirculated exhaust gas,
[0039] FIG. 12 is a schematic illustration of a turbocharger
arrangement with low-pressure exhaust gas recirculation with
thermal condensate disposal means, and
[0040] FIG. 13 is a schematic detailed illustration of the thermal
condensate disposal means in FIG. 12.
[0041] FIG. 1 shows a small detail of a turbocharger arrangement.
Here, a device 1 for cooling recirculated exhaust gas of a motor
vehicle with an internal combustion engine is illustrated, said
device having a condensate separator 3 which is arranged downstream
of an exhaust gas cooler 2 which is cooled by coolant and has an
exhaust gas outlet 4 and a condensate outlet 5. The direction of
flow of the exhaust gas stream is indicated by arrows in FIG. 1.
The function, like those in the exemplary embodiments 1 to 5
described below, is the same in each case, specifically the
condensate separator 3 extracts the moisture as far as possible
from the exhaust gas stream which is cooled by the exhaust gas
cooler 2 to approximately 150.degree. C. (temperature below dew
point taking into account the other parameter such as, in
particular, pressure and chemical composition) directly after the
discharge from the exhaust gas cooler 2. The dry exhaust gas stream
passes via an immersion pipe 6 out of the condensate separator 3
and is subsequently mixed with the intake air. The resulting charge
air stream is compressed further, cooled in the charge air cooler
and subsequently fed to the turbocharger (not illustrated).
[0042] In the present case, the recirculated exhaust gas stream has
passed through a particle filter before branching off from the
entire exhaust gas stream so that, apart from the separation of the
condensate there is as far as possible no separation of particles,
in particular no relatively large particles, which become deposited
and as a result increase the maintenance expenditure. However, in
particular small particles can serve as condensation nuclei and
have a positive effect on condensation.
[0043] In this context, according to the further five exemplary
embodiments the condensate droplets are separated in the condensate
separator 3 by making the exhaust gas stream rotate so that the
condensation droplets are not only entrained by the exhaust gas
stream in the axial direction but also in particular conveyed
outward and collect largely on the wall from where they drop
downward as a result of gravity, and can thus be carried away. The
pressure loss as a result of the condensate separator 3 is
relatively low here. Owing to the separation of the aggressive
condensate, the components arranged downstream of it are protected
so that the risk of corrosion can be significantly reduced.
[0044] According to the first exemplary embodiment illustrated in
FIG. 2, a centrifugal separator 3 which is in principle
conventional is provided as a condensate separator 3 which is part
of the device 1. The condensate which is precipitated flows
downward due to gravity through the condensate outlet 5 where an
opening with a collector vessel 7 in which the condensate is
collected is arranged. The collector vessel 7 is emptied when
necessary. It is to be noted in this context that compared to the
surroundings a partial vacuum prevails so that the condensate has
to be sucked away unless there is an increase in pressure, for
example due to the exhaust gas stream becoming blocked. A detailed
description of possible centrifugal separators will be provided at
a later point with reference to FIGS. 9 and 10.
[0045] According to the second exemplary embodiment illustrated in
FIG. 3, a shutoff valve 8 which is arranged in the exhaust gas
stream is provided in order to bring about an increase in pressure.
If the condensate is to be carried away, the shutoff valve 8 is
briefly closed so that the pressure in the device rises and the
condensate can flow away. It can be stored in a collector vessel
(not illustrated) until said vessel is emptied.
[0046] According to the third exemplary embodiment illustrated in
FIG. 4, which corresponds essentially to the first exemplary
embodiment, a pump 9 is arranged downstream of the collector vessel
7 and is activated automatically when a specific filling level of
the collector vessel 7 is reached so that, in particular in the
case of a low-pressure exhaust gas recirculating means which is
connected to a lower pressure than the ambient level, the exhaust
gas stream does not need to become blocked as is necessary in the
second exemplary embodiment in order to raise the partial vacuum in
the collector vessel 7 to the ambient level.
[0047] According to the fourth exemplary embodiment illustrated in
FIG. 5, a further possible way of increasing the pressure in the
collector vessel 7 is to provide two valves 10 at the condensate
inlet and condensate outlet thereof and a thin hose 11 with a
control valve 12 which connects the collector vessel 7 to the
high-pressure side of the charge air line so that when the control
valve 12 is opened the valve 10 on the condensate inlet is
automatically closed, the pressure in the collector vessel 7 rises
and when a pressure level which is raised compared to the
surroundings is reached the second valve 10 at the condensate
outlet opens automatically so that the condensate can be carried
away.
[0048] Of course, other variants for increasing the pressure in the
collector vessel in order to carry away the condensate are also
possible.
[0049] According to the fifth exemplary embodiment illustrated in
FIG. 6, a turbulence generator 13 is provided in conjunction with a
downstream, annular duct 14 as a condensate separator 3 and is
integrated into the line downstream of the exhaust gas cooler 2.
The turbulence generator 13 superimposes a rotational movement on
the exhaust gas stream so that again the condensate droplets which
are formed downstream of the exhaust gas cooler 2 owing to the
reduced temperature are carried outward and deposited on the wall.
The speed component of the exhaust gas stream in the longitudinal
direction carries along the condensate in the longitudinal
direction and thus passes into the duct 14 where it is carried away
downward and collects in a collector vessel 7 in accordance with
the first exemplary embodiment. For example, measures corresponding
to the previously described exemplary embodiments are possible for
emptying the collector vessel 7, in particular in the case of a
low-pressure exhaust gas recirculation means.
[0050] The condensate separator does not necessarily need to be
arranged directly downstream of the exhaust gas cooler. For
example, an arrangement with a subsequent charge air cooler is also
appropriate, in particular if the temperature only reaches or drops
below the dew point there so that in this case the charge air which
is composed of the intake air and the recirculated exhaust gas is
cooled. Correspondingly, it is in principle also possible to dry
the pure exhaust air.
[0051] According to a sixth exemplary embodiment (not illustrated
in the drawing), a filter which has a plastic nonwoven is arranged
as a condensate separator downstream of the exhaust gas cooler. The
condensate which is formed at said filter collects and runs away
downward where it is collected in a collector vessel.
[0052] FIGS. 7 and 8 illustrate examples of a possible arrangement
of a condensate separator 3 for high-pressure exhaust gas
recirculation (FIG. 7) and for low-pressure exhaust gas
recirculation (FIG. 8). In the process, the configuration can be
implemented in accordance with the previously described exemplary
embodiments in all cases. The lines of the low-pressure side are
illustrated in FIGS. 7 and 8 by thick, continuous lines and those
of the high-pressure side by dashed lines. The directions of flow
are respectively indicated by arrows.
[0053] According to the high-pressure exhaust gas recirculation
means illustrated in FIG. 7, the branching off of the exhaust gas
to be fed back from the exhaust gas stream which comes from the
engine M takes place on the high pressure side, that is to say
before the pressure is reduced. The intake air is compressed in a
compressor V, flows through a charge air cooler L and subsequently
the recirculated and cooled exhaust gas, which is dry after flowing
through the condensate separator 3, is fed to it. The charge air
stream is then fed to the engine M.
[0054] FIG. 8 shows an example of a low-pressure exhaust gas
recirculation means in which the branching off of the exhaust gas
to be fed back from the exhaust gas stream coming from the motor M
takes place on the low pressure side, that is to say after a
reduction in pressure. In order to prevent the compressor V and the
downstream charge air cooler L from being damaged and to protect
them against corrosion, said exhaust gas is passed through the
exhaust gas cooler 2 and the condensate separator 3, and only fed
to the intake air subsequently. The charge air stream which is then
formed by the recirculated exhaust gas and the intake air is cooled
in the charge air cooler L and fed to the engine M.
[0055] According to the seventh and eighth exemplary embodiments, a
centrifugal separator with a rotating expeller element or
centrifuge element 20 can be provided as the condensate separator 3
in order to avoid the dependence on the mass flow stream and to get
around the additional overall depth of a cyclone separator which is
required for installation, and in the present case the expeller
element or centrifuge element 20 is mounted on the shaft 21, of
prolonged design, of the turbocharger on which the compressor
impeller wheel 22 is also arranged, said expeller or centrifuge
element 20 being mounted upstream of the inlet into the compressor
V. In this way, the rotational speed of the centrifugal separator
is coupled to the rotational speed of the compressor impeller wheel
22 which is generally 120 000 to 150 000 rpm. The charge air
current which carries condensate droplets strikes the expeller
element or centrifuge element 20 so that the flow is forcibly
deflected and so that a large part of the condensate droplets are
deposited on the expeller element or centrifuge element 20, and as
a result of the high rotational speed they are thrown by the latter
in the outward direction where they collect and flow in the
direction of the condensate outlet 5. The deflection of the charge
air stream on the basis of the expeller element or centrifuge
element 20 in conjunction with the compressor inlet is configured
geometrically here in such a way that further condensate droplets
which have not been deposited on the expeller element or centrifuge
element 20 are also separated.
[0056] According to the seventh exemplary embodiment of a
condensate separator illustrated in FIG. 9, the expeller element or
centrifuge element 20 is embodied in the manner of a cup, the
opening pointing in the direction of the compressor V. Owing to the
Z like deflection of the charge air current, by 2.times.
approximately 180.degree. here, most of the condensate droplets are
precipitated before the charge air arrives at the compressor V. The
expeller element or centrifuge element 20 which is fabricated from
an aluminum alloy is plugged onto the end of the shaft 21 and
soldered to it.
[0057] FIG. 10 shows an expeller element or centrifuge element 20
for carrying away the condensate in a radial manner according to
the eighth exemplary embodiment for a condensate separator 3. Here,
the air is deflected outwards through approximately 9.sup.0.degree.
so that the condensate droplets strike the expeller element or
centrifuge element 20 from where they are thrown outward with high
kinetic energy due to the centrifugal force into an annular duct
which leads to the condensate outlet 5 and which has a
schematically indicated valve mechanism 23 which lets through the
condensate droplets which strike it with high kinetic energy but
prevents condensate from flowing back into the compressor space.
The expeller element or centrifuge element 20 which is fabricated
from plastic here is plugged onto the end of the shaft 21 and
bonded to it, and, as an additional securing means, the shaft end
has a hexagonal shape and the expeller element or centrifuge
element 20 has a corresponding internal shape.
[0058] FIG. 11 illustrates the low-pressure exhaust gas
recirculation means with two-stage cooling of the recirculated
exhaust gas (exhaust gas cooler 2) in addition to the charge air
cooling means (charge air cooler L) which has a single stage
(here). The exhaust gas coming from the engine M flows through the
turbine T here and flows, in the relaxed, cooled state, through a
filter F which is arranged downstream and by means of which
particles are removed from the exhaust gas. At a branching junction
it is possible for some of the exhaust gas from which particles
have been removed to be recirculated under valve control and for
the rest of the exhaust gas to pass outwards through the exhaust.
The recirculated quantity of exhaust gas is determined here by the
pressure gradient which occurs between the exhaust gas counter
pressure and the intake partial vacuum so that high exhaust gas
recirculation rates are possible with simple means.
[0059] The recirculated part of the exhaust gas is through a
two-stage exhaust gas cooler 2, with precooling being carried out
in the first stage 2' by means of the engine coolant which
circulates in an otherwise conventional engine cooling circuit.
Where necessary, a further reduction in the exhaust gas temperature
occurs in the second stage 2''. The second stage 2'' is part of a
low-temperature cooling circuit. The latter has an air-cooled
low-temperature cooler NK, downstream of which the high-temperature
cooler HK which cools the engine coolant is arranged in the air
stream, a compressor K for circulating the coolant and a charge air
cooler L and the second stage 2'' of the exhaust gas cooler 2 in
parallel branches, the coolant distribution being controlled using
valves.
[0060] In addition, a bypass B which is made available when
necessary under valve control, which runs parallel to the engine M
and can conduct charge air past it is provided for the charge air
stream or a part thereof.
[0061] As is apparent from FIG. 11, a condensate separator 3, by
means of which condensate can be removed from the cold,
recirculated exhaust gas before it is mixed with the sucked-in
fresh air is provided downstream of the second stage'' of the
exhaust gas cooler 2. Here, although not illustrated in more
detail, a further condensate separator in particular a centrifugal
separator such as is described above with reference to FIGS. 9 or
10, is arranged directly upstream of the compressor V.
[0062] In order to dispose of the condensate which collects and
which is classified as a hazardous material and therefore cannot be
stored onboard a vehicle, a thermal condensate disposal means 30 is
provided. In said means, the acids which are formed can be
converted into innocuous components using a multi-stage thermal
reactor. In addition, the condensate which is formed can be used to
precool the recirculated exhaust gas.
[0063] An example of the arrangement of such a condensate disposal
means 30 in a low-pressure exhaust gas recirculation means is
illustrated schematically in FIGS. 12 and 13. Here, condensate
which is collected at the exhaust gas cooler 2, upstream of the
compressor V and in or downstream of the charge air cooler L is
carried via lines to a central condensate collector 31 from which
it is fed via a line to a thermal reactor 32 which is part of the
thermal condensate disposal means 30. The thermal reactor 32 is
arranged downstream of the filter F and integrated into an exhaust
manifold of the engine. The lines carrying the condensate, in
particular the line from the condensate collector 31 to the thermal
reactor 32, have here a cross section which permits the condensate
to be conveyed in the form of capillary forces so that it is
possible to dispense with pumps. In addition, there is no provision
for significant storage of the condensate which occurs in the
engine system here but rather the condensate is largely passed on
directly to the thermal reactor 32, heated therein and subsequently
discharged.
[0064] As is apparent from FIG. 13, the condensate is used to cool
the recirculated exhaust gas in a first stage S1, for which purpose
a correspondingly embodied heat exchanger forms the first stage 2'
of the exhaust gas cooler 2, that is to say is arranged upstream of
the inlet of the actual exhaust gas cooler 2 so that essentially
the entire enthalpy change of the condensate can be used for the
first stage S1 of the means of cooling the exhaust gas. In the
process, the condensate is heated. For good thermal transfer, ribs
or corresponding measures which enlarge the surfaces are provided
for optimizing the transmission of heat from the exhaust gas to the
condensate.
[0065] In a second stage S2, the heated condensate is evaporated,
with the further heating being carried out here by means of a
self-controlling PTC (Positive Thermal Coefficient) heating element
to between approximately 250 and 300.degree. C., and subsequent
heating to between 350 and 450.degree. C. takes place in a third
stage S3. In this context, sufficient energy to activate the PTC
heating element is present irrespective of the operating state of
the engine. In addition, the PTC heating element is embodied in
such a way that it powers down automatically if no condensate has
occurred. The residual heating of the evaporated condensate in the
third stage is carried out here using an electrically heated
tubular heating element which has a surface temperature of 350 to
450.degree. C. and installations or filling elements with a large
surface and possibly catalytic effect.
[0066] Owing to the temperatures of the second and third stages S2
and S3, nitric acid decomposes into NO.sub.2, N.sub.2, H.sub.2O and
O.sub.2 and sulfuric acid or sulfurous acid into H.sub.2O and
SO.sub.2 and SO.sub.3, respectively, according to the following
reactions: 4 HNO.sub.3.fwdarw.4 NO.sub.2+2 H.sub.2O+O.sub.2 4
HNO.sub.3.fwdarw.2 N.sub.2+2 H.sub.2O+5 O.sub.2
H.sub.2SO.sub.4.fwdarw.SO.sub.3+H.sub.2O
H.sub.2SO.sub.3.fwdarw.SO.sub.2+H.sub.2O
[0067] After the third stage S3, the condensate which is now
innocuous is fed to the exhaust gas stream and disposed of via the
exhaust.
[0068] In order to ensure that no inadmissible MAK values occur, an
additional blower can be provided which ensures that the limiting
values are complied with irrespective of the functioning of the
condensate disposal means 30.
* * * * *