U.S. patent application number 13/058873 was filed with the patent office on 2011-07-28 for producing ageing gas for exhaust gas after-treatment systems.
Invention is credited to Michael Bahn.
Application Number | 20110183274 13/058873 |
Document ID | / |
Family ID | 40639507 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110183274 |
Kind Code |
A1 |
Bahn; Michael |
July 28, 2011 |
PRODUCING AGEING GAS FOR EXHAUST GAS AFTER-TREATMENT SYSTEMS
Abstract
The invention relates to a process of producing ageing gas for
ageing components for the after-treatment of exhaust gas in a
burner which comprises a combustion chamber with at least one fuel
injection nozzle and with a combustion gas supply system with means
for generating swirl, wherein the swirl of the combustion air is
set as a function of the selected combustion air ratio .lamda..
Inventors: |
Bahn; Michael; (Aachen,
DE) |
Family ID: |
40639507 |
Appl. No.: |
13/058873 |
Filed: |
August 26, 2008 |
PCT Filed: |
August 26, 2008 |
PCT NO: |
PCT/EP08/06982 |
371 Date: |
April 5, 2011 |
Current U.S.
Class: |
431/2 ;
431/354 |
Current CPC
Class: |
F01N 2550/04 20130101;
Y02T 10/26 20130101; F01N 3/2033 20130101; F01N 2240/14 20130101;
F23D 11/408 20130101; F23D 2900/11402 20130101; F01N 11/00
20130101; F01N 2550/02 20130101; Y02T 10/12 20130101; F01N 3/025
20130101; Y02T 10/47 20130101; F01N 2550/20 20130101; Y02T 10/40
20130101; F23N 2237/12 20200101; F23C 7/008 20130101; F23D
2900/14481 20130101 |
Class at
Publication: |
431/2 ;
431/354 |
International
Class: |
F23L 7/00 20060101
F23L007/00; F23D 14/62 20060101 F23D014/62 |
Claims
1. A process of producing ageing gas for ageing components for the
after-treatment of exhaust gas in a burner, the process comprising:
a combustion chamber with at least one fuel injection nozzle and
with a combustion gas supply system that can generate a swirl,
characterised in that the swirl of the combustion air is set as a
function of the selected combustion air ratio .lamda..
2. The process according to claim 1, characterised in that the
swirl of the combustion air is changed as a function of changes in
the combustion air ratio .lamda. during the production of ageing
gas.
3. The process according to claim 1, characterised in that, with a
combustion air ratio of .lamda.22 1 (lean/stoichiometric), the
swirl of the combustion air is set to be lower and is set to be
higher with a combustion air ratio of .lamda.<1 (rich).
4. The process according to claim 1, characterised in that the
entire flow of the combustion air can be mass flow controlled.
5. The process according to claim 1, characterised in that the
combustion air is divided into an inner primary air flow and an
outer secondary air flow, wherein the combustion air in the inner
primary air flow is supplied with a swirl.
6. The process according to claim 5, characterised in that the
combustion air in the outer secondary air flow is supplied in a
substantially swirl-free condition.
7. The process according to claim 1, characterised in that the
secondary air flow can be throttled, wherein the secondary air flow
is throttled more particularly for achieving a combustion air ratio
of .lamda.<1 (rich).
8. The process according to claim 1 characterised in that an axial
position of the burner flame inside the combustion chamber is
detected and that, with the burner flame having moved to the rear,
the swirl of the combustion air is increased and reduced when the
burner flame has moved to the front.
9. The process according to claim 1, characterised in that ageing
gas is returned from the combustion chamber in the form of a sheath
flow into the region of the fuel injection nozzle (primary ageing
gas return).
10. The process according to claim 9, characterised in that, when
the secondary air flow is throttled, the primary ageing gas return
flow is also reduced.
11. The process according to claim 1, characterised in that to the
ageing gas originally produced in the burner there is added
conditioned ageing gas in the combustion chamber treatment and
provides a secondary ageing gas return flow.
12. The process according to claim 11, characterised in that the
percentage of the conditioned ageing gas of the secondary ageing
gas return flow is modified for the purpose of maintaining a
predetermined ageing gas temperature.
13. The process according to claim 11, characterised in that the
conditioned ageing gas of the secondary ageing gas return flow in
the burner is added in the form of an annular sheath flow.
14. The process according to claim I characterised in that, for
re-starting the combustion chamber, in order to simulate an overrun
fuel cut-off, there is set a combustion air ratio .lamda.<1
(rich) and a high degree of swirl of the primary air.
15. The process according to claim 1, characterised in that, behind
the burner and in front of the components for the after-treatment
of exhaust gas, conditioned ageing gas is added to the ageing gas
produced in the burner and provides a tertiary ageing gas return
flow.
16. The process according to claim 15, characterised in that oil
and/or fuel and/or foreign gas and/or air is added to the
conditioned ageing gas of the tertiary ageing gas return flow.
17. The process according to claim 1 characterised in that the fuel
injection is controlled in cycles with a pre-pressure of at least
20 bar.
18. The process of ageing components for the after-treatment of
exhaust gas by subjecting same to ageing gas, characterised in that
the ageing gas for treating the components for the after-treatment
of exhaust gas is produced in accordance with claim 1.
19. A burner for producing ageing gas for ageing components used
for the after-treatment of exhaust gas, said burner comprising: a
combustion chamber with a combustion chamber axis, at least one
fuel injection nozzle and a combustion air supply line which is
provided with means for generating swirl, characterised in that the
means for generating swirl are adjustable in the sense of changing
the swirl intensity.
20. The burner according to claim 19, characterised in that an
annular sheath or funnel (61) in the combustion air flow is
positioned in front of the fuel injection nozzle (31), which sheath
or funnel (61) divides the combustion air flow into an inner
primary air flow and an outer secondary air flow, wherein swirl is
generated in the primary air flow.
21. The burner according to claim 20, characterised in that the
swirl is generated only in the primary air flow.
22. The burner according to claim 19, characterised in that the
swirl generating means comprise circumferentially distributed
pivotable swirl blades (62) positioned on axes arranged radially
relative to the combustion chamber axis.
23. The burner according to claim 19, characterised in that in the
burner there are provided means for controlling the volume flow of
the combustion air flow.
24. The burner according to claim 23, characterised in that the
means for controlling the volume flow of the combustion air flow
are arranged annularly in the secondary air flow.
25. The burner according to claim 23, characterised in that the
means for controlling the volume of the combustion air flow
comprise of a ring of adjustable apertured diaphragms (56), which
ring is arranged concentrically relative to the fuel injection
nozzle.
26. The burner according to claim 19, characterised in that there
are arranged means for detecting the axial position of the flame in
the combustion chamber (11), more particularly one temperature
sensor or a plurality of temperature sensors arranged along the
length of the combustion chamber.
27. The burner according to claim 19, characterised in that, in the
combustion chamber (11), there is provided a concentrically
arranged flame pipe (23) which ends in front of the combustion
chamber (11) and which, near the fuel injection nozzle (31),
comprises circumferentially distributed apertures (43) for the
returning ageing gas of the primary ageing gas return flow.
28. The burner according to claim 27, characterised in that the
exit apertures (43) in the flame pipe (23) are positioned in a
portion (42) of the flame pipe (23), which portion (42) is narrowed
like a nozzle.
29. The burner according to claim 19, characterised in that inside
the burner sheath (12), there is positioned a mixing pipe (21)
which is arranged concentrically relative to the combustion chamber
axis and which, together with the burner sheath (12), forms an
annular chamber (27) to which there is connected a supply port (26)
for conditioned ageing gas, wherein the mixing pipe (21) extends
beyond the length of the flame pipe (23) and, behind the end of the
flame pipe (23), comprises circumferentially distributed exit
apertures (22) for the conditioned ageing gas of the secondary
ageing gas return flow.
30. The burner according to claim 19, characterised in that the
fuel injection nozzle (31) is supplied by a high-pressure injection
valve which can be controlled in cycles.
31. The burner according to claim 30, characterised in that the
fuel injection nozzle (31) is combined with the high-pressure
injection valve to form a unit and is arranged inside the swirl
generating means.
32. A system for ageing components for the after-treatment of
exhaust gas by subjecting said components to an ageing gas produced
in a burner, characterised in that there is provided a burner (11)
according to claim 16 to which the components for the
after-treatment of exhaust gas are connected via an ageing gas
pipeline (100).
33. The system according to claim 32, characterised in that the
supply port (26) is connected to a pipeline (98) for ageing gas
which is produced in the burner (10) and subsequently
conditioned.
34. The system according to claim 33, characterised in that, in the
pipeline (98), there is arranged an ageing gas recooling device
(102).
35. The system according to claim 33, characterised in that, in the
pipeline (98), there is arranged a throttle flap (106) and a
controllably driven compressor (107).
36. The system according to claim 33 characterised in that that the
pipeline (98) is connected to a main ageing gas pipeline (100)
behind the components for the after-treatment of exhaust gas or to
an ageing gas bypass pipeline (114) in the bypass leading to the
components for the after-treatment of exhaust gas.
37. The system according to claim 33, characterised in that prior
to the pipeline (98) for conditioned ageing gas being connected to
the supply port (26), a branch pipeline (99) is branched off said
pipeline (98) and ends behind the burner (10) in the main ageing
gas pipeline (100).
38. The system according to claim 37, characterised in that feeding
pipelines (112, 113) for oil and/or fuel and/or foreign gas and/or
air end in the branch line (99).
Description
FIELD OF THE INVENTION
[0001] The present invention is related to a process for producing
ageing gas, and in particular for producing ageing gas for ageing
components related to an after-treatment of exhaust gas.
BACKGROUND OF THE INVENTION
[0002] Motor vehicles with internal combustion engines are subject
to emission laws which, nowadays, can only be complied with by
using exhaust gas after-treatment systems which adjoin, and are
connected to, the internal combustion engines in the exhaust gas
line. The exhaust gas after-treatment systems have to have the
service life which is specified by law. For the European Union,
after the introduction of exhaust gas stage EURO 4, there is
specified a durability in the form of a minimum driving performance
of 100,000 km, whereas after the introduction of exhaust gas stage
EURO 5, a durability in the form of a minimum driving performance
of 160,000 km has been specified. For homologizing a vehicle (type
approval), it is necessary to prove permanent durability of the
respective exhaust gas after-treatment systems. For this purpose,
there are permitted artificial ageing processes whose purpose it is
to simulate, in the course of rig testing, wear and damage
processes during the operation of a motor vehicle in the course of
the vehicle service life.
[0003] For monitoring the durability of exhaust gas after-treatment
systems during the operation of the vehicle, there are required
On-Board-Diagnosis systems (OBD) which, when the exhaust gas limit
values are exceeded, inform the driver of the faulty operation of
the exhaust gas after-treatment systems. Said On-Board-Diagnosis
systems are also tested for their efficiency during a type approval
operation using artificially aged exhaust gas after-treatment
systems.
Ageing
[0004] The "ageing" of a catalyst refers to the diminishing
efficiency of the exhaust gas after-treatment during operation,
inter alia as a result of the destruction of the catalytically
active layer. As a result of the reduction in the size of the
active surface it is no longer possible for all emissions to be
oxidised and reduced, so that the emissions behind the catalyst,
which are released into the environment, increase. Ageing of the
catalysts is substantially caused by two mechanisms which,
depending on the point of operation, can occur together or even
separately. Both mechanisms are also used for specifically ageing
catalysts.
Thermal Aging
[0005] Catalysts are designed to operate at temperatures of 200 to
950.degree. C. During this temperature range, the ageing process is
very slow. When the temperature increases to a value in excess of
850.degree. C., the ageing process is faster; it is referred to as
the so-called thermal ageing, a process which intensifies rapidly
if temperatures of more than 1000.degree. C. are reached, with the
active surfaces being reduced by sintering processes. At
temperatures of 1400.degree. C. and more the ceramic member melts,
which leads to total destruction. This is normally indicated by a
performance loss of the engine due to too high an exhaust gas
pressure in the catalyst.
Poisoning
[0006] There are two types of catalyst poisoning. On the one hand,
the active surface can be poisoned chemically by foreign
substances, for example fuel or oil additives, which chemical
poisoning, as a result of chemical reactions, partially destroys or
reduces the catalytic surface. In addition, there occurs mechanical
poisoning wherein the active layer is covered for example by lead
and sulphur from fuel and oil, which also leads to the reduction of
the catalytic surface.
OSC Measurements (Oxygen Storage Capacity)
[0007] To be able to obtain information on the degree of ageing of
a catalyst, it is necessary to make an OSC measurement which serves
to determine the oxygen storage capacity of a catalyst from which
it is then possible to derive an ageing condition. The older the
catalyst, the lower its storage capacity. OSC measurements are made
in production vehicles and during artificial catalyst ageing
processes.
[0008] The OSC measurement is carried out in the steady condition
of the exhaust gas temperature and of the mass flow. For this
purpose, the lambda signals are measured in front of and behind the
catalyst. The engine or burner is operated in such a way that,
within a short time, the exhaust gas abruptly changes from a rich
mixture (lambda<1) to a lean mixture (lambda>1). The phase
displacement between the signal in front of and behind the catalyst
(after the change in lambda) is proportional to the oxygen stored
in the catalyst.
Artificial Ageing
[0009] In the course of the artificial ageing process using an
ageing gas produced in a burner, it is possible to produce
endurance and limit catalysts. In the case endurance catalysts use
is made of ageing cycles whose ageing results are comparable to the
catalysts aged in road traffic. Measurements to determine the
damage to the catalyst to be tested are carried out at fixed
intervals. These measurements then enable vehicle manufacturers to
develop vehicle-specific catalysts in respect of structure, coating
and service life. If optimum adjustment has been achieved, the
catalyst can be used. In addition, further dynamic cycles like the
standard test cycle or the ZDAKW cycle as specified by law can be
used, with air and/or fuel being dynamically added in front of the
catalyst for generating an exothermal reaction.
[0010] Limit catalysts, on the other hand, are aged until they
reach the regionally fixed legal OBD emission limits. These limits
are then used for establishing a control-technical model for the
vehicle, which model is able to detect if the emission limits have
been exceeded. For measuring the degree of ageing of the catalysts,
the so-called OSC measurement is available at the burner test rig,
just as it is in the vehicle.
OBD Limit Catalyst Ageing (On Board Diagnosis)
[0011] When producing the OBD limit catalyst, the catalysts are
aged for a certain period of time at a constant point of operation.
For this ageing process, use is made of thermal ageing, the purpose
of said ageing method being to age a catalyst to such an extent
that it only just observes the OBD emission limit. Because,
depending on its coating, each vehicle-specific catalyst behaves in
a different way, the length of the ageing process cannot be
foreseen, which is the reason why the ageing process is divided
into intervals with subsequent OSC measurements in order to prevent
the catalyst from drifting beyond the limit value and thus cannot
be used if the ageing time is too long. In parallel to the OSC
measurements, there is carried out an exhaust gas test in order to
determine the emissions of the aged catalyst. For this purpose, the
catalyst is taken from the test rig and built into the associated
vehicle, with the measurement being carried out on a roller test
rig in realistic surroundings (real engine with exhaust gas
after-treatment system).
[0012] As the oxygen storage capacity and the emissions are
connected to one another anti-proportionally, but as determining
emissions is expensive, the OSC value serves as a measure for the
emissions. This means that OBD limit catalyst ageing is used to
determine the OSC value at which the emissions of the vehicle have
limit values. At a later stage, in a production vehicle, it is then
possible with the help of an OSC measurement, to detect a defective
catalyst and non-observance of emission values.
ZDAKW Ageing: Cooperation of the German Automotive Industry to
Determine the Further Development of Catalysts
[0013] The ZDAKW cycle was developed by the exhaust gas centre of
the German automotive industry. It was developed in order to
provide a standard test method for catalyst coatings. Said cycle
substantially consists of a high-temperature phase involving five
overrun fuel cut-offs and one poisoning phase with three
temperature levels. When the thrust is disconnected, the fuel
injection is briefly interrupted and, in parallel thereto, the
exhaust gas mass flow is reduced. As a result, the catalyst is
flushed with oxygen and a lambda value of approximately 8 is set.
When subsequently intensifying the mass flow and re-starting the
fuel injection, the lambda value is again increased to the set
value of 1. The purpose of this process is to simulate the driving
operation in cases of sudden deceleration and acceleration. During
the poisoning phase, at a low temperature level, a somewhat richer
mixture of the exhaust gas is guided via the catalyst, the result
being that the catalytically active layer is reduced by chemical
poisoning.
State of the Art
[0014] It is possible to simulate the process of ageing exhaust gas
after-treatment systems, more particularly exhaust gas catalysts,
on engine test rigs, but on the one hand it is expensive and on the
other hand it is difficult to reproduce because engine ageing
influences represent an influencing factor which cannot be
calculated.
[0015] Therefore, there was developed a process and a device
according to which ageing gas for aging exhaust gas after-treatment
systems is produced in burners in which, depending on the
individual case, Otto fuel or diesel fuel is burnt in certain
simulation cycles whose purpose it is resemble the production of
exhaust gas during vehicle operation. The respective operating
cycles of the burners used must be able to simulate any
interference like ignition failure and overrun fuel cut-off
[0016] From U.S. Pat. No. 7,140,874 B2 there is known a process and
a device for testing exhaust gas catalysts which contain a burner
which, in front of the combustion chamber, comprises a swirl plate
which is provided with a central through-aperture into which fuel
is injected by a fuel injection nozzle, and with circumferentially
distributed boreholes through which the combustion air flows into
the combustion chamber. At least some of said circumferentially
boreholes, from the entry end to the exit end, extend with
tangential components and radial components, which leads to a swirl
of the combustion air at the entrance to the combustion
chamber.
[0017] Producing said swirl plates is expensive, with optimum
combustion being possible at only one single operating point of the
burner, whereas the ageing cycles require several operating
conditions because the ageing gas has to be provided with different
temperatures and, optionally, also has to be produced with
different combustion air conditions. More particularly, this
applies if Otto fuel and diesel fuel is to be used in the same
burner.
SUMMARY OF THE INVENTION
[0018] It is therefore the objective of the present invention to
provide a process and a device which, under stable operating
conditions, provide ageing gases of different temperatures and
which are also suitable for producing an ageing gas with different
combustion air conditions under stable burner operating
conditions.
Production of Ageing Gas
[0019] The objective is achieved by providing a process of
producing ageing gas for ageing components used for the
after-treatment of exhaust gas, more particularly exhaust gas
catalysts, in a burner which comprises a combustion chamber and at
least one fuel injection nozzle, as well as a supply pipe for
combustion air with means for generating swirl, with the swirl of
the combustion air being set as a function of the selected
combustion air radio By specifically pre-setting the swirl value of
the combustion air, it is possible, in this way, to ensure a stable
operation under different combustion air conditions at different
process parameters--depending on the fuel used (Otto fuel or diesel
fuel) or in accordance with the required exhaust gas temperature
and/or the required exhaust gas composition.
[0020] The ageing gas is generated by burning a carbon containing
fuel with combustion air in the burner. The composition of the
ageing gas can be modified by adding additional gas and/or other
substances, more particularly oil, to achieve as close as possible
a similarity with natural engine exhaust gases. Additional gases
can be added in a pure form from storage containers, i.e. gas
cylinders. The ageing gas should have a temperature of
>250.degree. C., preferably >700.degree. C. and, more
particularly, 1000 to 1250.degree. C., but optionally also
<200.degree. C.
[0021] The combustion air ratio can be varied in predetermined
cycles in accordance with the test regulations. In this way, the
exhaust gas after-treatment device can be provided with different
ageing gas compositions and ageing gas temperatures in accordance
with the load spectrum such as it corresponds to mixed operational
conditions. By adjusting the parameters of the combustion air ratio
as well as fuel quantities and air quantities, the exhaust gas
after-treatment device can be subjected to cyclical thermal loads
and thus experiences conditions such as they occur under actual
driving conditions.
[0022] A typical ageing cycle is within a temperature range of 800
to 1250.degree. C. It is also possible to achieve special ageing
cycles in which the starting behaviour of the exhaust gas
after-treatment device at the test rig is copied.
[0023] A particularly effective way of ensuring a stable burner
operation, even under dynamic changes in the operating conditions,
is achieved if the swirl of the combustion air is varied as a
function of the changes in the combustion air ratio .lamda. in the
course of the production of the ageing gas.
[0024] It is particularly advisable if the swirl of the combustion
air ratio of .lamda.>1 (lean/stoichiometric) is set to be lower
than at a combustion air ratio of .lamda.<1 (rich combustion air
ratio).
[0025] The flow of the combustion air (fresh air) fed into the
burner must be mass flow controllable, more particularly by an
external combustion air supply system.
[0026] It has been found to be particularly advantageous if the
combustion air in an inner primary air flow of the combustion
chamber is subjected to swirl and in an outer secondary air flow is
supplied in a substantially swirl-free condition. More
particularly, this applies if the at least one fuel injection
nozzle is arranged centrally in the combustion chamber. An ignition
device has to be arranged in the combustion chamber at some
distance behind the fuel injection nozzle.
[0027] Furthermore, it is advantageous to vary also the supplied
combustion air quantity in order to adapt same to the changed
quantity of injected fuel without allowing excessive effects on the
swirl. It is therefore proposed that the external secondary air
flow can be throttled.
[0028] The fuel should be injected into the combustion chamber so
as to be controllable in cycles at a high pressure in excess of 20
bar.
[0029] According to an advantageous embodiment it is proposed to
add ageing gas in an internal return flow in the burner near the at
least one fuel injection nozzle of the combustion air. For this
purpose, there has to be generated a Venturi effect in the central
combustion air flow by means of which returned ageing gas can be
sucked off near the fuel injection nozzle. This process variant is
referred to as primary exhaust gas and ageing gas return.
[0030] In order to avoid any disadvantageous effect on the ageing
gas temperature, the primary ageing gas return flow is also reduced
when the secondary air flow is throttled.
[0031] In order to ensure stable, uniform combustion processes in
the combustion chamber, it is proposed according to a preferred
process that the axial position of the burner flame is detected for
example by means of a maximum temperature and that, if the burner
flame moves towards the rear, the swirl of the combustion air is
increased and that the swirl of the combustion air is reduced when
the burner flame moves towards the front.
[0032] When simulating the exhaust gas return such as it occurs in
an engine in order to achieve improved exhaust gas values, it is
proposed according to a further special type of process that
conditioned ageing gas is added in the combustion chamber to the
ageing gas originally produced in the burner.
[0033] To influence the ageing gas temperature to which the exhaust
gas after-treatment systems are subjected, the returned ageing gas
can be cooled and dried. This process variant is referred to as
secondary exhaust gas return and secondary ageing gas return.
[0034] The percentage of the secondary ageing gas return flow of
the burner, more particularly, is varied as a function of the
required ageing gas temperature. The ageing gas of the secondary
ageing gas return flow is added in the burner preferably in the
form of an annular sheath flow.
[0035] The conditioned ageing gas can be taken from a main ageing
gas pipeline behind the components for the exhaust gas
after-treatment or from a bypass ageing gas pipeline which bypasses
said components.
[0036] According to a further embodiment it is proposed that to the
ageing gas produced in the burner, there is added cold- or
hot-conditioned returned ageing gas behind the burner or before
entering the exhaust gas after-treatment components. In this way,
too, it is possible to influence the temperature of the ageing gas
entering the exhaust gas after-treatment system. The
above-described process variant is referred to as tertiary exhaust
gas return or ageing gas return.
[0037] Oil and/or fuels and/or foreign gas and/or air, such as,
age-related, they occur in the course of engine combustion with
increasing wear, can be added in front of the catalyst to the
ageing gas of the secondary and/or tertiary exhaust gas return flow
or to the exhaust gas, the advantage being the reproducibility of
said process stages when producing the ageing gas as a function of
time, i.e. as a function of the cycles of the production of ageing
gas.
[0038] The inventive process is particularly advantageous in that
it is possible to simulate the overrun fuel cut-off of an internal
combustion engine in that the fuel supply to the burner is
interrupted and that, to re-start the combustion chamber, there is
set a combustion air ratio of .lamda.<1 (rich fuel mixture) in
combination of a very high swirl rate of the primary air flow,
which results in very good ignition conditions, so that the cut-off
phases can be observed in a very controlled way. Also, with the
objective of reducing the mass flow, exhaust gas can be guided
through the catalyst in the bypass. To control the mass flows, it
is possible to use suitable exhaust gas flaps. In addition, it is
possible to age a plurality of catalysts in parallel and to control
the mass flows by suitable exhaust gas flaps. Furthermore, if
exhaust gas manifolds are provided, the temperature of the
individual partial mass flows can be set by a measured exhaust gas
return and/or by individual exhaust gas flaps.
Ageing Process
[0039] The invention comprises a process of ageing components for
the exhaust gas after-treatment, more particularly exhaust gas
catalysts by subjecting same to ageing gas which is produced in
accordance with the above-described conditions. Artificial ageing
of the entire exhaust gas after-treatment system takes place in
such a way that hot ageing gas with C-, HC- and/or NOx-containing
components is produced in a burner and guided through the exhaust
gas after-treatment system, wherein the hot ageing gas subjects the
exhaust gas after-treatment components for the after-treatment of
C-, HC- and/or NOx-containing components to the same loads in the
same way as engine exhaust gas naturally produced under actual
driving conditions.
Burner
[0040] Furthermore, the invention comprises a burner for producing
ageing gas for the ageing of components for the after-treatment of
exhaust gas, more particularly exhaust gas catalysts, which burner
comprises a combustion chamber with a combustion chamber axis and
at least one fuel injection nozzle and a combustion air supply line
which comprises swirl generating means which are adjustable in the
sense of changing the swirl intensity of the combustion air. Said
swirl generating means can be adjusted from the outside without
having to remove the burner in order to preset the swirl intensity
or adjust the swirl intensity during operation. Said adjustment can
take place in accordance with pre-programmed combustion cycles
and/or within the framework of control processes.
[0041] More particularly, the swirl generating means of the
combustion air supply line are circumferentially distributed swirl
blades which are arranged radially relative to the combustion
chamber axis and which are pivotable on journals. They preferably
engage one single rotatable adjusting ring which cooperates with
the swirl blades.
[0042] According to a preferred embodiment there is provided an
annular plate or funnel which is arranged in the combustion air
supply flow in front of the fuel injection nozzle and which divides
the combustion air flow into an inner primary air flow and an outer
secondary air flow, with the swirl generating means preferably
being positioned in the primary air flow. More particularly, it is
the combustion air flow positioned near the fuel injection nozzle
which has to be provided with a variable swirl, whereas the outer
secondary air flow which optionally constitutes a greater volume
flow percentage remains substantially swirl-free.
[0043] However, it is proposed furthermore that there are provided
means for controlling the volume of the combustion air flow, which
means, more particularly, can act on the outer secondary air flow.
The means for controlling the volume flow of the combustion air
flow are provided in the form of a ring which is arranged
concentrically relative to the fuel injection nozzle and which
comprises adjustable apertured diaphragms.
[0044] For detecting the axial position of the burner flame inside
the combustion chamber there can be provided one or more special
sensors, more particularly temperature sensors which are arranged
so as to be distributed along the length of the combustion
chamber.
[0045] Further design characteristics consists in that inside the
combustion chamber there is concentrically arranged a flame pipe
which ends in front of the end of the combustion chamber and which,
near the fuel injection nozzle, comprises circumferentially
distributed exit apertures for returning primary ageing gas. To
ensure that the latter is guided into an independent return flow,
it is proposed that the exit apertures in the flame pipe are
positioned in a flame pipe portion which is narrowed nozzle-like
and arranged behind the fuel injection nozzle, with a Venturi
effect occurring in the primary combustion air flow.
[0046] A further advantageous embodiment consists in that inside
the burner sheath, there is provided a mixing pipe which is
arranged concentrically relative to the combustion chamber axis,
which, together with the burner sheath, forms an annular chamber to
which there is connected a supply port for conditioned returning
ageing gas and which extends beyond the length of the flame pipe
and, behind the end of the flame pipe, comprises circumferentially
distributed exit apertures for the conditioned ageing gas. This
embodiment, more particularly, serves for adding secondary returned
conditioned ageing gas as described above in connection with the
various processes.
System Suitable for Ageing Purposes
[0047] The invention comprises a system for artificially ageing
exhaust gas catalysts and exhaust gas after-treatment systems which
are subjected to ageing gas produced in a burner, into which system
there is inserted a burner according to one of the previously
mentioned embodiments.
System Components
[0048] Such a system consist of the following components: air
supply line, fuel supply line, burner with mixing device, ageing
pipeline for the exhaust gas after-treatment components to be aged
and an ageing gas return line.
Air Supply
[0049] The air supply line is used to supply the burner with
combustion air for the purpose of producing, together with the
fuel, an ignitable mixture at a later stage. Fresh air is sucked in
via an air filter, which fresh air is compressed via a Roots
compressor which is driven by an asynchronous motor. As a result of
the pressure gradient relative to the ambient air at the exhaust
gas chimney behind the exhaust gas after-treatment system, there
occurs a mass flow in said direction. The asynchronous motor is
speed-controlled via a frequency converter. Subsequently, the
temperature of the compressed combustion air can be cooled down via
a counter flow heat exchanger. Behind the fresh air has passed
through the air filter, a hot film air mass sensor (HFM) measures
the mass flow which is controlled via a subsequently arranged
throttle valve. The quickly controlling throttle valve is essential
because the Root compressor is too inert for achieving the rapid
mass flow variations required for the various cycles. In this way,
the combustion air reaches the burner head with a certain mass flow
and a certain temperature.
Fuel Supply
[0050] By means of a fuel pump, the fuel is pumped from a tank into
the burner. A mass flow meter measures the fuel through-put. A
counter flow heat exchanger cools the fuel which is not required. A
high-pressure pump now increases the fuel pressure to 50 bar which
is required for the injection valve.
Burner with Mixing Device
[0051] At the entry end, an entry manifold, also referred to as the
burner head, forms the transition from the cold to the hot part of
the system. At the exit end, the combustion chamber forms the
transition to the exhaust gas after-treatment system via a
flange.
[0052] For cooling the components in the mixing device, the
two-shell entry manifold is cooled by cooling water sheath.
[0053] The mixing device substantially consists of the following
components: air controlling unit with swirl device and diaphragm,
injection nozzle with injection valve and flame pipe.
[0054] It is the purpose of the mixing device to mix the fuel and
the combustion air in such a way as to produce a combustible
mixture which is burnt in the flame pipe in order to provide, at
the burner exit, an exhaust gas mixture which resembles the exhaust
gases of an Otto engine or diesel engine.
[0055] After the exhaust gas has left the flame pipe, it is
gradually cooled down by adding the cooled conditioned ageing gas
of the secondary exhaust gas recirculation flow (EGR). By supplying
the ageing gas laterally, a swirl flow occurs around the mixing
pipe. Rebound plates and boreholes ensure that the colder returned
ageing gas is pressed into the inside of the combustion chamber, so
that, towards the rear, there is generated an ageing gas with an
ever decreasing temperature. The exhaust gas temperature at the
burner exit can additionally be influenced by adding specific
amounts of air, with the mass flow which subsequently flows through
the exhaust gas after-treatment system consisting of a fresh air
mass flow, an EGR mass flow and a fuel mass flow.
[0056] By measuring the temperature in several places of the
combustion chamber, it is possible to detect the position of the
flame and to set the position of the flame by varying the
swirl.
Ageing Path
[0057] Ageing takes place between two flange connections. The first
flange connection is directly behind the burner exit whereas the
second flange connection is located in front of a particle filter.
The flanges are arranged at a constant distance from one another,
so that the catalysts to be treated can be adapted to the system in
advance. As the geometry and exhaust gas line of the catalysts to
be aged usually greatly differ from one another, said adaptation
measures always have to be undertaken individually. As a rule,
every catalyst is provided with connecting muffs in front of and
behind the catalysts for lambda probes and with several threaded
muffs for thermo elements and temperature sensors. Depending on the
ageing capacity of the burner and the ageing gas requirements for
the catalysts, two or more catalysts can be connected in parallel
in the ageing path. For controlling the mass flow, at least one
bypass line leading to the catalysts can be provided in the ageing
path. Ageing gas return
[0058] The returning ageing gas flow removes part of the exhaust
gas mass flow in front of the exhaust gas chimney to mix same again
in a cooled condition with the original ageing gas. For this
purpose, the hot ageing gas is guided over a counter flow heat
exchanger which cools same down to 40.degree. C. The cooled ageing
gas is guided over a cyclone separator for the purpose of filtering
out the liquid phase after the cooling process. Now the mass flow
of the returned ageing gas is determined via a hot film air mass
sensor (HEM), to be able to control same via an adjoining throttle
valve and a Roots compressor, Finally, the cooled ageing gas
reaches the burner where, via the mixing pipe, it is added to the
hot, originally produced ageing gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] Preferred embodiments of an inventive burner and of an
inventive system for artificially ageing exhaust gas catalysts are
illustrated in the drawings and will be described below.
[0060] FIG. 1 is an inclined view of a complete inventive burner
with a partial section.
[0061] FIG. 2 is an inclined view of part of the burner with the
combustion chamber according to FIG. 1 with a partial section.
[0062] FIG. 3 is an inclined view of the front region of the burner
according to FIGS. 1 and 2 with an air supply arch with a partial
section.
[0063] FIG. 4 shows the mechanical part of the air supply system as
well as the beginning of the flame pipe according to FIGS. 1 to 3
in a longitudinal section.
[0064] FIG. 5 shows the design principles of an inventive system
for artificially ageing exhaust gas catalysts.
[0065] FIG. 6 shows an embodiment of an inventive system for
artificially ageing exhaust gas catalysts in a side view.
[0066] FIG. 7 is a diagram of OSC measurements made at a
catalyst.
[0067] FIG. 8 is a diagram of the ZDAKW catalyst ageing cycle.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0068] FIG. 1 shows an inventive burner 10 with a combustion
chamber 11, which burner 10 comprises an outer rotationally
symmetric burner sheath 12 which extends between an entry flange 1
and an exit flange 14 and comprises three length portions 16, 17,
18 whose diameter decreases from the entry flange to the exit
flange and which are connected to one another via conical
transition portions 19, 20. A carrier flange 15 which comprises an
outer collar and an inner annular projection to be described in
greater detail with reference to the following Figures is threaded
to the entry flange 13. The collar centres the entry flange 13 to
which there is attached the burner sheath 12. On its outside, the
inner annular projection at the carrier flange 15 carries a mixing
pipe 21 for returning conditioned ageing gas and extends, at a
radial distance, along the length of the first two portions 16, 17
of the burner sheath 12 and of the two conical transition portions
19, 20. From the transition portion 19 to the transition portion
20, with both portions being included, the mixing pipe 21 comprises
substantially uniformly distributed inlet apertures 22.
[0069] The inner annular projection at the carrier flange 15
carries a cylindrical flame pipe 23 which, in respect of length,
substantially extends along the first portion 16 of greatest
diameter of the burner sheath 12. Inside the flame pipe 23 there
are provided two rows of recirculation apertures 24 for a primary
ageing gas circulation which will be explained at a later
stage.
[0070] An ageing gas return pipe (port) 26 which, at a short
distance behind the entry flange 13, ends in an annular chamber 27
between the burner sheath 12 and the additional guiding pipe 21, is
attached to the burner sheath 12. Said ageing gas return pipe 26
serves to return the secondary ageing gas.
[0071] At the entry end in front of the flame pipe 23, there is
connected a mixing device 25 with a fuel injection nozzle 31 and a
air controlling device 32. The air controlling device 32 comprises
an adjustable swirl device and an adjustable throttle diaphragm for
the combustion air, which two devices will be explained at a later
stage. In front of the burner 10 there is provided an air supply
manifold 34 which is connected thereto by an attaching flange 33
and which comprises an inner jacket 35 and an outer jacket 36
between which there is formed a shell-type chamber 38 for cooling
water. In addition to the attaching flange 33, the air supply
manifold 34 comprises an entry flange (not shown here). Further
details of the parts mentioned latterly are given in the following
Figures.
[0072] The principle used for carrying out the combustion process
corresponds to that of a burner stabilised by swirl. From behind,
the fresh air flows out of the cooled air supply manifold 34 into
the mixing device 25 where the air flow is divided into an inner
primary air flow and an outer secondary air supply. In the case of
the primary air flow, the fresh air, on the inside, flows over the
swirl device. Then, in front of the primary air supply borehole in
the throttle diaphragm, the fresh air is mixed with the injected
fuel, and the combustible fuel-air mixture reaches the flame pipe
23. In the case of the secondary air flow, the fresh air is guided
around the swirl device and, via secondary air boreholes in the
throttle diaphragm, flows into the flame pipe and envelops the
fuel-air mixture, so that, during the combustion process, the edge
regions, too, are supplied with oxygen and so that part of the
ageing gas generated in the course of combustion is sucked back via
the recirculation bores 24 in the flame pipe 23. By changing the
aperture cross-section of the secondary air boreholes in the
throttle diaphragm, it is possible, to variably and divisibly
control the air quantity through the swirl device (primary air
borehole) and around same (secondary air boreholes). As a result,
the air flow speed at the exit of the mixing device 25 is changed,
so that there occurs a vacuum at the recirculation boreholes 24 of
the flame pipe 23. The recirculation boreholes 24 serve to
stabilise the flame, and via the air circulation boreholes 24
ageing gas on the outside of the flame pipe 23 is sucked up
(Venturi effect). In consequence, the ageing gas deposits itself
from the outside like a jacket around the flame.
[0073] In FIG. 2, any details identical to those shown in FIG. 1
have been given the same reference numbers. To that extent,
reference is made to the description above. In FIG. 2, the collar
28 and the annular projection 29 at the carrier flange 15 are
mentioned for the first time. On the collar 28, the flange 13 is
fixed with the mixing pipe 21. In the annular projection 29, there
is contained an inserted carrier ring 30 which carries the air
controlling device 32 as well as the fuel injection nozzle 31. FIG.
2 shows further details of the burner, i.e. swirl blades 41 between
the burner sheath 12 and the mixing pipe 21 as well as an ignition
device 45 with two electrodes 46, 47. In the air supply manifold 34
there can be seen a further through-sleeve 48 for attaching the
ignition device 45. Furthermore, it can be seen that the flame pipe
23 comprises a nozzle-like necking 42 near the air controlling
device 32, in which there are provided circumferentially
distributed gas supply apertures 43 through which the primary
quantity of recirculation gas is sucked up. Via a pipeline (not
shown), the central fuel injection nozzle 31 is supplied with fuel
and, through a through-sleeve 39 in the air supply manifold 34,
enters the latter. An inner shaft 65 for adjusting the swirl device
and a coaxially extending hollow shaft 68 for adjusting the
throttle diaphragm enter the air supply manifold 34 through a
further through-sleeve 40.
[0074] Details of the air controlling device 32 and its adjusting
mechanism will be described with reference to the following
Figures.
[0075] In FIG. 3, any details identical to those shown in the
previous Figures have been given the same reference numbers. To
that extent, reference is made to the description above. It can be
seen that the carrier ring 30 in the annular projection 29 is
connected to the flame pipe 23 in the same way as to the air
controlling device 32. The carrier ring 30 comprises a first
annular disc 51 with a plurality of air through-apertures 52 and a
central aperture for receiving the fuel injection nozzle 31. In the
direction of flow behind the annular disc 51 there is positioned a
rotatable annular disc 53 as well as a fixed annular disc 54. The
two annular discs 53, 54 are separated from one another by an
insulating disc 57. The annular discs, together, form a throttle
diaphragm. They each comprise a central aperture 55 for the primary
air and a ring of apertured diaphragms 56 for the secondary air. By
adjusting means not shown here, the annular disc 53 is rotatable
relative to the annular disc 54, so that the apertured diaphragms
56 in the annular disc 54 can be throttled and, respectively,
reduced in their through-cross-section.
[0076] Between the two annular discs 51 and 52, there extends an
initially cylindrical and then funnel-shaped annular sheath 61
which separates an inner primary combustion air flow ring from an
outer secondary combustion air flow ring. Inside the annular sheath
61 and thus inside the inner primary combustion air flow ring there
are positioned circumferentially distributed, adjustable swirl
flaps 62 on radially arranged rotary journals 63 through which the
inner primary combustion air flow ring can be influenced in respect
of swirl, whereas the outer secondary combustion air flow ring can
be adjusted by the adjustable apertured diaphragms 56 in respect of
the volume flow quantity.
[0077] In FIG. 4, any details identical to those shown in the
previous Figures have been given the same reference numbers. To
that extent, reference is made to the description above. FIG. 4
shows an adjusting device 64 which is supported in the
through-sleeve 40 and in the first annular disc 51 and which
comprises a rotatable inner shaft 65 which, via a pinion 66 acts on
an outer annular gear 67 at the second annular disc 53 and which
comprises a rotatable hollow shaft 68 which, via a pinion 69, acts
on a setting ring 70 for rotating the swirl flaps 62. At the
setting ring 70, there are arranged driving journals 60 which act
on the throttle flaps 62 which are pivotable on rotary journals 63.
FIG. 5 shows the design principles of a system for aging exhaust
gas catalysts, which system, as the central component, comprises a
burner 10 according to the invention. The system comprises part of
a fuel supply unit 71 and parts of a combustion air supply unit
81.
[0078] At the fuel supply unit 71 it is possible to identify a fuel
tank 72, a fuel conveying pump 73 as well as a low-pressure fuel
pump 74 and a high-pressure fuel pump 75 with an electric motor. A
mass flow sensor 76 is arranged behind the low pressure fuel pump
74. A return loop extending parallel to the low-pressure fuel pump
comprises a pressure regulating valve 77 and a fuel re-cooling
device 78. The returning loop extending parallel to the
high-pressure pump 75 comprises a pressure regulating valve 79 and
a fuel re-cooling device 80.
[0079] At the combustion air supply line 81 it is possible to see
an air filter 82 and a mass flow sensor 83 which are followed by a
throttle flap 84 and a Roots compressor 85 with a
frequency-controlled electric motor. Behind the compressor 85 there
is positioned a charge air cooler 86 in front of the entrance to
the burner 10.
[0080] When fuel and combustion air are supplied by the means 71,
81 as mentioned, the burner 10, when ignited by an ignition device,
produces ageing gas which can pass through exhaust gas catalysts
91, 92 and a diesel particle filter 95, and the exhaust gas
catalysts, for example, can be TWC- or DOC- or SCR- or
CDPF-catalysts and can be arranged parallel relative to one
another.
[0081] The main ageing line 100 is divided into two ageing gas
branch lines 115, 116 leading to the exhaust gas catalysts 91, 92
and a centrally positioned ageing gas bypass line 119. The branch
lines contain setting valves 93, 94 in front of the catalysts 91,
92 and setting valves 117, 118 behind the catalysts in which the
mass flows can be divided, i.e. set so as to be of equal size. In
the bypass line 114, there is provided a metering valve 120 and a
switching valve 121 which can be used to control the size of the
bypass flow and thus the mass flows leading to the catalysts. The
branch lines 115, 116 and the bypass line 119 are combined again to
form the main ageing gas line 100 in front of the theses particle
filter 95. The controllable burner 10 is used to run through
certain operating cycles which serve to effect standard ageing of
the exhaust gas catalysts 91, 92 and optionally of the diesel
particle filter 95.
[0082] The line diagram can be used analogously for treating
further parallel catalysts.
[0083] The main flow of the after-treated ageing gas is discharged
from the main ageing gas line 100 via an exhaust gas chimney 101,
while a partial flow, via a secondary return line 98, returns
secondary ageing gas after-treated as exhaust gas to the burner 10.
Optionally, via a secondary ageing gas bypass line 114, ageing gas
can be branched off behind the burner 10 and in front of the
exhaust gas after-treatment system and returned in the form of
secondary ageing gas to the burner. At the entry to the return line
98, there is arranged a regulating valve 122 for the exhaust gas
after-treated ageing gas, and in the return line 114, there is
positioned a regulating valve 124 for the non-after-treated ageing
gas by means of which the composition of the secondary ageing gas
can be varied. In the return line 98 for the secondary ageing gas,
there is arranged an exhaust gas heat exchanger 102 as well as a
condensate separator 103 with a controllable outlet valve 104. The
condensate separator 103 is followed by a mass flow sensor 105
which, in turn, is followed by a throttle flap 106 and a Roots
compressor 107 which is driven by a frequency-controlled electric
motor.
[0084] In front of the return line 98, before same enters the
burner 10, there branches off a return branch line 99 which, behind
the burner, ends in the main ageing gas line 100; the point of
entry is connected to a mixer 96 and can serve for returning the
so-called tertiary ageing gas. In the return branch line 99, there
is arranged a controllable shut-off valve 109. A mixer 108 can be
used for adding to the tertiary ageing gas a liquid such as oil or
fuel or foreign gases for each of which there are provided branch
lines 112, 113 leading to the mixer 108 with controllable inlet
valves 110, 111. In front of the return branch line 99 there
branches off an ageing bypass line 123 which, in the bypass leading
to the main ageing gas line, bypasses the mixer 96 and is divided
into two branch lines 125, 126 for cooled and conditioned ageing
gas, which each lead into ageing gas branch lines 115, 116 leading
to the exhaust gas catalysts 91, 92. Into each of the branch lines
125, 125 there are inserted regulating valves 127, 128 which are
used for measuring the added cooled ageing gas and by means of
which the ageing gas temperature in the exhaust gas catalysts can
be influenced, more particularly lowered.
[0085] FIG. 6 is a side view of a complete system, which is
simplified as compared to the diagrammatic view of the system shown
in FIG. 5.
[0086] There can be seen a burner 10 which is enveloped by an
insulating jacket 50 and which is followed by and connected to two
exhaust gas catalysts 91', 92' connected in series, as well as a
diesel particle filter 95. The main ageing gas line 100 ends in an
exhaust gas chimney 101. From said main line there branches off a
return line 98 in which there is arranged an ageing gas re-cooling
device 102 which is followed by a condensate separator 103 with an
outlet valve 104, which, in turn, is followed, in the return line
98, by a mass flow sensor 105 and a throttle flap 106. Behind the
throttle flap 106, in the line 98, there can be seen a Roots
compressor 107 which can be driven by a frequency-controlled
electric motor. Following the Roots compressor, the return line 98
laterally ends in the burner 10 in the starting region of the
combustion chamber. While the fuel supply system is not shown in
this Figure, it is possible, of the air supply system 81, to see
the air filter 83, the throttle flap 84, the Roots compressor 85
drivable by a frequency-controlled electric motor and the charge
air cooler 86.
[0087] FIG. 7 shows the diagram of an example of an OSC measurement
of lambda values as a function of time, measured by a lambda probe
which is fitted in front of the catalyst and whose measuring signal
is referred to as "lambda before cat", and by a lambda probe which
is fitted behind the catalyst and whose measuring signal is
referred to as "lambda after cat". To be able to provide
information on the degree of ageing of a catalyst, there is carried
out an OSC measurement which serves to determine the oxygen storage
capacity of a catalyst, from which the ageing condition can be
derived. The OSC measurement is used in production vehicles and for
measuring artificial catalyst ageing.
[0088] The OSC measurements are carried out in the steady condition
of the exhaust gas temperature and in mass flows. For this purpose,
lambda signals are measured in front of and behind the catalyst.
The burner is now supplied with fuel in such a way that, within a
short time, the exhaust gas abruptly changes from a fatty mixture
(lambda<1) to a lean mixture (lambda>1), with the curve aimed
at being represented by the curve "Nominal lambda". The phase
displacement between the before-catalyst signal "lambda before cat"
and the after-catalyst signal "lambda after cat" is proportional to
the oxygen stored in the catalyst. FIG. 7 shows such a measurement
taken at the catalyst ageing test rig.
[0089] The catalyst measured here still has a high oxygen storage
capacity. It can clearly be seen that the lambda value after the
catalyst (lambda after cat) increases more slowly than the lambda
signal before the catalyst (lambda before cat) and only seconds
later reaches its maximum value. A limit catalyst, on the other
hand, shows a different behaviour. Shortly after the maximum value
of the lambda signal of the sensor in front of the catalyst has
been reached, the lambda value at the sensor behind the catalyst
would reach maximum values. Both lambda signals would increase
nearly simultaneously.
[0090] FIG. 8 shows the diagram of the ZDAKW cycle which was
developed by the Exhaust Gas Centre of the German Automotive
Industry (ADA). It shows the nominal temperature T-nominal as a
function of time, with the nominal value of the combustion air
ratio .lamda.-soll equalling 1, with the exception of the phases of
the overrun fuel cut-off in which the combustion air ratio .lamda.
is set so as to be greater than/equal to 8. This cycle is
substantially composed of a high temperature phase with five thrust
disconnections and a poisoning phase with three temperature levels.
In the case of an overrun fuel cut-off, the fuel injection is
briefly interrupted and reduced in parallel to the exhaust gas mass
flow return. As a result, the catalyst is flushed with oxygen, with
the lambda value of greater than/equal to 8 being set. When
subsequently starting up and increasing the exhaust gas mass flow
return and re-introducing fuel injection, the lambda value
increases to the set value of .lamda.=1. This process is to
simulate driving with sudden deceleration and acceleration. During
the poisoning phase, at a low temperature level, a slightly richer
mixture of the exhaust gas is guided over the catalyst, the result
being that the catalytically active layer is reduced due to
chemical poisoning.
[0091] The high temperature phase of a duration of 600 seconds is
passed through 48 times. The poisoning phase of a duration of 30
minutes is passed through 8 times. The entire cycle lasts 96 hours.
The complete cycle corresponds to a driven distance of 80,000
km.
[0092] It is to be understood that various modifications are
readily made to the embodiments of the present invention described
herein without departing from the scope and spirit thereof. In
addition, Accordingly, it is to be understood that the invention is
not limited by the specific illustrated embodiments, but by the
scope of appended claims.
* * * * *