Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR OPERATING A REGENERATIVE DIESEI.
ENGINE PARTICULATE TRAP
The present inventlon relates to regenerating
diesel engine regenerative traps.
State of the art engine technology may allow a
diesel engine to emit as low as 0.6 g/ml particulates.
However, with more stringent particulate emission require-
ments to come into effect in 1985-1988, such as at a level
of 0.20 g/ml, the technology cannot meet such lower level
of particulate emissions without some form of particulate
trap. The most important materials used to date by the
prior art for the trap material have included monolithic
and librous ceramic filter materials (see U.S. Patent
4,276,071) and wire mesh (see U.S. Patent 3,499,269), each
mater1al having its own characteristic mode of trapping.
The particulates emitted and trapped throughout
the life of the vehicle by such a trap cannot be stored
since the amount can be typically 20 cubic feet for each
100,000 miles of engine use. As the particulates build
up, the exhaust system restriction is increased, commonly
referred to as back pressure. Thus a means is required to
remove the trapped material periodically, commonly
referred to as regeneration of the filter. One of the
most promising methods found to date is rejuvination of
the filter by thecmal oxidation of the carbonaceous
particles, which incinerate at about 1100F (550C).
Normal diesel engine exhaust temperatures rarely
reach 1100F during normal driving conditions. Therefore
an auxiliary temperatuce elevating means is necessary to
carry out thermal o~idation. The types of thermal
oxidation means used by the prior art hav~- generally
fallen into the following three categories: use of a fuel
fed burner (see U.S. patent 4,167,852 and Japanese
55-19934), use of an electric heater (see U.S. patents
4,270,936; 4,276,066; 4,319,896), and detuning techniques
which may be combined with any of the above for raising
the temperàture of the exhaust gas at selective times (see
U.S. patents 4,211,075; 3,499,269). These techniques have
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been used to burn the collected particulates in the
presence of excess oxygen.
Each of the prior art systems have certain
disadvantages associated with them which is described in
more detail in our copending Canadian patent application
Serial No. 446,496 filed January 31; 1984. More impor-
tantly, each of the prior art systems have been operated
by a control syst~m which is totally d~iver initiated and
driver controlled, failing to:
(a) initiate regeneration only when the filter
optimally needs regeneration;
(b) continue regeneration for a period which
produces optimum filter life, optimum filtration, and
maximum fuel economy for the vehicle; and
(c) be quickly responsive to a change in engine
conditions to permit the regeneration cycle to take place
under conditions of optimum filtration rather than
operate, as in the prior art, only when the engine is
functioning in a narrow range of conditions.
The invention is a method of regenerating a
filter (and the associated apparatus therefor) used to
extract and collect particulates from the exhaust gas of a
diesel engine. The method results in more economical
operation of the filtration system, less fuel losses when
operating the vehicle, and the system is more quickly
responsive to engine operating characteristics over a much
wider range than that known to the prior art.
The method comprises:
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Determining when the pressure of the exhaust
gas, measured at a station immediately upstream from the
filter, exceeds a predetermined variable maximum allowable
pressure and then initiating the following steps (a) to
(c):
(a) bypassing the exhaust gas around the filter
and conveying a flow of a combustion supporting gas to and
through the filter at a low flow rate (i.e., 5-7 CFM);
(b) raising the temperature of the combustion
supporting gas to a level effective to ignite at least a
leading portion of the particulate collection in the
filter; and
(c~ measuring the temperature of the heated
gases exiting from the filter, and when the temperature
exceeds a predetermined level, shutting off the flow of
heated combustion supporting gases conveyed to the filter
to bring about termination of the regeneration cycle.
The variable maximum allowable pressure can be a
value mathematically derived by measuring the instantan-
eous speed of the engine and the instantaneous fuel flowof the engine, then comparing the instantaneous back
pressure value with previously measured back pressures for
a clean filter operating under the instantaneou~s speed and
fuel flow conditions. If the difference between the two
values is greater than an acceptable a P, then the maximum
allowable pressure has been exceeded.
Preferably the temperature of the combustion
supporting gas is raised adding fuel to the combustion
supporting gas and either igniting the combustible mixture
by use of a glow plug, sparking device, or a heated,
preferably electrically heated, catalyst supporting member
effective to support the temperature required for igni-
tion, or by using an electrical heating element to raise
the temperature of the gas to ignition temperature. The
combustion supporting gas can be either air or exhaust
gas.
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Advantageously, the variable maximum allowable
pressure in the filter is mathematically and
experimentally determined ~o be proportional to
particulate collection in the filter in the range of
150-270 mg/in3, which in a desirable application will
permit regeneration to be initiated with a frequency of
- about 145 miles of vehicle operation. Preferably the
pressure may be measured by use of a thin diaphragm
transducer that reads the capacitance between a fixed
lQ element and the diaphragm. The temperature may be sensed
and measured by use of a thermocouple embedded in the
trailing portion of the filter.
Alternatively, the temperature of the filter at
its inlet portion may be measured. If the temperature of
such inlet filter portion exceeds a predetermined level,
the fuel supplied, to raise the temperature of the
combustion supporting gas,~ is shut off in advance of the
termination of regeneration. Regeneration will proceed by
way of the exothermic -reaction resulting from combustion
of the particulates.
Advantageously, the combustion supporting gas may
comprise a supply of fresh air to which is added
hydrocarbon fuel by way of an aspirated nozzle to form a
combustible mixture. The exhaust gas is bypassed around
the filter during such regeneration initiation.
The method may be fu~ther refined by shutting off
the fuel supply for a delayed period in the event there is
a failure to light the combustion supporting gas. This
delay period and shut off of fuel is initiated by sensing
3Q the temperature of the gas flow at the inlet to the
filter. If it does not exceed a predetermined value, such
delay period is initiated.
The present invention also includes an apparatus
for controlling the regeneration cycle of a filter of
exhaust gas for a diesel engine of a vehicle which has
become laden with particulates from the exhaust, compris-
ing (a) means for conveying combustion supporting gas
through at least a portion of the filter; (b) means for
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permitting the flow of either the exhaust gas or the
combustion supporting gas to and through the filter, the
flow permitting means regulating the flow of the combus-
tion supporting gas through. the filter at a low rate; (c)
means for heating the combustion supporting gas w~en
flowing to and throuyh the filter to a temperature of at
least 1100F; and (d) means for sequentially (i) actuating
- the flow permitting means to initiate bypass of exhaust
gas around the filter and flow of combustion supporting
gas through the filter in resp~nse to a sensed pressure of
the exhaust exceeding a predetermined variable maximum
allowable pressure, (ii) actuating the heating means to
raise the temperature of the combustion supporting gas to
ignite the particulates in the filter, and (iii) to shut
Offthe heating means in response to a sensed temperature
in the trailing portion of the filter which exceeds a
predetermined value indicating regeneration of the filter
is complete.
J~
S
The present inventi.on is described further, by
way of illustratioll, with reference to the accompanying
drawings, wherein:
Figure 1 is a schematic layout of the essential
apparatus components of this invention shown associated
with a control system, also in schematic form, to
illustrate the sequence o~ steps that must be taken during
a regener~tion cycle;
Figure 2 is a graphical illustration of the cold
flow pressure drop as a function of soot loading which
illustrates the minimum and maximum parameters for
initiating filter regeneration in response to a measured
pressure;
Figure 3 is a graphical illustration of
temperature as a function of time illustrating a
temperature map for the filter during a regeneration cycle
for the embodiment of Figure l;
Figure 4 is a view similar to that of Figure 1,
but illustrating an alternative embodiment using an
electrical heater for the means to raise the temperature
of the combustion supporting gas;
Figure 5 is a temperature map similar to Figure 3
for the apparatus of Figure 2; and
Figure 6 is a graphical illustration of fuel
economy as a function of vehicle miles using the trap
system of Figure 1.
A preferred mode for carrying out the invention
is illustrated in Figure 1. The apparatus components
necessary to carry out the method aspects will be
described first. The apparatus compr,ises a filter 10,
housing for the filter lOa, and ducts 11-12-13 for
conveying exhaust gas to a plenum 14 leading to the
frontal face 15 of the filter 10. During periods of
regeneration, the exhaust gas is bypassed around the
filter, throl~3h duct 16, and the flow of gas to the filter
is replacecl by a flow of combustion supporting gas from
duct 17.
A flow control means 18 is employed to carry out
the selective bypassin~ of the exhaust gas around the
filter and the introduction of the combustion supporting
gas to the filter during regeneration. A temperature
elevating means 19 is employed to heat the combustion
supporting gas during the regeneration period to a
lQ temperature level e~ective to ignite at least the leading
portion of the particulate collection within the filter
10. A sequential control means 20 is employed to sense
the back pressure of the exhaust gas (at 213 being
admitted to the filter during normal engine operation,
continuously sense the temperature of the filter at a
location 22 near the exit portion of the filter, to
continuously sense the temperature of the gases entering
the filter at 23, and sense the instantaneous fuel flow to
the engine as well as the instantaneous speed of the
vehicle en~ine. These sensed parameters are fed to an
onboard computer in control means 20 which mathematically
compares such sensed parameters for determining a variable
maximum allowable pressure which, if exceeded by the
instantaneously measured back pressure, will initiate the
regeneration cycle.
In Figure 1 -the means for conveying the
combustion supporting gas through at least a portion of
the filter com~rises the plenum chamber 14 into which is
fed a supply of compressed air from an air pump 25 which
3Q is operated electrically off the battery of the vehicle.
The supply of air is admitted or not admitted as
controlled by an air valve 26.
The means for controlling the flow of exhaust gas
from the engine comprises ducts 12~ 16 with a
Y-connection eEfective to normally permit exhaust gas to
flow through the branch 13 oE the Y into the plenum
chamber leading to the filter during normal engine
operation, and to pass through the other leg 16 of the Y
when regeneration is desireA. This means for controlling
the flow of either exhaust gas or the combustion
supporting gas to the Eiltee is also comprised of the
bypass valve 18, which is movable between a first and
second pOSitiOII by a vacuum motor 27. The vacuum motor is
1~ actuated by a vacuum reservoir 28 which is, of course,
created as a result of a vacuum pump 29 energized from the
automobile battery. The vacuum is admitted to the vacuum
motor by way of a valve 30.
The means for heating the combustion supporting
gas to a temperature effective to ignite the leading
portion of the particulate collection comprises a fuel
line 31 supplied from a pressurized fuel supply controlled
by a valve 32, the fuel supply being aspirated from a
nozzle 33 as a result of the interjection of air into the
nozzle along with the fuel for mixing therein and by the
separate supply of air through side vents 34 in the burner
housing 35. A glow plug 36 heated with sufficient energy
from a control 37 is effective to ignite the combustible
fuel/air mixture.
The method utilizing the above apparatus
essentially comprises:
(1) Determining when the pressure of the exhaust
gas (Ineasured at a station immediately upstream from the
filter) exceeds a predetermined variable maximu~ allowable
3Q pressure, a series o~ event for regeneration is initiated.
In this step a pressure sensor 21 is placed in the le~ of
the Y-connection leadiny to the filter so that the back
pressure of the exhaust is continuously monitored. Back
pressure is deEined hereill to mean exhaust gas pressure in
35 front of the filter. Variable maximum allowable pressure
is defined herein to mean a pressure which has been
mathematically derived by measuring the instantaneous back
pressure, instantaneous rpm of the engine, and the
instantaneous fuel flow o~ the engine and comparing it to
the measured back pressure for a clean filter at each of
the rpm and fuel flow combinations. When the predicted
allowable pressure exceeds a specific pressure drop for
any specific combination of rpm and fuel flow, the
regeneration cycle can be initiated because it indicates
that an optimal collection of particulates is present.
Considerable test data has been collected to indicate that
a certain minimum amount of particulates must be collected
to permit re~eneration to ef~ectively take place and
propogate and fully clean the trap. This minimum amount
15 is usually in the range of 150-~70 mg/i~3 (see Figure 3)
and will vary depending upon the nature of the filter
substrate and its corresponding porosity. It has further
been determined that a pressure drop of 40-65 inches of
water ~approximately 3-5 inches o~ mercury) for 110 in3
2~ alter volume is typically associated with said minimum
collection of particulates in case of a 1979 Opel vehicle
with 2.3 liter engine at steady 40 MPH (or 90 SCF~ Flow~.
Therefore, based upon these precalculations, the onboard
microcomputer of the vehicle ~athematically makes these
25 comparisons between the input data and derives a net
electrical signal in the event the measured pressure dro~
exceeds the predetermined variable maximum allowable
pressure.
(2) Next, a ~low of combustion supporting gas is
3a conveyed to and through the filter 10. This is brou~ht
about by a series of events which include turning on the
vacuum pump 29, which when su~icient vacuum is present in
the reservoir 28, permits the vacuum solenoid 27 to he
turned on~ which in turn actuates the bypass valve 18 to a
35 position where exhaust gas is bypassed around the ~ilter
and a flow of compressed air would be permitted into the
plenum 14. Next, the glow plug 36 is energized. Next,
the air pump ~5 is energized, causing compressed air to be
pumped through the air supply system, and followed by
actuation of the air solenoid valve 26, permitting the air
to be fed not only through the aspiration vents of the
burner unit, but through the nozzle 33 channel. Next, the
fuel solenoid valve 32 is actuated to permit pressurized
fuel to be transmitted through the fuel nozzle 33 along
with the air creating a combustible atomized fuel/air
mixture in the plenum 14. Since the glow plug is already
activated, the combustible mixture is immediately ignited,
elevating the flow of gases to a temperature of at least
1200F prior to entering the filter. In the event such
ignition does not take place, a thermocouple 23
immediately adjacent the front ace oE the filter senses a
temperature that is below the 1100F normally resulting
from ignition and thus sends a signal which shuts off the
fuel valve solenoid 32 for a predetermined delayed period
20 of time. After the delayed period o~ time, the fuel flow
is again instigated with the intent that the glow plug
would be effective to ignite the combustible mixture and
proceed with the ignition of the particulate collection.
Once the heated gas has been generated to the
25 ignition temperat~re of the particulates, the propogation
of the burning particulates will proceed over an expected
period of time, which is normally about two minutes (see
Figure 3), the peak temperature within the filter
progressing along the axial extent thereof.
3Q The method results in more economical operation
of the filtration system and less fuel losses when
operating the vehicle (see Figure 6). The system is more
responsive to engine operating characteristics over a much
wider range than that known to the prior art because in
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the regeneration mode the particulate filter is isolated
from the engine ~low and is independent of the engine
operation.
Alternatively, the fuel system control~
(31-32-33-34-36) can be eliminated. The glow plug 36 is
replaced by an electrical heating element 50 disposed
adjacent the inlet Eace 15 of the filter 10 (see Figure
4)~ A control system 51 employing a thermocouple control
52 is added to limit the surface temperature of the
heating element. The temperature map of the heater
element and for the inlet and outlet of the filter, for
this type of embodiment, is shown in Figure 5.
