U.S. patent number RE40,431 [Application Number 11/882,761] was granted by the patent office on 2008-07-15 for method of regulating an internal combustion engine.
This patent grant is currently assigned to GE Jenbacher GmbH & Co OHG. Invention is credited to Albert Fahringer, Johann Hirzinger, Reinhard Robitschko, Herbert Schaumberger.
United States Patent |
RE40,431 |
Robitschko , et al. |
July 15, 2008 |
Method of regulating an internal combustion engine
Abstract
Method of regulating an internal combustion engine in order to
reach presettable nitrogen oxide emission values of the internal
combustion engine, wherein the internal combustion engine is
supplied at least some of the time with a first fuel and at least
some of the time with a second fuel, the quantity of the first fuel
supplied to the internal combustion engine per unit of time being
controlled according to a preset control actual value or kept
constant and the quantity of the second fuel supplied to the
internal combustion engine per unit of time to reach a presettable
nitrogen oxide emission value being regulated according to at least
one recorded engine parameter.
Inventors: |
Robitschko; Reinhard (Jenbach,
AT), Schaumberger; Herbert (Schwaz, AT),
Hirzinger; Johann (Kossen, AT), Fahringer; Albert
(Kossen, AT) |
Assignee: |
GE Jenbacher GmbH & Co OHG
(Jenbach, AT)
|
Family
ID: |
34936612 |
Appl.
No.: |
11/882,761 |
Filed: |
August 3, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
11134083 |
May 20, 2005 |
07191772 |
Mar 20, 2007 |
|
|
Foreign Application Priority Data
|
|
|
|
|
May 21, 2004 [AT] |
|
|
A 888/2004 |
|
Current U.S.
Class: |
123/674; 123/575;
701/109; 123/679; 123/527; 123/299 |
Current CPC
Class: |
F02M
21/0215 (20130101); F02D 19/0642 (20130101); F02D
41/3011 (20130101); F02D 41/0027 (20130101); F02D
19/081 (20130101); F02B 23/0672 (20130101); F02D
41/1456 (20130101); F02D 19/0605 (20130101); F02B
23/0669 (20130101); F02D 2250/31 (20130101); Y02T
10/32 (20130101); Y02T 10/36 (20130101); Y02T
10/12 (20130101); Y02T 10/125 (20130101); F02B
23/0621 (20130101); F02D 2250/36 (20130101); Y02T
10/30 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02B 13/00 (20060101); G06F
19/00 (20060101) |
Field of
Search: |
;123/1A,3,27R,27GE,525-529,299,300,478,480,575,576,672,674,679,DIG.12
;261/26,35 ;48/199FM ;701/103-105,109 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
197 54 353 |
|
Dec 1997 |
|
DE |
|
0 259 382 |
|
Oct 1989 |
|
EP |
|
1 225 330 |
|
Apr 2006 |
|
EP |
|
2000-008897 |
|
Jan 2000 |
|
JP |
|
53-070219 |
|
May 2002 |
|
JP |
|
2002-155809 |
|
May 2002 |
|
JP |
|
2004-116398 |
|
Apr 2004 |
|
JP |
|
WO 01/59285 |
|
Aug 2001 |
|
WO |
|
03/076788 |
|
Sep 2003 |
|
WO |
|
Primary Examiner: Wolfe, Jr.; Willis R.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. A method of regulating an internal combustion engine in order to
reach presettable nitrogen oxide emission values of the internal
combustion engine, comprising: supplying the internal combustion
engine at least a portion of an operating time with a first fuel
and at least a portion of the operating time with a second fuel;
controlling a quantity of the first fuel supplied to the internal
combustion engine per unit of time according to one of a preset
control target value or a constant value; and regulating a quantity
of the second fuel supplied to the internal combustion engine per
unit of time by matching a mixture pressure influenced by the
quantity of the second fuel in an intake of the internal combustion
engine to a mixture pressure target value determined according to a
delivered output and a preset nitrogen oxide emission value of the
internal combustion engine so as to reach the preset nitrogen oxide
emission value.
2. The method of claim 1, wherein the first fuel is a first
combustible gas, and the second fuel is a second combustible
gas.
3. The method of claim 1, wherein the mixture pressure target value
determined according to the delivered output and the preset
nitrogen oxide emission value is further determined according to
corresponding target values intended for an operation of the
internal combustion engine with the first fuel and for an operation
of the internal combustion engine with the second fuel and further
according to a standardization factor x.
4. The method of claim 3, wherein the standardization factor x is
determined according to the calorific value or the CH.sub.4 content
of the first fuel or of the second fuel or of a fuel mixture.
5. The method of claim 3, wherein the mixture pressure target value
is further determined by taking into account fluctuations in the
composition of the first fuel or of the second fuel via previously
determined characteristics fields or by correction values and
corresponding measured values.
6. A method of regulating an internal combustion engine in order to
reach presettable nitrogen oxide emission values of the internal
combustion engine, comprising: supplying the internal combustion
engine at least a portion of an operating time with a first fuel
and at least a portion of the operating time with a second fuel;
controlling a quantity of the first fuel supplied to the internal
combustion engine per unit of time according to one of a preset
control target value or a constant value; and regulating the
quantity of the second fuel supplied to the internal combustion
engine per unit of time by matching a .lamda.-value influenced by
the quantity of the second fuel in an exhaust of the internal
combustion engine to a .lamda.-target value determined according to
a delivered output and a preset nitrogen oxide emission value of
the internal combustion engine so as to reach the preset nitrogen
oxide emission value.
7. The method of claim 6, wherein the first fuel is a first
combustible gas, and the second fuel is a second combustible
gas.
8. The method of claim 6, wherein the .lamda.-target value
determined according to the delivered output and the preset
nitrogen oxide emission value is further determined according to
corresponding target values intended for an operation of the
internal combustion engine with the first fuel and for an operation
of the internal combustion engine with the second fuel and further
according to a standardization factor x.
9. The method of claim 8, wherein the standardization factor x is
determined according to the calorific value or the CH.sub.4 content
of the first fuel or of the second fuel or of a fuel mixture.
10. The method of claim 8, wherein the .lamda.-target value is
further determined by taking into account fluctuations in the
composition of the first fuel or of the second fuel via previously
determined characteristics fields or by correction values and
corresponding measured values.
11. A method of regulating an internal combustion engine in order
to reach presettable nitrogen oxide emission values of the internal
combustion engine, comprising: supplying the internal combustion
engine at least a portion of an operating time with a first fuel
and at least a portion of the operating time with a second fuel;
performing a first operating mode at a first side of a preset
operation-switching point, the first operating mode including:
controlling a quantity of the first fuel supplied to the internal
combustion engine per unit of time according to one of a preset
control target value or a constant value; and regulating the
quantity of the second fuel supplied to the internal combustion
engine per unit of time according to at least one recorded engine
parameter so as to reach the preset nitrogen oxide emission value;
performing a second operating mode at a second side of the preset
operation-switching point, the second operating mode including:
controlling a quantity of the second fuel supplied to the internal
combustion engine per unit of time according to one of a preset
control target value or a constant value; and regulating the
quantity of the first fuel supplied to the internal combustion
engine per unit of time according to at least one recorded engine
parameter so as to reach the preset nitrogen oxide emission value;
and switching an operating mode of the internal combustion engine
between the first operating mode and the second operating mode.
12. The method of claim 11, wherein the first fuel is a first
combustible gas, and the second fuel is a second combustible.
13. The method of claim 11, wherein said switching comprises
switching an operating mode of the internal combustion engine so as
to change a mixing ratio between the first fuel and the second fuel
whereby both the first fuel and the second fuel are supplied to the
internal combustion engine.
14. The method of claim 11, wherein said switching comprises
switching an operating mode of the internal combustion engine such
that an operation using one of the first fuel and the second fuel
is replaced by an operation using the other of the first fuel and
the second fuel.
15. The method of claim 11, wherein the preset operation-switching
point is defined by a preset ratio between the quantity of the
first fuel supplied per unit of time and the quantity of the second
fuel supplied per unit of time.
16. The method of claim 15, wherein the preset ratio of the
operation-switching point is between 1:4 and 4:1.
17. The method of claim 15, wherein the preset ratio of the
operation-switching point is between 1:2 and 2:1.
18. A regulation section for use with an internal combustion
engine, said regulation section comprising: a fuel mixing device;
and a regulator operable to control said fuel mixing device to:
supply the internal combustion engine at least a portion of an
operating time with a first fuel and at least a portion of the
operating time with a second fuel; control a quantity of the first
fuel supplied to the internal combustion engine per unit of time
according to one of a preset control target value or a constant
value; and regulate a quantity of the second fuel supplied to the
internal combustion engine per unit of time by matching a mixture
pressure influenced by the quantity of the second fuel in an intake
of the internal combustion engine to a mixture pressure target
value determined according to a delivered output and a preset
nitrogen oxide emission value of the internal combustion engine so
as to reach the preset nitrogen oxide emission value.
19. The regulation section of claim 18, wherein said fuel mixing
device includes: a first volume flow dosage valve for supplying the
first fuel to the internal combustion engine; and a second volume
flow dosage valve for supplying the second fuel to the internal
combustion engine.
20. The regulation section of claim 18, wherein said fuel mixing
device includes: a volume flow dosage valve for supplying the first
fuel to the internal combustion engine; and a volume
flow-controllable gas mixer for receiving the second fuel and
supplying the second fuel to the internal combustion engine.
21. A regulation section for use with an internal combustion
engine, said regulation section comprising: a fuel mixing device;
and a regulator operable to control said fuel mixing device to:
supply the internal combustion engine at least a portion of an
operating time with a first fuel and at least a portion of the
operating time with a second fuel; control a quantity of the first
fuel supplied to the internal combustion engine per unit of time
according to one of a preset control target value or a constant
value; and regulate the quantity of the second fuel supplied to the
internal combustion engine per unit of time by matching a
.lamda.-value influenced by the quantity of the second fuel in an
exhaust of the internal combustion engine to a .lamda.-target value
determined according to a delivered output and a preset nitrogen
oxide emission value of the internal combustion engine so as to
reach the preset nitrogen oxide emission value.
22. The regulation section of claim 21, wherein said fuel mixing
device includes: a first volume flow dosage valve for supplying the
first fuel to the internal combustion engine; and a second volume
flow dosage valve for supplying the second fuel to the internal
combustion engine.
23. The regulation section of claim 21, wherein said fuel mixing
device includes: a volume flow dosage valve for supplying the first
fuel to the internal combustion engine; and a volume
flow-controllable gas mixer for receiving the second fuel and
supplying the second fuel to the internal combustion engine.
24. A regulation section for use with an internal combustion
engine, said regulation section comprising: a fuel mixing device;
and a regulator operable to control said fuel mixing device to:
supply the internal combustion engine at least a portion of an
operating time with a first fuel and at least a portion of the
operating time with a second fuel; perform a first operating mode
at a first side of a preset operation-switching point, the first
operating mode including: controlling a quantity of the first fuel
supplied to the internal combustion engine per unit of time
according to one of a preset control target value or a constant
value; and regulating the quantity of the second fuel supplied to
the internal combustion engine per unit of time according to at
least one recorded engine parameter so as to reach the preset
nitrogen oxide emission value; perform a second operating mode at a
second side of the preset operation-switching point, the second
operating mode including: controlling a quantity of the second fuel
supplied to the internal combustion engine per unit of time
according to one of a preset control target value or a constant
value; and regulating the quantity of the first fuel supplied to
the internal combustion engine per unit of time according to at
least one recorded engine parameter so as to reach the preset
nitrogen oxide emission value; and switch an operating mode of the
internal combustion engine between the first operating mode and the
second operating mode.
25. The regulation section of claim 24, wherein said fuel mixing
device includes: a first volume flow dosage valve for supplying the
first fuel to the internal combustion engine; and a second volume
flow dosage valve for supplying the second fuel to the internal
combustion engine.
26. The regulation section of claim 24, wherein said fuel mixing
device includes: a volume flow dosage valve for supplying the first
fuel to the internal combustion engine; and a volume
flow-controllable gas mixer for receiving the second fuel and
supplying the second fuel to the internal combustion engine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to Austrian Application No. A
888/2004, filed May 21, 2004, the contents of which are
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a method of regulating an internal
combustion engine, in particular with a lean operating mode, in
order to reach presettable nitrogen oxide emission values of the
internal combustion engine. The invention also relates to a
corresponding regulator and internal combustion engine.
It is already known from EP 0 259 382 B1 to operate an internal
combustion engine for driving an electric generator with constant
nitrogen oxide emission values, by regulating the mixture pressure
before the inlet valves of the cylinders according to the electric
output delivered by the generator. The target value of the mixture
pressure in the intake before the inlet valves is taken from a
characteristics field which shows the dependency of the mixture
pressure on the delivered electric output with constant emission
values. The measured actual value of the pressure before the inlet
valves is then regulated, via an adjustment of the fuel-to-air
ratio in a gas mixer, to its target value determined via the
characteristics field. The characteristics field used for this is
produced by gauging at least two operating points with identical
NO.sub.x emission values. It is possible, through this previously
known method, that an internal combustion engine can very precisely
observe the desired emission values in a wide output range. The
system known from the named European patent has the advantage that
there is practically no wear and ageing of sensitive sensors.
A further improved system according to the preamble is presented in
the European patent application EP 1 225 330 A2, in which the
regulation scheme known from EP 0 259 382 B1 has been supplemented
by an ignition point adjustment in order to provide, in every
operating condition, a regulation reserve for rapid reaction to
load changes. This regulation also serves to always run the
internal combustion engine with an optimum degree of
efficiency.
Each of the previous regulation methods is designed only for
operation with one fuel type. However, there are also internal
combustion engines--principally stationary--which are operated with
two different fuel types. No regulation method with which the
reaching of presettable nitrogen oxide emission values is assured
is known to date for such engines.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to create such a
regulation method for internal combustion engines.
This is achieved according to the invention by supplying the
internal combustion engine at least some of the time with a first
fuel and at least some of the time with a second fuel, the quantity
of the first fuel supplied to the internal combustion engine per
unit of time being controlled either according to a control target
value preset or kept constant, and the quantity of the second fuel
supplied to the internal combustion engine per unit of time being
regulated according to at least one recorded engine parameter in
order to reach the presettable nitrogen oxide emission value.
An idea underlying the present invention is thus, in the case of
internal combustion engines which are operated at least some of the
time, with two different fuel types, to control in an open-loop
mode the volume flow (=quantity supplied to the internal combustion
engine per unit of time) of the one first fuel according to fixed
preset values or to keep it constant. During this time, the
internal combustion engine is regulated in a closed-loop mode via
the volume flow of the other second fuel such that the exhaust
gases given off observe the preset emission values. Therefore, it
should be clear that "to control" should be understood as open-loop
mode operation and "to regulate" should be understood as
closed-loop mode operation.
There are various variants for the regulation according to the
invention. One which is preferred provides that the quantity of the
second fuel supplied to the internal combustion engine per unit of
time is regulated by matching a mixture pressure influenced by it
in an intake of the internal combustion engine to a mixture
pressure target value determined according to the output delivered
and the preset nitrogen oxide emission value of the internal
combustion engine. This requires a measuring apparatus in the
intake which determines the current mixture pressure before the
inlet valves. The actual value of the mixture pressure is matched
to its target value by suitable setting of the quantity of the
second fuel supplied per unit of time.
In another variant, however, instead of the mixture pressure, a
corresponding .lamda.-value in the exhaust gas can be measured.
With this variant, it is provided that the quantity of the second
fuel supplied to the internal combustion engine per unit of time is
regulated by matching a .lamda.-value influenced by it in an
exhaust of the internal combustion engine to a .lamda.-target value
determined according to the output delivered and the preset
nitrogen oxide emission value of the internal combustion
engine.
As is generally known, in this case the .lamda.-value describes the
proportion of air during combustion processes, .lamda.=1
corresponding to a stoichiometric combustion.
The method according to the invention is used particularly
preferably with, in particular stationary, gas engines, the first
fuel being a combustible gas and/or the second fuel being a second
combustible gas. Both the first and the second fuel can be mixtures
for example of various gases. It is also possible to add
constituents or gases not combustible per se to the first or second
fuel, for example in order to burn these.
The method according to the invention can be used particularly
favorably if a change of the mixing ratio of the two fuels or a
switch of operation of the internal combustion engine from
operation with the first fuel to operation with the second fuel is
proposed. In both cases, the method according to the invention
makes it possible during the whole switch from one to the other
fuel or during the whole change of the mixing ratio to operate the
internal combustion engine with presettable nitrogen oxide emission
values. To this end, in a first operating mode on this side of a
presettable operation-switching point the quantity of the first
fuel supplied per unit of time is controlled or kept constant and
the quantity of the second fuel supplied per unit of time is
regulated, and in a second operating mode on the other side of the
presettable operation-switching point, the quantity of the second
fuel supplied per unit of time is controlled or kept constant and
the quantity of the first fuel supplied per unit of time is
regulated. The operation-switching point, can be defined via
various parameters. A presettable relationship between the quantity
of the first fuel supplied per unit of time and the quantity of the
second fuel supplied per unit of time conveniently defines the
operation-switching point.
BRIEF DESCRIPTION OF THE DRAWINGS
Further details and features of the present invention will be seen
in the following description of the figures, in which:
FIG. 1 Is a diagram illustrating the relationship known in the
state of the art between the output P delivered by the internal
combustion engine and the mixture pressure p.sub.2 measured in the
intake of the internal combustion engine,
FIG. 2 Is a schematic view of an scheme according to the
invention,
FIGS. 3 and 4 Are schematic view showing details of variations
according to the invention of the design of a fuel-mixing
apparatus,
FIGS. 5 and 6 Are diagrams illustrating the relationships of the
output P and the mixture pressure p.sub.2 with the help of which
the regulation method according to the invention is illustrated,
and
FIG. 7 Is a diagram showing the pattern over time of the volume
flows when switching from an operation with a first fuel type to
operation with a second fuel type.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows schematically the dependency known in the state of the
art of the mixture pressure target value p.sub.2 on the output P
delivered by the internal combustion engine when operating with one
fuel type. Corresponding relationships between the .lamda.-target
value and the delivered output P exist analogously and are
therefore equally representable. However, because of the need for
brevity, further explanation of the method is given essentially
with reference to the relationship between p.sub.2 and P.
All those operating points of the internal combustion engine which
each have a specific nitrogen oxide emission value lie on the shown
solid characteristic line 10. The characteristic line or the
characteristics field is created by gauging, for example when
starting up the internal combustion engine. This happens by setting
a mixture pressure at an operating point 9 with given output P such
that the desired nitrogen oxide emission value of the internal
combustion engine results. This mixture pressure is then the
mixture pressure target value p.sub.2 at the given output P. In
order to create a characteristic line 10, at least a second
operating point 9 is then started by correspondingly setting
another output value P, with the mixture pressure p.sub.2 at which
the desired nitrogen oxide emission value is reached again being
determined. At first approximation, the two thus-determined
operating points 9 result in a characteristic line 10' (shown as a
dotted line). This can be linear or run with the help of known
polynomials or the like as a bent curve through the operating
points 9. If more than two operating points 9 are gauged with the
named procedure at a constant nitrogen oxide emission value, a
linear or curved pattern (characteristic line 10) can also result
from this.
In the case of internal combustion engines in which certain
operating parameters, such as for example the temperature t.sub.2
of the fuel/air mixture or the ignition point ZZP or the quality of
the supplied fuel can alter greatly, it may also be advisable to
also take account of the influence of there parameters. A
characteristic line generally then results. FIG. 1 shows by way of
example various dashed characteristic lines 10'' which result in
the case of corresponding gauging of operating points 9'' in each
case at constant nitrogen oxide emission values in each case and
different temperature values t.sub.2 in each case. When account is
taken of several influencing parameters, the overall result is then
a multidimensional characteristics field. Alternatively, taking a
single characteristic line 10 as a basis, but also corresponding
correction values for the temperature of the fuel/air mixture
t.sub.2 or the ignition point ZZP or the quality of the supplied
fuel, further influencing parameters can be taken into account. In
order to set limits to the outlay when gauging the characteristics
field according to the procedure described above, estimates can
also be applied if the influence of a specific parameter is
known.
FIG. 2 shows an engine diagram, reduced to essentials, with which
the method according to the invention can be carried out. Firstly
this shows, as is known per se, an output regulator in which a PID
controller 1 adjusts an output servocontrol 2 (for example a
throttle valve or an inlet valve) in such a way that the output P
delivered by the engine 5 corresponds to the desired output target
value P.sub.soll. According to the invention, a regulation section
is provided for the engine 5 with which, to reach constant nitrogen
oxide emission values NO.sub.x, a fuel mixing device 3 for at least
two fuels--as explained further below--is controlled on the one
hand and regulated on the other. Version variants according to the
invention for the fuel mixing device 3 are represented in FIGS. 3
and 4. These are also explained further below. In FIG. 2 itself, in
a first variant, a pressure-measuring apparatus 4 is arranged in
the intake 7 arranged behind the fuel mixing device 3 of the engine
5. This supplies the regulator 6 with a current measured value for
the mixture pressure before the valves. The variant in which,
instead of the mixture pressure, a .lamda.-value is used for
regulation is represented by broken lines. This can then be
measured in the exhaust by means of a .lamda.-sensor 4' customary
in the trade. In this variant also, the measured value is supplied
to the regulator 6. In addition to the measured output P and the
measured mixture pressure or .lamda.-value, other engine parameters
can be supplied to the regulator 6 according to the invention, such
as for example the temperature t.sub.2 of the fuel mixture or the
ignition point ZZP or the lower calorific value hu or the volume
flow 'V, in order to then be able to use the multi-dimensional
characteristics fields or relationships briefly represented with
the help of FIG. 1. The regulator 6 controls the fuel mixing device
3 according to the regulation process of the invention that is once
again described in detail further below.
FIG. 3 shows a first embodiment according to the invention for the
fuel mixing device 3. In this, two different fuel types A and B
(preferably two different combustible gases) are supplied to a
mixer 8 via settable volume flow dosage valves 11. In this mixer,
the two fuel types A and B are then blended with air to produce a
combustible gas mixture which is then supplied to the engine 5.
Although the shown mixing device 3 can of course also be used to
supply only fuel A or only fuel B to the engine 5, the method
according to the invention serves to operate the engine at least
part of the time with both fuels or switch the engine from
operation with one fuel to operation with the other fuel, while
still always reaching presettable nitrogen oxide emission values.
According to the invention, it is provided that the volume flow
dosage valve of the first fuel type A is controlled or kept
constant according to a control target value preset, while the
volume flow dosage valve 11 and thus the volume flow of the second
fuel type B is regulated according to an engine parameter, or vice
versa.
FIG. 4 shows a further variant of a fuel-mixing device 3 which can
also be used for a regulation method according to the invention.
Here, fuel B is supplied direct to an adjustable mixer 12. This
mixes fuel B with air L. This mixture is then supplied to a second
mixer 8, where the second fuel type A is also added. The quantity
of A supplied per unit of time can in turn be set via the volume
flow dosage valve 11. Here, too, according to the invention the
volume flow of the one fuel type can be controlled while the volume
flow of the other fuel type is regulated in order to reach the
presettable nitrogen oxide emission values.
It is explained with reference to FIG. 5 how the respective mixture
pressure target value p.sub.2 for various output values P when
operating with two different fuel types can now be determined
according to the invention. Firstly, characteristic lines 10 must
be determined separately from each other for both fuel types, as
explained with reference to FIG. 1. When gauging, the internal
combustion engine as known in the state of the art is operated in
each case with only one fuel, which may also be a mixture or
contain non-combustible admixtures.
FIG. 5 shows the determination of the mixture pressure target value
15, for the sake of clarity using only one characteristic line 10
for fuel A and only one other characteristic line 10 for fuel B. In
addition, only two operating points 9 each have been gauged for
both characteristic lines 10. All the operating points 13 and 14
between the gauged operating points 9 can be calculated from these
via equations or filed as a characteristics field in a suitable
memory of the regulator 6. Instead of a linear interpolation, bent
curves as characteristic lines 10 can also be the basis for the
calculation of the mixture pressure target value P.sub.2 15. This
calculation itself can be realized as an interpolation. Basically
it is always a momentary mixture pressure target value P.sub.2 15
which can either be calculated on the basis of the current preset
values or filed as a characteristics field.
A favorable variant provides that the calculation is based on the
corresponding target values 13 and 14 and a standardization factor
x. This can be determined for example according to the calorific
value or the CH.sub.4 content of the first fuel A or of the second
fuel B or of a volume flow of a fuel mixture. The standardization
factor x can stand in both a linear and a non-linear relationship
with the named parameters. Taking into account that the
standardization factor x is standardized to values between 0 and 1,
the following calculation rule results for the mixture pressure
target value p.sub.2 in point 15 (=p.sub.2 (15):
p.sub.2(15)=p.sub.2(13)+(p.sub.2-(14)-p.sub.2(13))x
Here, p.sub.2(13) and p.sub.2 (14) are the respective mixture
pressure target values are preset with the help of the
characteristic lines 10 for fuel type A and fuel type B. According
to the thus-calculated mixture pressure target value p.sub.2 (15),
the corresponding volume flow dosage valve 11 or the corresponding
volume flow-controllable gas mixer 12 of the fuel A or B to be
regulated is then operated, while the other volume flow dosage
valve 11 or the other volume flow-controllable gas mixer 12 for the
other fuel is kept constant or controlled according to fixed preset
values. The calculation, explained with reference to P.sub.2 and P,
of the target value 15 operates analogously in the case of a
regulation which is based on the .lamda.-value and the output
P.
FIG. 6 shows a variant of the invention in which, when calculating
the mixture pressure target value p.sub.2 (15) or the
.lamda.-target value, fluctuations in the quality of the second
fuel B must be taken into account, preferably via previously
determined characteristics fields or measured values corresponding
to correction factors. Thus, there frequently are fluctuations in
fuel quality, for example, when using waste gases as fuel. In the
shown example in FIG. 6 this is the case for fuel B. Owing to
corresponding quality fluctuations, the mixture pressure target
values for this fuel type then no longer lie on a characteristic
line, but in the area between two characteristic lines 10' and
10''. The respective current target value 13 for gas type B must
then be determined first, using characteristic lines 10' and 10''
gauged as usual, from the values 13' and 13''. An analogous
standardization function to that used to determine p.sub.2 (15) can
be used for this calculation, the standardization factor x being
replaced by another standardization factor y. y can for its part be
determined, for example, via the current calorific value or the
current composition of the fuel and depend on this in a linear or
non-linear manner. If the mixture pressure target value p.sub.2
(13) characteristic of the current quality of the fuel B is
calculated, the mixture pressure target value p.sub.2 (15) needed
for the regulation can, as shown with reference to FIG. 5, be
calculated from the mixture pressure target values p.sub.2 (13) and
p.sub.2 (14) with the help of the standardization factor x.
In the example shown, the CH.sub.4 content of fuel B fluctuates
between 40% and 60%. The characteristic line 10' represents the
relationship between P and p.sub.2 for fuel B with a CH.sub.4
content of 40%, the characteristic line 10'' represents the
corresponding relationship in the case of a CH.sub.4 content of
fuel B of 60%. If not only the quality of a fuel B but also that of
the other fuel A fluctuates, corresponding characteristic lines A'
and A'' (not represented here) must be gauged in order to
correspondingly calculate the mixture pressure target value p.sub.2
(14) from same.
FIG. 7 shows the patterns over time of the volume flow 16 of fuel A
and of the volume flow 17 of fuel B in the case of a switchover,
selected by way of example, of the operation of the internal
combustion engine from operation with the first fuel A to operation
with the second fuel B. The operation-switchover point is reached
at a preset ratio of the volume flows V'A to V'B at time t.sub.2.
The ratios in the operation-switchover point are favorably between
1:4 and 4:1 and particularly preferably between 1:2 and 2:1. At
time's less than t.sub.2 the volume flow of fuel A is regulated
according to the mixture pressure target value p.sub.2 (15), while
the volume flow of fuel B is increased following a preset incline.
At time t.sub.2 the switch into a second operating mode then takes
place. From this point in time on, the volume flow of fuel B is
regulated according to the mixture pressure target value p.sub.2
(15), while the volume flow of fuel A is reduced following a preset
incline.
The invention is not limited to the shown embodiments. Thus, the
method according to the invention can also be applied to the
operation of an internal combustion engine with more than two fuel
types, by for example controlling two fuel types according to fixed
preset values, while a third fuel type is regulated. A major
advantage of the method according to the invention is that even
when there are changes in the mixing ratio of different fuels at
any chosen point in time the reaching of the desired NO.sub.x
emission values is assured. In the simplest case the method
according to the invention can already be carried out on the basis
of only two characteristic lines (as shown in FIG. 5), the
remaining values can then be calculated online in each case or
filed in corresponding characteristics fields. A precise regulation
is thereby possible even with more complicated mixing systems, the
fuel mixture supplied to the engine being known at any time and
correspondingly able to be precisely taken into account in the
regulation. When converting an internal combustion engine operated
by the method according to the invention, exclusively known
components, such as mixers and volume flow dosage valves, can be
used.
* * * * *