U.S. patent application number 10/874670 was filed with the patent office on 2005-12-29 for strategy for fueling a diesel engine by selective use of fueling maps to provide hcci, hcci+cd, and cd combustion modes.
Invention is credited to Liu, Zhengbai, Wei, Puning.
Application Number | 20050284441 10/874670 |
Document ID | / |
Family ID | 35504242 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050284441 |
Kind Code |
A1 |
Liu, Zhengbai ; et
al. |
December 29, 2005 |
Strategy for fueling a diesel engine by selective use of fueling
maps to provide HCCI, HCCI+CD, and CD combustion modes
Abstract
A compression ignition engine (20) has a control system (26) for
processing data, one or more combustion chambers (22), and fuel
injectors (24) for injecting fuel into the chambers. The control
system controls fueling using a result of the processing of certain
data, such as engine speed and engine load, to select one of three
fueling modes (HCCI, HCCI+CD, CD) for operating the engine. When
the result of the processing selects the HCCI mode, the engine is
fueled to cause homogeneous-charge compression-ignition (HCCI)
combustion in all combustion chambers. When the result of the
processing selects the HCCI+CD mode, the engine is fueled to cause
HCCI combustion in some chambers and CD (conventional diesel)
combustion in the remaining chambers. When the result of the
processing selects the CD mode, the engine is fueled to cause CD
combustion in all chambers.
Inventors: |
Liu, Zhengbai; (Naperville,
IL) ; Wei, Puning; (Naperville, IL) |
Correspondence
Address: |
INTERNATIONAL ENGINE INTELLECTUAL PROPERTY COMPANY
4201 WINFIELD ROAD
P.O. BOX 1488
WARRENVILLE
IL
60555
US
|
Family ID: |
35504242 |
Appl. No.: |
10/874670 |
Filed: |
June 23, 2004 |
Current U.S.
Class: |
123/295 ;
123/305 |
Current CPC
Class: |
Y02T 10/128 20130101;
Y02T 10/12 20130101; F02D 41/40 20130101; F02D 41/0082 20130101;
F02D 41/3076 20130101; F02D 41/2412 20130101; Y02T 10/18 20130101;
F02D 41/3035 20130101; F02D 13/06 20130101 |
Class at
Publication: |
123/295 ;
123/305 |
International
Class: |
F02B 017/00; F02B
005/00 |
Claims
What is claimed is:
1. A method of operating a compression ignition engine comprising:
processing certain data to select one of plural fueling modes for
operating the engine, and a) when the result of the processing
selects a first fueling mode, fueling each of multiple combustion
chambers to create a substantially homogeneous air-fuel charge
within each such combustion chamber during a corresponding engine
cycle and compressing each charge to auto-ignition without
introducing any additional fuel after auto-ignition during that
corresponding engine cycle, b) when the result of the processing
selects a second fueling mode, i) fueling a first group of the
combustion chambers to create a substantially homogeneous air-fuel
charge within each combustion chamber of the first group during a
corresponding engine cycle and compressing each charge to
auto-ignition without introducing any additional fuel after
auto-ignition during that corresponding engine cycle, and ii)
fueling a second group of the combustion chambers by introducing
fuel at a time during the engine cycle when air in the
corresponding combustion chamber of the second group has been
compressed sufficiently to cause the fuel to combust as it is being
introduced, and c) when the result of the processing selects a
third fueling mode, fueling each of the combustion chambers by
introducing fuel at a time during the engine cycle when air in the
corresponding combustion chamber has been compressed sufficiently
to cause the fuel to combust as it is being introduced.
2. A method as set forth in claim 1 wherein the step of processing
certain data to select one of plural fueling modes for operating
the engine comprises processing data indicative of engine load.
3. A method as set forth in claim 2 wherein the step of processing
certain data to select one of plural fueling modes for operating
the engine comprises processing data indicative of engine
speed.
4. A method as set forth in claim 1 wherein in a graph of engine
speed vs. engine load whose origin corresponds to zero speed and
zero load, step a) occurs at engine speeds and loads within a first
zone of the graph that bounds the origin, step b) occurs at engine
speeds and loads within a second zone that bounds the first zone,
and step c) occurs at engine speeds and loads that bound the second
zone.
5. A method as set forth in claim 1 wherein fuel is introduced into
the combustion chambers by injection, and further including
controlling the pressure at which fuel is injected into both groups
of cylinders such that the injection pressure is substantially the
same for both groups.
6. A method as set forth in claim 5 further including controlling
the duration of fuel injection such that during the second mode,
the duration of fuel injection for one group is different from the
duration of fuel injection for the other group.
7. A method as set forth in claim 6 further including controlling
the timing of fuel injection such that during the second mode the
timing for the one group is different from the timing for the other
group.
8. A compression ignition engine comprising: a control system for
processing data; one or more combustion chambers; and a fueling
system for injecting fuel into the one or more combustion chambers;
wherein the control system controls the fueling system using a
result of the processing of certain data by the control system to
select one of plural fueling modes for operating the engine such
that a) when the result of the processing selects a first fueling
mode, each of multiple combustion chambers is fueled to create a
substantially homogeneous air-fuel charge within each such
combustion chamber during a corresponding engine cycle and each
such charge is compressed to auto-ignition without the introduction
of any additional fuel after auto-ignition during that
corresponding engine cycle, b) when the result of the processing
selects a second fueling mode, i) a first group of the combustion
chambers is fueled to create a substantially homogeneous air-fuel
charge within each combustion chamber of the first group during a
corresponding engine cycle and each charge is compressed to
auto-ignition without the introduction of any additional fuel after
auto-ignition during that corresponding engine cycle, and ii) a
second group of the combustion chambers is fueled by the
introduction of fuel at a time during the engine cycle when air in
the corresponding combustion chamber of the second group has been
compressed sufficiently to cause the fuel to combust as it is being
introduced, and c) when the result of the processing selects a
third fueling mode, each of the combustion chambers is fueled by
the introduction of fuel at a time during the engine cycle when air
in the corresponding combustion chamber has been compressed
sufficiently to cause the fuel to combust as it is being
introduced.
9. An engine as set forth in claim 8 wherein the certain data
comprises data indicative of engine load.
10. An engine as set forth in claim 9 wherein the certain data
comprises data indicative of engine speed.
11. An engine as set forth in claim 8 wherein in a graph of engine
speed vs. engine load whose origin corresponds to zero speed and
zero load, the first fueling mode occurs at engine speeds and loads
within a first zone of the graph that bounds the origin, the second
fueling mode occurs at engine speeds and loads within a second zone
that bounds the first zone, and the third fueling mode occurs at
engine speeds and loads within a third zone that bounds the second
zone.
12. An engine as set forth in claim 8 further including a fuel
injection system that introduces fuel into the combustion chambers
by injection, and wherein the control system controls the pressure
at which fuel is injected into both groups of cylinders during the
second mode such that the injection pressure is substantially the
same for both groups.
13. An engine as set forth in claim 12 wherein the control system
further controls the duration of fuel injection during the second
mode such that the duration of fuel injection for one group is
different from the duration of fuel injection for the other
group.
14. An engine as set forth in claim 13 wherein the control system
further controls the timing of fuel injection including controlling
the timing of fuel injection such that during the second mode the
timing for the one group is different from the timing for the other
group.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to internal combustion
engines. More specifically it relates to a control strategy for
selectively utilizing homogeneous-charge compression-ignition
(HCCI) in a way that takes advantage of HCCI's attributes in
different ways during different modes of engine operation. More
specifically the invention relates to a strategy for fueling an
engine to cause HCCI combustion in all cylinders during a first
mode, to cause HCCI combustion in less than all cylinders and CD
(conventional diesel) combustion in the remaining cylinders during
a second mode, and CD combustion in all cylinders during a third
mode.
BACKGROUND OF THE INVENTION
[0002] HCCI is a known process for fueling a diesel engine in a
manner that creates a substantially homogeneous air-fuel charge
inside an engine cylinder during a compression upstroke of an
engine cycle. After a desired quantity of fuel for the charge has
been injected into the cylinder to create a substantially
homogeneous air-fuel mixture, the increasing compression of the
charge by the upstroking piston creates sufficiently large pressure
to cause auto-ignition of the charge. In other words, the HCCI mode
of operation of a diesel engine may be said to comprise 1)
injecting a desired amount of fuel into a cylinder at an
appropriate time during the compression upstroke so that the
injected fuel mixes with charge air that has entered the cylinder
during the preceding intake downstroke and early portion of the
compression upstroke in a manner that forms a substantially
homogeneous mixture within the cylinder, and then 2) increasingly
compressing the mixture to the point of auto-ignition near or at
top dead center (TDC). Auto-ignition may occur as the substantially
simultaneous spontaneous combustion of vaporized fuel at various
locations within the mixture. No additional fuel is injected after
auto-ignition.
[0003] One of the attributes of HCCI is that relatively lean, or
dilute, mixtures can be combusted, keeping the combustion
temperatures relatively low. By avoiding the creation of relatively
higher combustion temperatures, HCCI can yield significant
reductions in the generation of NO.sub.x, an undesired constituent
of engine exhaust gas.
[0004] Another attribute of HCCI is that auto-ignition of a
substantially homogeneous air-fuel charge generates more complete
combustion and consequently relatively less soot in engine
exhaust.
[0005] The potential benefit of HCCI on reducing tailpipe emissions
is therefore rather significant, and consequently HCCI is a subject
of active investigation and development by many scientists and
engineers in the engine research and design community.
[0006] One aspect of HCCI seems to impose a limit on the extent to
which it can provide drastically reduced tailpipe emissions of soot
and NO.sub.x. At higher engine speeds and larger engine loads, the
rate of combustion is difficult to control. Consequently, known
engine control strategies may utilize HCCI only at relatively lower
speeds and smaller engine loads. At higher speeds and/or larger
loads, the engine is fueled so that the fuel combusts by
conventional diesel (CD) combustion upon being injected into charge
air that has been compressed within a cylinder to a pressure that
is sufficiently great to cause the fuel to combust as it is being
injected.
[0007] With the advent of processor-controlled fuel injection
systems capable of controlling fuel injection with precision that
allows fuel to be injected at different injection pressures, at
different times, and for different durations during an engine cycle
over the full range of engine operation, a diesel engine becomes
capable of both CD combustion and HCCI combustion.
[0008] As will be explained by later description, the present
invention takes advantage of the capabilities of those fuel
injection and processing systems to control fuel injections in
different ways depending on certain aspects of engine operation.
Exactly how any particular fuel injection system will be controlled
by an associated processing system in any given engine will depend
on specifics of the engine, the fuel injection system, and the
processing system.
[0009] Because a diesel engine that powers a motor vehicle runs at
different speeds and loads depending on various inputs to the
vehicle and engine that influence engine operation, fueling
requirements change as speed and load change. An associated
processing system processes data indicative of parameters such as
engine speed and engine load to develop control data for setting
desired engine fueling for particular operating conditions that
will assure proper control of the fuel injection system for various
combinations of engine speed and engine load.
[0010] Pending U.S. patent application Ser. No. 10/809,254
discloses a diesel engine and associated processor-controlled fuel
injection system that processes certain data to select one of
plural fueling modes for operating the engine. When a result of the
processing selects a first fueling mode (HCCI mode), the engine is
fueled during an engine cycle to create a substantially homogeneous
air-fuel charge within one or more combustion chambers. That charge
is compressed to combust by auto-ignition, with no more fuel being
introduced after auto-ignition. When a result of the processing
selects a second fueling mode (HCCI-CD mode), the engine is fueled
during an engine cycle to create a substantially homogeneous
air-fuel charge within the one or more combustion chambers. That
charge is compressed to combust by auto-ignition (HCCI), after
which more fuel is introduced into the one or more combustion
chambers to provide additional combustion (CD). That engine
utilizes HCCI combustion at relatively smaller loads and relatively
smaller speeds and what is referred to as HCCI-CD combustion at
relatively larger loads and relatively larger speeds.
SUMMARY OF THE INVENTION
[0011] The present invention relates to an engine, system, and
method for enhancing the use of HCCI combustion in a diesel engine
toward objectives that include further reducing the generation of
undesired constituents in engine exhaust, especially soot and
NO.sub.x, and further improving thermal efficiency. The invention
is embodied in the fuel injection control strategy, a strategy that
is programmed in an associated processing system.
[0012] According to principles of the present invention, the
utilization of HCCI combustion occurs in a different manner from
that described in U.S. patent application Ser. No. 10/809,254. The
present invention comprises three distinct modes of engine
operation: 1) an HCCI mode; 2) an HCCI+CD mode; and 3) a CD mode.
Each of these modes will be explained in detail hereinafter.
[0013] The HCCI mode is utilized at relatively smaller loads and
relatively lower speeds. The HCCI+CD mode is utilized at relatively
larger loads than those of the HCCI mode and at relatively higher
speeds than those of the HCCI mode. The CD mode is utilized at
still relatively larger loads than those of the HCCI+CD mode and at
still relatively higher speeds than those of the HCCI+CD mode.
[0014] The HCCI+CD mode enables the benefits of HCCI to be obtained
in a portion of the engine operating range between the portion of
the range where HCCI is exclusively used and the portion of the
range where CD is exclusively used.
[0015] One generic aspect of the present invention relates to a
method of operating a compression ignition engine wherein certain
data is processed to select one of plural fueling modes for
operating the engine.
[0016] When the result of the processing selects a first fueling
mode, each of multiple combustion chambers is fueled to create a
substantially homogeneous air-fuel charge within each such
combustion chamber during a corresponding engine cycle and each
charge is then compressed to auto-ignition without introducing any
additional fuel after auto-ignition during that corresponding
engine cycle.
[0017] When the result of the processing selects a second fueling
mode, a first group of the combustion chambers is fueled to create
a substantially homogeneous air-fuel charge within each combustion
chamber of the first group during a corresponding engine cycle and
the charges are compressed to auto-ignition without introducing any
additional fuel after auto-ignition during that corresponding
engine cycle. A second group of the combustion chambers is fueled
by introducing fuel at a time during the engine cycle when air in
the corresponding combustion chamber of the second group has been
compressed sufficiently to cause the fuel to combust as it is being
introduced.
[0018] When the result of the processing selects a third fueling
mode, each of the combustion chambers is fueled by introducing fuel
at a time during the engine cycle when air in the corresponding
combustion chamber has been compressed sufficiently to cause the
fuel to combust as it is being introduced.
[0019] A further generic aspect relates to a compression ignition
engine that operates according to the method just described.
[0020] In disclosed embodiment of the invention, the data that is
processed for selecting the particular mode comprises engine speed
data and engine load data. Injection pressure, duration, and timing
may differ from mode to mode. Fueling data for each of the various
modes are contained in maps in the engine control system.
[0021] The foregoing, along with further features and advantages of
the invention, will be seen in the following disclosure of a
presently preferred embodiment of the invention depicting the best
mode contemplated at this time for carrying out the invention. This
specification includes drawings, now briefly described as
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a representative graphic portrayal of fueling
strategy in accordance with principles of a first embodiment of the
present invention comprising an HCCI combustion mode for some
speed-load conditions, an HCCI+CD combustion mode for other
speed-load conditions, and a CD combustion mode for still other
speed-load conditions.
[0023] FIG. 2 is a general schematic diagram of portions of an
exemplary diesel engine relevant to certain principles of the FIG.
1 embodiment of the present invention.
[0024] FIG. 3 is a flow diagram illustrating an embodiment of the
inventive strategy utilized in the engine of FIG. 2.
[0025] FIG. 4A illustrates a generic fuel injection according to a
generic fueling map used for HCCI combustion.
[0026] FIG. 4B illustrates a generic fuel injection according to a
generic fueling map used for CD combustion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] FIG. 1 is a graph whose vertical axis represents engine load
and whose horizontal axis represents engine speed. At the origin of
the graph, engine load is zero, and engine speed is zero.
Respective solid lines 10, 12, and 14 demarcate three zones labeled
HCCI, HCCI+CD, and CD.
[0028] Zone HCCI covers an area that encompasses various
combinations of relatively smaller engine loads and relatively
lower engine speeds. Zone HCCI+CD covers an area that encompasses
various combinations of relatively larger engine loads and
relatively higher engine speeds than those of zone HCCI. Zone CD
covers an area that encompasses various combinations of still
relatively larger engine loads and still relatively higher engine
speeds than those of zone HCCI+CD.
[0029] When a compression ignition engine is operating at a speed
and load that falls within Zone HCCI, fuel is injected into the
engine cylinders in a manner that creates HCCI combustion. When the
engine is operating at a speed and load that falls within Zone
HCCI+CD, fuel is injected into some engine cylinders in a manner
that creates HCCI combustion in those cylinders, and into other
engine cylinders, in a manner that creates CD combustion. When the
engine is operating at a speed and load that falls within Zone CD,
fuel is injected into the engine cylinders in a manner that creates
CD combustion.
[0030] FIG. 2 shows schematically a portion of an exemplary diesel
engine 20 operating in accordance with the inventive strategy
defined by FIG. 1 for powering a motor vehicle. Engine 20 comprises
cylinders 22 within which pistons reciprocate. Each piston is
coupled to a respective throw of a crankshaft by a corresponding
connecting rod. Intake air is delivered to each cylinder through an
intake system (not specifically shown in the drawing) when a
respective intake valve is open.
[0031] The engine has a fueling system that comprises fuel
injectors 24 for the cylinders 22. The engine also has a
processor-based engine control unit (ECU) 26 that processes data
from various sources to develop various control data for
controlling various aspects of engine operation. The data processed
by ECU 26 may originate at external sources, such as various
sensors 28, and/or be generated internally. Examples of data
processed may include engine speed, intake manifold pressure,
exhaust manifold pressure, fuel injection pressure, fueling
quantity and timing, mass airflow, and accelerator pedal
position.
[0032] ECU 26 controls the injection of fuel into cylinders 22 by
controlling the operation of the fueling system, including
controlling the operation of fuel injectors 24. The processing
system embodied in ECU 26 can process data sufficiently fast to
calculate, in real time, the timing and duration of device
actuation to set both the timing and the amount of each injection
of fuel into a cylinder. Such control capability is used to
implement the inventive strategy.
[0033] Regardless of how data values for engine speed and engine
load are developed, this particular embodiment of the invention
uses instantaneous engine speed and instantaneous engine load to
select the particular fueling mode for the engine, either 1) the
HCCI mode for creating HCCI combustion in all cylinders, 2) the
HCCI+CD mode for creating HCCI combustion in some cylinders and CD
combustion in others, or 3) the CD mode for creating CD combustion
in all cylinders, and to then operate the fueling system to fuel
the engine according to the strategy of the selected fueling mode.
Alternately, a strategy may use only engine load to select the
particular mode.
[0034] FIG. 3 shows a flow diagram 30 for the inventive strategy as
executed by the processing system of ECU 26. The reference numeral
32 represents the start of the strategy. A step 34 processes engine
speed data and engine load data to determine which the three
fueling modes of FIG. 1 is to be selected. One way of selecting the
mode is by providing one or more maps in the processing system to
define the three zones and comparing data values for instantaneous
engine speed and engine load according to the maps.
[0035] When step 34 selects HCCI mode, diagram 30 discloses that
fuel will be injected into each cylinder to create HCCI combustion
in all cylinders (reference numeral 36). FIG. 4A illustrates a
generic example of fueling for HCCI combustion, as represented by
the rectangular zone 38 shown in a dimensionless graph of injection
pressure versus crankshaft rotational position. FIG. 4B illustrates
a generic example of fueling for CD combustion, as represented by
the rectangular zone 42 shown in a graph of injection pressure
versus time.
[0036] Fueling for HCCI combustion differs from fueling for CD
combustion in several ways that can be seen by comparing FIG. 4A
with FIG. 4B.
[0037] In each Figure, the distance along the horizontal axis from
the origin to the beginning of the corresponding zone 38, 42
represents timing of injection during an engine cycle. It can be
seen that timing for CD combustion could be advanced relative to
that for HCCI combustion.
[0038] It can also be seen that the duration of injection,
represented by the width of each zone, is longer for CD combustion
than for HCCI combustion. Fuel injection pressure, represented by
the height of each zone, is substantially the same for both HCCI
and CD combustion.
[0039] Within either zone 38 or 42, actual injection may take place
in any manner suitable for causing the respective type of
combustion. For example, HCCI combustion may result from one or
more discrete injections, but regardless of the number of discrete
injections, the HCCI mode introduces fuel into a cylinder during a
compression upstroke of the piston that reciprocates in the
cylinder. The fuel mixes with charge air that entered the cylinder
during the immediately preceding intake downstroke and early
portion of the compression upstroke so that the resulting air-fuel
mixture is a substantially homogeneous one. The fueling concludes
before any combustion occurs. When the charge has been compressed
sufficiently to auto-ignite, HCCI combustion commences.
[0040] When step 34 selects CD mode, diagram 30 discloses that fuel
will be injected into each cylinder to create CD combustion in all
cylinders (reference numeral 40). CD combustion may result from one
or more discrete injections, but regardless of the number of
discrete injections, the CD mode introduces fuel into a cylinder
near the top of a compression upstroke of the piston that
reciprocates in the cylinder. The fuel mixes with charge air that
has been compressed to pressure sufficiently great to cause CD
combustion to occur as fuel is being injected.
[0041] When step 34 selects HCCI+CD mode, diagram 30 discloses a
step 44 that causes fuel to be injected to create HCCI combustion
in some cylinders and CD combustion in others. FIG. 2 shows an
example of a V-type engine have two banks of cylinders G1, G2, each
containing equal numbers of cylinders to get better engine
balance.
[0042] During the HCCI+CD mode, the cylinders of bank G1 are fueled
to cause HCCI combustion to occur in them while the cylinders of
bank G2 are fueled to cause CD combustion to occur in them. The
cylinders of bank G1 are fueled in the manner of FIG. 4A while
those of bank G2 are fueled in the manner of FIG. 4B.
[0043] The selection of those cylinders that are to be fueled in
one way and those that are to be fueled in the other way may be
fixed or variable. In other words it is possible that in the
HCCI+CD mode, a particular cylinder may be fueled in one way at
certain times and in the other way at other times. The strategy
iterates at a suitable rate to assure that load/speed changes are
promptly followed and the appropriate fueling mode performed.
[0044] When a cylinder is to be fueled for HCCI combustion, the
processing system utilizes a corresponding fueling map or maps that
provide fueling parameters suited for causing fuel to be injected
consistent with zone 38 for the particular engine speed and
load.
[0045] When a cylinder is to be fueled for CD combustion, the
processing system utilizes a corresponding fueling map or maps that
provide fueling parameters suited for with causing fuel to be
injected consistent with zone 42 for the particular engine speed
and load.
[0046] Hence in FIGS. 3, 4A, and 4B, the designation FM1 represents
fueling maps for HCCI combustion and the designation FM2 represents
fueling maps for CD combustion.
[0047] The invention has the following advantages:
[0048] 1) It can concurrently reduce NO.sub.x and soot.
[0049] 2) It has high thermal efficiency.
[0050] 3) It can cover the whole operating range of an engine.
[0051] 4) It can be used in heavy-duty, medium-duty, and light-duty
diesel engines.
[0052] 5) The invention can be implemented in the processor alone,
provided that the processor has sufficient capacity, and this makes
the invention quite cost-effective.
[0053] While a presently preferred embodiment of the invention has
been illustrated and described, it should be appreciated that
principles of the invention apply to all embodiments falling within
the scope of the following claims.
* * * * *