U.S. patent application number 13/654340 was filed with the patent office on 2013-05-02 for fuel injection strategies in opposed-piston engines with multiple fuel injectors.
This patent application is currently assigned to Achates Power, Inc.. The applicant listed for this patent is Achates Power, Inc.. Invention is credited to Clark A. Klyza, Fabien G. Redon.
Application Number | 20130104848 13/654340 |
Document ID | / |
Family ID | 47430035 |
Filed Date | 2013-05-02 |
United States Patent
Application |
20130104848 |
Kind Code |
A1 |
Klyza; Clark A. ; et
al. |
May 2, 2013 |
Fuel Injection Strategies in Opposed-Piston Engines with Multiple
Fuel Injectors
Abstract
In an opposed-piston engine, two or more fuel injectors are
mounted to a cylinder for direct side injection into the cylinder.
The injectors are controlled so as to inject either a single fuel
pulse or a plurality of fuel pulses per cycle of engine operation
in order to initiate combustion during varying engine speeds and
operating conditions.
Inventors: |
Klyza; Clark A.; (San Diego,
CA) ; Redon; Fabien G.; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Achates Power, Inc.; |
San Diego |
CA |
US |
|
|
Assignee: |
Achates Power, Inc.
San Diego
CA
|
Family ID: |
47430035 |
Appl. No.: |
13/654340 |
Filed: |
October 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61628248 |
Oct 27, 2011 |
|
|
|
Current U.S.
Class: |
123/445 |
Current CPC
Class: |
F02D 41/3094 20130101;
F02D 41/403 20130101; F02M 69/045 20130101; F02M 55/025 20130101;
F02M 69/465 20130101; F02B 75/282 20130101; Y02T 10/44 20130101;
F02D 41/402 20130101; F02M 69/10 20130101; F02D 41/405 20130101;
F02M 69/04 20130101; Y02T 10/40 20130101 |
Class at
Publication: |
123/445 |
International
Class: |
F02M 69/04 20060101
F02M069/04 |
Claims
1. A method of operating fuel injectors located for direct side
injection of fuel into a cylinder of an opposed-piston engine,
comprising: causing a pair of opposed pistons to move in the
cylinder; and, injecting fuel from first and second fuel injectors
into a combustion chamber of the engine defined between the end
surfaces of the pistons as the pistons approach top dead center
locations, such that fuel injected by the first fuel injector
includes at least a pilot injection followed by a main injection,
and fuel injected by the second fuel injector includes at least a
pilot injection followed by a main injection.
2. The method of claim 1, wherein each pilot injection is separated
in time from its following main injection by at least an
inter-pulse gap (IPG).
3. The method of claim 2, wherein the pilot injections injected by
the first and second fuel injectors are offset by an amount of time
less than the IPG.
4. The method of claim 3, wherein the main injections injected by
the first and second fuel injectors are substantially
simultaneous.
5. The method of claim 1, wherein fuel injected by the first fuel
injector includes a first pilot injection and a second pilot
injection delayed from the first pilot injection by at least an
inter-pulse gap (IPG), and the main injection is delayed from the
second pilot injection.
6. The method of claim 5, wherein the pilot injection injected by
the second fuel injector occurs in time between the first and
second pilot injections of the first fuel injector.
7. The method of claim 6, wherein the main injections of the first
and second fuel injectors occur substantially simultaneously in
time.
8. The method of claim 6, wherein the main injections of the first
and second fuel injectors overlap in time.
9. The method of claim 1, wherein fuel injected by the first fuel
injector further includes at least one post injection following the
main injection.
10. The method of claim 1, wherein fuel injected by the second fuel
injector further includes at least one post injection following the
main injection.
11. A method of operating fuel injectors located for direct side
injection of fuel into a cylinder of an opposed-piston engine,
comprising: causing a pair of opposed pistons to move in the
cylinder; and, injecting fuel from first and second fuel injectors
between the end surfaces of the pistons as the pistons approach top
dead center locations, in which fuel is injected by the first fuel
injector with a first split injection, and fuel is injected by the
second fuel injector with a second split injection.
12. The method of claim 11, wherein each of the first and second
split injections includes a pilot injection separated in time from
a following main injection by at least a minimum interval.
13. The method of claim 12, wherein the pilot injection of the
first split injection is offset from the pilot injection of the
second split injection by an amount of time less than the minimum
interval.
14. The method of claim 13, wherein the main injections of the
first and second injections are substantially simultaneous.
15. The method of claim 11, wherein the first split injection
includes a first pilot injection and a second pilot injection
delayed from the first pilot injection by at least a minimum
interval, and the main injection is delayed from the second pilot
injection.
16. The method of claim 15, wherein the pilot injection of the
second split injection occurs in time between the first and second
pilot injections of the first split injection.
17. The method of claim 16, wherein the main injections of the
first and second split injections occur substantially
simultaneously in time.
18. The method of claim 16, wherein the main injections of the
first and second split injections overlap in time.
19. The method of claim 11, wherein the first split injection
further includes at least one post injection following the main
injection.
20. The method of claim 11, wherein the second split injection
further includes at least one post injection following the main
injection.
21. A fuel injection system for an opposed-piston engine,
comprising: at least one cylinder with a pair of pistons disposed
in opposition for movement between top and bottom dead center
positions therein; a plurality of fuel injectors positioned for
direct side injection of fuel into the cylinder, between the
pistons; a control unit responsive to engine operating conditions
for generating fuel injection control signals; and, an injector
driver responsive to first control signals for generating fuel
injector actuation signals operative to cause a first fuel injector
to emit a first split injection and to cause a second fuel injector
to emit a second split injection.
22. The fuel injection system of claim 21, wherein each of the
first and second split injections includes a pilot injection
separated in time from a following main injection by at least a
minimum interval.
23. The fuel injection system of claim 22, wherein the first and
second split injections overlap.
24. The fuel injection system of claim 22, wherein the pilot
injection of the first split injection is offset from the pilot
injection of the second split injection by an amount of time less
than the minimum interval.
25. The fuel injection system of claim 21, wherein the injector
driver is further responsive to second control signals for causing
each of the first and second fuel injectors to emit a single
injection.
26. A fuel injection system for an opposed-piston engine,
comprising: at least one cylinder with a pair of pistons disposed
in opposition for movement between top and bottom dead center
positions therein; a plurality of fuel injectors positioned for
direct side injection of fuel into the cylinder, between the
pistons; a control unit responsive to engine operating conditions
for generating fuel injection control signals when the pistons are
near top dead center locations in the cylinder; and, an injector
driver responsive to first control signals for generating first
fuel injector actuation signals operative to cause a single fuel
injector to inject fuel into the cylinder and for generating second
fuel injector actuation signals operative to cause at least two
fuel injectors to inject fuel into the cylinder.
27. The fuel injection system of claim 26, wherein the first fuel
injector actuation signals are further operative to cause the
single fuel injector to inject fuel into the cylinder by a split
injection.
28. The fuel injection system of claim 26, wherein the second fuel
injector actuation signals are further operative to cause each fuel
injector to inject fuel into the cylinder by a split injection.
Description
PRIORITY
[0001] This application claims the benefit of U.S. provisional
application for patent No. 61/628,248, filed Oct. 27, 2011, for
"Fuel Injection Strategies in Opposed-Piston Engines with Multiple
Fuel Injectors".
BACKGROUND
[0002] The present disclosure relates to fuel injection strategies
for opposed-piston engines with direct side injection. In
particular, the present disclosure concerns fuel injection in
opposed-piston cylinders equipped with multiple injectors.
[0003] Efficient combustion is a fundamental challenge inherent in
diesel engine operation. This challenge is typically addressed in
conventional diesel engines by injecting fuel from a central
location on the fire deck directly into an appropriately shaped
combustion chamber defined between the end surface of the piston
and the fire deck.
[0004] In opposed-piston architecture, two pistons are disposed
crown to crown in a cylinder where they move in opposition between
top dead center (TDC) and bottom dead center (BDC) positions. The
combustion chamber is defined in the cylinder, between the end
surfaces of the pistons as they approach TDC. Consequently, it is
not possible to mount a fuel injector in a central position facing
the end surface of a piston in an opposed-piston engine. Instead, a
fuel injector mounting site is typically located on the sidewall of
the cylinder, between the TDC locations of the piston end surfaces.
This results in the direct side injection configuration that is
characteristic of opposed-piston engine design. That is to say,
fuel is injected directly into the combustion chamber, through the
sidewall of the cylinder.
[0005] A problem with direct side injection is that the injected
fuel travels radially or tangentially into the cylinder,
transversely to the axis of charge air swirl, which can inhibit
air/fuel mixing and result in incomplete and/or uneven combustion.
Accordingly, it is desirable to improve the fuel injection
capabilities of opposed-piston engines with direct side
injection.
SUMMARY
[0006] In one aspect, the present disclosure is directed to a fuel
injection method and system for improved direct side injection in
an opposed-piston engine so as to enhance air/fuel mixing and
improve combustion.
[0007] In another aspect, the present disclosure is directed to an
opposed-piston engine including at least one cylinder equipped with
two or more fuel injectors for direct side injection into the
cylinder. Each of the injectors is controlled so as to inject
either a single fuel pulse or a plurality of fuel pulses per cycle
of engine operation in response to varying engine speeds and
operating conditions.
[0008] In a further aspect, the present disclosure relates to
injecting fuel from first and second fuel injectors into a
combustion chamber of an opposed-piston engine defined between the
end surfaces of opposed pistons as the pistons approach top dead
center locations, such that fuel injected by the first fuel
injector includes at least a pilot injection followed by a main
injection, and fuel injected by the second fuel injector includes
at least a pilot injection followed by a main injection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross sectional view of an opposed-piston engine
cylinder with a single fuel injector mounted for direct side
injection into cylinder bore space between the end surfaces of a
pair of opposed pistons.
[0010] FIG. 2 is a cross sectional view of an opposed-piston engine
cylinder with multiple fuel injectors mounted for direct side
injection into cylinder bore space between the end surfaces of a
pair of opposed pistons.
[0011] FIG. 3 is a schematic diagram of a preferred fuel injection
system for an opposed-piston engine.
[0012] FIG. 4 is a graph showing injector actuation and injection
rates for the single fuel injector construction of FIG. 1.
[0013] FIG. 5 is a graph showing injector actuations and injection
rates embodying a first control strategy for the multiple fuel
injector construction of FIG. 2.
[0014] FIG. 6 is a graph showing injector actuations and injection
rates embodying a second control strategy for the multiple fuel
injector construction of FIG. 2.
DETAILED DESCRIPTION
[0015] FIG. 1 illustrates a cylinder for an opposed-piston engine,
with the cylinder shown in cross section. The cylinder 10 has
exhaust and intake ports 12 and 14 located in the vicinity of
respective ends of the cylinder. An electrically-actuated fuel
injector 20 has a nozzle 22 seated in a hole 24 drilled through the
sidewall of the cylinder 10. The hole 24 is located between bore
locations 26 and 27 corresponding to respective TDC positions of
the end surfaces of a pair of opposed pistons (not shown) disposed
in the cylinder bore. When the pistons are at or near their TDC
positions, the fuel injector 20 is operated to inject a spray of
fuel 30 into the cylinder bore space between the piston end
surfaces.
[0016] FIG. 2 is a cross sectional view of an opposed-piston engine
cylinder 40 with multiple electrically-actuated fuel injectors 50
mounted for direct side injection into cylinder bore space between
the end surfaces of a pair of opposed pistons. Each fuel injector
50 has a nozzle 52 seated in a hole 54 drilled through the sidewall
of the cylinder 50. The holes 54 are located between bore locations
corresponding to respective TDC positions of the end surfaces of
the pair of opposed pistons 58 and 59 disposed in the cylinder
bore. As the pistons 58 and 59 move toward TDC, turbulently-moving
charge air is compressed between their end surfaces. When the
pistons 58 and 59 are at or near TDC, one or each of the fuel
injectors 50 is operated to inject a respective spray of fuel 60
into compressed charge in the cylinder bore space between the
piston end surfaces. The fuel is mixed into the compressed,
turbulent charge air and the heat produced by compression causes
the air/fuel mixture to ignite.
[0017] A fuel injection system for an opposed-piston engine is
shown in schematic diagram form in FIG. 3. The fuel injection
system 100 includes an opposed-piston engine 103 having one or more
cylinders. Each cylinder has a construction corresponding to that
of the cylinder 40 of FIG. 2; thus, each cylinder 40 has a pair of
opposed pistons (not shown) disposed for opposed movement therein
and multiple fuel injectors 50 between the TDC locations of the
pistons. For example, each cylinder has two fuel injectors 50.
Preferably, fuel is fed to the fuel injectors 50 from a fuel source
160 that includes a rail/accumulator mechanism to which fuel is
pumped from a reservoir. A fuel return manifold 162 collects fuel
from the fuel injectors 50 and the fuel source for return to the
reservoir.
[0018] An engine control unit (ECU) 162 receives data from a
variety of sensors (not shown) that measure parameter values
related to operating conditions of the engine, the transmission,
and so on. The ECU 162 includes a fuel injection control
mechanization that implements fuel injection control procedures in
response to measured parameter values obtained from the sensors.
These control procedures cause the generation of output control
signals that are coupled to an electronic multichannel injector
driver 165. In response to the control signals, the injector driver
165 generates drive signals on separate dedicated channels to
operate the fuel injectors 50. In other words, the injector driver
165 electronically enables the operation of each fuel injector 50
independently of every other fuel injector 50.
[0019] Preferably, each fuel injector 50 includes or is associated
with an electrically-operated actuator (such as a solenoid) that
operates the injector. Preferably, the actuator is controlled by
respective drive signal produced by the injector driver 165. A
representative drive signal is illustrated by a pulse-width
modulated (PWM) waveform 167, for example. Each such waveform has a
first edge 168 that sets an actuator to a first state and a second
edge 169 that resets the actuator from the first to a second state.
Preferably, the first state opens the nozzle of the fuel injector
50, initiating emission of a pulse of fuel 60 (also called "an
injection") into the cylinder 40; while the second state closes the
nozzle of the fuel injector 50, terminating the injection.
Alternatively, the fuel injection system 100 may be equipped to
respond to other types and/or shapes of drive signals.
[0020] Presuming that pulse-width modulated waveforms are used to
operate the fuel injectors 50, the duration of any one injection
emitted by a fuel injector corresponds to the width of the drive
pulse: a narrow pulse produces an injection of short duration; a
wide pulse produces an injection of longer duration. The fuel
injection system 100 is designed to operate each injector in a
plurality of fuel injection modes that include one or more
injections. In a first mode of operation, a fuel injector emits a
single injection into a combustion chamber in order to initiate
combustion. In a second mode of operation, called a "split
injection", a fuel injector emits two or more injections into a
combustion chamber to initiate combustion: at least one first,
relatively narrow, injection (called a "pilot` injection) is
followed by a second, relatively longer, injection (called a "main
injection"). The pilot and main injections are separated by a time
interval. In order to produce split injections with well-defined
shapes and precisely-timed durations, the operations of the fuel
injection system 100 are also designed to observe a minimum time
interval (called "an inter-pulse gap" or IPG) measured between
successive edges of successive drive signal pulses. Failure to
adhere to the inter-pulse gap can result in overlapping injections
or variability in the quantity of fuel injected.
[0021] The fuel injection system 100 is further designed to
transition from single to split injection, and from split to single
injection, as required by engine operating conditions. Further,
with multiple independently-controlled fuel injectors for each
cylinder, the design of the fuel injection system 100 enables
transition from operating a single fuel injector per cylinder to
operating a plurality of fuel injectors per cylinder, and from
operating a plurality of fuel injectors per cylinder to operating a
single fuel injector per cylinder, as required by engine operating
conditions.
[0022] Fuel Injection with a Single Injector per Cylinder: With
reference to FIGS. 1 and 4, an opposed-piston engine in which each
cylinder has only a single fuel injector is constrained in that a
certain orifice area is necessary in order to introduce a fuel
charge in a given number of crank angle degrees at a particular
engine speed. This limitation can be detrimental to spray quality
and may adversely limit minimum pilot fuel available. Further, a
single injector actuated by a solenoid has limitations in that an
IPG must be observed in order to assure the previous injection has
completed and residual magnetism in the solenoid has decayed. A
single injector actuation (drive) signal curve 180 and fuel
injection rate curve 182 are shown in FIG. 4. The graph shows a
split injection including two pilot injections 182p1, 182p2, and a
main injection 182m. A first actuation pulse 180a1 starts at 1
millisecond (msec) and is followed by pilot injection 182p1
approximately 0.5 msec later. Following the end of the first pilot
injection 182p1, a second actuation pulse 180a2 starts at 2 msec.
The rising edge of the second actuation pulse 180a2 occurs about
0.75 msec after the falling edge of the first actuation pulse
180a1. Presume that 0.75 msec is the IPG. If the IPG is disregarded
and the second actuation pulse 180a2 starts prior to the end of the
first injection 182p1, then the quantity of injected fuel and
timing of the second pilot injection 182p2 can deviate from
intended values. This is due to reduced injection response time on
the second pilot injection 182p2 resulting in errors in both timing
and quantity. Manifestly the minimum interval imposed by the IPG
limits the number of injections that can be applied in a given
crank angle by a single injector.
[0023] Fuel Injection with Multiple Injectors Per Cylinder: With
reference to FIGS. 2 and 5, an opposed-piston engine includes at
least one cylinder equipped with multiple injectors actuated
sequentially and/or simultaneously. For example, as per FIG. 5, two
fuel injectors 50 are operated according to the actuation and
injection curves shown in FIG. 5. There are three pilot injections
shown, two (192p1 and 192p2) from a first of the fuel injectors 50,
and one (193p) from the second fuel injector. Presume that the two
actuation pulses 190a1 and 190a2 that cause the two pilot
injections 192p1 and 192p2 are subject to the same IPG as the fuel
injector of FIG. 1 (0.75 msec). The actuation pulse 191a causes the
third pilot injection 193p to occur between the two pilot
injections 190a1 and 190a2, thus providing three tightly-grouped
pilot injections occurring in the time a single injector can
provide a maximum of two pilot injections. This results in a
maximum number of injections, N.sub.max, in a given time. For
example, using two injectors N.sub.max is given by:
N.sub.max=N.sub.1 max+ (N.sub.1max-1), where N.sub.1 max is the
maximum number of injections from one fuel injector, under the
constraint of a minimum interval. With additional injectors and
overlapping injections provided by multiple fuel injectors, greater
numbers of injections can be achieved in a given time than can be
with a single fuel injector. Because the fuel injectors are
disposed at different circumferential positions on the periphery of
the cylinder, they inject into different regions of the combustion
chamber, and available air is not an issue with this method. The
main injections 192m+193m produce an aggregate main injection as
shown in FIG. 5 that results in substantially simultaneous
actuation of both injectors 50, as indicated by the alignment of
the two main actuation pulses 190m and 191m. This doubles the rate
of injection into the combustion chamber and cuts the duration of
the aggregated main injection in half.
[0024] An example of using multiple injectors in order to
rate-shape the injected quantity of an aggregated main injection is
shown in FIG. 6. As in FIG. 5, injection includes staggered split
injections from two fuel injectors that results in three tightly
grouped pilot injections. The group of pilot injections is followed
by a rate-shaped aggregate main injection 200m. As shown, the
second fuel injector is first actuated to create the first portion
200m1 of the main injection. After an appropriate delay, the first
fuel injector is also actuated so that both fuel injectors
introduce fuel simultaneously. As is evident in FIG. 6, fuel is
injected at a first rate during the first portion 200m1, and the
rate of injection increases in the second portion 200m2. The rate
of injection is thereby "shaped". Relative shifts of the main
actuation pulses and/or changes in their durations can produce
different shapes in the aggregate main injection. The ability to
rate-shape reduces pre-mixed spikes and allows for much smoother
combustion and reduced emissions.
[0025] In FIG. 6, a post injection 210 is shown following the
aggregate main injection 200m. The post injection 210 can be
produced by actuating the first injector alone, thus providing a
minimal fuel charge for the post injection. If desired, multiple
post injections can be applied by multiple actuations of either
injector or by sequential actuation of both injectors similar to
that described for the grouped pilot injections.
[0026] As should be evident, direct side injection in an
opposed-piston engine having a plurality of
electronically-controlled fuel injectors located in the same
cylinder allows for multiple degrees of freedom not available with
a single fuel injector. Injections can be simultaneous, sequential
or staggered thus affording very closely spaced injections and rate
shaping. These extra degrees of freedom offer enhanced performance
and emission possibilities. Using multiple fuel injectors allows
for the injector nozzle holes to be optimally sized with respect to
spray characteristics while at the same time providing the
flexibility of being able to increase the number of holes available
to allow for rapid introduction of the fuel charge. Conversely,
independently controlled fuel injectors allow for decreasing the
number of holes at low fuel demand in order to lengthen injection
time and to smooth combustion. Having the ability to actuate a
single injector or multiple injectors in a given cycle allows the
use of higher rail pressure at lower quantities, providing superior
spray quality in comparison to that available from a single
injector having high flow properties. Furthermore, by actuating
multiple injectors sequentially at various positions around the
periphery it is possible to have many injections of varying or
similar quantity introduced into the cylinder at various locations
and with full authority regarding the timing of said
injections.
[0027] Although fuel injection strategies for opposed-piston
engines have described with reference to representative
embodiments, it should be understood that various modifications can
be made without departing from the underlying principles.
Accordingly, the patent protection to be afforded these strategies
is limited only by the following claims.
* * * * *