U.S. patent application number 12/872146 was filed with the patent office on 2012-03-01 for system and method for operating an internal combustion engine.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Wontae Hwang, Adam Edgar Klingbeil, Roy James Primus.
Application Number | 20120048218 12/872146 |
Document ID | / |
Family ID | 43877351 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048218 |
Kind Code |
A1 |
Klingbeil; Adam Edgar ; et
al. |
March 1, 2012 |
SYSTEM AND METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE
Abstract
An internal combustion engine is operated in accordance with a
Miller cycle. The engine includes a piston disposed in the engine
cylinder and configured to reciprocate between a top dead center
position and a bottom dead center position of the engine cylinder.
An air intake valve is coupled to the cylinder. The air intake
valve is closed when the piston is about the bottom dead center
position in the engine cylinder. An exhaust valve is coupled to the
engine cylinder. The exhaust valve is opened for a predetermined
time period when the piston is about the bottom dead center
position of the engine cylinder after closing the intake valve so
as to exhaust a predetermined quantity of fresh charge from the
engine cylinder via the exhaust valve.
Inventors: |
Klingbeil; Adam Edgar;
(Ballston Lake, NY) ; Hwang; Wontae; (Clifton
Park, NY) ; Primus; Roy James; (Niskayuna,
NY) |
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
43877351 |
Appl. No.: |
12/872146 |
Filed: |
August 31, 2010 |
Current U.S.
Class: |
123/90.1 |
Current CPC
Class: |
Y02T 10/142 20130101;
F02D 13/028 20130101; Y02T 10/12 20130101; F02D 13/0269 20130101;
F02D 13/0273 20130101; F02D 23/02 20130101 |
Class at
Publication: |
123/90.1 |
International
Class: |
F01L 1/00 20060101
F01L001/00 |
Claims
1. A method for operating an internal combustion engine in
accordance with a Miller cycle, comprising: moving a piston from a
top dead center position towards a bottom dead center position in
an engine cylinder; closing an intake valve of the internal
combustion engine when the piston is about the bottom dead center
position in the engine cylinder; opening an exhaust valve for a
predetermined time period when the piston is about the bottom dead
center position of the engine cylinder after closing the intake
valve so as to exhaust a predetermined quantity of fresh charge
from the engine cylinder via the exhaust valve.
2. The method of claim 1, wherein the predetermined time period
corresponds to a predetermined degree of crank angle.
3. The method of claim 1, wherein about the bottom dead center
position comprises a crank angle of less than or equal to 90
degrees from the bottom dead center position of the engine
cylinder.
4. The method of claim 1, comprising operating the internal
combustion engine comprising a four-stroke engine.
5. The method of claim 1, comprising operating the internal
combustion engine comprising a two-stroke engine.
6. The method of claim 1, comprising opening the exhaust valve for
the predetermined time period when the piston is about the bottom
dead center position of the engine cylinder after closing the
intake valve during an intake stroke.
7. The method of claim 1, comprising opening the exhaust valve for
the predetermined time period when the piston is about the bottom
dead center position of the engine cylinder after closing the
intake valve during a compression stroke of the piston.
8. The method of claim 1, further comprising compressing intake air
in the engine cylinder after closing the exhaust valve when the
piston is moved from the bottom dead center position towards the
top dead center position of the engine cylinder during the
compression stroke of the piston.
9. The method of claim 1, wherein exhausting a predetermined
quantity of fresh charge from the engine cylinder via the exhaust
valve comprises reducing a compression ratio compared to an
expansion ratio of the internal combustion engine.
10. An internal combustion engine operated in accordance with a
Miller cycle, the internal combustion engine comprising: an engine
cylinder; a piston disposed in the engine cylinder and configured
to reciprocate between a top dead center position and a bottom dead
center position of the engine cylinder; an air intake valve coupled
to the cylinder; wherein the air intake valve is closed when the
piston is about the bottom dead center position in the engine
cylinder; and an exhaust valve coupled to the engine cylinder;
wherein the exhaust valve is opened for a predetermined time period
when the piston is about the bottom dead center position of the
engine cylinder after closing the intake valve so as to exhaust a
predetermined quantity of fresh charge from the engine cylinder via
the exhaust valve.
11. The engine of claim 10, wherein the predetermined time period
corresponds to a predetermined degree of crank angle.
12. The engine of claim 10, wherein about the bottom dead center
position comprises a crank angle of less than or equal to 90
degrees from the bottom dead center position of the engine
cylinder.
13. The engine of claim 10, wherein the internal combustion engine
comprises a four-stroke engine.
14. The engine of claim 10, wherein the internal combustion engine
comprises a two-stroke engine.
15. The engine of claim 10, wherein the exhaust valve is opened for
the predetermined time period when the piston is about the bottom
dead center position of the engine cylinder after closing the
intake valve during an intake stroke of the piston.
16. The engine of claim 10, wherein the exhaust valve is opened for
the predetermined time period when the piston is about the bottom
dead center position of the engine cylinder after closing the
intake during a compression stroke of the piston.
17. The engine of claim 10, wherein the internal combustion engine
has a lower compression ratio compared to an expansion ratio.
18. An internal combustion engine operated in accordance with a
Miller cycle, the internal combustion engine comprising: an engine
cylinder; a piston disposed in the engine cylinder and configured
to reciprocate between a top dead center position and a bottom dead
center position of the engine cylinder; an air intake valve coupled
to the cylinder; wherein the air intake valve is closed when the
piston is about the bottom dead center position in the engine
cylinder; and an exhaust valve coupled to the engine cylinder; a
controller communicatively coupled to the air intake valve and the
exhaust valve and configured to control at least one of the air
intake valve, the exhaust valve, wherein the exhaust valve is
opened for a predetermined time period when the piston is about the
bottom dead center position of the engine cylinder after closing
the intake valve so as to exhaust a predetermined quantity of fresh
charge from the engine cylinder via the exhaust valve.
19. The engine of claim 18, wherein the predetermined time period
corresponds to a predetermined degree of crank angle.
20. The engine of claim 18, wherein about the bottom dead center
position comprises a crank angle of less than or equal to 90
degrees from the bottom dead center position of the engine
cylinder.
21. The engine of claim 18, wherein the internal combustion engine
comprises a four-stroke engine.
22. The engine of claim 18, wherein the internal combustion engine
comprises a two-stroke engine.
23. The engine of claim 18, wherein the controller is configured to
open the exhaust valve for the predetermined time period when the
piston is about the bottom dead center position of the engine
cylinder after closing the intake valve during an intake stroke of
the piston.
24. The engine of claim 18, wherein the controller is configured to
open the exhaust valve for the predetermined time period when the
piston is about the bottom dead center position of the engine
cylinder after closing the intake valve during a compression stroke
of the piston
25. The engine of claim 18, wherein the engine has a lower
compression ratio compared to an expansion ratio.
Description
BACKGROUND
[0001] The invention relates generally to a system and method for
operating an internal combustion engine and, more specifically, to
a system and method for operating an internal combustion engine in
accordance with a Miller cycle for a turbocharged system.
[0002] In certain applications, the turbocharged engines are used
in different environmental conditions. These environmental
conditions can adversely affect engine performance, efficiency,
exhaust pollutants, and other engine characteristics. For example,
diesel engines operating in such environmental conditions are
subject to greater loads, lower atmospheric pressures, lower
temperatures due to colder climate, lower air density due to lower
atmospheric pressure, and so forth. At such conditions, the
compressor and the turbocharger speed can increase beyond a
preselected limit without suitable control measures.
[0003] Surge is one unstable operating condition of the compressor.
Most compressors have a stability limit that is defined by a
minimum flow rate on a pressure-rise versus flow-rate
characteristic curve. Surge margin refers to a margin of safety
between a normal operating point and a stability limit of the
compressor. Events, both external and internal to the compressor,
may occasionally move compressor operation to a point that is
beyond its stability limit, causing a surge condition.
[0004] A Miller cycle is a modification of a conventional Otto or
Diesel cycle in a four-stroke internal combustion engine. The
Miller cycle is aimed at reducing the effective compression ratio
while maintaining the expansion ratio. This lowers the in-cylinder
adiabatic compression temperature, which enables a reduction in
nitrogen oxide (NOx) emissions.
[0005] The Miller cycle has been traditionally implemented by
either closing the intake valve early before the end of the intake
stroke, or closing the intake valve late during the compression
stroke. In the prior method, the amount of intake charge is
reduced, and is expanded to a lower pressure when the piston
reaches bottom dead center (BDC), compared to the typical case
where intake valve is closed near BDC at the end of the intake
stroke. Because of the lower initial pressure, the pressure at the
end of the compression stroke is reduced, resulting in a lower
effective compression ratio. The latter method can be achieved by
keeping the intake valve open until the start of the compression
stroke, or closing the intake valve near the end of the intake
stroke and reopening it during the compression stroke. Compression
starts only when all the valves are closed in the compression
stroke, thus the effective compression ratio is reduced. The lower
amount of charge in the cylinder due to the Miller cycle would
result in a loss in power. Thus a supercharger or turbocharger is
typically used to compensate for this loss.
[0006] The Miller cycle typically requires increased boosting to
maintain sufficient airflow, often times pushing the compressor
closer to the surge limit. Redesign of the compressor increases the
cost and complexity of implementing the Miller cycle. In another
application, the Miller cycle is implemented together with a bypass
loop for allowing compressed air to bypass the engine and mix with
the exhaust stream. However, exhausting compressed air directly to
the turbine results in wastage of energy. Also, such a strategy is
not feasible in systems where an exhaust pressure is greater than
an intake pressure.
[0007] For these and other reasons there is need for embodiments of
the invention.
BRIEF DESCRIPTION
[0008] In accordance with one embodiment of the present invention,
a method for operating an internal combustion engine in accordance
with a Miller cycle is disclosed. The method includes moving a
piston from a top dead center position towards a bottom dead center
position in an engine cylinder and closing an intake valve of the
internal combustion engine when a piston is about the bottom dead
center position in the engine cylinder. The method further includes
opening an exhaust valve for a predetermined time period when the
piston is about the bottom dead center position of the engine
cylinder after closing the intake valve so as to exhaust a
predetermined quantity of fresh charge from the engine cylinder via
the exhaust valve.
[0009] In accordance with another embodiment of the present
invention, an internal combustion engine operated in accordance
with a Miller cycle is disclosed. The engine includes a piston
disposed in the engine cylinder and configured to reciprocate
between a top dead center position and a bottom dead center
position of the engine cylinder. An air intake valve is coupled to
the cylinder. The air intake valve is closed when the piston is
about the bottom dead center position in the engine cylinder. An
exhaust valve is coupled to the engine cylinder. The exhaust valve
is opened for a predetermined time period when the piston is about
the bottom dead center position of the engine cylinder after
closing the intake valve so as to exhaust a predetermined quantity
of fresh charge from the engine cylinder via the exhaust valve.
[0010] In accordance with another embodiment of the present
invention, an internal combustion engine operated in accordance
with a Miller cycle is disclosed. The engine includes a controller
communicatively coupled to the air intake valve and the exhaust
valve and configured to control at least one of the air intake
valve, the exhaust valve. The exhaust valve is opened for a
predetermined time period when the piston is about the bottom dead
center position of the engine cylinder after closing the intake
valve so as to exhaust a predetermined quantity of fresh charge
from the engine cylinder via the exhaust valve.
DRAWINGS
[0011] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0012] FIG. 1 is a diagrammatical representation of a turbocharged
system having an internal combustion engine operated in accordance
with embodiments of the present invention;
[0013] FIG. 2 is a diagrammatical representation of an internal
combustion engine in accordance with the embodiment of FIG. 1;
and
[0014] FIG. 3 is a valve lift profile of an intake valve and an
exhaust valve of an internal combustion engine operated in
accordance with embodiments of the present invention.
DETAILED DESCRIPTION
[0015] In accordance with certain embodiments of the present
invention, a method of operating an internal combustion engine in
accordance with a Miller cycle is disclosed. The method includes
moving a piston from a top dead center position towards a bottom
dead center position in an engine cylinder and closing an intake
valve of the internal combustion engine when a piston is about the
bottom dead center position in the engine cylinder. The method
includes opening an exhaust valve for a predetermined time period
when the piston is about the bottom dead center position of the
engine cylinder after closing the intake valve during a compression
stroke of the piston so as to exhaust a predetermined quantity of
fresh charge from the engine cylinder via the exhaust valve. In
accordance with a specific embodiment of the present invention an
internal combustion engine operated in accordance with a Miller
cycle is disclosed. As discussed herein below, the exhaust valve of
the engine is re-opened after closure of the intake valve during a
compression stroke of the engine. In accordance with the
embodiments of the present invention, the Miller cycle enables
reduction in nitrogen oxide emissions with little or no penalty in
fuel economy. This facilitates further optimization of the engine,
whereby nitrogen oxide emissions are maintained within limits and
fuel economy is improved. It should be noted herein although the
"fresh charge" discussed herein is with reference to "fresh charge
of air", in certain other embodiments; the "fresh charge" may also
include "fresh charge of recirculated exhaust gas".
[0016] Referring to FIG. 1, a turbocharged system 10 in accordance
with certain embodiments of the present technique is disclosed. In
the illustrated embodiment, the turbocharged system 10 includes a
turbocharger 12 and a compression-ignition engine, e.g., diesel
engine 14. The illustrated engine 14 includes an air intake
manifold 16 and an exhaust manifold 18. An intake valve 17 is
coupled to the intake manifold 16 and an exhaust valve 19 is
coupled to the exhaust manifold 18. The turbocharger 12 includes a
compressor 20 and a turbine 22 and is operated to supply compressed
air to the intake manifold 16 for combustion within a cylinder 21.
The turbine 22 is coupled to the exhaust manifold 18, such that the
exhaust gases expand through the turbine 22, putting work onto and
rotating the turbocharger shaft 24 connected to the compressor 20.
The compressor 20 draws ambient air through a filter 26 and
provides compressed air to a heat exchanger 28. The temperature of
air is increased due to compression through the compressor 20. The
compressed air flows through the heat exchanger 28 such that the
temperature of air is reduced prior to delivery into the intake
manifold 16 of the engine 14.
[0017] In the illustrated embodiment, the turbocharged system 10
also includes a controller 30 communicatively coupled to the intake
valve 17 and the exhaust valve 19 and configured to control at
least one of the intake valve 17, the exhaust valve 19. In one
embodiment, the controller 30 is an electronic logic controller
that is programmable by a user. In another embodiment, the
controller 30 is an electronic valve-timing controller for the
engine 14 and specifically an exhaust valve-timing controller. A
plurality of fuel injection pumps 32 drive a plurality of fuel
injectors 34 for injecting fuel into the plurality of cylinders 21
of the engine 14. A piston 36 is slidably disposed in each cylinder
21 and reciprocates between a top dead center and a bottom dead
center positions. As discussed in greater detail below, the engine
14 is operated in accordance with a Miller cycle. Instead of
manipulating the intake valve closing time, the exhaust valve 19 is
re-opened after closing of the inlet valve 17 for a short time
period during the compression stroke to reduce the compression
ratio.
[0018] Referring to FIG. 2, the engine 14 in accordance with the
embodiment of FIG. 1 is illustrated. As discussed above, the intake
valve 17 is coupled to the intake manifold 16 and the exhaust valve
19 is coupled to the exhaust manifold 18. The piston 36 is slidably
disposed in each cylinder 21 and reciprocates between a top dead
center position (represented as TDC) and a bottom dead center
position (represented as BDC). The piston 36 is coupled to a
crankshaft 38. In one embodiment, the engine 14 is a four-stroke
engine. In another embodiment, the engine 14 is a two-stroke
engine.
[0019] For a typical 2-stroke cycle engine and a 4-stroke cycle
engine, a device, such as a compressor, is used to increase the
flow of air into the engine cylinder. The compressor compresses the
air and forces it into the intake manifold of the engine. Thus,
more air at constant pressure is available as required during the
cycle of operation. The increased amount of air, as a result of
compressor action, fills the cylinder with a fresh charge. During
the scavenging process, the increased amount of air facilitates to
clear the combustion gases from the cylinder. In a two stroke cycle
engine, the scavenging process occurs during a latter part of the
piston down stroke (expansion stroke) and the early part of the
piston upstroke (compression stroke). In a four stroke cycle
engine, scavenging occurs when the piston is about the top dead
center position during the latter part of a piston upstroke
(exhaust) and the early part of a piston down stroke (intake
stroke). The intake and exhaust valves are both open during the
scavenging process. The overlap of intake and exhaust valve timings
permits the air from the blower to pass through the cylinder into
the exhaust manifold, cleaning out the exhaust gases from the
cylinder and, at the same time, cooling the hot engine parts.
[0020] As discussed previously, surge is one unstable operating
condition of the compressor. Events, both external and internal to
the compressor, may occasionally move compressor operation to a
point that is beyond its stability limit, causing a surge
condition. The engine is operated in accordance with a Miller cycle
to reduce compressor surge. Conventional implementation of Miller
cycle in the engine involved altering the valve closing timing of
an intake valve of the engine cylinder. Such implementation of
Miller cycle is difficult to achieve with typical two-stroke
engines, where the intake valve opening and closing event is often
symmetric about bottom dead center. In accordance with the
embodiments of the present invention, instead of manipulating the
intake valve closing time, the exhaust valve is re-opened after
closing of the inlet valve for a short period of time during the
compression stroke to reduce the compression ratio. Implementation
of Miller cycle in accordance with the embodiments of the present
invention is equally feasible on both 2-stroke and 4-stroke
engines.
[0021] As known to one skilled in that art, the compression ratio
of an internal-combustion engine is a value that represents the
ratio of the volume of a combustion chamber; from a largest
capacity to a smallest capacity. In other words, compression ratio
is the ratio between the volume of the combustion chamber when the
piston is at the bottom dead center position, and the volume of the
combustion chamber when the piston is at the top dead center
position. A geometric compression ratio can be changed with a
movable plunger at the top of the cylinder head. The effective
compression ratio can be reduced from the geometric ratio by using
a variable valve actuation (i.e. variable valve timing permitting
Miller cycle) or by implementing a fixed-cam Miller-cycle
strategy.
[0022] Geometric compression ratio (CR.sub.Geom) of the engine 14
is represented as:
CR Geom = V BDC V TDC ##EQU00001##
where V.sub.BDC is the volume of the combustion chamber at the
bottom dead center position in the cylinder 21 and V.sub.TDC is the
volume of the combustion chamber at the top dead center position in
the cylinder 21.
[0023] Miller compression ratio (CR.sub.Miller) of the engine 14 is
represented as:
CR Miller = V EvC V TDC ##EQU00002##
where V.sub.EVC is the effective volume of the combustion chamber
of the cylinder 21 during compression stroke.
[0024] In accordance with the embodiment of the present invention,
the exhaust valve 19 is re-opened after intake valve 17 is closed.
In one embodiment, the exhaust valve 19 is re-opened after the
intake valve 17 is closed at the bottom dead center position. In a
specific embodiment, the exhaust valve 19 is opened after a
predetermined time period after closure of the intake valve 17
during the compression stroke. In another specific embodiment, if
the intake valve 17 is closed early, for example, 40 degrees before
bottom dead center position; the exhaust valve 19 is opened while
the piston 36 is still travelling down (nominally the intake
stroke, although the intake valve 17 has closed). In such an
embodiment, the exhaust valve 19 is also open during the early part
of the compression stroke.
[0025] In accordance with another embodiment, if the intake valve
17 is closed early, for example, 40 degrees before bottom dead
center position; the exhaust valve 19 is opened at bottom dead
center or during the compression stroke so that the pressure in the
cylinder 21 is sufficient to prevent exhaust gas from being drawn
into the cylinder 21 only to be re-exhausted during the compression
stroke. In accordance with yet another embodiment, the intake valve
17 is closed late, for example, 40 degrees after the bottom dead
center position and the exhaust valve 19 is opened during the
compression stroke after the intake valve 17 has closed.
[0026] In accordance with the embodiment of the present invention,
the valve timing of the exhaust valve 19 is altered compared to a
conventional Otto or diesel cycle engine. As the piston 36 moves
upwards towards the top dead center position during the early part
of the compression stroke, the fresh charge is partially expelled
through the exhaust manifold 18 by opening the exhaust valve 19.
Typically, such loss of charge air would result in a loss of
performance due to less available air for the combustion reactants.
However, in the Miller cycle, the loss of trapped air mass in the
cylinder 21 can be compensated by increasing the intake manifold
pressure. In accordance with the embodiments of the present
invention, the Miller cycle is implemented in such a way that
significant compression of the cylinder contents starts after the
piston 36 has pushed out the "extra" charge and the exhaust valve
19 is closed. In one embodiment, the exhaust valve 19 may be closed
at around 20% to 30% into the compression stroke. In other words,
the actual compression occurs in the latter 70% to 80% of the
compression stroke.
[0027] Referring to FIG. 3, lift profile of the exhaust valve and
the intake valve of the engine in accordance with an exemplary
embodiment of the present technique. The lift profile of the
exhaust valve is represented by the reference numeral 40 and the
lift profile of the intake valve is represented by the reference
numeral 42. With reference to the lift profile 40, the flat
portions 44, 46, 48 represent exhaust valve closed position, and
the projected portion 50, 52 represent exhaust valve open position.
With reference to the lift profile 42, the flat portions 54, 56
represent intake valve closed position, and the projected portion
58 represent intake valve open position.
[0028] As discussed previously, during the scavenging process, the
increased amount of air facilitates to clear the combustion gases
from the cylinder. In a two-stroke cycle engine, the scavenging
process occurs during a latter part of the piston down stroke
(expansion stroke) and the early part of the piston upstroke
(compression stroke). In a four-stroke cycle engine, scavenging
occurs when the piston is about the top dead center position during
the latter part of a piston upstroke (exhaust) and the early part
of a piston down stroke (intake stroke). The intake and exhaust
valves are both open during the scavenging process. In the
illustrated embodiment, the scavenging process is indicated by the
area 60. The area 60 is the overlapping area of the projected
portion 50 indicative of exhaust valve open position and the
projected portion 58 indicative of the intake valve open position.
The scavenging typically occurs when the piston is about the top
dead center position in the engine cylinder.
[0029] In accordance with the exemplary Miller cycle of the present
technique, when the piston is about the bottom dead center position
of the engine cylinder, the exhaust valve is opened (in other words
re-opened) after closing the intake valve so as to exhaust a
predetermined quantity of intake air from the engine cylinder via
the exhaust manifold. This is clearly evident from FIG. 3, which
shows the opening of the intake valve represented by the projection
52 after closing of the exhaust valve at point 62. The
predetermined time period for maintaining the exhaust valve in open
position corresponds to a predetermined degree of crank angle. It
should be noted herein that the term "about the bottom dead center
position" for operating the exemplary cycle may correspond to a
crank angle of less than or equal to 90 degrees from the bottom
dead center position.
[0030] In one embodiment, the closing of the intake valve and the
re-opening of the exhaust valve may occur at the same instant. In
another embodiment, the exhaust valve is re-opened after a
predetermined time period after closing the intake valve. In a
specific embodiment, the intake valve is closed at the bottom dead
center position of the piston and the exhaust valve is opened
during the compression stroke. In another specific embodiment, if
the intake valve is closed early before bottom dead center
position; the exhaust valve is opened while the piston is still
travelling down and also maintained in an open state during the
early part of the compression stroke.
[0031] In accordance with the embodiments of the present technique,
the compression ratio is reduced by opening the exhaust valve early
in the compression stroke after closing the intake valve. Under
normal (non-Miller) operation, the compression ratio is effectively
equal to the expansion ratio. In accordance with the Miller cycle
of the present technique, the compression ratio is reduced without
changing the expansion ratio. The effective compression ratio is
reduced because the mixture in the cylinder does not undergo
compression until the exhaust valve is closed during the
compression stroke. This effectively reduces gas temperatures,
enabling the start of combustion to be advanced without increasing
the nitrogen oxide emission levels.
[0032] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *