U.S. patent application number 13/782802 was filed with the patent office on 2013-07-11 for egr for a two-stroke cycle engine without a supercharger.
This patent application is currently assigned to Achates Power, Inc.. The applicant listed for this patent is Achates Power, Inc.. Invention is credited to Eric P. Dion.
Application Number | 20130174548 13/782802 |
Document ID | / |
Family ID | 48742946 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130174548 |
Kind Code |
A1 |
Dion; Eric P. |
July 11, 2013 |
EGR for a Two-Stroke Cycle Engine without a Supercharger
Abstract
A two-stroke cycle, turbo-driven, opposed-piston engine with one
or more ported cylinders and uniflow scavenging has no
supercharger. The engine includes a high pressure EGR loop and a
pump in the EGR loop to boost the pressure of the recirculated
exhaust products.
Inventors: |
Dion; Eric P.; (Encinitas,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Achates Power, Inc.; |
San Diego |
CA |
US |
|
|
Assignee: |
Achates Power, Inc.
San Diego
CA
|
Family ID: |
48742946 |
Appl. No.: |
13/782802 |
Filed: |
March 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13068679 |
May 16, 2011 |
|
|
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13782802 |
|
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Current U.S.
Class: |
60/605.2 ;
123/568.11 |
Current CPC
Class: |
F02B 37/02 20130101;
F02B 25/08 20130101; F02M 26/05 20160201; F02B 25/06 20130101; F02B
2075/025 20130101; F02B 75/02 20130101; F02M 26/08 20160201; F02M
26/23 20160201; F02B 2275/14 20130101; Y02T 10/12 20130101; F02B
75/28 20130101; Y02T 10/121 20130101; F02D 41/0007 20130101; F02B
29/0406 20130101; F02B 47/08 20130101; F02D 41/0077 20130101; F01B
7/02 20130101; F02B 37/04 20130101; F02M 26/34 20160201; F02B 39/10
20130101; Y02T 10/144 20130101; F02B 37/10 20130101 |
Class at
Publication: |
60/605.2 ;
123/568.11 |
International
Class: |
F02B 47/08 20060101
F02B047/08 |
Claims
1. A uniflow-scavenged, two-stroke cycle engine including at least
one cylinder with piston-controlled exhaust and intake ports and a
charge air channel coupled to at least one intake port of the
engine, in which the engine has no supercharger and comprises: a
high pressure exhaust gas recirculation (EGR) loop having a loop
input coupled to an exhaust port of the cylinder and a loop output
coupled to the charge air channel; a pump in the EGR loop to pump
exhaust gas through the EGR loop into the charge air channel; and,
a turbocharger with a charge air output coupled to the charge air
channel, a turbine input coupled to the exhaust port, and a turbine
output coupled to an exhaust output.
2. The uniflow-scavenged, two-stroke cycle engine of claim 1, in
which the charge air channel includes at least one cooler, wherein
the loop output is coupled in series with the at least one
cooler.
3. The uniflow-scavenged, two-stroke cycle engine of claim 2, in
which the EGR loop includes a variable valve between the loop input
and the pump.
4. The uniflow-scavenged, two-stroke cycle engine of claim 3, in
which the pump is a variable capacity pump.
5. The uniflow-scavenged, two-stroke cycle engine of claim 1,
further including a turbocharger with a charge air output coupled
to the charge air channel and a turbine input coupled to the
exhaust port.
6. The uniflow-scavenged, two-stroke cycle engine of claim 5, in
which the turbocharger includes a power-assist system.
7. The uniflow-scavenged, two-stroke cycle engine of claim 1,
further including a power-assist system coupled to the
turbocharger.
8. A uniflow-scavenged, opposed-piston engine including at least
one cylinder with piston-controlled exhaust and intake ports, an
exhaust channel coupled to at least one exhaust port of the engine,
and a charge air channel coupled to at least one intake port of the
engine, in which the engine has no supercharger and comprises: a
power-assisted turbocharger with a compressor output coupled to the
charge air channel, a turbine input coupled to the exhaust channel,
and a turbine output coupled to an exhaust output an exhaust gas
recirculation (EGR) loop having a loop input coupled to the exhaust
channel upstream of the turbine input and a loop output coupled to
the charge air channel downstream of the compressor output; an
electrically-driven pump in the EGR loop to pump exhaust gas
through the EGR loop into the charge air channel; an
electrically-controlled variable valve in the EGR loop between the
loop input and the pump; and, a control unit connected to provide
control signals for the power-assisted turbocharger, the pump, and
the valve.
9. The uniflow-scavenged, opposed-piston engine of claim 8, in
which the EGR loop further includes an EGR cooler in series with
the pump.
10. A method of operating a non-supercharged, uniflow-scavenged,
opposed-piston engine with one or more cylinders, in which charge
air is pressurized and then cooled in at least one cooler and
provided to an intake port of each of the one or more cylinders, by
pumping engine exhaust gas in a high pressure exhaust gas
recirculation (EGR) loop to an input of the at least one air charge
cooler.
Description
PRIORITY AND RELATED APPLICATIONS
[0001] This application is a continuation-in-part of
commonly-assigned U.S. patent application Ser. No. 13/068,679,
filed May 16, 2011, which claims priority to U.S. provisional
application for patent 61/395,845 filed May 18, 2010, and to U.S.
provisional application for patent 61/401,598 filed Aug. 16,
2010.
[0002] This application contains subject matter related to that of
commonly-assigned PCT application US2013/026737, filed Feb. 19,
2013.
BACKGROUND
[0003] The field is two-stroke cycle internal combustion engines.
Particularly, the field relates to ported, uniflow-scavenged,
two-stroke cycle engines with exhaust gas recirculation. More
particularly, the field includes two-stroke cycle engines with one
or more ported cylinders and uniflow scavenging in which an exhaust
gas recirculation (EGR) construction provides a portion of the
exhaust gasses produced by the engine in previous cycles for
mixture with incoming charge air to control the production of NOx
during combustion.
[0004] A two-stroke cycle engine is an internal combustion engine
that completes a power cycle with a single complete rotation of a
crankshaft and two strokes of a piston connected to the crankshaft.
One example of a two-stroke cycle engine is an opposed-piston
engine in which a pair of pistons is disposed in opposition in the
bore of a cylinder for reciprocating movement in opposing
directions. The cylinder has inlet and exhaust ports that are
spaced longitudinally so as to be disposed near respective ends of
the cylinder. The opposed pistons control the ports, opening
respective ports as they move to their bottom center (BC)
locations, and closing the ports as they move toward their top
center (TC) locations. One of the ports provides passage of the
products of combustion out of the bore, the other serves to admit
charge air into the bore; these are respectively termed the
"exhaust" and "intake" ports.
[0005] In FIG. 1, a two-stroke cycle internal combustion engine 49
is embodied by an opposed-piston engine having at least one ported
cylinder 50. For example, the engine may have one ported cylinder,
two ported cylinders, three ported cylinders, or four or more
ported cylinders. Each cylinder 50 has a bore 52 and exhaust and
intake ports 54 and 56 formed or machined in respective ends
thereof. The exhaust and intake ports 54 and 56 each include one or
more circumferential arrays of openings in which adjacent openings
are separated by a solid bridge. In some descriptions, each opening
is referred to as a "port"; however, the construction of a
circumferential array of such "ports" is no different than the port
constructions shown in FIG. 1. Exhaust and intake pistons 60 and 62
are slidably disposed in the bore 52 with their end surfaces 61 and
63 opposing one another. The exhaust pistons 60 are coupled to a
crankshaft 71, the intake pistons are coupled to the crankshaft
72.
[0006] When the pistons 60 and 62 of a cylinder 50 are at or near
their TC positions, a combustion chamber is defined in the bore 52
between the end surfaces 61 and 63 of the pistons. Fuel is injected
directly into the combustion chamber through at least one fuel
injector nozzle 100 positioned in an opening through the sidewall
of a cylinder 50.
[0007] With further reference to FIG. 1, the engine 49 includes an
air management system 51 that manages the transport of charge air
provided to, and exhaust gas produced by, the engine 49. A
representative air management system construction includes a charge
air subsystem and an exhaust subsystem. In the air management
system 51, the charge air subsystem includes a charge air source
that receives intake air and processes it into charge air, a charge
air channel coupled to the charge air source through which charge
air is transported to the at least one intake port of the engine,
and at least one air cooler in the charge air channel that is
coupled to receive and cool the charge air (or a mixture of gasses
including charge air) before delivery to the intake port or ports
of the engine. Such a cooler can comprise an air-to-liquid and/or
an air-to-air device, or another cooling device. The exhaust
subsystem includes an exhaust channel that transports exhaust
products from exhaust ports of the engine to an exhaust pipe.
[0008] With reference to FIG. 1, the air management system 51
includes a turbocharger 120 with a turbine 121 and a compressor
that rotate on a common shaft 123. The turbine 121 is coupled to
the exhaust subsystem and the compressor 122 is coupled to the
charge air subsystem. The turbocharger 120 extracts energy from
exhaust gas that exits the exhaust ports 54 and flows into the
exhaust channel 124 directly from the exhaust ports 54, or from an
exhaust manifold 125. In this regard, the turbine 121 is rotated by
exhaust gas passing through it. This rotates the compressor 122,
causing it to generate charge air by compressing intake air. In
some instances, the charge air subsystem includes a supercharger
110; in these instances, the charge air output by the compressor
122 flows through a charge air channel 126 to a cooler 127, whence
it is pumped by the supercharger 110 to the intake ports. Air
compressed by the supercharger 110 can be output through a cooler
129 to an intake manifold 130. The intake ports 56 receive charge
air pumped by the supercharger 110, through the intake manifold
130. Preferably, but not necessarily, in multi-cylinder
opposed-piston engines, the intake manifold 130 is constituted of
an intake plenum that communicates with the intake ports 56 of all
cylinders 50.
[0009] The air management construction shown in FIG. 1 is equipped
to reduce NOx emissions produced by combustion by recirculating
exhaust gas through the ported cylinders of the engine. The
recirculated exhaust gas is mixed with charge air to lower peak
combustion temperatures, which lowers NOx emissions. This process
is referred to as exhaust gas recirculation ("EGR"). The EGR
construction shown in FIG. 1 utilizes exhaust gasses transported
via an EGR loop external to the cylinder into the incoming stream
of fresh intake air in the charge air subsystem. The recirculated
gas flows through a conduit 131 under the control of the valve
138.
[0010] EGR constructions for a uniflow-scavenged two-stroke cycle
opposed-piston engines require a positive pressure differential
from the intake manifold to the exhaust manifold in order to
scavenge the cylinders during their port open periods. Thus, the
pressure in the intake port of a cylinder must always be greater
than in the exhaust port in order for exhaust gas to flow through
the EGR channel into the charge air subsystem. In instances
illustrated by FIG. 1, a supercharger in the charge air channel
provides this positive pressure. However, there are other instances
in which a turbo-charged opposed-piston engine may not include a
supercharger. In such cases, there is a need to ensure positive
flow of recirculated exhaust gasses for effective EGR
operation.
SUMMARY
[0011] A solution to the problem is to equip an EGR loop of a
turbo-driven opposed-piston engine with a pump in the EGR loop to
boost the pressure of the recirculated exhaust products.
[0012] In one aspect, EGR is provided by an EGR loop having an
input coupled to an exhaust port of the cylinder and a loop output
coupled to the charge air channel. A pump in the EGR loop generates
a pressure differential between the exhaust port and the charge air
channel that causes the exhaust gas to flow through the EGR loop to
the charge air channel where it mixes with charge air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a conceptual schematic diagram of a two-stroke
cycle engine of the opposed-piston type in which aspects of an air
management system with EGR are illustrated.
[0014] FIG. 2 is a conceptual schematic drawing illustrating a
construction for EGR in a turbocharged two-stroke cycle
opposed-piston engine without a supercharger.
DETAILED DESCRIPTION
[0015] The EGR construction described in this specification is
presented in an explanatory context that includes a
uniflow-scavenging, two-stroke cycle engine of a type having at
least one ported cylinder in which a pair of pistons is disposed
with their end surfaces in opposition. A "ported" cylinder includes
one or more of intake and exhaust ports formed or machined in a
sidewall thereof. This explanatory context is intended to provide a
basis for understanding a specific EGR construction embodiment by
way of an illustrative example.
[0016] With reference to FIG. 2, an opposed-piston engine having a
construction similar to that of the engine seen in FIG. 1 is
equipped with an EGR loop that channels exhaust gas from the
exhaust subsystem into the charge air subsystem, but without the
aid of a supercharger in the charge air subsystem. Preferably, the
EGR loop construction is a high pressure configuration. In this
regard, a high pressure EGR loop circulates exhaust gas obtained
from the exhaust channel 124 through a loop input upstream (prior
to the input) of the turbine 121 to a mixing point downstream
(following the outlet) of the compressor 122. In this EGR loop the
EGR valve 138 is operated to shunt a portion of the exhaust gas
from the exhaust manifold 125 through the conduit 131 to be mixed
with charge air output by the compressor 122 into the conduit 126.
If no exhaust/air mixing is required the EGR valve 138 is fully
shut and charge air with no exhaust gas is delivered to the
cylinders. As the EGR valve 138 is increasingly opened, an
increasing amount of exhaust gas is mixed into the charge air. This
loop subjects the exhaust gas to the cooling effects of the cooler
127. A dedicated EGR cooler 129 can be incorporated into the
conduit 131 in series with the valve 138.
[0017] EGR loop construction including a pump: The high-pressure
EGR loop construction seen in FIG. 2 includes an EGR pump 200 in
series with the EGR valve 138. The outlet of the valve 138 is
connected to the input of the EGR pump 200 whose purpose is to
raise the pressure of recirculated exhaust gas from the level in
the exhaust manifold 125 to the level in the intake manifold 130.
The pressure is applied by the pump 200 from a point in the conduit
131, as opposed to the application of pressure in the charge air
subsystem by a supercharger. This pressure creates a pressure
differential between the intake and exhaust manifolds that pumps a
portion of exhaust gas from the exhaust manifold 125 to the conduit
126 where it is mixed with the charge air and recirculated
therewith into the intake manifold 130. Preferably, the pump 200 is
an electrically-controlled, variable-speed pump, but other pump
types (hydraulically-controlled, for example) are possible.
[0018] Power-assisted turbocharger: It is useful that the
turbocharger 120 be assisted In order to ensure a continuous
positive pressure differential across the manifolds 125, 130 while
the engine 49 is operating. In this regard, the turbocharger 120
includes a power-assist system 210, which can comprise, for example
an electric motor/generator unit, that boosts turbocharger
operation during start and low load conditions so as to add energy
to the charge air flow when unassisted turbocharger operation is
inadequate for it. Alternative turbo power-assist devices include
hydraulic or pneumatic mechanisms. A turbocharger with a
power-assist system is referred to as a "power-assisted
turbocharger."
[0019] Control mechanization: An EGR control process for an EGR
system that utilizes the construction illustrated in FIG. 2 is
executed by an electronic control unit (ECU) 149 in response to
specified engine operating conditions by automatically operating
the valve 138, the pump 200, and the power assist system 210. Of
course, operation of valves, throttles, and other associated
elements that may be used for EGR and air management control can
include any one or more of electrical, pneumatic, mechanical, and
hydraulic actuating operations. For fast, precise automatic
operation, it is preferred that valves, including the EGR valve
138, be high-speed, high-resolution, computer-controlled devices
with a continuously-variable settings.
[0020] Preferably an EGR control process automatically operates the
EGR system described and illustrated herein based upon one or more
parameters relating to recirculated exhaust gas and to a mixture of
recirculated exhaust gas and charge air. Parameter values are
determined by a combination of one or more of sensors,
calculations, and table lookup so as to manage the values of
individual parameters and one or more ratios of EGR and mixture
parameters in one or more cylinders.
[0021] An EGR construction for a two-stroke cycle engine without a
supercharger has been described with reference to an opposed-piston
engine having two crankshafts; however, it should be understood
that various aspects of this EGR system can be applied to
opposed-piston engines with one or more crankshafts. Moreover,
various aspects of this EGR construction can be applied to
opposed-piston engines with ported cylinders disposed in
opposition, and/or on either side of one or more crankshafts.
Accordingly, the protection afforded to this construction is
limited only by the following claims.
* * * * *