U.S. patent application number 13/920724 was filed with the patent office on 2013-12-19 for system and method for the production of compressed fluids.
The applicant listed for this patent is Regents of the University of Minnesota. Invention is credited to William Keith Durfee, David B. Kittelson, Lei Tian.
Application Number | 20130333368 13/920724 |
Document ID | / |
Family ID | 49754657 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130333368 |
Kind Code |
A1 |
Durfee; William Keith ; et
al. |
December 19, 2013 |
SYSTEM AND METHOD FOR THE PRODUCTION OF COMPRESSED FLUIDS
Abstract
The invention herein described consists of a single-cylinder
free-piston engine system comprising a combustion cylinder, a
compression cylinder, a seal between the two cylinders and a piston
assembly, capable of being produced in a miniature scale (e.g.,
less than 10 cubic centimeters volume). The combustion cylinder
consists of a holding chamber wherein fuel enters through a fuel
inlet port before combustion, a combustion chamber wherein
combustion occurs according to an HCCI process, after which the
excess fuel and exhaust leaves the engine system through a port for
exhaust, and a port extending from the holding chamber to the
combustion chamber. The compression cylinder comprises a
compression chamber wherein a compressible a compressible fluid
enters through an inlet port, is compressed by the single-cylinder
engine system, and the compressed fluid exits through an outlet
port, and a rebound chamber wherein energy from the combustion
process is conserved by a rebound element.
Inventors: |
Durfee; William Keith;
(Edina, MN) ; Kittelson; David B.; (Minneapolis,
MN) ; Tian; Lei; (Minneapolis, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Regents of the University of Minnesota |
St. Paul |
MN |
US |
|
|
Family ID: |
49754657 |
Appl. No.: |
13/920724 |
Filed: |
June 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61660981 |
Jun 18, 2012 |
|
|
|
Current U.S.
Class: |
60/370 ;
417/364 |
Current CPC
Class: |
A61H 1/0266 20130101;
A61H 2201/164 20130101; A61H 1/0237 20130101; F02B 71/045 20130101;
A61H 2201/12 20130101; F01B 11/04 20130101; A61H 2201/165
20130101 |
Class at
Publication: |
60/370 ;
417/364 |
International
Class: |
F01B 11/04 20060101
F01B011/04 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] This invention was made with Government support under grant
No. EEC-0540834, awarded by the National Science Foundation. The
Government has certain rights in this invention.
Claims
1. A system for providing pressurized or compressed fluid
comprising a fluid pumping/compression cylinder coupled to a
combustion cylinder and a rebound chamber, and a piston assembly
contained at least partially and capable of movement within the
combustion cylinder and the pumping/compression cylinder, wherein:
the combustion cylinder comprises a holding chamber on a first side
of a combustion piston, the holding chamber comprising at least a
fuel inlet; and a combustion chamber on a second side of the
combustion piston; wherein the holding chamber and the combustion
chamber may be connected by at least one passage that is openable
and closeable by movement of the combustion piston; and wherein the
pumping/compression cylinder comprises a fluid chamber on a first
side of a pumping/compression piston; and wherein the rebound
chamber comprises a rebound system; wherein the pumping/compression
chamber comprises at least one inlet and at least one outlet.
2. The system of claim 1 wherein the piston assembly is a free
piston assembly and is not connected to a crankshaft.
3. The system of claim 1 wherein the piston assembly comprises a
piston rod connected on one end to a combustion piston head and on
the other end to a compression piston head.
4. The system of claim 1 wherein the piston assembly comprises a
starting element.
5. The system of claim 4 wherein the starting element comprises a
compressed fluid starter, an electromagnetic starter, a
spring-loaded starter, or a starting handle.
6. The system of claim 4 wherein the starting element comprises a
bar extending beyond the outer cylinder.
7. The system of claim 1 wherein the compression cylinder comprises
the rebound chamber.
8. The system of claim 1 wherein the compression chamber comprises
the rebound chamber.
9. The system of claim 1 wherein the holding chamber comprises the
rebound chamber.
10. The system of claim 1 wherein the rebound system comprises an
elastic element.
11. The system of claim 10 wherein the elastic element comprises a
spring.
12. The system of claim 10 wherein the elastic element comprises a
pneumatic or hydraulic system.
13. The system of claim 1 wherein the combustion chamber is
configured to utilize loop-flow scavenging to remove exhaust.
14. The system of claim 1 wherein the combustion chamber includes
at least one inlet port and at least one exhaust port and wherein
the orientation of the inlet port relative to the exhaust port
enables scavenging.
15. The system of claim 19 wherein the inlet ports and exhaust
ports are positioned such that as the piston assembly moves away
from the combustion chamber, the exhaust ports are exposed before
the inlet ports are exposed.
16. The system of claim 20 wherein the exposure of the port for
exhaust and the inlet port or ports are controlled electronically
through a sensory assembly.
17. The system of claim 1 comprising a seal coupled to the
combustion cylinder and the compression cylinder so that fuel is
substantially prevented from escaping from the combustion cylinder
into the compression cylinder.
18. The system of claim 17 wherein the seal comprises a jaw
seal.
19. The system of claim 18 wherein the seal comprises polyether
ether ketone.
20. The system of claim 1 wherein the compression cylinder
comprises a means for preventing collisions between metal
elements.
21. The system of claim 20 wherein the means for preventing
collisions comprises an elastic element.
22. The system of claim 21 wherein the means for preventing
collisions comprises a rubber bumper.
23. A method for providing compressed fluid comprising the steps
of: intaking fuel and oxygen within a combustion chamber;
compressing fuel and oxygen by a piston within the combustion
chamber by a first movement of a piston assembly and causing
ignition of the fuel and oxygen mixture; combusting the fuel and
oxygen mixture; causing a second movement of a piston assembly as a
result of the combustion within the combustion chamber, wherein the
second movement is opposite in direction from the first movement;
storing potential energy in a rebound system; compressing a fluid;
releasing compressed fluid; releasing potential energy from the
rebound system; causing a third movement of the piston assembly in
an opposite direction from the second movement by action of the
released energy from the rebound system and from energy of the
compressed fluid within a compression chamber; intaking a next
cycle of fuel and oxygen; and exhausting combusted fuel and oxygen
from the combustion chamber.
24. The method of claim 23, wherein the intaking of fuel and oxygen
comprises supplying fuel and oxygen to a holding chamber within a
cylinder that includes the piston assembly comprising a piston rod
connected between a combustion piston and a compression piston, the
combustion chamber being positioned on one side of the combustion
piston within the cylinder and the holding chamber being positioned
on an other side of the combustion piston within the cylinder, and
further wherein the intaking steps comprise fluidly flowing fuel
and oxygen from the holding chamber to the combustion chamber
through a passage within the cylinder.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Patent Application No. 61/660,981,
filed Jun. 18, 2012 and titled "SYSTEM AND METHOD FOR THE
PRODUCTION OF COMPRESSED FLUIDS", which is incorporated herein by
reference in its entirety.
FIELD
[0003] The present invention relates generally to a fluid pumping
or fluid compression engine, such as utilizing an internal
homogeneous-charge combustion ignition (HCCI) free-piston engine
design. Such a fluid pump or compressor is capable of producing
compact fluid power for applications requiring mobility.
BACKGROUND
[0004] There is a need for compact fluid pumps and compressors in
fields such as orthotics, power tools, and robots. Applications in
such fields require portable power to pressurize or compress fluid.
For example, power tools may include pneumatic nail guns, branch
clippers, garden pruners, or load lifting assistants. Such portable
power is commonly derived from an electrical air compressor powered
by a battery. However, the weight and energy density of the battery
often limit portability. As an alternative, an internal combustion
(IC) engine can be used as a compressed fluid power source in such
applications. Compared to a battery, a miniaturized combustion
engine can provide higher power density and higher energy
density.
[0005] However, IC engines are difficult to miniaturize to sizes
below approximately 10 cm.sup.3(cubic centimeters). Challenges in
miniaturizing existing IC engines to a small size include
fabrication, control, friction, and blow-by leakage. For example, a
four-stroke IC engine is difficult to fabricate at a miniature
scale due to additional features such as a camshaft, valves, and
rocker arms. As another example, in a two-stroke IC engine, spark
plugs, fuel injectors, and various sensors are all difficult to
miniaturize in order to operate in a small engine.
[0006] An alternative configuration involves homogeneous-charge
combustion ignition (HCCI) engines. Such engines typically use a
crankshaft. These engines also utilize active control schemes
comprising mounted sensors and an actuator to regulate rebound,
spark ignition or diesel compression ignition, and proper
alignment. Due to the complexity of such a configuration and the
need for a crankshaft, miniaturizing a full-scale HCCI crankshaft
engine would be difficult.
[0007] Yet another alternative configuration utilizes a free-piston
engine. A free-piston engine is a type of internal combustion
engine not having a crankshaft. Without a crankshaft, this
configuration is more compact and simpler than some other
configurations. However, free-piston engines are difficult to
regulate requiring active controls to regulate piston motion.
Incorporating active control schemes at a miniature scale presents
difficulties, especially given the limited space available in a
miniature engine.
[0008] Another configuration involves glow plug ignition engines
used in applications such as model aircraft to power a fluid
compressor. Such engines are small in size and utilize glow plug
ignition, wherein a glowing hot platinum wire is used in the
combustion chamber to ignite the fuel air mixture through its
thermal energy and catalytic effect. The problem with this engine
configuration is low thermal efficiency caused by a slow combustion
process. Furthermore, the use of a glow plug in this configuration
limits further miniaturization.
[0009] Because of the inherent challenges in miniaturizing existing
engine configurations, it would be beneficial to develop an engine
that can be fabricated at a miniature scale, operate with
reasonable power for portable use, and have a high enough
power-to-weight ratio to be effective in orthotics, power tool, and
robotics applications.
SUMMARY
[0010] A system for providing pressurized and/or compressed fluid
comprising a fluid pump/compression cylinder, coupled to a
combustion cylinder and a rebound chamber, and a piston assembly
contained at least partially and capable of movement within the
combustion cylinder and the fluid pump/compression cylinder,
wherein the combustion cylinder comprises a holding chamber and a
combustion chamber, and wherein the holding chamber and the
combustion chamber may be connected by at least one port, and
wherein the fluid pump/compression cylinder comprises a
pump/compression chamber, and wherein the rebound chamber comprises
a rebound system, and wherein the pump/compression chamber may
comprise at least one inlet and at least one outlet.
FIGURES AND TABLES
[0011] FIG. 1 is a schematic diagram of an exemplary embodiment of
the engine being used in conjunction with an orthotic leg/foot
apparatus.
[0012] FIG. 2 is a schematic diagram of the exemplary embodiment of
the engine of FIG. 1 being used in conjunction with an orthotic
leg/foot apparatus as provided to a person's leg and foot.
[0013] FIG. 3 is a schematic diagram of an exemplary embodiment of
the present invention showing an exterior of an engine
cylinder.
[0014] FIG. 4 is schematic cross-sectional view of an engine
cylinder according to an exemplary embodiment of the present
invention.
[0015] FIG. 5 is schematic cross-sectional view similar to FIG. 4,
but at an angle from the top of an engine cylinder according to an
exemplary embodiment of the present invention.
[0016] FIG. 6 is a schematic cross-sectional view of a cylinder at
a certain stage in the combustion cycle according to an exemplary
embodiment of the present invention.
[0017] FIG. 7 is a schematic cross-sectional view of a cylinder at
a different stage that in FIG. 6 in the combustion cycle according
to an exemplary embodiment of the present invention.
[0018] FIGS. 8-10 are schematic cross-sectional views showing
scavenging flow patterns.
[0019] FIG. 11 is a schematic diagram of a piston assembly, seal,
and spring according to an exemplary embodiment.
[0020] FIG. 12 is a schematic diagram of the piston assembly, seal,
and spring of FIG. 11 but shown from a angle to the side.
[0021] FIG. 13 is a schematic diagrams of an engine cylinder
showing a slot for a starting element provided in a compression
cylinder according to an exemplary embodiment.
[0022] FIG. 14 is an enlarged portion of the view of FIG. 13
showing the slot, a starting element and an absorption element at
the end of the slot.
[0023] FIG. 15 is a schematic diagram of a valve according to
exemplary embodiment of the present invention.
[0024] FIG. 16 is a schematic diagram of another valve according to
exemplary embodiment of the present invention.
[0025] FIG. 17 is a schematic diagram of yet another valve
according to exemplary embodiment of the present invention.
[0026] FIGS. 18-25 are graphical representations representing data
from various experiments related to the performance of a free
piston engine design of the present invention.
[0027] FIG. 26 is a perspective view of an exemplary embodiment of
an engine design according to the present invention.
[0028] FIG. 27 is a perspective view in cross-section of the
exemplary embodiment of an engine design of FIG. 26 and according
to the present invention.
[0029] FIG. 28 is a schematic diagram of the energy balance of an
engine according to an exemplary embodiment of the present
invention.
DESCRIPTION
[0030] Small, light-weight portable engines producing compressed
fluids are capable of use in applications such as orthotics, power
tools, and robots. An example of such an engine is shown in FIGS.
1A and 1B, where the engine provides compressed fluid to power an
orthotic leg/ankle system that may assist for example injured or
disabled persons in walking. FIGS. 1 and 2 show the engine 10
attached to the back of the orthotic leg/ankle system 11. According
to a preferred embodiment, the engine 10 uses a liquid fuel and is
free of external electric power cords and heavy electric batteries
that could limit portability.
[0031] Designs according to the present invention are useful for
compressing fluid, such as gases including air, as well as for
hydraulic pumps, wherein non-compressible fluids, such as certain
liquids, are pressurized and accumulated so as to generate
hydraulic power, or as for alternator designs, wherein linear
motion is converted to electrical energy, to generate electricity.
The uniqueness of the designs of the present invention is based
upon the extraction of work from linear motion of one or more
pistons, as opposed to the extraction of work from rotary shaft
output. As a result, piston pneumatic pumps, hydraulic pumps and
alternators are contemplated applications for small engines of the
present invention. For purposes of describing certain preferred
embodiments of the present invention with the understanding that
engines of the present inventions can be used as stated above, a
fluid compression apparatus is described as follows.
[0032] Referring to FIG. 3, an engine cylinder is shown comprising
a combustion cylinder 12 and a compression cylinder 14, which
components may be made integrally or as separate components and
connected together. The engine cylinder also comprises a fuel inlet
16, an exhaust outlet 18, a fluid inlet 20 and a compressed fluid
outlet 22, as are shown. The engine cylinder may comprise a metal
alloy (such as an aluminum alloy) or other suitable materials.
[0033] As shown in FIGS. 4 and 5, the combustion cylinder 12 may
comprise a combustion chamber 24 and a holding chamber 26. The
combustion cylinder 12 is shown as comprising an outer cylinder 28
and a cylinder liner 30. The cylinder liner 30 may comprise metal
or metal alloys (e.g. steel, titanium or brass), layered metals
(e.g. chrome-coated brass, anodized aluminum, or other
electroplated metals), polymer-coated materials (e.g.
polytetrafluoroethylene (PTFE, e.g. Teflon.RTM.) coated metals), or
ceramic or ceramic-coated (e.g. diamond coated) materials or other
suitable materials. A piston assembly 31 is illustrated comprising
a piston rod 32, connected on one end to a combustion piston-head
34 and on the other end to a compression piston-head 36. Also, a
rebound element 38 is shown located within the cylinder. As shown,
one end of the piston assembly extends into and through the holding
chamber and further into the combustion chamber. The combustion
piston-head 34 is shown located inside the combustion cylinder.
Piston and rod connection techniques including wrist pins and the
like are well known and any such connection is contemplated.
According to a preferred embodiment, as shown in FIGS. 3-7, the
piston assembly 31 comprises a free piston assemble, i.e., the
piston assembly 31 is not connected to a crankshaft so as to
provide linear output, i.e. compression or fluid pumping from the
compression cylinder 14.
[0034] In some embodiments, the piston assembly 31 may also
comprise a starting element 40. According to exemplary embodiments
as illustrated, the starting element 40 comprises a starting handle
for manual starting, but could otherwise comprise a compressed
fluid starter, an electromagnetic starter, a spring-loaded starter,
or otherwise. The purpose of the starting element is to cause at
least one compression of fuel/air mix within the combustion chamber
24 so as to allow for a first combustion within the combustion
chamber 24 to drive the piston 34 and thus piston assemble 31 away
from the end of the combustion chamber 24.
[0035] The combustion cylinder 12 also comprises the inlet 16 as
such can be operatively connecting a fuel source (e.g. a carburetor
or a fuel injector system). The inlet preferably opens into the
holding chamber 26. It accordance with a preferred embodiment, the
holding chamber 26 is connected for fluid communication to the
combustion chamber 24 by way of a passage 42 that opens into the
combustion chamber 24 at a determined position (discussed more
below) by way of a port 43. The passage 42 may comprise a space
provided along and within the wall of the combustion cylinder liner
30 to fluidly connect the combustion and holding chambers 24 and
26. For example, the space may be created by removing material from
the combustion cylinder liner 30. The combustion cylinder 12 also
comprises the outlet or exhaust 18 for connecting the combustion
chamber 24 to a space outside the combustion cylinder. In an
exemplary embodiment, the space outside the combustion cylinder 12
is an exhaust system.
[0036] The compression cylinder 14 comprises a compression chamber
44 with the compression cylinder shown as connected to one end of
the combustion cylinder 12. According to an preferred embodiment,
the compression cylinder 14 may also comprise an outer cylinder 46
and a cylinder liner 48. The cylinder liner may comprise metal or
metal alloys (e.g. steel, titanium or brass), layered metals (e.g.
chrome-coated brass, anodized aluminum, or other electroplated
metals), polymer-coated materials (e.g. PTFE coated metals), or
ceramic or ceramic coated (e.g. diamond coated) materials, or other
suitable materials. Alternatively, the compression cylinder 14 may
also comprise glass or polymeric materials (e.g. PTFE). A seal 50
(described in greater detail below) is preferably located at one
end of the combustion cylinder 12, forming a boundary between the
holding chamber 26 and another chamber, such as the compression
cylinder or another (intermediate) chamber (e.g. the rebound
chamber). As shown in FIGS. 4 and 5, the seal 50 preferably
includes a plurality of disc-like elements 52 that are supported in
position by being sandwiched between the ends of the combustion
cylinder 12 and the compression cylinder 14. As shown in FIGS. 11
and 12, these discs 52 are slotted as shown at 53 so as to allow
for passage of the piston rod 32 as it is movable back and forth.
By using plural discs 52, an effective boundary can be provided to
the holding chamber 26 so that inlet gas/air mixture or other
combustible fuel does not flow into the compression cylinder or any
of its chambers. The slots 53 are preferably tightly fit to the
piston rod's 32 diameter to minimize leakage. The pistons are
rigidly connected so as to move together. The result is a holding
chamber 26 sealed on the one side bounded by the seal 50 that
varies in volume with movement of the combustion piston 34 without
regard to the movement of the compression piston 36.
[0037] Referring again to FIGS. 4 and 5, according to a preferred
embodiment, the piston assembly 31 extends into the compression
chamber 44. The piston assembly 31 is also shown extending into and
through a rebound chamber 54. The compression piston-head 36 is
positioned to be located inside the compression cylinder 14. The
compression cylinder 14 also preferably comprises the fluid inlet
20 and the compressed fluid outlet 22. The fluid inlet 20 can thus
connect the compression chamber 44 to a space outside of the
compression cylinder 14. For example, the space outside of the
compression cylinder 14 may be the environment. According to an
embodiment of the present invention, the compressed fluid outlet 22
may connect the compression chamber 44 to a compressed fluid
storage system, for example an accumulator, schematically shown in
FIGS. 4 and 5. Many types of fluid accumulators are well-known, and
any of such accumulators could be used in accordance with the
present invention.
[0038] As shown in FIGS. 4 and 5, according to a preferred
embodiment, the compression cylinder 14 also comprises the rebound
chamber 54. According to any exemplary embodiment, the rebound
chamber 54 also comprises an elastic rebound element 38 (e.g. an
element that does not experience permanent deformation when
compressed). For example, the rebound chamber 54 may house a spring
as the rebound element 38 that may comprise a coil spring, a wave
spring, or another embodiment to store and return sufficient
energy. The spring may comprise metal or metal alloys (e.g. steel,
titanium or beryllium) other suitable materials. Alternatively, the
rebound element may be configured as a system, such as a pneumatic,
electrical, magnetic, or hydraulic system. According to alternative
embodiments, the rebound element can be housed in either of the
holding chamber 26 or the compression chamber 44. According to a
preferred embodiment as illustrated, the rebound element 38 of a
compressive type can be located within the rebound chamber 54.
According to a preferred embodiment, the rebound chamber 54 and the
rebound element 38 may be located between the seal 50 and the
compression piston-head 34, as seen in FIGS. 4 and 5. More
specifically within the illustrated embodiment, the spring as the
rebound element 38 sits against a seat portion 58 (see FIGS. 11 and
12) of the manual start element 40 and against the internal edge of
the compression cylinder sleeve 48 so as to provide an effective
bias to the start element 40, which is fixed with the piston rod 32
for axial movement thereof along with the combustion piston 32.
According to an alternative embodiment, one end of a spring may be
attached to the piston rod 32.
[0039] As shown in FIG. 6, according to an embodiment of the
present invention, the engine may comprise a two-stroke engine
utilizing a scavenging process allowing exhaust to exit while a
fuel mixture enters the combustion chamber 24. As the piston
assembly 31 moves away from the combustion end of the cylinder, the
exhaust outlet may be exposed to the combustion chamber 24, letting
out the exhaust, slightly before the fuel inlet port 43 is exposed,
letting in the fuel mixture and allowing for the completion of the
scavenging process. The fuel mixture may comprise a fuel (e.g., a
hydrocarbon mixture, such as diesel fuel, an alcohol, such as
methanol, or another gaseous or liquid fuel, such as dimethyl
ether) and a source for oxygen (e.g. air). The fuel mixture may
also comprise a lubricating agent, such as oil or other suitable
lubricant. According to an exemplary embodiment, the fuel mixture
may comprise, as necessary, between 1 and 20 percent lubricating
agent. In alternative embodiments, other methods to lubricate the
engine may include utilizing a separate lubricant reservoir,
lubricant dripping, or lubricant impregnated materials. In
embodiments utilizing fuel injection methods, the oxygen source may
enter the combustion chamber through an inlet valve.
[0040] Referring again to FIG. 6, according to the illustrated
embodiment, movement of the piston assembly toward the compression
end causes the compression piston-head 36 to compress fluid within
the compression chamber 44, which in turn causes positive pressure
to build-up in the compression chamber 44. The compressed fluid may
then be let out of the compression chamber 44 through the fluid
outlet 22, which may be regulated by a compressed fluid outlet
valve or the like. The movement of the combustion piston-head 36
toward the compression-end of the cylinder also causes a
compression of the rebound element 38 for example by causing the
compression spring to be compressed, as shown in FIG. 6.
[0041] According to the exemplary embodiment as shown in FIG. 7,
approximately at the time the piston assembly 31 begins to move
back toward the combustion-end of the cylinder, a homogenous or
near homogeneous fuel-oxygen mixture is preferably initiated so as
to enter through the fuel inlet 16 into the holding chamber 26. The
fuel inlet 16 may be regulated by a fuel inlet valve or the like as
are conventionally known. According to an exemplary embodiment, the
fuel inlet valve may comprise a reed valve or other method wherein
the fuel inlet 16 and outlet 18 for exhaust valves are exposed to
the combustion chamber 24 at the appropriate time. In alternative
embodiments, a fuel inlet valve and the outlet for exhaust may be
controlled electronically and may comprise a sensor assembly. As
the piston assembly 31 begins to move toward the compression-end of
the engine, the combustions piston head 34 begins to pressurize the
fuel mixture while the piston head 34 is still blocking the
mouth(s) of the port(s) according to an embodiment. Further
movement of the piston assembly toward the compression end (as seen
FIG. 6) exposes the port 43 of the passage 42 and the outlet 18 for
exhaust, allowing the positive pressure of the fuel mixture to
cause the mixture to enter the combustion chamber 24 from the
holding chamber 26 and through the passage 42 and out the port(s)
43 so as to also simultaneously force the exhaust out of the
combustion chamber 24 through the outlet 18 for exhaust. According
to alternative embodiments, fuel and/or a source for oxygen may be
injected directly into the combustion chamber 24 (e.g. direct
injection). Alternatively, fuel and/or a source for oxygen may be
separately introduced.
[0042] As shown in FIG. 7, according to the illustrated embodiment,
the compressed rebound element 38 (e.g. spring) will exert a
biasing force causing the piston assembly 31 to move (i.e. return)
toward the combustion-end of the cylinder. The movement of the
compression piston-head 36 away from the compression end may lower
the pressure in the compression chamber 44 due to the simultaneous
or nearly simultaneous closing of the fluid outlet valve 22. As the
compression piston head 36 moves, fluid (e.g. air) may enter
through the fluid inlet 20, which may be regulated by a fluid inlet
valve, into the compression chamber 44.
[0043] The movement of the piston assembly 31 toward the
combustion-end of the cylinder (as seen in FIG. 7) will eventually
effectively block the port 43 of passage 42 and the exhaust outlet
18. According to a preferred embodiment, the movement of the piston
assembly 31 may continue until the fuel-oxygen mixture reaches a
compression corresponding to sufficient pressure and temperature,
to cause ignition of the charge and initiating combustion. The
force of combustion may cause positive pressure to build-up in the
combustion chamber pushing the piston assembly 31 toward the
compression-end of the cylinder.
[0044] As shown in FIGS. 8-10, the combustion cylinder 12 may
comprise one or more ports, which ports would include an inlet 43
(as the port opening directly into the combustion chamber 24) and
an outlet or exhaust 18 (as a portion opening directly from the
combustion chamber 24). The ports may be configured to enable
scavenging, such as cross-flow scavenging, uni-flow scavenging, or
loop-flow scavenging (also known as Schnuerle type scavenging).
According to an exemplary embodiment, the combustion cylinder 12
comprises the two or more ports as shown in FIGS. 8-10 in a
configuration taking advantage of loop-flow scavenging. As shown in
FIG. 9, the mouths of the ports 43 and 18 can be positioned such
that the inlet flow is directed away from the exhaust outlet such
that the gases initially enter a combustion chamber 24 moving away
from the exhaust outlet 18. As shown in FIG. 10, the configuration
may comprise three (or more) ports 43 wherein the port 43 located
opposite the exhaust outlet 18 in the combustion chamber 24 is also
directed away from the exhaust outlet 18.
[0045] As shown in FIGS. 11 and 12, the piston assembly 31 may
comprise a piston rod 32, connected on one end to a combustion
piston-head 34 and on another end to a compression piston-head 36,
and a compression element as a rebound element 38. According to an
exemplary embodiment, the compressing element 38 is at least
partially provided inside the compression cylinder 14 above the
compression piston-head 36. The piston assembly 31 may comprise one
or more wrist or other type pins attaching the piston-heads to the
piston rod 32. The piston rod 32 may comprise one or multiple
diameters throughout its length to accommodate assembly, for
example, to accommodate the diameter of the pin used to attach a
piston-head to the piston rod 32. The combustion piston head 34 may
be comprised of metal (e.g. titanium, steel, or aluminum), metal
alloys, or metal mixtures. The compression piston head 36 may also
be comprised of metal or metal alloys (e.g. titanium, steel, or
aluminum), polymeric materials (e.g. PTFE, nylon, or other
polymers)), ceramic materials, graphite, or other suitable
materials.
[0046] Multiple variables, such as the operating frequency, affect
the efficiency and the output power of the engine. The power output
of the engine can be adjusted to accommodate the requirements of
the planned end-use application. For example, a 10 W output may be
appropriate for an orthotic appliance, whereas a lift-assist
application may require a power output as high as 100-200 W. To
achieve the desired power output, the frequency of the engine can
be adjusted by the selection of the materials and construction of
the piston assembly and the rebound element. Also, the frequency
and the displacement may be varied. For example, the material and
dimensions of the piston heads and piston rod may be chosen to
reach a suitable weight relative to the stiffness (i.e. the spring
constant or spring rate) of the rebound element (e.g. spring). On
the other hand, a suitable rebound element may be chosen to match
the weight of the piston assembly and to achieve an optimal rebound
effect. For example, a rebound element that is too stiff will
absorb too much of the energy created by combustion, thus lowering
the output power of the engine. A rebound element that is not stiff
enough will have difficulty returning the piston assembly back into
position to pressurize and ignite the fuel, thus causing poor or
incomplete combustion. According to a preferred embodiment, the
rebound effect causes sufficient compression of the fuel-oxygen
mixture to ignite the mixture without the use of another source of
ignition, such as a glow plug or a spark plug. An optimal operating
frequency will minimize leakage and friction, and maximize
compressed fluid output power. Other materials (e.g. for the engine
cylinders) may be chosen keeping in mind the desired portability
and light weight. For example, according to a preferred embodiment,
the engine cylinders may comprise aluminum or aluminum alloys, as
opposed to heavier metals.
[0047] The seal 50, for example, can comprise a double jaw seal, as
such may be used to isolate the holding chamber 26 from the rebound
chamber 54. The seal configuration is preferably chosen so that it
fits tightly around the piston rod 32 while permitting the piston
rod to slide along the slots 53 and the seal 50 effectively
prevents a substantial amount of fuel-oxygen mixture from escaping
from the holding chamber 26 into another area, for example, a
rebound chamber or a compression chamber. The seal 50 may comprise
multiple elements 52, as described above, with each element 52 made
up of polyether ether ketone (PEEK), bronze, PTFE, or other
suitable material or combination of materials. The efficiency of
the seal 50 affects the leakage of fuel from the holding chamber
26. A tighter, more efficient seal will improve (i.e. lessen)
leakage and advantageously allow for smaller bore-size engines
(e.g. a few millimeters or micro- or nano-scale engines) to be
operational.
[0048] As shown in FIG. 13, the starting handle element 40 may
extend through an axially extending slot 60 provided along a wall
of the compression cylinder 14 according to an exemplary
embodiment. In alternative embodiments, another method of initially
displacing the piston assembly may be used such that a starting
handle may not be required. FIG. 14 shows an alternative embodiment
of the slot 60 comprising a means, such as a rubber bumper 62 for
preventing impact (e.g. a spring, air chamber, or the like)
positioned to prevent the starting handle element 40 from impacting
the cylinder wall at the end of the slot.
[0049] According to exemplary embodiments, many different types of
valves may be chosen for the various inlets and outlets. For
example, stacked valves shown in FIGS. 15 and 16 can be chosen to
control the flow of compressed fluid from the device. Such a
stacked valve construction can be designed based upon well-known
and conventional techniques where the stacked elements together
control the fluid flow from the device outlet. As shown in FIG. 17,
the valve at the fuel inlet may be a Reed-type valve according to
an exemplary embodiment, as Reed valves themselves are well known.
The valve may comprise metal or metal alloys, such as stainless
steel, steel, titanium, or other suitable materials.
EXAMPLES
[0050] A number of experiments were conducted to study the
construction and operating parameters of engines in accordance with
the present invention. The experiments were conducted either by
utilizing various computerized models, or by studying prototypes of
engine designs.
[0051] In the first example, engine blow-by leakage was modeled and
compared against experimental data utilizing a small glow-plug
engine. As shown in FIG. 18, simulation data of heat transfer alone
and heat transfer and leakage were compared to experimental data
measuring motoring peak pressure. Results from the model and
experimental data show that motoring peak pressure increases with
engine speed, as measured by rotations per minute, indicating that
miniature engines can be run at high speed to avoid excessive
blow-by leakage.
[0052] In another example, engine leakage and friction efficiencies
were modeled in combination to determine optimal engine speeds
(i.e. frequencies) as shown in FIG. 19. High engine speed may
reduce leakage and heat transfer losses but may increase friction
loss. Considering these two factors, optimal operating ranges were
approximately between 100 and 150 Hz. Along with knowledge of a
target engine output power, engine speed assists in determining the
appropriate engine size.
[0053] In the third example, the combustion cylinder pressure,
piston position, compressed air reservoir pressure, engine
frequency and indicated mean effective pressure (IMEP) were modeled
using a computer model and a glow ignition prototype engine (a
remote-control-aircraft engine) to estimate the compressed fluid
power output of the engine. As shown in FIG. 20, the combustion
chamber pressure built up from about 15 bar to about 20 bar and
above after the piston movement began to expose the exhaust outlet
to the combustion chamber and scavenging occurred, supplying the
engine with fresh fuel-oxygen mixture for the next cycle, thus
increasing the pressure. As shown in FIG. 21, pressure in the
compressor chamber rose with operating time as pressure in the
reservoir attached to the compressed fluid outlet rose. Engine
frequency also increased with operating time to approximately a
range between 112 and 123 Hz as predicted by the model. Compressed
fluid power was calculated to be approximately 5 W.
[0054] In the fourth example, the complex and unrestrained motion
of a free-piston, glow-plug configuration was measured as piston
speed versus piston position as shown in FIG. 22. As a comparison,
the free-piston model data and experimental data were compared to a
model crank engine as shown in FIG. 23. The free-piston model
accurately fits with the resulting experimental data indicating
that the model was able to accurately predict engine dynamics.
[0055] The fifth experiment was conducted comparing a free-piston
engine with a crankshaft engine of the same size also utilizing
glow-plug ignition. Results, as shown in FIG. 24, indicate that a
higher compression ratio of around 10 in the free-piston engine
resulted in average cycle efficiency of approximately 18.1 percent
as compared to the compression ratio of 5.3 and average cycle
efficiency of about 22 percent of the crankshaft engine.
[0056] The sixth experiment was conducted to compare model HCCI
performance with model glow-plug ignition performance and
experimental glow plug performance. Results, as shown in FIG. 25,
indicate that model glow-plug ignition performance accurately
predicted the experimental glow-plug ignition performance. The
model predicts that the heat release efficiency of the HCCI
free-piston engine will be approximately 41 percent as compared to
the 25 percent of the glow-plug engine.
[0057] A miniature fluid compression engine is illustrated within
FIGS. 26 and 27. The cylinder was specifically constructed for test
purposes and was made of stainless steel with cylinder liners made
of chrome plated brass. The dimensions of this specific example of
an engine of the present invention includes the device being
approximately 110 millimeters in length and approximately 38
millimeters in diameter with a 12.5 millimeter inside bore. With an
attached carburetor and muffler, the engine system was
approximately 75 millimeters wide. The operating frequency of the
engine was optimized by adjusting the weight of the piston assembly
and the stiffness of the spring to avoid leakage (which may be
caused by a low frequency), high friction and noise (which may be
caused by a high frequency). The pistons were preferably made of
aluminum alloy, resulting in a weight of the moving parts of 33
grams. The spring system was made of steel and had a 1500 N/m
resistance, measured approximately 2.5 millimeters in height at
rest and has a pre-load force of 19 N. The system utilized glow
plug ignition, a manual starter and a methanol-based fuel mixture.
Using these parameters, the desired operating frequency of 100 Hz
was achieved. As constructed, the combustion cylinder chamber had a
volume measuring 0.13 cubic centimeters with a compressor cylinder
chamber volume of 2.0 cubic centimeters when the spring was fully
extended. When the spring was compressed completely, the engine
cylinder chamber volume measured 1.7 cubic centimeters with a
compressor cylinder chamber volume of 0.36 cubic centimeters.
Designed with a 2 mm over-stroke, the engine is able to account for
variations in piston travel, resulting in weak and strong cycles.
The piston travel is long enough to enable scavenging and of a
length that would result in metal to metal collision without the
use of a bumper. Therefore a rubber bumper was incorporated to
absorb some of the shock of the manual ignition handle impacting
the cylinder. The energy balance of the engine is shown
schematically in FIG. 28.
[0058] It is important to note that the construction and
arrangement of the elements of the inventions as described in this
application and as shown in the figures above is illustrative only.
Although some embodiments of the present inventions have been
described in detail in this disclosure, those skilled in the art
who review this disclosure will readily appreciate that many
modifications are possible without materially departing from the
novel teachings and advantages of the subject matter recited.
Accordingly, all such modifications are intended to be included
within the scope of the present inventions. Other substitutions,
modifications, changes and omissions may be made in the design,
operating conditions and arrangement of the preferred and other
exemplary embodiments without departing from the spirit of the
present inventions.
[0059] It is important to note that the system and method of the
present inventions can comprise conventional technology (e.g.,
engine cylinders, pistons, valves, carburetors, mufflers, fuels,
lubricants, etc.) or any other applicable technology (present or
future) that has the capability to perform the functions and
processes/operations indicated in the FIGURES. All such technology
is considered to be within the scope of the present inventions.
* * * * *