SYSTEM AND METHOD FOR THE PRODUCTION OF COMPRESSED FLUIDS
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.
This application claims the benefit under 35 U.S.C. §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.
GOVERNMENT RIGHTSThis 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.
FIELDThe 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.
BACKGROUNDThere 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.
However, IC engines are difficult to miniaturize to sizes below approximately 10 cm3(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.
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.
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.
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.
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.
SUMMARYA 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.
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
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.
Referring to
As shown in
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.
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.
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
Referring again to
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Referring again to
According to the exemplary embodiment as shown in
As shown in
The movement of the piston assembly 31 toward the combustion-end of the cylinder (as seen in
As shown in
As shown in
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.
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.
As shown in
According to exemplary embodiments, many different types of valves may be chosen for the various inlets and outlets. For example, stacked valves shown in
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.
In the first example, engine blow-by leakage was modeled and compared against experimental data utilizing a small glow-plug engine. As shown in
In another example, engine leakage and friction efficiencies were modeled in combination to determine optimal engine speeds (i.e. frequencies) as shown in
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
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
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
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
A miniature fluid compression engine is illustrated within
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.
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.
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.
Type: Application
Filed: Jun 18, 2013
Publication Date: Dec 19, 2013
Inventors: William Keith Durfee (Edina, MN), David B. Kittelson (Minneapolis, MN), Lei Tian (Minneapolis, MN)
Application Number: 13/920,724
International Classification: F01B 11/04 (20060101);