HK1178230B - Two-stroke engine and related methods - Google Patents

Description

Two-stroke engine and related method

Technical Field

The present invention relates generally to internal combustion engines and more particularly to an improved two-stroke engine.

Background

Internal combustion engines are known for generating power, for example for driving a vehicle. In an internal combustion engine, the working fluid of the engine includes air and fuel and combustion products. Further, useful work is produced by the expansion of hot gases acting directly on moving surfaces of the engine, such as the top of a piston, wherein the reciprocating linear motion of the piston is converted into rotational motion of a crankshaft by a connecting rod or similar device.

Conventional internal combustion engines may be of the two-stroke or four-stroke type. In a conventional four-stroke engine, power is derived (recover) from the combustion process in four separate piston motions or strokes of a single piston. In such engines, the piston moves through a power stroke once for every two single revolutions (revolutions) of the crankshaft. In a conventional two-stroke engine, on the other hand, power is derived from the combustion process in only two piston movements or strokes of the piston. In such engines, each single rotation of the piston of the crankshaft moves through a power stroke once.

While two-stroke engines are known to have advantages over their corresponding four-stroke counterparts, their operation makes them somewhat undesirable in certain applications. For example, it is known that conventional two-stroke engines have poor combustion control, which results in relatively high emission levels. In some cases, the emissions associated with conventional two-stroke engines are too high to comply with the regulations set forth for vehicle polluting emissions. In addition, conventional two-stroke engines require the user to provide a mixture of fuel and oil in a predetermined ratio to operate the engine, which can be inconvenient.

What is needed, therefore, is a two-stroke engine that addresses these and other drawbacks associated with conventional two-stroke engines.

Disclosure of Invention

In one embodiment, a two-stroke engine is provided. The engine includes a crankshaft rotatable about an axis, and an engine block including a combustion cylinder and a compression cylinder. A first piston is slidably disposed within the combustion cylinder and is operatively coupled to the crankshaft for reciprocating movement within the combustion cylinder through a power stroke during each rotation (i.e., a single rotation) of the crankshaft about the axis. The second piston is slidably disposed within the compression cylinder and is operatively coupled to the crankshaft for reciprocating movement within the compression cylinder such that fresh air is received and compressed in the compression cylinder during each rotation (i.e., a single rotation) of the crankshaft about the axis.

The conduit provides fluid communication between the combustion cylinder and the compression cylinder, and the fuel injector communicates with the combustion cylinder to admit fuel into the combustion cylinder. First and second rotary valves in the engine block are operatively coupled to the crankshaft for rotation relative to the crankshaft. The first and second rotary valves are each rotatable to selectively admit fresh air into the compression cylinder and to allow compressed air to flow into the conduit. The first and second rotary valves are operable such that compressed air in the compression cylinder is communicated to the combustion cylinder via the conduit and substantially all of the contents of the combustion cylinder are purged prior to allowing fuel to enter the combustion cylinder through the fuel injector.

In certain embodiments, each of the first and second rotary valves is operatively coupled to the crankshaft to rotate at about half the rotational speed of the crankshaft. In one aspect of a particular embodiment, the conduit may define a first volume for holding air and the combustion cylinder may define a first maximum volume for holding air and fuel, wherein the first volume is greater than the maximum volume of the combustion cylinder. Additionally or alternatively, the compression cylinder may define a second maximum volume for holding air that is greater than the first maximum volume of the combustion cylinder. The duct may include a plurality of fins for cooling air in the duct. In one embodiment, the first rotary valve includes a first passage extending generally transverse to a first rotary valve axis of rotation, and wherein rotation of the first rotary valve intermittently provides fluid communication between the compression cylinder and the conduit through the first passage. The second rotary valve may include a second passage extending generally transverse to the second rotary valve axis of rotation, wherein rotation of the second rotary valve intermittently provides fluid communication between the compression cylinder and the source of outside air through the second passage.

The first and second rotary valves may be positioned adjacent ends of the compression cylinder and may rotate about respective axes that are substantially parallel to each other and to a rotational axis of the crankshaft. A fuel injector is operatively coupled to the conduit for injecting fuel into the conduit. The engine may also include an exhaust pipe in fluid communication with the combustion cylinder for exhausting exhaust gas from the combustion cylinder. The exhaust pipe may expand from a first cross-sectional area at a location adjacent the combustion cylinder to a second cross-sectional area greater than the first cross-sectional area at another location distal the combustion cylinder. The exhaust pipe may include at least one sidewall that is inclined at an angle of about 45 ° relative to a longitudinal axis of the exhaust pipe.

Drawings

FIG. 1 is a schematic perspective view of an exemplary embodiment of a two-stroke engine according to the present disclosure.

Fig. 2A is a cross-sectional view taken generally along line 2A-2A in fig. 1, showing the first and second pistons thereof in respective first orientations.

Fig. 2B is a view similar to fig. 2A, showing the first and second pistons in respective orientations different from those in fig. 2A.

Fig. 2C is a view similar to fig. 2A and 2B, showing the first and second pistons in respective orientations different from those in fig. 2A and 2B.

Fig. 2D is a view similar to fig. 2A-2C, showing the first and second pistons in respective orientations different from those in fig. 2A-2C.

FIG. 3 is a schematic top view of another exemplary embodiment of a two-stroke engine according to the present disclosure.

Detailed Description

Referring to the drawings, and in particular to FIG. 1, an exemplary two-stroke engine 10 according to the present disclosure includes a crankshaft 12 rotatable about an axis of rotation 14 and disposed within an engine block 20 of the engine 10. The engine 10 includes a compression cylinder 26 and a combustion cylinder 28, and first and second pistons 36, 38 (fig. 2A) slidably disposed in the compression and combustion cylinders 26, 28, respectively. As described in further detail below, engine block 20 is connected to an air supply via a conduit 40, and to a fuel supply (not shown), wherein a mixture of fuel and air is delivered to combustion cylinders 28 for combustion. The combustion residues are discharged from the engine body 20 through an exhaust pipe 46. The spark plug 50 is coupled to the combustion cylinder 28 and provides an ignition source for the combustion of the air/fuel mixture in the combustion cylinder 28. Air is supplied to the compression cylinder 26 via conduit 40 and from the compression cylinder 26 to the combustion cylinder 28 via conduit 51, the air being controlled by rotation of a pair of rotary valves 60,62 disposed in a head portion 64 of the compression cylinder 26. As described in greater detail below, the control unit 70 controls operation of the engine 10, and in particular the flow of fuel into the combustion cylinders 28 via fuel injectors 72.

The first and second rotary valves 60,62 of the exemplary embodiment are generally parallel to each other and rotate about respective first and second axes 60a, 62a, which in turn are generally parallel to the rotational axis 14 of the crankshaft 12. The first and second rotary valves 60,62 are coupled to the crankshaft 12, such as through gears (not shown), such that rotation of the crankshaft 12 causes the rotary valves 60,62 to rotate. More specifically, in the exemplary embodiment, the coupling between the crankshaft 12 and the first and second rotary valves 60,62 is such that the rotary valves 60,62 are rotatable with respect to the crankshaft 12. For example, and without limitation, the coupling between the first and second rotary valves 60,62 and the crankshaft 12 may be such that the rotary valves 60,62 rotate at approximately half the rotational speed of the crankshaft 12. Further, in the exemplary embodiment, the first rotary valve 60 and the second rotary valve 62 may be positioned such that each is positioned approximately midway between the center of the compression cylinder 26 and its sidewall.

Referring now to fig. 2A-2D, the operation of the two-stroke engine 10 is illustrated. As described above, the first and second pistons 36, 38 are slidably disposed within the compression and combustion cylinders 26, 28, respectively, for reciprocating movement within the compression and combustion cylinders 26, 28. The first and second pistons 36, 38 are, in turn, operatively coupled to the crankshaft 12 by respective first and second connecting rods 80, 82 eccentrically coupled to the crankshaft 12. Thus, the reciprocating linear motion of first and second pistons 36, 38 causes crankshaft 12 to rotate, e.g., generally in the direction of arrow 85. Although not shown, the crankshaft 12 is, in turn, coupled to a pulley or drive train to thereby provide a source of power, for example, to a vehicle on which the engine 10 is mounted.

Referring specifically to fig. 2A, the first rotary valve 60 is shown in an open position, providing fluid communication between the conduit 40 for supplying air and the compression cylinder 26. More specifically, the first rotary valve 60 includes a first passageway 88 that extends generally transverse to the rotational axis 60a of the first rotary valve 60 such that rotation thereof intermittently provides fluid communication between the interior of the compression cylinder 26 and the conduit 40 supplying air as shown in the figures. Likewise, the second rotary valve 62 includes a second passage 93 extending generally transverse to the rotational axis 62a of the second rotary valve 62 such that rotation thereof intermittently provides fluid communication between the interior of the compression cylinder 26 and the conduit 51.

In fig. 2A, the first rotary valve 60 is in an open position such that air from the conduit 40 fills the interior of the compression cylinder 26 (arrow 91) when the first piston 36 is in a position defining a first maximum volume 86 for holding air for the compression cylinder 26 as shown in fig. 2A. The illustrated position of first piston 36 corresponds to a bottom-most position of first piston 36. Rotation of the first rotary valve 60 away from the position generally shown in fig. 2A causes the first rotary valve 60 to close, which thereby closes any fluid communication between the conduit 40 supplying air and the compression cylinder 26. In the view shown (fig. 2A), the second rotary valve 62 is in the closed position, i.e., such that no flow is permitted between the compression cylinder 26 and the conduit 51.

Further, in the view shown in fig. 2A, the second piston 38 is in a position within the combustion cylinder 28 such that there is fluid communication between the conduit 51 and the combustion cylinder 28 through the port 94 of the combustion cylinder 28. This fluid communication allows air or a mixture of fuel and air to flow from the conduit 51 into the combustion cylinder 28, as generally indicated by arrow 96. The illustrated bottom-most position of the second piston 38 defines a maximum holding volume 100 for holding the air/fuel mixture within the combustion cylinder 28.

In one aspect of this embodiment, the amount of air flowing from the conduit 51 and into the combustion cylinder 28 is such that substantially all of the contents of the combustion cylinder 28 are purged by the air flowing from the conduit 51 into the combustion cylinder 28. In this regard, substantially all of the contents (e.g., exhaust gases and unburned residues, if any) previously retained in the combustion cylinder 28 are exhausted through the exhaust conduit 46 (arrow 106). In this particular embodiment, the shape and size of the conduit 51, as well as the size of the compression cylinder 26 relative to the size of the combustion cylinder 28, facilitates substantially complete removal of the contents of the combustion cylinder 28. More specifically, in this embodiment, the shape and size of the conduit 51 defines a holding volume 110 for the compressed air in the conduit 51, which volume 110 is greater than the maximum volume 100 for holding the air/fuel mixture of the combustion cylinder 28, such that when pressurized air in the conduit 51 flows into the combustion cylinder 28, substantially all of the contents of the combustion cylinder 28 are replaced by clean air and discharged through the exhaust tube 46.

Likewise, the maximum volume 86 of the compression cylinder 26 is greater than the maximum volume 100 of the combustion cylinder 28 to further facilitate substantially complete purging of the contents of the combustion cylinder 28. More specifically, the compression cylinder 26 supplies a sufficiently large volume of compressed air to the conduit 51 to enable such substantially complete purging. For example, and without limitation, the amount of air available for purging from the conduit 51 may exceed approximately 100% of the maximum volume 100 of the combustion cylinder 28, such that a portion of the clean air supplied by the conduit 51 is allowed to flow out of the combustion cylinder 28 via the exhaust pipe 46 before closing the port 113 that communicates the interior of the combustion cylinder 28 with the exhaust pipe 46. Thus, not only is all combustion residues expelled from the combustion cylinder 28 by the purge air, but even some clean air is expelled, thereby providing substantially complete purging of the contents of the combustion cylinder 28. In this embodiment, the fuel injector 72 coupled to the conduit 51 is controlled by the control unit 70, and the control unit 70 instructs the fuel injector 72 to supply fuel into the conduit 51 only after substantially all of the exhaust gas of the combustion cylinders 28 has been expelled. For example, and without limitation, the control unit 70 may instruct the fuel injector 72 to supply fuel into the conduit 51 only after at least about 15% of the compressed air in the conduit 51 has flowed into the combustion cylinder 28. Thus, this operation allows a substantially clean mixture of air and fuel to be present in the combustion cylinder 28 prior to combustion, virtually without any previous combustion residue present in the combustion cylinder 28.

Referring to fig. 2B, the first rotary valve 60 is shown in a closed position and the second rotary valve 62 is shown in an open position, providing fluid communication between the compression cylinder 26 and the conduit 51. In this regard, air is compressed by movement of the first piston 36 in a direction toward the head portion 64 of the compression cylinder 26. Compressed air flows from the compression cylinder 26 and into the conduit 51 (arrow 114) via the second passage 93 of the second rotary valve 62. The conduit 51 of this exemplary embodiment has a plurality of fins 120 extending from a main portion of the conduit 51 that allow for heat transfer between the air in the conduit 51 and the ambient environment to thereby control the temperature of the air passing through the conduit 51. In this regard, for example, the temperature of the air in conduit 51 may be controlled to be less than about 180 ° f. In the illustrated view (fig. 2B), the first piston 36 is shown moving in the compression cylinder 26 toward the head portion 64, while the second piston 38 is shown blocking fluid communication between the combustion cylinder 28 and the conduit 51, and blocking fluid communication between the combustion cylinder 28 and the exhaust tube 46, allowing air to be compressed by the first piston 36 into the conduit 51. For example, and without limitation, the air in conduit 51 may be pressurized to less than about 60 psi. Further, in the illustrated position of the second piston 38, the second piston 38 moves upward, thereby compressing the mixture of air and fuel held in the combustion cylinder 28.

Referring to FIG. 2C, the second piston 38 is shown having reached a target position within the combustion cylinder 28, and the spark plug 50 is shown igniting the mixture of air and fuel held in the combustion cylinder 28, thereby initiating a power stroke of the second piston 38. In fig. 2C, the second rotary valve 62 is in a closed position such that air held in the conduit 51 is not permitted to flow back into the compression cylinder 26. Further, the position of the second piston 38 within the combustion cylinder 28 is such that fluid communication between the combustion cylinder 28 and the conduit 51 and the exhaust pipe 46 is blocked. As the second piston 38 moves downward in the power stroke (i.e., toward the position shown in fig. 2A), fluid communication is reestablished between the combustion cylinder 28 and the exhaust conduit 46 such that combustion residues are exhausted from the combustion cylinder 28 and through the exhaust conduit 46.

In the view shown in fig. 2D, the first piston 36 moves downward to allow the compression cylinder 26 to subsequently be filled with fresh air (as described above), and the second piston 38 moves downward to allow exhaust gas to flow from the combustion cylinder 28 through the exhaust pipe 46. As the second piston 38 advances toward its bottom-most position (fig. 2A) and through the port 94 and the exhaust port 113, clean air flows from the conduit 51 into the combustion cylinder 28 and substantially replaces any combustion residue that may be present in the combustion cylinder 28. The exhaust gas will also begin to flow out of the combustion cylinder 28 and through the exhaust pipe 46.

As described above, movement of the second piston 38 within the combustion cylinder 28 from the topmost position toward the position generally shown in FIG. 2A defines a power stroke of the engine 10. Likewise, movement of the second piston 38 within the combustion cylinder 28 from the position generally shown in FIG. 2A to the position generally shown in FIG. 2C defines the intake, exhaust, and compression strokes of the engine 10.

As shown by the sequence shown in fig. 2A-2D, two strokes of first piston 36 and two strokes of second piston 38 occur during a single rotation (i.e., a single rotation) of crankshaft 12. Such operation, and in particular the two strokes of the second piston 38 within the combustion cylinder 28, thereby defines a two-stroke operation of the engine 10. In this two-stroke operation, exhaust gases are substantially completely purged from the combustion cylinder 28 and at the time the control unit 70 instructs the fuel injector 72 to inject fuel into the conduit 51, resulting in substantially complete atomization of the fuel injected into the engine 10. The substantially complete purge also prevents mixing or contamination of the unburned raw fuel in the combustion cylinder 28 with fresh fuel or clean air directed into the combustion cylinder 28. This operation eliminates or at least significantly reduces the formation of hydrocarbons.

In the exemplary embodiment shown in the figures, the location of the fuel injector 72 in the conduit 51, and the control timing for injecting fuel into the conduit 51, is such that the fuel is injected directly into the higher velocity, high temperature compressed purge air flowing into the combustion cylinder 28 via the conduit 51, which provides sufficient time for complete atomization of the fuel. Complete atomization, in turn, minimizes the cold start problems observed in conventional engines, particularly when using alcohol-based fuels. Alternatively, it is contemplated that fuel injector 72 may be coupled directly to combustion cylinder 28, rather than directly to conduit 51.

In the exemplary embodiment, a cross-sectional shape of exhaust pipe 46 varies from a location coupled with combustion cylinder 28 to a location remote from combustion cylinder 28. More specifically, in this embodiment, the exhaust pipe 46 has a larger cross-sectional area at a distal location of the combustion cylinder 28 relative to an adjacent location of the port 113 of the combustion cylinder 28. Further, in this particular embodiment, the exhaust tube 46 includes a sidewall 122, the sidewall 122 defining an angle of approximately 45 ° with respect to the longitudinal axis 46a (fig. 2A) of the exhaust tube 46. This configuration allows the spent contents of the combustion cylinder 28 to flow through the exhaust pipe 46 with relatively low pressure and ease.

The engine described above may use different types of fuels, such as alcohol-based renewable fuels, hydrogen, or propane, without the need to add lubricating oil to the fuel. This allows for a significant increase in engine fuel economy and power output, as well as a reduction in engine emissions, when compared to conventional two-stroke or four-stroke engines. In addition, the relatively small number of engine 10 parts provides a weight reduction compared to conventional engines. The relatively small number of parts also results in a reduction in the cost of manufacturing the engine. It is estimated that the engine may achieve a thermal efficiency of 1.25 due to the substantially complete elimination of the hot residual gases from the combustion cylinder 28, which also results in a reduction or elimination of parasitic losses as compared to conventional two-stroke and four-stroke engines.

Although these figures show an engine having one combustion cylinder and one compression cylinder, one of ordinary skill in the art will readily recognize that an engine having any even number of cylinders may be suitable for applying the principles described above. For example, and without limitation, the engine may have an even number of cylinders, with previously defined pairs of compression cylinders and combustion cylinders, with each compression cylinder being in fluid communication with one compression cylinder in a manner generally shown in the above figures and described above. In such multi-cylinder engines, a plurality of fuel injectors may be present and may be controlled independently or alternatively by a single control unit. Further, in the engine, a plurality of spark plugs are operably (e.g., electrically) coupled to each other and to an ignition device by a cable in a manner known to those skilled in the art. Further, it will be appreciated that various conventional engines presently configured to operate in conjunction with gasoline may be converted to conform to the structure and operation of the exemplary engines shown and described herein. Engines according to the present disclosure may also have various cylinder configurations or arrangements, such as an inline arrangement, a V-arrangement, opposing cylinders, or various other configurations.

An exemplary engine having more than one compression cylinder and more than one combustion cylinder is illustrated in fig. 3, where like reference numerals refer to like features in the previous figures. Fig. 3 shows an exemplary engine 180 having three compression cylinders 26a,26b and 26c in fluid communication with three combustion cylinders 28a,28b,28c via respective conduits 51a,51b and 51c, respectively. Air is supplied to each compression cylinder 26a,26b,26c via a respective conduit 40a,40b,40c, while fuel is supplied to the compression cylinder 28a,28b,28c via a respective fuel injector 50. Exhaust gas and air from each combustion cylinder 28a,28b,28c is exhausted from the engine 180 via a common exhaust pipe 196, as schematically depicted. Sets of bearings 200,202 support each rotary valve 60,62, respectively, of the engine 180 for respective rotation thereof, while a pump 210 is schematically depicted to supply oil, fuel and/or coolant fluid to an engine block 211 of the engine 180. A plurality of seals 212 are disposed between the compression cylinders 26a,26b,26c to prevent fluid flow therebetween, while the bearings 200 are sealed and/or lubricated by oil supplied by the pump 210. In one aspect of this embodiment, the coolant supplied by the pump 210 may be used to cool the air in the conduits 51a,51b,51c, the compression cylinders 26a,26b,26c, and/or the combustion cylinders 28a,28b,28 c. The pair of gears 215,216 control rotation of the rotary valves 60,62 and are coupled to a crankshaft (not shown in this figure).

While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention to restrict or in any way limit the scope of the appended claims to such detail. The various features shown and described herein can be used alone or in combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept.

Claims (20)

1. A two-stroke engine, comprising:

a crankshaft rotatable about an axis;

an engine block including a combustion cylinder and a compression cylinder;

a first piston slidably disposed within the combustion cylinder and operatively coupled to the crankshaft for reciprocating movement within the combustion cylinder through a power stroke during each rotation of the crankshaft about the axis;

a second piston slidably disposed within the compression cylinder and operatively coupled to the crankshaft for reciprocating movement within the compression cylinder such that fresh air is received and compressed in the compression cylinder during each rotation of the crankshaft about the axis;

a conduit providing fluid communication between the combustion cylinder and the compression cylinder;

a fuel injector in communication with the combustion cylinder to allow fuel into the combustion cylinder;

first and second rotary valves in the engine block and operatively coupled to the crankshaft for rotation relative to the crankshaft, the first and second rotary valves being respectively rotatable to selectively admit fresh air into the compression cylinder and to allow compressed air to flow into the conduit; and

the first and second rotary valves being operated such that compressed air in the compression cylinder is communicated to the combustion cylinder via the conduit and substantially all of the contents of the combustion cylinder are purged prior to allowing fuel to enter the combustion cylinder through the fuel injector;

wherein the conduit is open to the combustion cylinder during purging;

wherein the conduit defines a first volume for holding air and the combustion cylinder defines a first maximum volume for holding a mixture of air and fuel, the first volume of the conduit being sufficient to place a volume greater than the first maximum volume of the combustion cylinder.

2. The engine of claim 1, wherein each of the first and second rotary valves is operatively coupled to the crankshaft for rotation at about half the rotational speed of the crankshaft.

3. The engine of claim 1, wherein the first volume of the conduit is greater than the first maximum volume of the combustion cylinder for purging substantially all contents of the combustion cylinder plus an additional volume of clean air.

4. The engine of claim 1, wherein the compression cylinder defines a second maximum volume for holding air, the second maximum volume being greater than the first maximum volume for purging substantially all of the contents of the combustion cylinder plus an additional volume of clean air.

5. The engine of claim 1, wherein the duct includes a plurality of fins for controlling the temperature of air in the duct.

6. The engine of claim 1, wherein the first rotary valve includes a first passage extending generally transverse to an axis of rotation of the first rotary valve, and wherein rotation of the first rotary valve intermittently provides fluid communication between the compression cylinder and an external air source.

7. The engine of claim 1, wherein the second rotary valve includes a second passage extending generally transverse to an axis of rotation of the second rotary valve, and wherein rotation of the second rotary valve intermittently provides fluid communication between the compression cylinder and the conduit through the second passage.

8. An engine as defined in claim 1, wherein the first and second rotary valves are positioned adjacent ends of the compression cylinder and are rotatable about respective axes that are substantially parallel to each other and to a rotational axis of the crankshaft.

9. The engine of claim 1, wherein the fuel injector is fluidly coupled to the combustion cylinder to inject fuel into the combustion cylinder.

10. The engine of claim 1, further comprising:

an exhaust pipe in fluid communication with the combustion cylinder for exhausting exhaust gas from the combustion cylinder, the exhaust pipe expanding from a first cross-sectional area at a location adjacent the combustion cylinder to a second cross-sectional area greater than the first cross-sectional area at another location distal the combustion cylinder.

11. The engine of claim 10, wherein the exhaust pipe includes at least one sidewall that is inclined at an angle of approximately 45 degrees relative to a longitudinal axis of the exhaust pipe.

12. The engine of claim 1, wherein the fuel injector is coupled to the conduit.

13. The engine of claim 1, wherein the engine block defines a head portion of the compression cylinder, the first and second rotary valves being disposed in the head portion.

14. A method of manufacturing a two-stroke engine, the method comprising:

coupling a crankshaft to first and second pistons reciprocally movable within combustion and compression cylinders, respectively, of the engine;

fluidly coupling the combustion cylinder and the compression cylinder to each other via a conduit;

providing a pair of valves to control the flow of air into the compression cylinder and from the compression cylinder to the conduit to pressurize the air in the conduit; and

providing a holding volume for air in at least one of the compression cylinder or the conduit operative to expel substantially all combustion residues and a predetermined volume of clean air from the combustion cylinder, the holding volume being greater than a first maximum volume defined by the combustion cylinder for holding a mixture of air and fuel.

15. A method of generating power in a two-stroke engine, the method comprising:

reciprocating first and second pistons within combustion and compression cylinders, respectively, of the engine, the first and second pistons coupled to a crankshaft to rotate the crankshaft and thereby generate power;

operating a valve to direct air from the compression cylinder to the combustion cylinder via a conduit, the conduit defining a first volume for holding air and the combustion cylinder defining a first maximum volume for holding a mixture of air and fuel, the first volume of the conduit being greater than the first maximum volume of the combustion cylinder;

directing fuel into the combustion cylinder;

combusting a mixture of air and fuel in the combustion cylinder; and

exhaust gas and a predetermined volume of clean air are exhausted from the combustion cylinder using air provided from the compression cylinder.

16. The method of claim 15, further comprising:

controlling fuel into the combustion cylinder such that at least 15% of the air obtained from the conduit is allowed to flow into the combustion cylinder and out through its exhaust pipe before the fuel is allowed to enter.

17. The method of claim 15, further comprising:

controlling the temperature of air in the conduit to less than 180 ° F.

18. The method of claim 15, further comprising:

controlling the air pressure in the conduit to less than 60 psi.

19. The method of claim 15, further comprising:

a control fluid is supplied to the engine to cool at least one of the combustion cylinder, the compression cylinder, or the conduit.

20. The method of claim 15, further comprising:

coupling the engine to an oil-free fuel source, the fuel comprising one of an alcohol-based renewable fuel, hydrogen, or propane.