Heavy fuel rotary engine with compression ignition

A rotary engine that starts and operates on compression-ignition of a heavy fuel without a secondary ignition source. The rotary engine includes a rotor housing that forms an epitrochoidal-shaped chamber having linear side portions extending between rounded end portions. A three-flanked rotor is disposed in the chamber to rotate and operate in a manner similar to that of a common Wankel-style rotary engine. The rotor and chamber are configured to provide a compression ratio sufficient to produce compression-ignition of a heavy fuel. The rotor includes apex seal and side seal mounting blocks formed from hardened materials and that are simply removable from the rotor for replacing apex and side seals. The apex seals may include multiple non-parallel seal members at each apex and the apex seals and the side seals may overlap or intersect a corner seal to increase sealing under high compression loads produced by the rotor/chamber configuration.

BACKGROUND

Internal combustion engine design and development has long favored reciprocating piston engine configurations over rotary engine configurations, also referred to as Wankel engines after the inventor Felix Wankel. However, as manufacturing and design techniques and material technologies advance, rotary engine designs become more interesting and potentially useful for powering a wide variety of devices and vehicles.

Rotary engines can provide a variety of advantages including, for example, high power-density, low vibration, design simplicity, fewer components, compact size, and low engine weight. However, disadvantages like low fuel efficiency and frequent maintenance requirements have historically plagued the operation of such designs.

Much of the research, development, and commercial application of rotary engines has been directed toward designs that operate on spark-ignition of fuels like gasoline. A multitude of organizations such as the United States National Aeronautics and Space Administration (NASA), the United States Army Research Laboratory, the Curtis-Wright Corporation, and the John Deere Company (Deere & Company), among others have also investigated heavy fuel applications of rotary engines, e.g., fuels such as diesel, Jet-A, Jet-A1, JP-5, and JP-8, among others. However, the research and development has thus far failed to produce a viable, compression-ignition, heavy-fuel rotary engine.

A major difficulty encountered with heavy fuel applications is that the compression ratio needed to support compression ignition of the heavy fuel has not been achievable. For example, geometries of the rotor and housing that provide sufficient compression ratios also produce a long, thin combustion chamber which could result in incomplete burning of the fuel, small engine displacement relative to the engine size, heavy mechanical strain on the engine components, and greater component size and strength requirements, and greater engine complexities, among others. Many attempts have been made to produce a rotary engine capable of starting and operating on heavy fuels, but have concluded that such an engine is not practical and requires use of ignition sources, such as spark-plugs glow-plugs, pre-combustion chambers, or other internal and/or external ignition aids. See for example, U.S. Pat. No. 6,125,816 to Louthan et al. and “A Review of Heavy-Fueled Rotary Engine Combustion Technologies” by Chol-Bum M. Kweon, Army Research Laboratory ARL-TR-5546, May 2011 (hereinafter referred to as Kweon).

SUMMARY

Exemplary embodiments are defined by the claims below, not this summary. A high-level overview of various aspects thereof is provided here to introduce a selection of concepts that are further described in the Detailed-Description section below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. In brief, this disclosure describes, among other things, a rotary engine that starts and operates using compression ignition of heavy fuels without use of another internal or external ignition aid.

The rotary engine comprises a rotary engine of a design commonly referred to as an eccentric, pistonless, or Wankel-type rotary engine having a rotor housing that defines an epitrochoidal-shaped, two-lobed chamber in which a three-sided rotor is disposed to rotate in a planetary motion about an eccentric drive shaft. The epitrochoidal shape of the chamber is configured to provide generally circular, rounded endwalls with parallel, linear sidewalls extending therebetween thereby eliminating an inwardly protruding bump or pinching in of the chamber walls found in known rotary engine housing configurations.

The rotor includes three flanks that meet at three respective apexes. The chamber and the rotor are configured to provide compression ratios sufficient to produce compression-ignition of a heavy fuel, e.g. compression ratios greater than 13:1 or greater than about 15:1 or greater than about 18:1, without the use of an additional ignition source such as a spark-plug or other internal or external ignition aid.

A fuel injection system is provided that includes a plurality of fuel injection nozzles disposed along a wall of the chamber to align with a combustion region formed between the rotor flank and the chamber wall. The fuel injection system is configured to provide fuel injection pressures greater than about 300 pounds per square inch (psi). Air induction systems, such as turbo chargers or super chargers among others, may also be provided to increase pressures within an intake region of the chamber.

The rotor housing further includes a pair of end plates that each couple to and enclose a respective end of the housing. Each of the end plates forms a port that is positioned to align with either an intake chamber or an exhaust chamber formed between the rotor flanks and the wall of the chamber. The end plates are configured to be interchangeable or to allow operation of the rotor in either a clockwise or counter-clockwise direction such that the port formed in the end plate can be employed as either an intake or an exhaust port.

Apex seals are provided at each apex of the rotor and extend between the apex and the wall of the chamber. The apex seals are disposed in an apex-seal holder comprised of a hardened, wear-resistant material. The holder is removably coupled to the rotor to enable simple removal from the rotor along with the associated apex seals and thus simple replacement of worn apex seals. Side seals are provided on each end face of the rotor extending into contact with the respective end plate and are similarly disposed in side-seal holders that are simply removable and replaceable on the rotor. The apex and side seals may be configured to overlap with a corner seal at or adjacent to the apexes of the rotor to increase sealing between chambers.

DETAILED DESCRIPTION

The subject matter of select exemplary embodiments is described with specificity herein to meet statutory requirements. But the description itself is not intended to necessarily limit the scope of claims. Rather, the claimed subject matter might be embodied in other ways to include different components, steps, or combinations thereof similar to the ones described in this document, in conjunction with other present or future technologies. Terms should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described. The terms “about”, “approximately”, or “substantially” as used herein denote deviations from the exact value by +/−10%, preferably by +/−5% and/or deviations in the form of changes that are insignificant to the function.

With reference toFIGS. 1-10, an eccentric, high-compression, heavy fuel, rotary engine10is described in accordance with an exemplary embodiment. The rotary engine10starts and operates using compression-ignition of a heavy fuel without the use or need for a secondary ignition source like a spark plug or other internal or external ignition aid. The rotary engine10is described herein as being an eccentric rotary engine, but may also be referred to as a pistonless or a Wankel-style engine in that the engine10includes components and operational characteristics that are generally similar to known rotary engines like those developed by Dr. Felix Wankel and described in, for example, U.S. Pat. No. 2,988,065 to F. Wankel et al. But the engine10includes novel features not found in such prior designs that enable operation in ways deemed not practical or possible by such known designs.

The rotary engine10comprises a housing12, a pair of end plates14,16, a rotor18, and a drive shaft19. The rotary engine10is described herein with respect to a single housing12and rotor18, however it is foreseen that the rotary engine10may comprise multiple housings12and rotors18arranged to operate together. For example, in one embodiment a plurality of housings12and rotors18are disposed in series along the length of a single drive shaft19and are operated together to drive the drive shaft19.

As depicted inFIG. 6, the housing12is a generally planar component having a thickness that is just larger than a thickness of the rotor18. The housing12includes an interior wall20extending parallel to the thickness of the housing12that forms an epitrochoidal-shaped, open-ended chamber22. The epitrochoidal shape of the chamber22is somewhat elongated with rounded end portions24and linear, parallel side portions26connecting therebetween. The housing12may include a number of fuel injection ports28disposed along the interior wall20to align with associated regions within the chamber22as described more fully below. Intake and exhaust ports may also be provided along the interior wall20at desired locations.

The end plates14,16couple to opposite faces of the housing12and enclose the chamber22therebetween. An intake port30and an exhaust port32are provided by the end plates14and/or16; both the intake port30and the exhaust port32may be provided by the same end plate14or16, or one port30,32can be provided in each of the end plates14and16. In one embodiment, the end plates14and16are identical and are thus interchangeable and their respective ports30,32take an intake or exhaust function based on their position within the engine10. In another embodiment, the placement and configuration of the intake port30and the exhaust port32in the end plates14,16is such that the rotor18can be operated to rotate in either clockwise or counter-clockwise direction with the ports30and32functioning for either intake or exhaust depending on the direction of rotation. One or both of the end plates14,16may be configured to couple between two housings12, as depicted inFIG. 6, or between the housing12and an intermediate component (not shown) in embodiments in which multiple housings12and rotors18are employed.

The rotor18comprises a generally planar component having three equal sides or flanks34, respective pairs of which meet at respective apexes36, as depicted inFIG. 8. The rotor18is configured with a thickness just less than that of the housing12such that the rotor18is disposable within the chamber22and between the end plates14,16. The flanks34are dimensioned to enable planetary rotational motion of the rotor18within the chamber22while maintaining the apexes36in very close and substantially constant proximity to the interior wall20at all times.

With reference toFIGS. 8-10, apex seals38are provided at each apex36to seal opposite ends of a space40formed between the respective flank34and the interior wall20. Each apex seal38comprises a rib of material that protrudes from the apex38a distance sufficient to engage the interior wall20in sliding contact and that extends substantially the thickness of the chamber22between the end plates14,16. The apex seal38may protrude a further distance and be at least partially bent, curved, or angled to maintain sliding contact with the interior wall20. The apex seal38may include a biasing means42such as a spring or similar component configured to bias the seal38into sliding contact with the interior wall20.

As depicted inFIGS. 8 and 9, a secondary apex seal44may be provided. In another embodiment, additional apex seals may be provided in addition to the apex seal38and the secondary apex seal44. The secondary apex seal44is configured similarly to the apex seal38but is arranged in an orientation that is not parallel to the apex seal38. For example, the secondary apex seal44protrudes in a slightly different direction than the apex seal38. One or both of the apex seal38and the secondary apex seal44are preferably oriented with very little or no trailing angle, e.g., only slightly angled opposite the direction of rotation of the rotor18or aligned with a radius of the rotor18. In one embodiment, one or both of the apex seal38and the secondary apex seal42are aligned with a trailing angle of less than about 10°, or less than about 5°, or between about 2° and 0°. Such an orientation may reduce an amount of a gas and heavy fuel mixture that is able to pass by the apex seals38,42when under high compression.

A corner seal46is provided at or adjacent each apex36and protrudes from each end face48,50of the rotor18in the direction of the thickness of the rotor18. Each corner seal46overlaps or intersects the respective apex seal36and secondary apex seal44.

The apex seals38and44and the corner seals46are coupled to the rotor18via a respective apex seal mounting block52which is removably disposed in a cutout54in the rotor18at a respective apex36. The mounting block52is comprised of a material having a hardness that is greater than that of the body or remainder of the rotor18and that has greater wear resistance than, for example, the flanks34of the rotor18. For example, the rotor18may be constructed from an aluminum alloy while the mounting blocks52are constructed from a high-strength, wear-resistant steel alloy. The mounting blocks52are coupled to the rotor18via a plurality of fasteners56, such as bolts, screws, or the like. The cutout54and the mounting block52may also be formed with one or more complimentary surface features, such as mating flanges and slots, that engage or interlock to increase the strength of the coupling therebetween.

End faces48,50of the rotor18are provided at opposite ends of the rotor thickness and lie in proximity to the respective end plates14,16. Side seals58are provided on each end face48,50to seal between the respective end faces48,50and end plates14,16. The side seals58extend along the end faces48,50spaced apart from and generally following the contour of the flanks34. Preferably, a pair of side seals58are provided spaced apart along the end faces48,50and extending parallel to one another, however, any number of side seals58may be employed. The side seal58overlap and/or intersect the corner seals46at each apex36. The side seals58may be biased to protrude from the end faces48,50and into sliding contact with the respective end plate14,16.

The side seals58are disposed in side seal mounting blocks60which are removably coupled within a trough62formed in the end faces48,50of the rotor18, as depicted inFIG. 9. Like the apex seal mounting blocks52, the side seal mounting blocks60may be constructed from a material having a greater hardness than that of the body of the rotor18to increase wear resistance. The side seal mounting blocks60are also similarly coupled to the rotor18via a plurality of fasteners56and may include surface features that compliment or mate with corresponding features formed within the trough62to increase the strength of the coupling.

One or more fuel injectors64are installed on the housing12in communication with each of the fuel injection ports28. The fuel injectors64are configured to provide a heavy fuel into the chamber at high pressures and may employ a common rail-type high-pressure manifold. In one embodiment, the heavy fuel is provided at a pressure between about 300 pounds per square inch (psi) and greater than about 30,000 psi, or at about 15,000 psi, or about 26,000 psi.

Referring again toFIG. 6, the drive shaft19comprises an elongate shaft having a lobe66extending radially outward about a portion of the circumference of the drive shaft19and offset to one side from a rotational axis of the drive shaft19. The drive shaft19is installed through apertures in the end plates14and16and the rotor18such that the lobe66is aligned within a central aperture68in the rotor18. The central aperture68, the rotor18, and the lobe66are coaxially aligned which offsets the rotational axis of the rotor18from that of the drive shaft19. The central aperture68of the rotor18includes a ring gear or similar toothed portion70that meshes with a static gear coupled to one of the end plates14,16and through which a non-lobed portion of the drive shaft19also passes. Thereby, rotation of the rotor18or of the drive shaft19moves the rotor18in a planetary rotational motion about the static gear.

With reference now toFIGS. 1-5, operation of the rotary engine10is described in accordance with an exemplary embodiment. As discussed previously, the rotary engine10is an eccentric or Wankel-style rotary engine and operation thereof generally follows that of a Wankel-style rotary engine. As such, the spaces40between each flank34and the interior wall20of the chamber22move and change shape and size as the rotor18rotates within the chamber22. And each space40is undergoing a different portion of the combustion cycle relative to the other spaces40at any given time. For simplicity of explanation, only one space40is described herein although one of skill in the art will recognize the applicability of this description to each of the other spaces40as they too move through the same regions within the chamber22.

Beginning initially with an intake phase of the rotary engine10operation, the rotor18is positioned such that the intake port30in the end plate14is open to the space40, as depicted inFIG. 1. As the rotor18rotates (clockwise as depicted inFIGS. 1-5) the space40also moves clockwise around the chamber22and draws air in through the intake port30until reaching a maximum volume, Vmax,FIG. 2, as the rotor18moves over and closes off the intake port30.

When initiating operation or starting the rotary engine10, the drive shaft19is rotated to drive initial rotation of the rotor18. Conversely, after operation of the rotary engine10is initiated, the combustion process of the rotor18drives the rotation of the drive shaft19as described below. The initial rotation of the drive shaft19may be provided by a second gasoline or heavy-fuel rotary or reciprocating engine, an electric motor, or a hand-operated mechanism, among others. However, the initial combustion within the rotary engine10is produced by compression-ignition of a heavy-fuel within the rotary engine10alone and without a secondary ignition source or aid.

The intake air may be drawn into the space40by movement of the rotor18or one or more compression systems, air injection systems, or other aids may be associated with the rotary engine10to compress and or force additional air into the space40through the intake port30. For example, one or more turbo-charger or super-charger systems among other compression systems can be employed. The compression systems may be driven by the rotary engine10or may be driven or powered by a separate power source which may include a second rotary engine, a gasoline or heavy-fuel piston engine, an electric motor, or the like. In one embodiment, a second intake port30′ (FIG. 7) through which the compressed air from the compression system is forced into the space40is provided. The second intake port30′ may be configured like the intake port30to be closed by the rotor18or can include another valve or shutoff means. Additionally, the air may be preheated and/or combined with other gases or fluids prior entering the space40to affect characteristics such as the temperature, pressure, and/or flammability of the air.

As the rotor18continues its rotation, the space40enters a compression phase in which the volume of the space40is decreased thereby compressing the air contained therein. Compression continues until reaching a minimum volume, Vmin, of the space40, as depicted inFIG. 3. A heavy fuel such as diesel, Jet-A, Jet-A1, JP-5, and JP-8, among others is injected via the fuel injectors64into the space40just before and/or as the space40reaches its minimum volume to provide a fuel-air mixture. The heavy fuel is injected at very high pressures, e.g., greater than 300 psi or preferably around 26,000 psi, which may provide an atomized spray with a high surface to volume ratio with increased combustion properties and may further increase the pressure within the space40. One or more fuel injectors64may be employed at various locations along the interior wall20that align with the space40when in the compression phase. The fuel injectors64may be further configured to provide the fuel into the space40at one or more different times relative to the rotation or position of the rotor18and may be directed to spray in one or more different directions or into one or more different areas within the space40.

Compression of the fuel-air mixture in the space40generates heat and pressure sufficient to cause the fuel injected therein to ignite under compression-ignition without the use of a secondary ignition source such as a spark from a spark-plug or a high temperature surface such as a glow-plug. The ratio between the maximum volume and the minimum volume, e.g., the compression ratio provided is greater than about 13:1 which is known to be able to support compression-ignition. Preferably, the compression ratio is greater than about 15:1, or greater than ratios of about 18:1, 20:1, 25:1, or 30:1, among other ratios within or greater than these ranges. Although, particular compression ratio values are provided herein, it is to be understood that all ratios greater that 13:1, e.g. 15:1, 17:1, etc. are within the scope of this disclosure.

Such compression ratios are obtained, at least in part, by the configuration of the interior wall20of the chamber22and the corresponding configuration of the flanks34of the rotor18. As discussed previously above, the interior wall20includes side portions26that are linear. Additionally, the flanks34of the rotor18are substantially continuous smooth surfaces that extend between the apexes36. As such, the volume between the interior wall20and the flank34is minimized and thus the compression ratio is maximized. In contrast, known designs provide side portions of the chamber that bow or pinch inward and flanks of the rotors include recesses, troughs, or similar depressions that extend into the body of the rotor. These features limit the ability of the volume of the space to be minimized and thus the air therein to be compressed. Such known designs thus cannot achieve high-pressures or compression ratios sufficient to support true compression-ignition of heavy-fuels without the use of a secondary ignition source or aid.

Combustion of the heavy-fuel and air mixture in the space40moves the space40through an expansion phase, as depicted inFIG. 4. The combustion applies a force on the rotor18that drives the planetary rotational motion thereof and thus drives rotation of the drive shaft19. Rotation of the rotor18and expansion of the space40continues until the rotor18begins to move past or over the exhaust port32which allows the combusted fuel-air mixture to be expelled through the port32in an exhaust phase, depicted inFIG. 5. Rotation of the rotor18continues to close off the space40from the exhaust port32and to open the space40to the intake port30(FIG. 1) at which point the cycle begins again.

Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the scope of the claims below. Embodiments of the technology have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to readers of this disclosure after and because of reading it. Alternative means of implementing the aforementioned can be completed without departing from the scope of the claims below. Identification of structures as being configured to perform a particular function in this disclosure and in the claims below is intended to be inclusive of structures and arrangements or designs thereof that are within the scope of this disclosure and readily identifiable by one of skill in the art and that can perform the particular function in a similar way. Certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations and are contemplated within the scope of the claims.