Abstract:
In some aspects, there is provided an apparatus. The apparatus may include a cylinder for a reciprocating steam engine, wherein the cylinder further comprises a cylinder ring. The cylinder ring may include a face and a heel, wherein the face makes contact with a piston of the reciprocating steam engine, wherein the heel inserts into a cavity formed on an inner surface of the cylinder, wherein the cavity is positioned in a region of the inner surface proximate to a top of the piston, when the piston is at a bottom dead center position. Related apparatus and methods are also described.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of the following provisional application, which is incorporated herein by reference in its entirety: U.S. Ser. No. 61/219,768, entitled “Cylinder Rings for Engines,” filed Jun. 24, 2009. 
     
    
     FIELD 
       [0002]    The present disclosure generally relates to engines and, in particular, steam engines. 
       BACKGROUND 
       [0003]    A steam engine performs work using steam. Generally, the process of using steam to perform work begins by heating water to generate steam. The steam is then used to drive an engine which performs work, such as for example by driving a piston to power machinery, generate electricity, and the like. 
       SUMMARY 
       [0004]    In some aspects, there is provided an apparatus. The apparatus may include a cylinder for a reciprocating steam engine, wherein the cylinder further comprises a cylinder ring. The cylinder ring may include a face and a heel, wherein the face makes contact with a piston of the reciprocating steam engine, wherein the heel inserts into a cavity formed on an inner surface of the cylinder, wherein the cavity is positioned in a region of the inner surface proximate to a top of the piston, when the piston is at a bottom dead center position. 
         [0005]    In another aspect, there is provided an apparatus comprising a cylinder for a reciprocating steam engine. The cylinder may include an inner surface. The cylinder may further include an insulating ring and an annular cooling chamber. The annular cooling chamber may extend around the inner surface of the cylinder and contact a region of the inner surface of the cylinder, wherein the region of the inner surface is proximate to a top of the piston, when the piston is at a bottom dead center position. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. Further features and/or variations may be provided in addition to those set forth herein. For example, the implementations described herein may be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed below in the detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    In the drawings, 
           [0008]      FIG. 1  depicts a cross-section view of a portion of a steam engine including cylinder rings and a ring holder; 
           [0009]      FIG. 2  depicts a closer view of a portion of the cylinder rings and the ring holder depicted at  FIG. 1 ; 
           [0010]      FIGS. 3A-3B  depict examples of the cylinder rings and the ring holder; 
           [0011]      FIG. 4  depicts an example of the cylinder rings implemented using springs; and 
           [0012]      FIG. 5  depicts an example of a cylinder cooled using an annular cooling region. 
       
    
    
       [0013]    Like labels are used to refer to same or similar items in the drawings. 
       DETAILED DESCRIPTION 
       [0014]      FIG. 1  depicts a cross-section view of a portion of a steam engine  100 . The steam engine  100  includes one or more inlet valves  105 A-D to a cylinder  110  having inlets  107 A-D through which high-pressure, high-temperature steam is admitted into cylinder  110 . The cylinder  110  also includes exhaust valves  112 A-H, such as for example Unaflow exhaust valves  112 C, D, E, and F and auxiliary exhaust valves  112 A, B, G, and H. When the exhaust valves are opened, these valves allow exhaust steam to flow through for example the exhaust ports, such as Unaflow exhaust ports  114 C, D, E, and F and the auxiliary exhaust ports  112 A, B, G, and H. The portion of the steam engine  100  also includes a piston  120 , which moves within the cylinder  110 . In some example embodiments, the steam engine  100  includes cylinder rings  132 A-B and a ring holder  130 . 
         [0015]    Although the description herein uses a steam engine and, in particular, a Universal Unaflow steam engine, other types of engines may be used as well including reciprocating steam engines, a compound steam engine, a Unaflow steam engine, an internal combustion engine, and any other type of engine. 
         [0016]    Before describing the cylinder rings  132 A-B further, the following provides a general description of the operation of steam engine  100 . 
         [0017]    The inlets  107 A-D enable steam to flow into the cylinder  110  under the control of inlet valves  105 A-D. For example, when the inlet valves  105 A-B are open, high-pressure, high-temperature steam is admitted into the upper portion  170  of the cylinder  110 , and then the valves  105 A-B close such that the steam expands and pushes the piston  120  towards the lower portion  180  of cylinder  110 , at which point the piston  120  is at, or near, the bottom dead center of the stroke. At approximately bottom dead center, or slightly before or after, the exhaust valves  112 C-D are opened, allowing a portion of the steam to exhaust through the exhaust ports  114 C-D. When a Unaflow steam engine is used, the Unaflow steam engine (when compared with a counter-flow steam engine) may have a larger portion of the steam exhausted through the Unaflow exhaust ports, which are farther from the hotter inlet ports than the exhaust ports mounted in, or near, the cylinder head containing the inlet ports, reducing thus the energy loss that results from contact between cooler expanded steam and hotter parts of the cylinder valves. 
         [0018]    When the piston is at approximately bottom dead center, the inlet valves  105 C-D open to admit high-pressure, high-temperature steam via inlet ports  107 C-D into the lower portion  180  of the cylinder  110 , driving the piston  120  upward. Also, when the piston  120  is at approximately bottom dead center, auxiliary exhaust valves  112 A-B are opened, so that as piston  120  is driven upward, the piston  120  pushes most of the steam remaining in upper cavity  170  out of Unaflow exhaust ports  114 C-D and auxiliary exhaust ports  114 A-B. After piston  120  covers Unaflow exhaust ports  114 C-D, Unaflow exhaust valves  112 C-D are closed. After piston  120  covers auxiliary exhaust ports  114 A-B, auxiliary exhaust valves  112 A-B are closed. Once the piston  120  is driven towards the top of the cylinder  110 , the cycle repeats with the opening of inlet valves  105 A-B. Although the foregoing provided a general description of an operating mode of a steam engine, other operating modes may be used as well. 
         [0019]    The piston  120  may be considered double acting, such that when the piston  120  is at about the bottom dead center of its travel, the inlet valves  105 C-D open to admit steam into the lower portion  180  of the cylinder  100 , driving the piston  120  upward. And, when the piston  120  is at about the top dead center of its travel, the inlet valves  105 A-B open to admit steam into the upper portion  170 , driving the piston  120  downward. 
         [0020]    The cylinder  110  includes an inner surface  124  and an outer surface  126 . In some example embodiments, one or more cylinder rings  132 A-B are positioned in annular grooves in the ring holder  130 . The one or more cylinder rings  132 A-B and the ring holder  130  are positioned between the upper and lower portions  170  and  180  of cylinder  110 . Although  FIG. 1  depicts a single ring holder  130 , other quantities of ring holders may be used as well. 
         [0021]    In some example embodiments, the cylinder rings  132 A-B are positioned at a so-called “cold region” of cylinder  110 . The cold region is typically the region of the cylinder wall proximate to the top of piston  120 , when the piston  120  is at or near the bottom dead center portion of the stroke. 
         [0022]    In a double acting piston, such as for example piston  120  depicted at  FIG. 1 , the cold region is at about the middle portion of the cylinder  110 . Thus, in the example of  FIG. 1 , the cold region corresponds to the area of the inner surface  124  proximate to the top of piston  120 , when the piston is at, or near, the bottom dead center of the stroke. The cold region in the example of  FIG. 1  also corresponds to the region of the inner surface of the cylinder that is proximate to the bottom of piston  120 , when the piston is at, or near, the top dead center of the stroke. Regardless of whether the piston  120  is at top dead center or bottom dead center, the cold region, in the example of  FIG. 1 , corresponds to substantially the same region of the inner surface  124  of piston  120 . 
         [0023]    The cold region—where the cylinder rings  132 A-B and ring holder  130  are positioned—may be a relatively cooler portion of the cylinder  110 , when compared to the steam inlets  107 A-D through which relatively high-temperature and high-pressure steam enters the cylinder  110 . Moreover, the compression of the steam by piston  120  may further contribute to the high temperatures near inlets  107 A-D. In a double-acting piston engine, the temperature of the cylinder  110  typically decreases from the inlets  107 A-B to the cold region and then increases again when approaching inlets  107 C-D. 
         [0024]    The cylinder rings  132 A-B may be configured in series, i.e., one above the other. The cylinder rings  132 A-B may consist of any sealing material including, for example, grey cast iron, ductile iron, steel, and any other suitable material. 
         [0025]    The cylinder rings  132 A-B are configured to be inserted into the annular grooves of the ring holder  130 . While seated in the grooves of the ring holder  130 , the cylinder rings  132 A-B provide a seal by pushing against the moving, exterior surface of the piston  120 . Moreover, the cylinder rings  132 A-B and the ring holder  130  may also provide a mechanism from which lubricant may be applied to the piston  120  to reduce friction. Because the cylinder rings  132 A-B are located in the cold region of the cylinder  110 , the lubricants used in cylinder  120  may operate at a lower temperature, when compared to approaches which do not place the cylinder rings at the cold region. This may enable the inlet steam to be provided at even higher temperatures and pressures, without raising the lubricant to its breakdown temperature. The ability to use increased temperatures and pressures of inlet steam may result in increased power and efficiency for the engine  100 . For example, a steam engine may have an inlet steam temperature of about 600 degrees Fahrenheit, which is a temperature at which most lubricants breakdown, but the cold region may have a temperature of about 248 degrees Fahrenheit or less (which may be below the breakdown temperature of some lubricants). 
         [0026]    Furthermore, as the piston  120  moves within cylinder  110 , the cylinder rings  132 A-B push against the moving, exterior surface of the piston  120 . The pressure of the cylinder rings  132 A-B against the moving piston  120  may be sufficient to prevent gas (e.g., steam) from leaking between the surface of the moving piston  120  and cylinder rings  132 A-B. The cylinder rings  132 A-B are typically forced toward the moving surface of the piston  120  with sufficient force to exceed the force that tends to push the cylinder rings  132 A-B away from the moving surface of piston  120 . The force pushing a cylinder ring away from the surface of the piston is approximately the contact area of the ring to the piston multiplied by the average of the pressures above and below the cylinder ring. 
         [0027]      FIG. 2  depicts a closer view of a portion of the cylinder rings  132 A-B and the ring holder  130 . In the example of  FIG. 2 , the cylinder rings  132 A-B are positioned between the upper cavity  170  and the lower cavity  180  in the so-called cold region of the cylinder  110 . 
         [0028]    The cylinder rings  132 A-B may be annular and shaped to fit securely into the cavity provided by the ring holder  130 . The cylinder rings  132 A-B and the ring holder  130  may extend around the perimeter of the cylinder, such that the face of each of the cylinder rings extends beyond the inner surface of the cylinder to enable contact with the piston. The face of the cylinder ring refers to the portion of the cylinder ring making contacting with the piston  120 . The cylinder rings  132 A-B may each include a heel (e.g., heel  230 A), which is distal to the face. The cylinder rings  132 A-B may be positioned serially, i.e., one above the other. The distance from the inside of the ring annulus to the outside of the ring annulus is typically larger than the maximum distance from the inside cylinder surface to the outside piston surface, so that the piston prevents the ring from sliding out of the ring holder. 
         [0029]    In the example embodiment of  FIG. 2 , the cylinder ring  132 A includes a substantially flat face, two parallel sides that extend perpendicularly from the face, and a heel  230 A-B. As noted, the cylinder ring may have one or more steps as depicted at  230 A-B. Although  FIG. 2  depicts a stepped shape for the cylinder ring, other shapes may be used as well. 
         [0030]    The ring holder  130  may also include insulating rings  210 A-B. The insulating rings  210 A-B may be an annular ring around the perimeter of the cylinder  110 . The insulating rings  210 A-B may each be used to further insulate the cylinder rings  132 A-B from the warmer portions of the cylinder  110 . The insulating rings  210 A-B may comprise any insulating material, although in some implementations the insulating rings  210 A-B comprise compacted mineral fiber or silicone rubber covered in stainless steel or covered in titanium foil to withstand high temperatures. For lower temperatures of about 260 degrees Fahrenheit of less, the insulating rings may comprise a compressed vegetable fiber with a foil covering (or without the foil) and phenolic resin or a hard rubber. 
         [0031]    In the example of  FIG. 2 , the cylinder rings  132 A-B are stepped, although in some implementations the steps may be omitted. The steps  230 A and C are distal to the face of the cylinder rings, and are used as a surface upon which pressure may be applied. For example, pressurized lubricant may be applied via lubricant supply channel  240  (e.g., formed within the ring holder as a tubular enclosed passage). The pressurized lubricant applies a force to the steps  230 A and C, which drives the cylinder rings  132 A-B towards the moving, exterior surface of the piston  120 . The ring holder  130  may also include a return drain, such as channels  250 A-B to allow excess lubricant to drain. 
         [0032]      FIG. 2  depicts two supply channels  240 A-B and two drain channels  250 A-B, however other quantities of supply and drain channels may be used as well. The supply and drain channels may be implemented as tubular enclosed passages in a direction radial to the axis of the cylinder. 
         [0033]    A pressurized lubricant may be forced to the edge of the cylinder rings  132 A-B to lubricate the area where the faces of cylinder rings  132 A-B come in contact with piston  120 . The pressurized lubricant traveling via channels  240 A-B may also apply pressure to the steps  230 A and  230 C, forcing the cylinder rings  132 A-B to make contact at sufficient pressure with the moving piston  120 . The lubricant may also be at a higher pressure than the pressure on the power side of the ring (e.g., at region  290 ) during some portions of the engine cycle in order for the lubricant to flow towards the face of the cylinder rings by flowing between the cylinder ring and the ring holder. Even though the lubricant pressure may at times be substantially higher than the average pressure on the face of the cylinder ring that is in contact with the piston, the fact that the area of the step (e.g., step  230 A) is less than the area of the face of the cylinder ring, results in the pressure of the cylinder ring toward the piston to be as low as practical while retaining the cylinder ring in contact with the piston. In some implementations, if it were not for the fact that the areas of steps are less than the areas of the cylinder ring faces, the force of the lubricant on the distal face of the cylinder ring might force the cylinder rings  132 A-B to be pressed against piston  120  at a pressure that is higher than necessary, resulting in additional friction between the cylinder ring and the piston (which may result in loss of power and efficiency). 
         [0034]    The lubricant at  240 A-B may be provided at a constant pressure to force the cylinder rings  132 A-B towards the piston  120 . Alternatively, the lubricant pressure  240  may be varied. 
         [0035]    For example, when the piston  120  cycles through power and exhaust strokes, the pressure within the cylinder varies. During power strokes, the pressure on the power side of a cylinder ring is higher than the pressure on the non-power side. During non-power exhaust strokes, the pressure difference between the power side and non-power side of the cylinder ring is relatively lower, and the total force tending to push the cylinder ring away from the piston is relatively lower. The pressure of the lubricant may be cyclically varied, such that both the lubricant pressure and thus the pressure forcing the cylinder rings  132 A-B against the moving surface of the piston  120  are varied to maintain a seal against the piston  120  and provide adequate lubricant flow, while keeping the pressure as low as possible to minimize friction between the cylinder ring and the piston. 
         [0036]    When the piston  120  is not in a power portion of the cycle, the pressure at region  290  may decrease. When this is the case, the pressure of the lubricant traveling via lubricant supply channels  240 A-B and applying pressure on steps  230 A and C may be reduced, without compromising the sealing and lubricating aspects of the cylinder rings  132 A-B. When compared to a constant pressure approach, varying the pressure of the lubricant may reduce the amount of pressure exerted by the cylinder rings  132 A-B against the surface of the piston  120 , which may yield enhanced engine  100  power and efficiency by reducing friction. 
         [0037]    The lubricant may be supplied to the space adjacent to the step at a pressure that ensures the steam in the cylinder does not leak significantly along the high-pressure edge of the cylinder ring. The space adjacent to the larger step  230 B is drained to allow the lubricant to flow out at a much-reduced pressure. The reduced pressure may be more or less than the pressure in the cylinder on the low pressure side of the sealing ring. Control of the pressure of the lubricant on the smaller step  230 A may provide sufficient force on the sealing ring to prevent excessive gas leakage past the cylinder ring. The ratio between the areas of the smaller surface of step  230 A and the larger surface  230 B may be configured to control the pressure, the flow of lubricant into the cylinder, and/or the leakage of steam from the cylinder into the lubricant flow (which may minimize both leakage and friction). 
         [0038]    The lubricant may be a liquid lubricant or a two-phase lubricant consisting of liquid and gas/steam. The lubricant may be one or more of the following: oil, water, steam, gas, finely divided solid or any mixture, solution, or dispersion of these. In some implementations, using a mixture of gas (e.g., steam) with a liquid lubricant or a solid lubricant may enable the cylinder ring to slightly move while seated in the cavities (or grooves) of the ring holder to accommodate the dynamic movement of the piston. 
         [0039]      FIG. 3A  depicts a portion of cylinder rings  132 A-B and ring holder  130 . In the example of  FIG. 3A , the cylinder rings  132 A-B are annular rings having a corresponding steps distal to the face of the cylinder ring. In some implementations, the steps (e.g., steps  230 A and C) are each about 25% of the overall thickness of the cylinder ring. The cylinder rings  132 A-B are shaped to fit securely into mating groves  330 A-B of the ring holder  130 .  FIG. 3A  depicts a portion of the cylinder rings  132 A-B, ring holder  130 , and grooves  330 A-B. However, the cylinder rings  132 A-B, ring holder  130 , and grooves  330 A-B extend around the perimeter of the cylinder  110  (e.g., around the cold region of cylinder  110 ). 
         [0040]      FIG. 3B  depicts each of cylinder rings  132 A-B. In some implementations, the cylinder rings  132 A-B may be segmented  362 A-D to form an annular ring, which is inserted into the mated cavity (or groove) of the ring holders to securely hold the cylinder rings. The one or more segments  362 A-D may have one or more corresponding gaps between the ends of the segments to allow for the completed rings  132 A-B to change circumference in order to maintain a seal while accommodating dynamic motion of the piston and also accommodate variations due to manufacturing tolerances and thermal expansion and contraction. The segmentation of the rings also facilitates assembly and disassembly. The joints between the segments are configured as typical sealing joints, such as for example halving joints, to minimize leakage through the gaps. 
         [0041]    Although the cavities of the ring holder  130  into which the cylinder rings are inserted are sized to make close contact with the cylinder rings, the cavities may be configured to provide sufficient space between the surfaces of the rings and ring holder to allow lubricant to flow within the space and flow to the face of each of the cylinder rings. 
         [0042]    Although two cylinder rings are depicted  FIGS. 1-4 , other quantities of cylinder rings may be used as well. Moreover, the use of multiple cylinder rings may divide the pressure drop across each cylinder ring. 
         [0043]      FIG. 4  depicts another example of an implementation of the cylinder rings  132 A-B. In the example of  FIG. 4 , the cylinder rings  132 A-B are positioned in the so-called cold region of the cylinder  110 . However, cylinder rings  132 A-B are forced against the moving surface of the piston  120  using springs  420 A-B. Although  FIG. 2  and  FIG. 4  depict examples of using springs and lubricant, a combination of both may be used as well. 
         [0044]    In the example of  FIG. 4 , the cylinder rings  132 A-B also include insulation, such as insulating rings  410 A-D. The cylinder rings  132 A-B may extend around the perimeter of the cylinder  110 , and may also be positioned within the ring holder  130  using spacers, such as for example spacers  430 A-D. 
         [0045]    In some implementations, the so-called cold region in the middle of the cylinder  110  is further cooled using a coolant. This may be accomplished by a channel extending around the cold region of the arrangements depicted in  FIGS. 1-4  through which coolant flows, or by other cooling mechanisms, such as fins cooled by air flow. 
         [0046]      FIG. 5  depicts cylinder  110  further configured to include an insulator  510  and an annular cooling chamber  520 , which provides a cool region (e.g., an annular cooling region) on the inner surface of the cylinder  110 . The annular cooling chamber  520  may include a coolant to cool the region. 
         [0047]    In the configuration of  FIG. 5 , the cylinder rings are removed from the cold region and replaced with a typical set of piston rings  530 A-D located near the top and bottom of the piston  590 , although the annular cooling chamber  520  and insulator  510  may be used with cylinder rings as well. 
         [0048]    The annular cooling chamber  520  forms a cavity around the interior surface of the cylinder  110 . The annular cooling chamber  520  may cool the interior surface of the cylinder  100  at the cold region  560 . The cold region  560  forms an annular region around the interior surface of the cylinder  110 . 
         [0049]    In some implementations, the annular cooling chamber  520  may be insulated from hotter portions of the engine using the insulator  510 . The insulator  510  may be implemented as an annular jacket around the annular cooling chamber  520 . The insulator  520  may extend around the perimeter of the cylinder wall. The coolant in water channel  520  may be any type of liquid or gas including one or more of the following: water, ethyl glycol, oil, air, and the like. The coolant may be circulated into the annular cooling chamber  520  and cooled by a variety of mechanisms, such as for example a radiator. The coolant cools the surface of the cold region  560  sufficiently so that the piston rings  530 A-B are cooled when traversing the cold region  560 , which occurs when piston  120  is shortly before, at, and after the bottom dead center. 
         [0050]    Shortly before, during, and after piston  120  is at top dead center, piston rings  530 C-D traverse cold region  560  and are thus cooled. Each set of piston rings at either the top end of piston  120  (piston rings  530 A-B) or the bottom end of piston  120  (piston rings  530 C-D) traverses both the cold region toward the center of the cylinder and one of the hotter regions toward the end of the cylinder, and is alternately heated and cooled. Since heating and cooling is not instantaneous, the temperature excursion of the piston rings  530 A-D is less than the difference between the extremes of temperature found at the hotter regions and the cold region of the cylinder. In particular, the maximum temperature reached by the piston rings may be substantially less than the maximum temperature reached by the steam in the cylinder or the maximum temperature of the cylinder walls, cylinder ends, piston walls, and/or piston ends. The cooling provided by the coolant in the cooling channel serves to further reduce the maximum temperature reached by lubricant in contact with the piston rings. As a result, the temperature and pressure of the inlet steam may be raised to a higher level without causing the lubricant to exceed the breakdown temperature of the lubricant. 
         [0051]    Furthermore, the use of inlet steam at higher temperature and pressure may enable operation of the engine at a higher power and efficiency. For example, in an a typical engine without an annular cooling chamber  520  and a cooling region, the temperature of the piston rings may cycle between a maximum of 310 degrees Fahrenheit and a minimum of 255 degrees Fahrenheit. With the addition of the annular cooling chamber  520 , the temperature of the piston rings may cycle between a maximum of 220 degrees Fahrenheit and a minimum of 165 degrees Fahrenheit. This would in turn enable the temperature of the inlet steam to be increased by approximately 150 degrees Fahrenheit without causing the lubricant to exceed the lubricant&#39;s breakdown temperature. Although some of the examples described herein provide temperatures, these values are merely examples. 
         [0052]    In some of the example embodiments described herein, it may be desirable to maintain the temperature of the cylindrical wall of the piston as low as possible as some or all of the piston wall comes in contact with the cylinder rings or piston rings, and it may also be desirable to keep the temperature of the cylinder rings or piston rings as low as possible. The highest temperatures that the piston will be exposed to may be at the top surface of the piston when the piston is near top dead center, or at the bottom surface of the piston when the piston is near bottom dead center. The piston walls may be kept cooler by increasing the thermal resistance between the top or bottom surfaces of the piston and the cylindrical piston walls. This can be accomplished by inserting a ring of insulating material between the top or bottom surfaces of the piston and the piston walls. The insulating rings are located near the top or bottom ends of the piston walls. In the case where piston rings are used, the insulating ring may be located between the piston ring (or set of rings) and the top (or bottom) surface of the piston that is proximate to the piston rings. This thermal isolation between the top or bottom surface of the piston and the piston wall may also be implemented by constructing the top and bottom surfaces of the piston from material that has a relatively low thermal conductivity while being able to withstand the high temperatures that the ends of the cylinder are exposed to. An example of such a material is a stainless steel alloy with low thermal conductivity. 
         [0053]    While the mechanisms described herein are described in the context of double-acting piston engines, the described mechanisms may also be used with single-acting piston engines, including both steam engines and internal combustion engines. 
         [0054]    The foregoing description is intended to illustrate but not to limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims.