Patent Publication Number: US-10774645-B1

Title: High efficiency steam engine

Description:
I. CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of pending application Ser. No. 15/914,417 filed Mar. 7, 2018, which is a continuation-in-part of application Ser. No. 15/794,486 filed Oct. 26, 2017, now U.S. Pat. No. 10,273,840, which is a continuation-in-part of application Ser. No. 15/077,576 filed Mar. 22, 2016, now U.S. Pat. No. 9,828,886, which is a continuation-in-part of application Ser. No. 13/532,853 filed Jun. 26, 2012, now U.S. Pat. No. 9,316,130, which is in turn a continuation-in-part of Ser. No. 12/959,025, filed Dec. 2, 2010, now U.S. Pat. No. 8,448,440 all of which are incorporated herein by reference. 
    
    
     II. FIELD OF THE INVENTION 
     This invention relates to high efficiency steam engines and to improved valve mechanisms and operating methods for such engines. 
     III. BACKGROUND OF THE INVENTION 
     Much of the epic progress during the industrial revolution in the United States during the 19 th  and 20 th  century was powered by steam. However, the thermal efficiency of steam powered piston engines could not match that of the Otto or Diesel engines developed at the end of the 19 th  century. A substantial improvement in steam engine efficiency was however made when the uniflow steam engine was developed by Professor Stumpf in Germany and improved further in the U.S. by C. C. Williams high compression uniflow engine based on compression as described in U.S. Pat. Nos. 2,402,699 and 2,943,608 in which steam is compressed to boiler pressure by the piston return stroke thereby raising the steam temperature for example 95 to 342 degrees hotter than feed steam in a sizeable clearance volume that may be 7% to 14.5% of displacement. The thermal efficiency of even these engines while improved, could not however reach that of the internal combustion engine. 
     Recently, a substantial further advance has been made through the development of steam engines operating on a cycle that employs essentially zero clearance between the piston and the cylinder head at the end of the exhaust stroke while at the same time any steam in the cylinder is under zero compression; a Z-Z operating principle. This arrangement achieves a remarkable increase in thermal efficiency as disclosed in U.S. Pat. Nos. 8,448,440, 9,316,130, 8,661,817, 9,828,886 and pending U.S. patent application Ser. No. 15/794,486 filed Oct. 26, 2017, now U.S. Pat. No. 10,273,840 all of which are assigned to the Applicant&#39;s assignee and incorporated herein by reference. Engines described in the latter five patents listed above provide a thermal efficiency which ranges from an improvement of about 15% to an extraordinary 59% better than the best performing high compression uniflow engines which are widely recognized to have the highest thermal efficiency of any steam engine previously known (see  FIG. 1 ). The outstanding efficiency of the engines built according to the Z-Z patents listed above results from several factors including the Z-Z operating principle as well as benefits arising from the use of a unique, fast acting inlet valve which can open fully in some embodiments in less than 1 millisecond thereby avoiding losses formerly caused by a restriction in the flow of steam (also sometimes called “wire drawing”) through the steam inlet valve while the valve is being opened by a cam or eccentric which may take as much as ⅓ to ½ of a crankshaft rotation resulting in reduced efficiency and power output. By contrast, since the inlet valve of Z-Z engines of the present invention is opened fully almost instantly while the piston clearance is virtually zero, work output begins at the highest steam supply pressure earlier in the cycle thereby providing more power while also eliminating losses associated with having to compress to supply pressure a substantial quantity of steam that remains in the cylinder. One aim of the present invention is to be able to achieve these advantages disclosed in the Z-Z patents listed above. 
     While efficiency has been greatly improved in the five patents listed, several deficiencies were discovered. Valve springs when overheated can lose their temper preventing peak performance. Fiber packing and other nonmetallic seals can create friction or become worn and leak. Valve lifters (projections between a valve and the piston) used to push valve open by piston motion can become weakened due to progressive fracture under cyclic loading over time. 
     In view of these and other deficiencies it is therefore one object of the present invention to retain the high efficiency and other advantages of the Z-Z engine patents noted above while actuating one or more valves by piston movement with little or no wear even when opening or closing the valve in under 1 millisecond. 
     Another object is to yieldably bias inlet and exhaust poppet valves without the need of springs. 
     Another object is to extend the working life of the engine valves subject to progressive fracture under cyclic loading while reducing the reciprocating mass of the valves and valve train. 
     Still another object is to find a way to retain the high thermal efficiency advantages of a zero clearance with zero compression operating principle while reducing the mass of a reciprocating valve train that includes one half the mass of the valve spring. 
     Another object is to eliminate or reduce leakage of working fluid while providing a way of actuating a steam inlet or exhaust valves without a camshaft system by timing at least one steam valve electrically using a computerized electric engine control unit (ECU) and without the necessity of forming valves from a ferromagnetic material. 
     It is a more specific object to maintain the high thermal efficiency that characterizes the virtual zero or near zero clearance with zero or near zero pressure steam cycle of U.S. Pat. Nos. 8,448,440, 9,316,130, 9,828,886 and Ser. No. 15/794,486, now U.S. Pat. No. 10,273,840 wherein steam admission is accurately timed and cut off automatically at any selected time using a relatively low mass steam inlet valve that is able to reciprocate at over 50 cycles per second without the need of a spring, cam shaft assembly or eccentric system and without a valve lifter on the piston that contacts the valve to push it open or closed. 
     Another object is to hold exhaust valves closed reliably yet assure that they can be opened with a small amount of valve work that does not significantly reduce thermal efficiency so as to thereby achieve higher overall thermal efficiency than the best reciprocating steam engines currently in commercial use. 
     These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims. 
     SUMMARY OF THE INVENTION 
     This invention concerns a high efficiency steam engine having steam inlet and exhaust valves that communicate with a steam expansion chamber located in a cylinder between a piston and cylinder head. Steam inlet and exhaust valves are poppet type valves located in the cylinder head or piston, each having a stem mounted for reciprocation in a valve guide. One or more of the valve stems have a thrust surface either as a part of the stem, connected to the stem or on the end of a small valve piston at or attached to the stem. Each thrust surface is in a cavity containing fluid such as steam under pressure to produce a force which acts to open or close the valve proportional to the fluid pressure in the cavity. The exhaust valve is closed proximate an end of the exhaust stroke. Little or no clearance as described in U.S. Pat. Nos. 9,316,130 and 9,828,886 is provided between the piston and cylinder head. The steam inlet valve can be opened and then held open by a steam pressure differential across it. During the power stroke, the steam inlet valve is closed at a selected time to cut off steam admission to the cylinder under the control of an ECU or other timer. 
     In one embodiment, an armature on the exhaust valve is held in contact with an electromagnet by magnetic attraction so that when the current is turned off at a selected time, the pressurized fluid propels the armature away from the electromagnet closing the exhaust valve thereby cutting off the flow of exhaust steam out of the steam expansion chamber proximate TDC. In another embodiment of the invention the exhaust valve is forced shut by steam that is compressed within a recess in the exhaust valve by a plunger on the piston. This causes the steam expansion chamber to be sealed proximate but prior to an end of the exhaust stroke enabling a small residual quantity of steam then trapped in the steam expansion chamber to be compressed by movement of the piston at the termination of the exhaust stroke to a pressure sufficient to open the inlet valve due to the force exerted on the inlet valve by the steam compressed proximate TDC. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph showing the improvement in thermal efficiency of the invention computed from the performance graphs of  FIG. 2 . 
         FIG. 2  graphs the rate of steam consumption calculated per horsepower hour for the invention at various cutoff settings compared with the corresponding performance of an example of the most efficient high compression reciprocating steam engines previously known. 
         FIG. 3  is a top view of one engine cylinder embodying the invention. 
         FIG. 4  is a vertical cross sectional view of the cylinder, cylinder head and piston taken on line  4 - 4  of  FIG. 3  with the piston close to top dead center. 
         FIG. 5  is a vertical cross sectional view taken on line  5 - 5  of  FIG. 3  showing the exhaust valve assembly. 
         FIG. 5A  is a partial bottom view of the selector valve  74  shown in  FIG. 5 . 
         FIG. 6  is a partial vertical sectional view similar to  FIG. 5  showing a different cylinder of the engine wherein the electromagnet is replaced by a fluid pressure cavity or chamber at one end of the exhaust valve. 
         FIG. 6A  is a diagrammatic illustration of an electric solenoid operated two-way valve shown in  FIG. 6 . 
         FIG. 7  is a partial enlarged view of  FIG. 6 . 
         FIG. 8  is a view of a valve similar to those shown in  FIGS. 4 and 6  in which an external spring is used. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to  FIGS. 1 and 2  which show that a very sizeable improvement in thermal efficiency is provided by the present invention compared with what is generally acknowledged to be the most efficient uniflow steam engine design known.  FIG. 1  (which is derived from  FIG. 2 ) shows that at a 16% cutoff the thermal efficiency of the invention is over 15% better, at 12% cutoff it is almost 25% better and at an 8% cutoff where the prior art is at or near a stall condition there is an extraordinary 59% improvement of thermal efficiency in engines using the present invention. The present invention is about 20% better when each engine is run at its optimum efficiency. In a typical steam engine, the efficiency improves as the cutoff is lowered.  FIG. 1  shows that it is in this lower cutoff range where the present invention makes possible the greatest improvement. 
       FIG. 2  illustrates in the upper graph the performance of a 2 cylinder double expansion high compression steam engine powered by biomass (wood) producing 473 hp to provide 300 KW @ an assumed 85% generator efficiency compared to an equivalent engine embodying the present invention with both operating under the same conditions listed in  FIG. 2 . The term “steam rate” in the Figures refers to the pounds of steam calculated using established thermodynamic relationships to produce a given power output. An inefficient engine of course consumes steam at a higher steam rate than an efficient one. For example in  FIG. 2  the high compression compound engine of the prior art (upper graph) at a 10% cutoff consumes 15.6 lbs./hp-hr compared with 12.3 lbs./hp-hr for the invention. In  FIG. 1  the efficiency improvement of the invention over the prior art at different cutoff values is computed by comparing the two graphs shown in  FIG. 2 . The thermodynamic formulas used for computing the results shown in  FIG. 2  are given in Applicant&#39;s U.S. Pat. No. 8,448,440, Column 4, line 48 to Column 6, line 21. 
     Refer now to  FIGS. 3-5  which illustrate a form of the invention having at least one cylinder using an electromagnet for opening a secondary exhaust valve. As best seen in  FIGS. 4 and 5 , the engine has a cylinder head  10  bolted to a cylinder  12  in which a piston  14  is sealingly and slidably mounted. The piston  14  is operatively coupled to a crankshaft  16  by a connecting rod  18  to form a steam expansion chamber  20  between the piston  14  and the cylinder head  10 . The primary exhaust comprises several circumferentially spaced apart uniflow ports  22  in the cylinder  12  which open when the top of the piston  14  reaches its bottom center position at the end of each power stroke causing steam pressure in the chamber  20  to collapse to condenser pressure as it is returned to a condenser (not shown) in a closed circuit that is described for example in Applicant&#39;s prior U.S. Pat. No. 8,448,440. 
     Inlet valve  24  ( FIGS. 3 and 4 ) has a cup shaped head slidably and sealingly mounted within an inlet valve bore  26  defining a cutoff control chamber  28  between the head of inlet valve  24  and a valve cover  30  which is fastened to the top of the cylinder head  10 . The circular head of the valve  24  has a tapered surface that forms a seal on a valve seat  25 . Extending through the cover  30  is a valve guide  32  in which the stem  34  of valve  24  is slidably mounted. Axially spaced apart grooves in stem  34  comprise a labyrinth seal in which each successive groove creates a disturbance that interrupts the outward flow of steam until flow is completely choked off without the use of fiber or rubber packing. At the upward end of the valve stem  34  is secured an inlet valve piston  36  which is slidably and sealingly mounted within a cylindrical valve cavity  38  in enclosure  39  that during operation is filled with a pressurized fluid such as steam, hydraulic fluid or lubricating oil introduced through a supply pipe  40  to apply pressure on a thrust surface at the top of piston  36 . In this embodiment steam is used. The steam is fed from a steam generator  42  through pipe  40  to a pressure regulator  44  of suitable known commercially available construction to provide the desired closing force between the valve  24  and seat  25 . The pressure regulator  44  can be adjusted by the ECU to change the closing force on valve seat  25  depending upon operating conditions such as RPM, load or other variables. Typically a moderate force of 30-60 lbs. on valve stem  34  is sufficient to hold it down. Any condensate or steam in the cavity  38  is returned to a condenser (not shown) through line  37 . 
     A cutoff control valve  46  is threaded into a tube  48  affixed to the cylinder head  10  to control the rate at which high pressure steam passes through the ducts  50 ,  51  into the chamber  28 . The further valve  46  is opened, the more rapidly chamber  28  will be filled with steam from chamber  20  thus reducing the time for the pressure in chamber  28  to equal that in chamber  20  which in turn results in a reduction in the cutoff of steam entering expansion chamber  20  from the steam generator  42  through pipes  52  and  53  into the circular steam chest  54  surrounding valve  24 . It will be noted that the lower face of valve  24  is flush with the surrounding inward surface of the cylinder head and that the upper surface of the piston  14  is also flat so that the surfaces conform to one another. The clearance at TDC in chamber  20  is reduced to a very narrow gap preferably less than 0.125 inch and most preferably in the range of about 0.020 to about 0.030 inch as described more fully in Applicant&#39;s prior U.S. Pat. Nos. 8,448,440 and 9,316,130 for the purpose of achieving a greatly improved level of thermal efficiency as noted above in connection with  FIGS. 1 and 2 . 
     Refer now to  FIGS. 3 and 5  which show diagrammatically an electromagnet  60  secured to the top of the cylinder head  10  and provided with a central bore  62  surrounding a valve guide  64  for the valve stem  66   a  of an exhaust valve  66  that has a valve head with a circular tapered surface  66   b  which when closed forms a seal on the tapered exhaust port  68 . The upper part of the valve stem  66   a  has a larger diameter than a lower section  66   c  within valve guide  68  so as to form a cavity  70  that has a downwardly facing thrust surface within the valve guide  64 . Attached to the free outward end of the upper part  66   a  of the valve stem by a screw  61  is an armature  63  that contacts the poles of the electromagnet  60  when valve  66  is open. 
     In operation, steam or other fluid enters the cavity  70  through supply pipe  72  and an optional rotating selector valve  74  that has a passage  74   a  for filling cavity  70  with, e.g., high pressure steam through passage  73  so as to close valve  66  by applying a moderate upward cyclical force, e.g., 30-60 lbs. intermittently on the upper thrust surface of cavity  70 . A second passage  74   b  is provided for intermittently emptying cavity  70  into the steam expansion chamber  20  through passage  73  and  75  to reduce the load on electromagnet  60  when exhaust valve  66  is being opened. The valve  74  ( FIG. 3 ) has a drive shaft  74   c  which is connected to rotate valve  74  at the speed of crankshaft  16 . In this way the cavity  70  can be filled and emptied intermittently to alternately close exhaust valve  66  at TDC just as the power stroke begins and then empty steam from cavity  70  following the power stroke so that the electromagnet  60  can more quickly open the exhaust valve  66  during the exhaust stroke without being opposed by pressurized steam in cavity  70 . If desired, instead of using valve  74 , a two way type of reciprocating valve described below and shown in  FIG. 6A  can be used to cyclically fill and empty chamber  70  intermittently. During the power stroke, steam pressure in chamber  20  holds the exhaust valve  66  closed. When a steady, i.e., continuous yieldable biasing force on the exhaust valve is desired, steam can be fed directly from a pressure regulator  44  through passage  43  and neither of valves  74  or  82  is used. 
     Refer now to  FIG. 6  which shows an embodiment of the invention in which fluid pressure is used to open an exhaust valve  80  in place of the electromagnet of  FIGS. 3 and 5 . In  FIG. 6  downward valve opening pressure is provided by pressurized fluid as already described in connection with  FIG. 4  and the same numbers refer to corresponding parts. The exhaust valve  80  has a valve stem  34  which reciprocates within a valve guide  32  as in  FIG. 4 . The steam in this example which is used for applying a downward pressure on valve  80  is supplied through a pipe  40  into the cavity  38  within enclosure  39  for applying either a continuous downward force on valve  80  to yieldably bias it to an open position or alternatively an optional two way selector valve  82  can be used. 
     Refer now to  FIG. 6 a    which shows how an intermittent downward force can if desired be provided on valve  80  through the operation of the selector valve  82  to direct high pressure fluid (steam) alternately through supply pipe  40  into chamber  38  when exhaust valve  80  is to be opened then out of chamber  38  through pipes  40  and  84  into the steam expansion chamber  20  when exhaust valve  80  is to be closed. In  FIG. 6 a    a two way valve  82  is depicted diagrammatically for cyclically and intermittently filling and then emptying the chamber  38  through pipe  84  to the expansion chamber  20 . Valve  82  is an electric solenoid operated valve similar to a fuel injector valve of the type used in the internal combustion engines of cars and trucks. In this example an armature  86  that is surrounded by solenoid  88  controlled by the ECU to run at engine speed and located near the center of valve stem  90  is slidably supported to oscillate between springs  91  and  98  for moving a valve head  90   a  at one end of the valve stem  90  axially between valve seats  92  and  94  to direct steam supplied from pressure regulator  44  through pipe  45  alternately; either into the chamber  38  through pipe  40  when valve  80  is opening or when valve head  90   a  is retracted as shown, steam will then flow back out of chamber  38  and through pipe  84  to the expansion chamber  20  thereby reducing the force required to seat valve  80 . 
     To avoid efficiency losses caused by using eccentrics, cams, push rods and rockers, the intake and exhaust valves of the present invention are operated by piston movement without a part of the piston making physical contact with an inwardly facing surface of a valve. The exhaust valve  80  of  FIG. 6  is closed by means of a plunger  100  (also shown in more detail in  FIG. 7 ) mounted on the top of the piston  14  in position to enter an inwardly facing recess  101  in the inward surface of the head  80   a  of the exhaust valve  80 .  FIG. 7  shows how the piston  14  is provided with a cylindrical projection  102  on which an inverted cup-shaped circular cap  104  is held in place by a screw  106  that passes through a hole at the center of the cap  104  which is slightly larger than the shaft of the screw to allow the cap to move laterally slightly if necessary by engagement with the inside surface of the recess in case initial alignment is not optimal. If desired, the cap can be eliminated and projection  102  can be provided with spaced labyrinth grooves like those on the valve stems. Alternatively, the valve  80  having no recess can be closed by an Inconel washer spring designated 43 in U.S. Pat. No. 8,448,440. 
     Briefly, the engine is operated as follows. Starting is accomplished with a suitable electric starter motor. Steam is exhausted in two phases; the primary exhaust is through the uniflow ports  22  and then during at least a first portion of the exhaust stroke steam is exhausted through the exhaust valve  80  mounted in the cylinder head. The expansion chamber  110  is then sealed by valve  80  late in the exhaust stroke when the piston is proximate but prior to a top dead center position to thereby limit the portion of the stroke during which steam is thereafter compressed within the expansion chamber. Valve  80  closes just after the plunger  100  shown in  FIGS. 6 and 7  enters the recess  101 . Steam which is then compressed within the recess  101  forces the valve upwardly to the closed position shown in  FIG. 7  with the tapered circular edge of the valve  80  sealed against the valve seat  108 . The plunger and recess  101  are dimensioned so that with the piston at TDC, the plunger cannot contact the back wall of the recess  101 . Steam is then compressed in the steam expansion chamber  110  during the remaining terminal fraction of the exhaust stroke approaching zero clearance such that the compressed cylinder steam is able to open the inlet valve  24  ( FIG. 4 ) at least partially with a level of compression work that is greatly reduced by beginning compression proximate TDC and compressing down to a narrow gap of, for example, 0.020 inch. The reduced valve work required assures that a high thermal efficiency is maintained. 
     Once the exhaust valve  80  is seated as shown in  FIG. 7 , the pressure from the blast of steam entering clearance volume  110  opens inlet valve  24  fully typically in less than 1 ms. and also holds the exhaust valve closed during the power stroke until the primary exhaust blow down through the uniflow ports  22  ( FIG. 4 ) takes place whereupon steam pressure in cavity  38  opens the exhaust valve. The narrow gap ( FIG. 7 ) defining the clearance  110  between the piston  14  in the cylinder head  10  is preferably much less than 0.125 inch and typically around 0.020 inch. Because of the pressure developed in the recess  101  as the piston approaches TDC, the exhaust valve will close proximate to but slightly before the piston reaches TDC at the terminal end of the exhaust stroke. 
     Adjustments to the steam pressure in the cavity  38  as initially selected by the operator and later by the ECU are used to set the piston clearance from the cylinder head when the exhaust valve becomes seated and this in turn determines the final pressure reached in the clearance volume  110  at TDC. The time between the cylinder pressure rise sent to the ECU from a pressure sensor  111  ( FIG. 6 ) and TDC sent from crankshaft  16  to the ECU can be used by regulator  44  for controlling the pressure in cavity  38  of  FIG. 6  to begin compression in chamber  20  at the time desired. A better understanding of operating conditions is made possible by graphing cylinder pressure vs. volume (PV) on a computer screen. Therefore with the components constructed and arranged as described, a very high pressure can be reached in chamber  110  with the expenditure very little work; and the pressure produced in the cylinder  12  in this way beginning when the clearance is for example 0.125 inch and ending when the clearance is 0.020 inch is much greater than that required to open the inlet valve  24  ( FIG. 4 ) at least partially which in turn allows high pressure steam entering the minute clearance space to drive the inlet valve open fully, typically in less than 1 ms. Due to the small reciprocating mass of the inlet and exhaust valves as shown in the drawings, the forces required to accelerate the valves are substantially reduced. One test article had a bore of 3.75 inches, stroke of 3.07 inches and cylinder displacement of 564 mL. The weight of the 1 inch diameter titanium exhaust valve of the size shown in  FIG. 6  was 0.08 pounds. This can improve both valve acceleration and the occurrence of valve float. 
     Refer now to  FIG. 8 . When the pressure applied to the poppet valves does not need to be varied and the spring would not be adversely affected by heat, the spring operated valve of  FIG. 8  can be used in place of the fluid operated valves of  FIGS. 4 and 6 . It can be seen that the valve stem  34  extends through a valve guide  32  that has a spring holder  123  secured to its upper end which is provided with several outwardly opening circumferentially spaced apart notches  124 , through which extend an equal number of coupling rods  126  that are connected between a spring retainer tube  128  which also acts as a heat barrier and an end plate  130  that is secured to the outer end of the valve stem  34 . Tube  128  can be formed from a low thermal conductivity alloy such as stainless steel type 304 or Hastelloy C with a fibrous or ceramic liner. A compression spring  132  is mounted between the end plate  130  and the tube  128  to exert a downward force on the valve stem  34 . Placement of the spring outside of the heat barrier  128  where it is exposed to the cooling effect of the surrounding air helps to prevent it from overheating. 
     The various features and benefits of the present invention working together even make it possible in some embodiments of this invention to achieve a thermal efficiency exceeding that of a steam turbine in smaller sizes, such as those under 1000 horsepower while also having a lower cost. The features and advantages noted above also make the invention well suited for applications such as electric power generation or the co-generation of heat and power as well as to power a vehicle or to generate solar power and as a steam expander for an internal combustion engines to recover waste heat. A major advantage of the invention over internal combustion engines is its ability to use a variety of low grade fuels including waste or unrefined liquid fuels and low cost biomass without producing harmful nitrogen compounds generated by internal combustion engines. 
     Many other variations within the scope of the appended claims will be apparent to those skilled in the art once the principles disclosed herein are read and understood.