Patent Publication Number: US-8109097-B2

Title: High efficiency dual cycle internal combustion engine with steam power recovered from waste heat

Description:
This application is a continuation-in-part of Ser. No. 12/075,042 filed Mar. 7, 2008, now U.S. Pat. No. 7,997,080. The applicants claim the benefit of the following provisional and non-provisional applications entitled INTERNAL COMBUSTION ENGINE WITH AUXILIARY STEAM POWER RECOVERED FROM WASTE HEAT, Ser. No. 60/905,732 filed Mar. 7, 2007; Ser. No. 12/075,042 filed Mar. 7, 2008 (Pub. No. 2008/0216408A1) now U.S. Pat. No. 7,997,080; Ser. No. 61/192,254 filed Sep. 17, 2008 and Ser. No. 61/194,608 filed Sep. 29, 2008 which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to internal combustion engines with supplemental steam power obtained from waste combustion heat and to a combination internal combustion (I.C.) engine and steam engine. 
     BACKGROUND 
     Internal combustion engines although highly developed, dependable and relied upon for almost all road transportation throughout the world generally lose about 72-75% of the fuel heating value through radiation, engine coolant and exhaust. The measured brake horsepower of a typical six-cylinder spark ignition automobile was only 21% of the fuel heating value at 72 MPH and only 18% at 43 MPH,  Internal Combustion Engine Fundamentals , J. B. Heywood, McGraw Hill 1988 pg. 675. Meanwhile, increasing fuel prices and shortages mount steadily as world supplies dwindle and air pollution problems continue. While there have been several attempts to provide greater efficiency in an internal combustion engine by recovering energy from waste heat, prior proposals have had marked shortcomings. One prior system developed by BMW International (U.S. Pat. No. 6,834,503) requires, in addition to the internal combustion engine, an entirely separate steam expander that is connected to the internal combustion engine by a belt to recover power from engine coolant and an exhaust powered steam generator. This arrangement adds considerably to the size, weight and expense of the power plant as well as placing limitations on thermal recovery. Because of space constraints in a vehicle, the volume and weight of the complete unit is critical. Porsche AG developed a waste heat turbine that was geared to an I.C. engine (U.S. Pat. No. 4,590,766). 
     The present invention aims to provide a way to recycle steam continuously in a closed circuit (no steam exhaust) through a high efficiency expander where economy of operation is the prime consideration while the same time improving I.C. emissions. Attempts have been made to combine a gas and steam engine for recovering waste engine heat, examples of which are the Still engine (GB Patent 25,356 of 1910 and 28,472 of 1912 and U.S. Pat. No. 1,324,183) and Mason U.S. Pat. No. 3,921,404. Still has a cylinder cover below the piston that provides a thin annular chamber which allows steam to flow in and out between the cover and the piston from an opening in the cylinder wall. In a counterflow engine, steam pressure throughout the entire cylinder falls close to atmospheric during the entire exhaust stroke producing a drop in steam temperature which cools cylinder walls allowing condensation of the steam admitted on the next power stroke. This robs the engine of power that would otherwise be available by reducing the mean effective cylinder pressure of the incoming charge of steam. However, the efficiency of steam engines operating on what is known as the uniflow principle achieve much greater efficiency than in a counterflow steam engine by reducing the condensation of steam. The inventor of a steam-only uniflow engine described in U.S. Pat. Nos. 2,402,699 and 2,943,608 reported tests showing a thermal efficiency of 38.2% at 3450 RPM. A double acting hollow piston uniflow engine is described in  Marks Standard handbook for Mechanical Engineers,  1987 Section 9-37 as the “last great improvement in design” but it is unsuited for use as a combination internal combustion and steam car engine in part due to overheating of the piston. 
     One object of the present invention is to provide a combined internal combustion and steam engine that overcomes thermal inefficiencies inherent in prior combination engines but has the advantage of utilizing I.C. components (piston, cylinder, connecting rod and crankshaft) and efficiency gains that result from sharing some of the I.C. mechanical losses as well as having a compact unobstructed combustion chamber without pockets or extensions as present in an F head (opposing valve) engine thereby permitting a high performance, high compression four I.C. valve hemispherical chamber construction. A more specific object is to provide a combination engine in which internal combustion and steam act on the same piston without steam condensing on the cylinder or piston walls or heads upon admission so as to eliminate condensation losses previously inherent in prior double acting combination engines. To accomplish this, the invention must provide an I.C. steam engine with protection against losses inherent in filling the clearance space or those due to chilling of steam chamber walls by low-pressure exhausted steam as good or better than in what as known as a uniflow engine. An important requirement in a double acting I.C. and steam engine is the need for a mechanism that uses the least possible added cylinder length to minimize engine size and weight. However, it is also necessary to prevent burnt I.C. gas/oil and blow-by gas from contaminating the steam and thereby reducing steam generator and condenser efficiency. The invention aims to add as little as possible to the cylinder length to accommodate steam yet not contaminate the steam with oil or combustion products. Another general objective of the present invention is to provide a power source for more efficiently utilizing waste heat that is built into the internal combustion engine itself so that a separate steam engine or expander is unnecessary, making possible better recovery of waste energy from the internal combustion engine as well as a reduction in the over-all volume of the power unit and its production cost together with improved operating flexibility so that the engine is well adapted for powering vehicles especially cars, buses, trucks, locomotives or aircraft. It is a more specific object of the present invention to obtain the outstanding efficiency advantages of a combustion piston having an adjacent steam chamber that is able to provide both an effective zero steam chamber clearance and a gain in mean cycle temperature. Another object is to make possible reliable steam admission timing while providing variable steam cutoff in an engine that derives power from steam and combustion acting upon a piston yet is flexible enough to operate efficiently with large variations in load and steam generator output. Yet another object is to more efficiently recover lost combustion heat by conductive transfer to a working fluid within the engine itself as well as a more efficient way of recovering waste heat from I.C. engine coolant and from engine exhaust gases. Another more specific object is to provide a way to capture and remove oil and blow-by gas before it can enter a steam line. Still another object is to find a way to accurately vary steam cutoff in an internal combustion-steam hybrid engine while being able to recompress residual steam to throttle pressure within a combustion piston. 
     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. Topic headings are for convenience of the reader and not intended to be in any way limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a semi-diagrammatic vertical sectional view of one cylinder of an engine in accordance with the invention with the combustion cylinder head elevated and rotated 90 degrees about a vertical axis to show the valves, the piston being shown at the top dead center position; 
         FIG. 2  is a partial view of the lower half of the cylinder of  FIG. 1  on an enlarged scale showing the piston at the bottom dead center position; 
         FIG. 3  is a perspective view of the crosshead and upper portion of the connecting rod; 
         FIG. 4  is a transverse vertical sectional view of the crosshead taken on line  4 - 4  of  FIG. 3 , also showing the crosshead guide column; 
         FIG. 5  is a greatly enlarged partial vertical sectional view showing a portion of the cylinder wall and piston at the bottom dead center position; 
         FIG. 5A  is a view similar to  FIG. 5  to illustrate additional oil rings; 
         FIG. 6  is an exploded perspective view of the steam cylinder head or cap and piston; 
         FIG. 7  is a partial vertical cross sectional view of the steam cylinder head or cap on an enlarged scale to show the double seated balanced poppet valve; 
         FIG. 8  is a vertical sectional view showing another form of steam admission valve; 
         FIG. 9  is a schematic diagram of the invention as applied to a 4-cylinder car engine showing steam circulation; 
         FIG. 9A  is a schematic diagram to show the source of supplemental combustion air fed to the afterburner; 
         FIG. 9B  is a diagram similar to  FIG. 9  showing an alternative condenser and heat recovery circuit; 
         FIG. 10  is a vertical sectional view of a stepped piston engine in accordance with the invention; 
         FIG. 11  is a perspective view of the piston of  FIG. 10 ; 
         FIG. 12  is a schematic diagram showing the recovery of braking energy; 
         FIG. 13  is a partial vertical sectional view showing a bump valve in accordance with the invention; 
         FIG. 14  is a schematic diagram showing the control used for changing engine displacement during operation; 
         FIG. 15  is a partial vertical sectional view of the center of the cap showing the piston rod packing and crosshead; 
         FIG. 16  is a perspective view of one form of metallic packing; 
         FIG. 17  is a perspective view of another form of metallic packing; 
         FIG. 18  is a diagrammatic perspective end view of one cylinder and the steam camshafts of an engine having two steam admission valves in series within a combustion piston according to the invention; 
         FIG. 19  is a diagrammatic vertical sectional view on line  19 - 19  of  FIG. 18  to show the steam camshafts and crankshaft; 
         FIG. 20  is a partial vertical sectional view of the lower cylinder head or cap and cylinder similar to  FIG. 19  on a slightly larger scale; 
         FIG. 21  is a diagram showing the valve opening sequences of a pair of series connected steam admission valves; 
         FIG. 22  is a diagrammatic end elevational view partly in section that shows optional concentric steam admission valves according to the invention; 
         FIG. 23  is a diagrammatic perspective view partly in section broken away to show the cylinder cap, steam admission valves and the crosshead guide with a pipe to supply steam directly to the admission valves; 
         FIG. 24  is a diagrammatic vertical cross section of a portion of the cylinder cap showing an auxiliary clearance volume chamber and a pressure regulating valve; and 
         FIG. 25  is a schematic diagram of one form of engine installation assembly and engine control. 
     
    
    
     SUMMARY OF THE INVENTION 
     This invention concerns a high efficiency composite internal combustion and steam engine especially suited for use in cars and trucks which includes one or more combustion chambers for burning fuel to power a piston by combustion as well as at least one expandable chamber within the engine that is powered by steam generated from what would have been waste heat from the combustion chamber. Previous systems for recovering waste exhaust heat and waste heat from the combustion chamber coolant in a dual cycle engine have been inefficient. To overcome this and other deficiencies, the present invention provides a combined cycle engine which employs the advantage of using high temperature, i.e. superheated steam with a way of accomplishing uniflow steam operation inwardly of each internal combustion piston to improve operating efficiency as well as benefiting from a way to provide variable steam cutoff through the use of one or a pair of series connected, inwardly retractable, steam pressure balanced valves that are located in a cylinder cap which is sealed within each piston operating in cooperation with steam recompression and a provision for achieving effective clearance volume changes that vary with engine speed to thereby further increase efficiency and the specific power output from the waste heat energy recovered. In one example of a cutoff control, a camshaft is coupled for changing the phase of one or a pair of steam admission valves to vary valve overlap, thus providing continuous regulation of the steam cutoff to further reduce specific fuel consumption. Depending upon the application of the engine, the cylinder cap which is placed adjacent to a steam exhaust port can be unheated but if advantageous is capable of being heated to the temperature of the superheated steam supply or, if desired, can have a device for providing an intermediate controlled degree of heating to provide optimum power. Engine coolant can be evaporated in the engine-cooling jacket to form steam which is then superheated by I.C. exhaust gases within an engine exhaust manifold for powering the steam expansion chamber within each piston. Heating of the cylinder cap makes it possible in some engine applications to achieve high efficiencies which surpass those in what is known as a uniflow steam engine to provide additional power from waste combustion heat; an efficiency level that is much higher than in an ordinary counterflow steam engine. The engine also has the flexibility needed under non-uniform steam generator pressure and engine load conditions that occur in vehicles through a provision for variable steam displacement. Another aspect of the invention concerns a more efficient way to recover combustion heat that is contained in the combustion chamber coolant and in the I.C. exhaust gas using an exhaust powered superheater comprising an engine exhaust manifold for supplemental combustion of unburned fuel while also providing for the direct conduction of the heat produced in the combustion chamber to increase the enthalpy of expanding steam within the steam expansion chamber inside of each piston. The invention thus provides an improved heat recovery, heat exchange, steam generator and superheater system for generating steam with a way to better construct a steam expansion chamber, steam cylinder head and valving, heated steam exhaust area, a provision for steam recompression to admission pressure inside of a combustion piston so as to achieve an effective zero clearance and a gain in mean Rankine cycle temperature along with a steam supply arrangement that is able to act on each piston within an I.C. engine so as to more effectively economize on fuel, make a more efficient combined gas and steam engine, balance the steam displacement with steam generator output to use steam more efficiently, and provide other features that will be apparent from the following description. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to the drawings. Shown diagrammatically in  FIGS. 1-8  is a combination internal combustion engine and steam engine  10  that has a cylinder  12  containing a cup shaped trunk style piston  14  which, unlike ordinary pistons, is machined and ground to precise tolerances both outside at  16  as well as in the inside at  18  and is positioned to reciprocate within an annular space  11  between the inside wall  12   a  of the cylinder  12  and a stationary steam cylinder head. While a single cylinder and piston is shown for convenience in some views, the invention is of course applicable to multi-cylinder engines as well. 
     The steam cylinder head which is located within the piston  14  comprises a flat hub, disk or circular cap  20  that may be, say, ¼ to ½ inch in thickness supported at the free upper end of an integral crosshead guide column  20   a  which is secured to the crankcase  21  by bolts  21   a  ( FIGS. 1 and 2 ) that extend into openings  21   b  ( FIG. 6 ) in base  20   d  shown at the lower end of column  20   a  in  FIGS. 1 ,  2  and  6 . The disk or cap  20  acts as a top or end cap for the guide column  20   a  as well as one end of a steam chamber  44  and has at its outer edge a cylindrical surface  19   a  as a part of a downwardly extending collar  19  that is dimensioned to provide a sliding fit within the piston  14  and is grooved to support compression rings  20   b  which provide a sliding seal with the inner cylindrical surface of the piston  14 . It can be seen that the cap  20  traverses the cylinder  12  in a location that is spaced from its ends. Mounted within the cylinder cap  20  between the outer surface  19   a  and the center of the cap  20  is the steam inlet valve  48 . The space between the column  20   a  and the cylinder  12  comprises a steam chest  46  containing high-pressure, high temperature steam at substantially throttle pressure which is admitted to the steam expansion chamber  44  below the piston  14  when valve  48  is opened, driving the piston  14  upwardly. Cylinder  12  can be independently bolted to the crankcase  62 , if desired, to accommodate steam&#39;s thermal disparities rather than being cast en block as shown. 
     At the top of cap  20  is a bushing  22  suitably sealed with packing for a piston rod  24  which is secured to the piston by a nut  24   a  that can be notched for a spanner wrench. The piston rod slides through the bushing  22  and is secured to a connecting rod  28  for transmitting power to a crankshaft  30  inward of the piston. At the inner end of the piston rod  24  is a piston style crosshead  25  with a partially cylindrical outer surface  25   a  ( FIG. 3 ) that slides within an inner cylindrical bore  27  of the cap supporting column  20   a  which serves as a crosshead guide to take up the side thrust of the connecting rod  28 . Consequently, piston friction is reduced and piston slap common to most I.C. engines is eliminated. The crosshead is coupled to the connecting rod by a wrist pin  26 . The alloys used in the piston  14  and cap  20 , are selected to provide a predetermined balanced amount of expansion during startup. When an aluminum piston is used, the interior wall  18  can be electroplated with porous chromium by a well-known method or covered by a steel sleeve  14   d  ( FIG. 19 ) to provide a hard piston ring contact surface. The steel sleeve can be spaced slightly from the aluminum piston skirt in most places to reduce weight and heat loss from steam within chamber  44 . In operation, the skirt of the piston  14  reciprocates in the annular space  11  between the cylinder wall  12  and the cap  20  as steam is admitted into the steam expansion chamber  44  inside the piston from the steam chest  46  through the admission valve  48  to raise the piston. 
     A conventional internal combustion chamber  34  above the piston crown  14   a  of the piston  14  is enclosed at the top of the cylinder by a cylinder head  35  (shown 90° out of rotational alignment with the cylinder so that the valves can be seen) which has an inlet valve  36 , an exhaust valve  38  and port  37 , chambers  39  for coolant circulation, and a spark plug  40  operating as a four stroke (Otto) cycle I.C. engine that burns gasoline or other fuel in the combustion chamber  34  but which can be a diesel engine or a two stroke cycle engine, if desired. The combustion chamber  34  is cooled by a coolant at  39  circulated through a water jacket  12   b  of the cylinder  12  is compact, unobstructed, has no side pockets and, if desired, can even be of high performance, high compression, four overhead I.C. valve hemispherical construction to avoid detonation. 
     Within the wall of the cylinder  12  and extending around it nearly in alignment but slightly above the top of cap  20  is a steam exhaust manifold  50  which communicates with the interior of the cylinder  12  through spaced steam exhaust ports  51 . It can be seen in  FIG. 2  that the steam inlet valve  48  and steam exhaust ports  51  are located in approximate lateral alignment but the exhaust ports are outward of the cap  20  at a slightly higher elevation. In operation, exhaust gas expelled through the exhaust port  37  of the I.C. engine passes through a steam generator to be described below which recovers waste heat by boiling water or other heat transfer liquid to form steam that is admitted by the inlet valve  48  into the steam expansion chamber  44  within the piston from the steam chest  46  through an inlet passages  46   a  and  46   b  ( FIG. 7 ). Exhaust steam escapes through the steam exhaust manifold  50  to low-pressure steam return line  52  when the piston reaches the top dead center position as piston exhaust openings  14   b  in the piston skirt become aligned ( FIG. 1 ) with ports  51  to act as an automatic exhaust valve, thus, in effect, providing a self-contained steam engine below each piston  14  of the I.C. engine. It will be noted that the automatic exhaust valve opens and closes while the steam chamber  44  is in an expanded state. Exhaust steam is condensed, then reheated and continuously recirculated back to the steam expansion chamber  44  in a sealed circuit that is separate from the I.C. engine intake and exhaust gas thus seldom requiring replacement. 
     It can be seen that the cap  20  serves as the lower (steam) cylinder head for the steam expansion chamber  44 , seals the chamber, provides support for the steam inlet valve  48  and establishes the clearance volume of steam chamber  44  which is purposely kept small to insure efficient operation (see  FIG. 2  which shows the piston at the bottom dead center position). It is important to note that since both the inside top wall of the piston and top wall of the cap have the same shape (a flat plane), the clearance volume can be made as small as desired. The arrangement of chamber  44 , cap  20 , steam chest  46 , and piston  14  as shown makes it possible for the entire lower end of the steam expansion chamber  44  to be steam jacketed including the steam inlet valve  48  and the top surface of the cap  20  which may therefore, when desired, be kept close to the elevated temperature of the steam chest  46  e.g. 1000 P.S.I.@ 850° F. thereby preventing loss of power due to chilling or steam condensation on those parts within chamber  44 . It will be noted that the exhaust ports  51  unlike uniflow ports of an ordinary steam engine are located on the cylinder wall adjacent to a heated engine surface, namely, the cylinder cap  20 , all of which except around piston rod  24  can be heated externally throughout operation when advantageous by the steam chest  46 . Low-pressure steam is exhausted through line  52  when chamber  44  is over 50% and preferably over 75% expanded to its full volume. As illustrated, the exhaust will begin to open when chamber  44  is about 89% fully expanded. After port  51  closes, throughout substantially the remaining inward stroke of the piston, residual low-pressure steam is recompressed to reach admission pressure. To reduce heat loss, the wall of the guide  20   a  can be made of two concentric tubes with a dead air space between them. 
     The construction shown in  FIGS. 1-8  produces a marked improvement in operating efficiency compared to a conventional counterflow engine. For example, assuming a 800 p.s.i. throttle pressure and a 10% cutoff, the uniflow steam rate of the engine described and shown in  FIGS. 1-8  is calculated to be 8.2 lb./HP-Hr, while in an equivalent counterflow engine the steam rate is calculated to be 11 lb./HP-Hr so that the invention is able to make possible a 25% improvement. At a 12.5% cutoff, the engine of  FIGS. 1-8  is calculated to have a steam rate of 8.3 lb./HP-Hr. vs. 10.4 for a conventional counterflow engine (a 20% improvement). 
     The piston, steam exhaust valve and cap  20  are constructed to enable the inward stroke to bring residual steam up to the admission pressure. This produces an effective zero clearance in chamber  44  so that the entire steam mass as it enters is totally consumed by admission and expansion work and is therefore more efficiently utilized while at the same time achieving a gain in mean cycle temperature. Efficiency can be better than a uniflow steam engine because unlike the uniflow engine, where the piston surface adjacent the exhaust valve cannot be heated, here the entire adjacent cap  20  ( FIGS. 1 and 2 ) above high-pressure steam chest  46  can be externally steam jacketed and thus heated continuously when it is advantageous by the steam chest  46  so as to prevent chilling the incoming charge of steam. It is of salient importance to note that the invention enables low-pressure steam exhausted through line  52  to be kept away from the heated area below cap  20 . 
     In the past, fiber shaft packing shown at  22   a  in  FIG. 2  of the kind commonly used in steam powered vehicles had to be replaced at regular intervals and became scorched if high temperature steam was used. To avoid these problems, to prevent condensed steam from seeping into the crankcase and provide long life, an alternative metallic packing  175  can be used, if desired, with superheated steam as shown in  FIGS. 15-17 . Packing  175  is composed of a soft alloy such as Babbitt or other metal alloy used in marine steam engine packing which needs replacement no more often than the piston rings and bearings etc. Each metallic shaft packing ring  175  is provided with sloped outer walls  175   a  resting on a similarly inclined seat  176   a  provided within one of two or more stacked bronze rings  176  that open upwardly toward the steam expansion chamber  44 . The shaft packing rings  175  can be split for example into four pieces as shown in  FIG. 17  or, if desired, can have a single lap joint as shown in  FIG. 16 . Each packing ring  176  is pressed onto its seat for example by means of compression springs  178  that are mounted in pockets on the top of each ring  175 . The slope of the seat  176   a  is chosen so that the packing will not become too tight causing excessive power to be lost in friction. In operation, the packing rings  175  are able to rise slightly off their seats against the force of the springs. Optionally, the inner cylindrical bore  27  of guide  20   a  has two opposing air transfer channels e.g. longitudinal recesses  179  facing the wrist pin to permit free air flow around the crosshead except at the extreme upper end of the guide  20   a . The metallic packing rings  175  are therefore able to cooperate with the adjacent cylindrical piston type crosshead  25  provided in the example shown in  FIG. 15  with an optional piston ring  173  for returning any gas in vapor or liquid back through the packing to the steam expansion chamber  44  when pressure builds up below the packing as the crosshead  25  approaches the top dead center position above recesses  179  to thereby prevent seepage into the crankcase. The packing  175  and  176  shown in the figures can be supplemented, if desired, with an additional ring of fiber packing (not shown). Lubrication is supplied to the packing  175  and to the crosshead  25  through an oil line  177 . Alternatively, if desired, a more conventional crosshead ( FIG. 3 ) can be used with flat sides to permit the flow of air around it. To eliminate any potential steam condensation in the crankcase  62 , the steam exhaust line  52  can be placed in contact with it for heating the oil in the sump enough to drive off moisture. 
     Steam Valve Structure 
     It is essential that the steam engine assembly be constructed in a way that will enable it to operate at relatively high r.p.m.s since a gas engine needs to operate with a piston speed around 3,000 feet per minute. The valves must therefore have a low mass and be free from a tendency to float at high r.p.m.s. While any suitable steam valve can be used, one form of balanced poppet valve  48  is shown diagrammatically by way of example in  FIG. 7 . The valve  48  is a balanced double seated poppet valve having upper and lower valve faces  47   a  and  47   b  each resting on its own seat at the top and bottom of inlet passage  46   a  within the cap  20 . Chamber  44  communicates through inlet passages  46   a  and  46   b  with the steam chest  46  when valve  48  is opened. Resistance to movement that would otherwise exist due to high steam pressure is balanced by lower valve face  47   b  which is slightly larger than valve face  47   a  resulting in a small upward force from steam that is easily overcome by the cam  64  ( FIG. 2 ). During operation, when the cam  64  lowers the valve  48 , steam will flow from steam chest  46  into the steam expansion chamber  44  below the piston  14  through the inlet passages  46   a  and  46   b  driving the piston upwardly. If the lower valve face  48   b  has an o.d. of ¾ inches, its spindle diameter is ⅛ inch, the i.d. of the upper valve  48   a  is 9/16 inches and the pressure is 750 lb/in. 2  then the net upward pressure on the valve would be about 130 lbs. plus the spring force. The closing force can be further offset, if desired, by a balancing plunger (not shown) at the lower end of the valve stem. Assuming the difference between the i.d. of the lower seat and the o.d. of the upper seat is 1/64 inch, the resulting downward (opening) force would be 12.4 lb. when the pressure in 44 builds to 750 p.s.i. and 16.5 lb. at 1000 p.s.i. The valve heads can be rotatably mounted on their stems if desired to equalize wear with pitched radial blades as shown in  FIG. 7  to impart rotation. To better enable the valve  48  to rotate freely during operation, it can be connected to valve lifter rod  4   a , if desired, by a rotary coupling such as a snap ring or ball coupling within a sleeve  8   b  ( FIG. 2 ). Valve lifter rod  4   a  opens the valve when retracted by rocker  64   a  supporting a wheel  64   b  in contact with a three-dimensional cam indicated diagrammatically at  64  that is shifted axially in operation by a servomotor S 1  which is controlled by a central engine management (C.E.M.) computer  305  ( FIG. 14 ) to optimize the valve cut off. The seats of valve  48  can be flat or conical and of such inclinations that they have a common apex to help assure equality of thermal deformation. Both the valve and the seats can be cast from the same material to assure equal thermal expansion. However, if different metals are used, a known form of Skinner self-expanding poppet valve can be used having spring metal packing rings between upper and lower telescopically related valve parts to allow about 0.003 to 0.004 in. telescopic action. Compared to sliding valves, the double seated balanced poppet valves are especially advantageous since being hollow they have a low mass, require no lubrication, have a relatively small lift (travel) for a full port opening and more adequate admission at very early cut off in a variable cut off operation as here. If desired, two side-by-side valves  48  can be connected by a bridge (not shown) for being opened by a single lifter rod. 
       FIG. 8  shows an alternative unbalanced poppet valve  31  which is biased upwardly to its seated position against a valve seat  32  above it by spring  31   a . Threaded onto the lower end of the unbalanced poppet valve  31  is a sleeve  33  with a boss at its upper end that is lowered during operation by a valve lifter viz, a rocker arm  35   b  having a bifurcated end with an opening  35   a  extending around the stem of poppet valve  31  for pressing on the boss to open valve  31 . The stem of valve  31  extends through a valve guide  31   b  which is threaded at its outer end into the base  20   d  of the cap supporting column  20   a . Valve  31  can function as a relief valve on the down stroke when pressure in chamber  44  exceeds that in  46 . 
     Alternatively, in place of a poppet valve, a bump valve  182  ( FIG. 13 ) can be used. The bump valve  182  is opened during operation by a valve lifter  180  threaded into the lower surface of the piston crown  14   a  in a position aligned with valve  182  so that when the piston descends, lifter  180  will open bump valve  182  by separating its annular valve face  182   a  from a seat  184  concentric with an inlet port  185  extending through the top of the cylinder head  20  adjacent valve  182 . Valve  182  is normally seated by a spring  186  supported by a spring retainer  188  which is threaded through a bridge  190  that is integral with the cylinder head and column  20   a . The bump valve  182  provides a fixed cutoff. More than one, e.g. four bump valves can be provided in which case the piston  14  should have four aligned valve lifters  180 . 
     Working Fluid 
     The working fluid used for producing steam can be distilled or deionized water or mixtures of water and alcohol or other known binary fluid mixtures such as ammonia and water as well as hydrocarbon liquids such as isobutane or isopentane among others which is recycled continuously in a sealed circuit. The term “steam” herein is used broadly to include vapors of these and other working fluids as well as steam from water. To prevent freezing when water is used, a small pilot light which consumes only a quart of fuel per week that has been developed by Saab-Scania, Inc., can be used in cold weather. A self-draining system has also been previously developed to avoid freezing. 
     Collection of Blow-by Gas and Oil 
     As best seen in  FIG. 5  which shows the piston in the bottom dead center position, the piston  14  is provided with a pair of compression rings  54  and a special oil ring  55  that has a pair of vertically spaced apart strippers with sharp downwardly directed edges  55   a  and  55   b  that carry excess oil downwardly through the cylinder to a circular collection channel  56  that has circumferentially spaced ports in the cylinder wall  12   a  above the steam outlet manifold  50 . Throughout operation, the collection channel  56  receives and carries excess oil and blow-by gas to the crankcase  62  through a return duct  60  before it can enter the steam exhaust manifold  50 . Any oil that enters the feed water is removed by filtration or by a settling tank or centrifuge (not shown). 
     Refer now to  FIG. 5   a  which shows an optional alternate form of oil collection channel. In this alternative embodiment, the collection channel  56  that returns blow-by gas and oil to the sump is a continuous groove in the cylinder wall which is provided with a pair of centrally contracting slotted wiper rings  59  that, unlike ordinary piston rings, have a working face on their interior surface against which the piston slides during operation. If wiper rings  59  are used, the skirt of the piston should be iron or aluminum jacketed within a steel sleeve or plated with porous chromium. The wiper rings  59  rest in contact with one another within the collection channel  56  and press inwardly on the outer wall of the piston. They are pinned in place or to one another with their gaps separated. Each wiper ring  59  has several radial passages or slots  59   a  through which oil and blow-by gas is carried to the return duct  60  that leads to the crankcase  62 . Consequently, the small amount of oil and blow-by combustion gas which is forced past the rings  54  and  55  is caught by the collection channel  56  by wiper rings  59  and is carried to the sump so as to minimize contamination of the steam by combustion gases and waste oil. Remaining oil and particulate matter is removed from condensed steam by filtration and an optional settling tank or centrifugal separator (not shown) if needed. If the centrally contracting wiper rings  59  are used, they can be cut from cast pipe stock of a suitable diameter, then spread outwardly so that the cut ends are separated by a distance of about a ½ an inch enabling the ring to be placed on a circular burnisher of the same diameter as the piston so that the inner working surface can be correctly shaped while expanded to provide a circular inside surface having the same diameter as the o.d. of the piston. Rings can then be pinned to one another with gaps opposite each other to prevent leakage, compressed and installed at the same time. 
     At the bottom of the piston are two more compression rings  54  ( FIG. 2 ) on opposite sides of piston exhaust openings  14   b . All of the piston rings  20   b ,  54  and  55  are held in place by pins so that their ends will miss the ports in the wall of the cylinder and piston  14 . 
     Sealing the Cylinder Cap and Exhausting Steam 
     Refer now to  FIGS. 2 and 6 . To maintain steam pressure in the steam expansion chamber  44 , the cap  20  has three compression rings  20   b , the bottom one of which can be an oil ring that skims off excess oil from the inside of the piston  14  and returns it through openings in the cap  20  to the crankcase  62  through line  20   c . During operation, the piston  14  as already noted has a finished cylindrical e.g. polished inner surface which slides on the outer surface of the cap  20 . When the exhaust ports are uncovered by the piston exhaust openings  14   b  acting as an exhaust valve, any moisture on the top of the cap  20  is swept out of the cylinder rather than being left in it to be evaporated again during the exhaust stroke as is the case in a counterflow engine. As noted previously, on the down stroke, the remaining steam in the cylinder is compressed in the clearance space to the admission pressure. Lubrication is provided between the cap  20  and the piston  14  by pressure feed line  20   f  that carries oil from an oil pump (not shown). A spring loaded relief or bypass valve (not shown) can be provided in the cap  20 , if desired, to prevent excessive pressures in chamber  44  during start up or in case the condenser fails. Any oil or condensate in the steam chest can be removed through drain  60   a.    
     From the steam exhaust manifold  50 ; the low-pressure steam passes through pipe  52  to a condenser and then to a boiler which will be described below. From the boiler where it is turned to steam, the steam flows through high pressure steam line  49  to the high-pressure steam chest  46  and into the steam expansion chamber  44  through valve  48  thereby completing an endless circuit as it is continuously recycled throughout operation. 
     Timing Steam Admission 
       FIGS. 2-8  and  13  illustrate how steam is supplied to the cylinder. The steam inlet valve  48  is opened by a valve rocker  64   a  extending normal to the plane of the drawing (the free end of which is shown partly in section in  FIG. 2 ) supporting a wheel  64   b  in contact with a camshaft  61  which is geared to the crankshaft  30  for opening valve  48  each revolution. The rocker is connected to the crankcase by a pivot pin located behind the wheel  64   b . Together the camshaft  61 , cam  64  and rocker  64   a  comprise a valve retractor for opening the steam inlet valve  48  against the closing force of steam pressure in chamber  46  and valve spring  63 . If mounted on the same camshaft that is used for the I.C. valves, the cams for the steam inlet valves should have two lobes 180° apart so that the steam valves open each revolution. The camshaft  61  can be gear-driven, e.g. using helical gears in a known manner for advancing or retarding the camshaft cam  64  thereby advancing or retarding the steam cutoff. Alternatively, each cam  64  of camshaft  61  is a three-dimensional cam contoured along its length as shown in  FIGS. 1 and 2  to provide for different cutoffs by the action of servomotor S 1  sliding the camshaft  61  axially ( FIG. 2 ) as described above. For example, each cam  64  is shaped to provide, say, a 5% cutoff at one end and a 50% cutoff at the other. Thus, computer  305  by sliding the camshaft  61  axially can select an optimum cutoff to provide the most efficient operation and the best gas mileage for a vehicle. 
     Engine Management Control 
     One example of a controller for adjusting each of the engine operating regulators including the inlet valve cutoff cam  64  by servomotor S 1 , the operation of steam throttle T by servomotor S 2 , and the combustion engine operating controls is a central engine management (C.E.M.) computer  305  ( FIG. 14 ) with components of the same general kind as those used in engine controls for cars and trucks. The C.E.M. is connected to one or more input sensors that indicate the condition of operating variables which are used in the present invention for minimizing fuel consumption at each steam generator pressure, engine RPM and loading. The monitored steam engine operating variables are used to continuously control engine operation by adjusting the steam throttle setting T, the variable cutoff cam  64  and other engine operating regulators to maximize heat recovery and to minimize both fuel consumption and the discharge of pollutants. The C.E.M. computer  305  is also used to provide cylinder compounding and to balance engine displacement with steam generator output as will be described more fully below in connection with  FIG. 14  under the heading STEAM DISPLACEMENT CONTROL. 
     Steam Engine Efficiency and Enthalpy Losses 
     As seen in  FIG. 2 , the entire top wall of cap  20  above steam chest  46  (typically about 3 to 6 times the top area of column  20   a ) keeps the cap  20 , valve  48  and piston close to the temperature of the incoming steam as noted above. The lower part of the cylinder can be insulated, a small part of which is shown at  12   c , as well as the crosshead guide  27  as partially shown at  20   e  to minimize heat losses from the steam chest  46 . 
     Engines of the type described for example in U.S. Pat. Nos. 1,324,183 and 3,921,404 operate on a counterflow principle in which steam at atmospheric pressure is exhausted as the piston descends. By contrast, the steam engine assembly of the present invention, which is located below the crown of piston  14 , is able to surpass even the performance of the uniflow steam engine which is noted for its unusually high efficiency. In a uniflow engine, steam flows out at the center of the cylinder only during the short period of time when the piston uncovers the exhaust ports but the piston ends adjacent the ring of exhaust ports are unheated. In the present invention, the alignment of piston exhaust openings  14   b  in the piston skirt with exhaust ports  51  in the cylinder wall allow steam to escape briefly to the exhaust manifold  50  surrounding the cylinder  12  at the upper end of each stroke when the chamber  44  is in an expanded state. When the exhaust ports  51  are uncovered, any moisture that collects on the top of the heated cap  20  will be swept horizontally out of the cylinder, rather than being left for re-evaporation. On the down stroke, steam left in the steam chamber  44  is compressed to the admission pressure but unlike the uniflow engine both upper and lower adjacent surfaces of the clearance space  44  are heated (the crown of the piston  14  being heated by the I.C. combustion chamber and the lower end of the cylinder including the cap  20 , valve  48 , and piston skirt being heated by the high-pressure steam in chamber  46 ) thereby keeping the cylinder and piston hot. In this way, potential chilling of engine surfaces is prevented more effectively than in the uniflow engine. Steam recompression as in a uniflow engine avoids the intermittent cooling that takes place in a counterflow steam engine while the heating of the cap  20  adjacent the exhaust ports  51  minimizes condensation of the fresh charge of steam thereon, thus maintaining a level of efficiency higher than that of the uniflow engine.  FIGS. 2 ,  7  and  8  show how the cap  20  containing the steam intake valve  48  is steam jacketed to provide heat for keeping the steam cylinder head surface of  20   a  heated adjacent the ring of exhaust ports  51  throughout operation. 
     Steam engine efficiency is also enhanced by the direct conduction of heat from the burning gas in combustion chamber  34  through the piston crown  14   a  of the piston to the steam under the piston. Of the fuel heating energy that is lost when the fuel is burned, about 8% is lost during combustion and about 6% during expansion. Much of this lost heat is transferred into the crown and upper part of the piston and in turn to the steam in chamber  44 . The head of the piston can be maintained at a safe operating temperature due to the large volume of steam passing through the chamber below the piston. 
     To further improve efficiency, and make up for the negative torque on the down stroke (especially at low speeds), the steam chamber  44  is optionally connected to an auxiliary displacement chamber  45  ( FIG. 2 ) in the piston head of, say, 2 in. 3  for a steam cylinder displacement of 40 in. 3  through a throttling duct or restriction  47  of about 0.18 inch in diameter to act as a variable auxiliary clearance volume for limiting down stroke compression pressure in chamber  44  to throttle pressure at various throttle settings based on a known flow throttling principle so as to provide a greater effective clearance volume at low RPMs due to the greater flow through the restriction while providing reduced flow at high RPMs thereby limiting the charge entering the cylinder. This action provides the effect of an earlier cutoff at high RPMs for increasing Rankine engine efficiency. This feature and the net positive torque of three out of each four strokes provided by I.C. and steam power working together results in a reasonably even running engine. A negative torque of about 10-12% of the net positive torque of the other three strokes will occur only during the I.C. intake stroke. The invention provides more even torque than an I.C. engine for a given number of pistons since the steam below each piston will provide one power stroke per revolution and greater torque at reduced RPMs because steam engines do not need high revs to develop their power. A 4-cylinder engine will have six power strokes instead of two per revolution including four from steam expansion. Chamber  45  also lightens the piston and is self-draining if any condensate is present. 
     Lubrication can be supplied in any suitable manner, e.g. by means of continuous pressure feed lines  20   f  and  57  ( FIG. 2) and 177  ( FIG. 15 ) which meter oil to the cap wall, the piston and cylinder through the cylinder wall as well as by conventional pressure feed through the crankshaft and connecting rod or by a splash or oil jet from the sump (not shown). 
     Thermal Energy Recovery 
     Refer now to  FIG. 9  which illustrates one preferred form of thermal recovery assembly and method in accordance with the present invention. In a typical I.C. engine, the brake power output is about 25-28% and losses amount to about 72-75% of the heating value of the fuel under the conditions of use (see  I.C. Engine Fundamentals  by J. B. Heywood, 1988 page 674). I.C. energy losses include those from the exhaust, the coolant and miscellaneous losses such as radiation from the engine and exhaust system and exhaust kinetic losses. The system for recovering this thermal energy shown in  FIG. 9  includes the engine  10 , a steam generator  100 , an economizer  102 , a steam superheater  104 , two countercurrent liquid-to-liquid heat exchangers  106  and  108 , a condenser  112  and radiator  110 . As outlined above, the low-pressure steam is collected in a chamber or manifold  50  surrounding each of the cylinders and is exhausted through the low-pressure steam return line  52 . The steam return line  52  is connected by line  114  to the countercurrent flow heat exchanger or regenerator  106  which can consist of a pair of tubes mounted one inside the other, the inner one being formed from a material such as copper that is a good conductor of heat. Regenerator  106  acts as a secondary preheater for preheating the feed water flowing through the inner tube  116  which is then carried to the economizer  102  through line  118 . The economizer  102  can be in steam generator casing  124  but if separate (as shown) better counterflow heat transfer is assured. The economizer  102  in the example shown is a countercurrent flow heat exchanger in which preheated feed water is heated further by engine exhaust gases that flow in heat conductive relationship with the feed water passing through a coil of tubing  120  within the economizer for providing preheated water to the steam generator  100 . 
     While various steam generators can be used, a monotube steam generator or flash steam generator of seamless steel or nickel alloy tubing typically 7/16″ diameter coiled in a series of flat spirals or wound to form concentric frustocones or as described in U.S. Pat. No. 5,845,609 is preferred. The coils of tubing  122 , in the steam generator, that receive the preheated feed water from the economizer  102  are in this way exposed during operation to the continuous circular flow of hot engine exhaust gas that enters the casing  124  of the steam generator  100  through tangential inlet opening  126  and leaves through a tangential outlet opening  128  in the opposite direction from the flow of feed water and steam through the coil  122  to again provide a countercurrent-flow exchange of heat so that the last of steam to leave the top coil  122  of the steam generator has been heated the most and is exposed to the highest temperature engine exhaust entering through the tangential inlet opening  126  at the hottest part of the steam generator  100 . While only a few coils have been shown in the steam generator, many more are used in practice. A length of ⅝ inch o.d. mild seamless steel tubing that makes a total of 24 flat coils of 17.5 feet each totaling 420 feet of tubing (which amounts to 75 square feet of heating surface) can provide a 41 HP steam generator that does not cause excessive I.C. exhaust back-pressure losses. Although the steam generator shown and described is preferred, other known water tube steam generators can provide efficient energy recovery. For example, a LaMont flash tube steam generator developed an efficiency of 85% (see  Heat Engines  by R. H. Grundy, 1952 pages 452 &amp; 453) and a Benson steam generator during tests yielded a thermal efficiency of about 90% (see  Theory and Practice of Heat Engines  by D. A. Wrangham 1960 pages 710 and 711). The present invention is able to provide equal or better efficiencies since the temperature of gas in the steam generator  100  is not reduced by dilution with a relatively cool incoming air stream as is the case in an ordinary steam generator in which air is blown by a fan into the burner of the steam generator. The heating rate in a tube type steam generator is also faster than a standard steam generator. Some flash tube steam generators can get high steam pressure in as little as 15-30 seconds which indicates that quite efficient heat transfer is being achieved. A circulation pump in a parallel circuit (not shown) can be provided to maximize heat transfer. 
     Refer now to  FIG. 9B  which illustrates a somewhat different circuit for steam and coolant circulation. In  FIG. 9B  the steam generator, the auxiliary combustor and economizer are the same as already described in connection with  FIG. 9  but the following components are arranged differently: condensate preheater  160 , condenser  162 , filter  164 , condensate pump  166  and a thermostatically controlled bypass valve  170 . In operation, wet steam and condensate from the regenerator  106  flows through the bypass valve  170  to the top of condenser  162 . However, at lower condensate temperatures, valve  170  allows a greater fraction to bypass the condenser  162  through pipe  172  to filter  164  from which it is fed by condensate pump  166  to the first stage countercurrent flow condensate heat exchanger  160  where it is heated as closely as possible to a temperature approaching that of the hot coolant leaving the engine for a maximum temperature gain e.g. to about 100° C.-115° C. Engine coolant itself is fed in the opposite direction by water pump  109  so that upon exiting through pipe  111 , it will have transferred virtually all of its thermal load to the condensate while being cooled as it reenters the engine  10  to the temperature of the condensate leaving condenser  162 . The bypass valve  170  diverts as little as possible through the condenser  162  for maintaining the condensate and coolant at the optimum design temperature selected for the particular engine  10  that is used. Circulation of the steam to and from the engine through the economizer  102  and the secondary condensate preheater  106  is the same as already described in connection with  FIG. 9 . 
     The thermal energy recovery method and apparatus of the present invention, as described above and particularly in connection with  FIGS. 9 ,  9 A, and  9 B, is outstanding for application in an automobile or other vehicle because of its high efficiency in recovering waste heat and its relatively light weight. However, other heat exchange arrangements are well known as described for example in U.S. Pat. Nos. 4,087,974; 4,201,058; 4,300,353; 4,351,155; 4,803,958; 6,834,503; 6,964,168; 7,013,644, some of the features of which can also be used in recovering waste energy from the internal combustion section of the engine of  FIGS. 1-8 . All references cited are incorporated herein by reference as fully and completely as though they were reproduced in full in the text of the present application. 
       FIGS. 9-9B  are intended to diagram the circulation of steam and coolant in a general way. Other well known components (not shown) including temperature and pressure sensors, check valves, liquid storage tanks, thermostatic engine coolant valves, fans for radiator/condenser, pressure gauges and relief valves, drains, and the like, all familiar to those skilled in the art are used conventionally. To minimize heat loss, components that are at elevated temperatures are thermally insulated conventionally for example as shown partially in  12   c  and  20   e  in  FIG. 2 . 
     Superheater Assembly 
     In accordance with the present invention, a superheater  104  is provided at the location of the exhaust manifold of a standard I.C. engine. The superheater  104  which is somewhat larger than a standard exhaust manifold of an ordinary I.C. engine acts as an afterburner that forms part of an exhaust manifold for recovering additional waste energy while removing some pollutants e.g. CO and hydrocarbons. Inside is a series of coils  130  of stainless steel tubing for superheating the steam produced in the boiler  100  by heat transferred from the engine exhaust gases introduced into the superheater  104  through exhaust gas inlet pipes  141 - 144  which are themselves connected directly to the exhaust passages  37  in the cylinder head  35 . Because the superheater  104  is between the boiler and the cylinders and is connected in close proximity e.g. 2-10 inches from the exhaust ports  37  by inlet pipes  141 - 144 , the coils of tubing  130  inside it are exposed to the greatest heat with steam flowing counter to the flow of exhaust gases. To maximize exhaust gas temperatures while also reducing pollutants, heated secondary air is injected into pipes  141 - 144  via injectors supplied with air from a blower  148  via air supply line  146 .  FIG. 9A  shows how supplemental air entering pipe  147  is heated by I.C. exhaust pipe  103  as blower  148  transfers it to I.C. exhaust passages  141 - 144 . It can therefore be seen that the coils  130  are exposed to both combustion products; those produced in the engine cylinder as well as those that result from the combustion of unburned gas that takes place within the superheater due to the injection of secondary air. The blower  148  e.g. a positive displacement vane or roots blower can be driven from the engine, by an electric motor  150  or by a small capacity exhaust gas or steam turbine (not shown) connected to line  114 . Exhaust gas entering the superheater  104  through the exhaust passages  141 - 144  can be as high as about 900° C. but the most common range is about 400° C.-600° C. The auxiliary air supply introduced through the supplemental air supply line  146  will oxidize much of the unburned hydrocarbons and carbon monoxide present in the exhaust gas which may amount to as much as 9% of the heating value of the fuel. To optimize combustion and increase residence time, the superheater  104  is made much larger than a standard exhaust manifold, typically around 6-8 inches or more in diameter for a four-cylinder engine. Optional swirl guides  105  with pitched radial blades give the gas a swirling action and increase residence time within the superheater  104  to enhance the combustion of unburned gas which is advantageous since it has been found that a 1.5% CO removal results in a 220° K temperature rise (Heywood Id. page 658). It will be seen that the superheater  104  is an afterburner that is made an integral part of the exhaust manifold itself where the I.C. exhaust gas at the highest temperature enters at several e.g. 4 points with combustion taking place therein where the monotube boiler steam runs in a counterflow direction to incoming exhaust gas to thereby provide superheat at the highest temperature since the monotube boiler line passes through the afterburner, entering furthest from the engine and leaving near the upstream end of the afterburner. It will also be noted that the steam flows from the boiler into the superheater which receives upstream exhaust gases just as they exit the engine and while they are being further heated by the combustion of previously unburned hydrocarbons and other combustible gases resulting from the injection of hot air from the secondary air supply line  146 . Consequently, the invention makes possible the recovery of heat from unburned gas and fuel which in an ordinary engine amounts to about 3-9% of the heating value of the fuel. 
     Briefly, the circulation of steam and condensate is as follows: from the engine exhaust through lines  52  and  114  then, through regenerator  106  and line  107  to the condenser  112 . Condensate from the condenser passes through filter  113 , pump  115 , through the first preheater  108  then through regenerator  106  (leaving at 220° F.-240° F.) to the economizer  102 , steam generator  124 , superheater  104  then through steam throttle T, high-pressure steam line  49  and solenoid operated selector valves V to the steam chambers  46  and inlet valves  48 . The condensed steam is fed by condensate pump  115  from a filter  113  to a primary heat exchanger  108  where it is heated by the engine coolant fed in the opposite direction through a line  117  by a pump  109 . Thus, the engine coolant transfers its heat to the condensate first and is then cooled further by passing through the radiator  110  from which it is circulated back through the engine cooling passages  35  and  12   b  via hose  111 . 
     The driver&#39;s foot throttle lever can control the throttle set point as a command to C.E.M. computer  305  which in turn positions the servos S 1  and S 2  for the cutoff and steam throttle respectively to optimize efficiency and maximize gas mileage continuously while the vehicle is in operation. Engine power can be thus controlled by a combination of steam throttle T and cutoff settings to minimize fuel consumption. Alternatively, the steam throttle T can be operated for example as described in U.S. Pat. No. 4,300,353 with pressure and temperature controlled as described in the Carter U.S. Pat. Nos. 3,908,686 and 4,023,537. The drivers foot throttle can be set to open the steam throttle T before the I.C. throttle is opened to use stored energy, if any, before burning more fuel, with continued movement of the foot pedal then set to open the I.C. throttle. 
     Steam Displacement Control 
     One objective of the invention is to operate efficiently at a variable load and steam generator pressure that results from variations in waste I.C. heat and vehicle driving requirements. Some steam generator output accommodation can be accomplished with the variable cutoff  64 . However, the invention also includes a mechanism for changing steam displacement to provide the required flexibility under varying operating conditions. In accordance with the invention, valves V are opened sequentially by the C.E.M. computer to increase displacement and are closed sequentially by the C.E.M. computer to as closely as possible match steam engine displacement with the steam output entropy from the steam generator and superheater, the objective being to maintain a more constant ratio between them throughout operation as the engine speed changes during startup and under varying traffic conditions. To accomplish this, an engine load sensor (torque meter) or a steam pressure sensor at the steam generator or cylinder is connected to the C.E.M. computer  305  which opens valves V in a step-wise manner as steam generator output rises. Consequently, when the steam generator output is low, only one or two steam cylinders are used with more added as the steam generator output increases to maintain good efficiency as the heat output of the I.C. engine changes. For example, in a steam powered car, other things being equal, lowering steam engine displacement from an excessive displacement of 200 CID to 140 CID at a constant steam rate of 8.5 lb./HP-Hr. is calculated to improve fuel economy from 9.9 MPG initially to 14.4 MPG (a substantial 45% improvement in fuel economy) by better matching steam generator output and engine displacement. 
     One example of an engine displacement control in accordance with the invention is shown in  FIG. 14 . It will be seen that steam is fed to the cylinders of the multicylinder engine  10  from steam generator  100  through throttle T via steam line  49  and four solenoid operated valves V to the engine cylinders as described above. The steam generator is provided with sensors for operating variables such as temperature and pressure sensors (not shown) which are connected to the engine management computer  305  by conductors  300 ,  302  and by conductor  303  for indicating heat supplied to the steam generator (Btu/hr). The load on the engine  10  and engine RPM is transmitted to the C.E.M.  305  via lines  306  and  308 . While the engine is running, the C.E.M. carries out real time computation of the optimum engine displacement under existing operating conditions for achieving the best gas mileage. This result is then used to operate the solenoid-controlled valves V via conductors  304 ′- 307 ′. If each steam cylinder of the engine  10  has the same displacement, then the valves V are opened in sequence to provide engine flexibility with respect to steam generator output by matching displacement with the operating conditions being experienced so as to increase the displacement, e.g. in a step-wise manner from 15 in. 3  to 30, 45, and finally 60 in. 3  as the steam pressure, temperature or heat supplied to the steam generator increases while reducing the displacement responsive to decreased steam generator output or engine load, all according to predetermined operating parameters for maintaining the best steam engine efficiency under the conditions of operation sensed by the computer while the engine is running as well as before starting or when coasting down. When there is no load on the engine, e.g. when coasting, the throttle T or all valves V are shut by the C.E.M. computer  305  but this is overridden upon depressing the foot throttle. Other operating variables such as I.C. manifold pressure and vehicle speed can be monitored to provide additional operating conditions to the controller  305  as well as those indicated. In designing the engine, the optimum displacement chosen for steam operation can be achieved by selecting a particular piston i.d. or piston rod o.d. If a thicker piston skirt is needed, an optional dead air space can be provided in the piston between the piston skirt and a concentric liner sleeve  14   d  ( FIG. 19 ) if desired. Admission valves of steam chambers which are receiving no steam can be held open as exhaust valves are held open in U.S. Pat. No. 2,196,980 if desired. To further reduce piston weight and enhance cooling the piston crown can enclose a hollow annular chamber (not shown) containing a quantity of sodium or other heat conductor to promote heat transfer. See Ford U.S. Pat. No. 6,904,876 for a sodium cooled piston and Toyota U.S. Pat. No. 4,712,600. 
     Steam Cylinder Compounding 
     It is well known that a compound steam engine can provide greater efficiency at pressures over about 150 pounds per square inch. Using the solenoid operated valves (not shown) between the exhaust line  52  of a cylinder and the high pressure steam line  49  of one or more cylinders, exhaust steam from one cylinder can be sent to a cylinder made with a greater displacement or to two or more cylinders of the same displacement to achieve compounding through automatic control thereof by the C.E.M. computer e.g. from cylinder  1  to both of cylinder  2  and  3  with no receiver. 
     Heat Transfer and Operating Temperatures 
     As in any engine, it is necessary to maintain components at temperatures that will not impair proper lubrication. In a typical water-cooled four stroke spark ignition engine that was tested, temperature measurements taken at the top of the piston and at various locations around and behind the top ring varied from about 290° C. to about 340° C. Therefore, running the engine  10  with steam at 300° C.-350° C. should be acceptable for all applications since both aluminum and cast iron pistons can operate with the piston head at temperatures ranging from 200°-400° C. in a standard I.C. engine. The exhaust valve and spark plug can safely run at around 310° C. to 340° C. In the present invention, the I.C. head and cylinder are both water-cooled. Since the cylinder walls of the combustion chamber are cooled by the water jacket, the piston head has the greatest potential for overheating. Heat transfer and cooling of the piston  14  is an important consideration. As seen in  FIG. 2 , when the steam inlet valve  48  opens, the pressurized steam will stream upwardly and rush across the lower surface of the piston crown  14   a  and will thereby carry away excess heat as its enthalpy rises. At typical highway cruising speeds as much as about 0.3 lbs. of steam per second will flow across the lower surface of the piston head for carrying away heat so as to avoid overheating of the piston head even though the initial temperature of burning gas in the combustion chamber ranges from 2000° C.-2400° C. It will be noted that the invention makes it possible to conserve energy due to the direct conduction of heat from the combustion chamber to the steam streaming across the lower surface of the piston head as the steam is introduced beneath the piston thereby raising the pressure of the steam while at the same time combustion heat also prevents condensation of the steam on and around the piston head. If desired, the lower surface of the piston head can be provided with cooling fins to promote heat transfer to the steam. 
     Thermal Losses that are Available for Recovery 
     The following tables showing fuel energy utilization and loss are derived from Heywood Id. 1988, pages 674 and 675. To evaluate efficiency, brake power is compared with heat transferred to the coolant and to the exhaust as well as other losses that together make up the lower heating value of the fuel being used. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 TYPICAL FUEL ENERGY DISTRIBUTION 
               
               
                 IN SPARK IGNITION ENGINES 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Brake Power 
                 26% 
                   
               
               
                 Lost to Coolant 
                 23% 
                 Available for Recovery 
               
               
                 Miscellaneous Losses 
                  8% 
               
               
                 Sensible exhaust enthalpy 
                 26% 
                 Available for Recovery 
               
               
                 Kinetic exhaust enthalpy 
                  3% 
               
               
                 Lost to exhaust systems by 
                  5% 
               
               
                 radiation 
               
               
                 Incomplete combustion 
                 5-9%  
                 Available for Recovery 
               
               
                   
                 100%  
               
               
                 Total available for recovery: 
                 54-58%   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 FUEL ENERGY DISTRIBUTION OBSERVED IN 
               
               
                 6 CYLINDER SPARK IGNITION AUTOMOBILE 
               
            
           
           
               
               
               
               
            
               
                   
                 43 MPH 
                 72 MPH 
                   
               
               
                   
                 1100 RPM 
                 1800 RPM 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Brake Power 
                 18% 
                 21% 
                   
               
               
                 Coolant Load 
                 54% 
                 43% 
                 Available for Recovery 
               
               
                 Exhaust enthalpy 
                 21% 
                 27% 
                 Available for Recovery 
               
               
                 Misc. radiation from 
                 2.5%  
                 3.2%  
               
               
                 exhaust systems 
               
               
                 Incomplete 
                 4.5%  
                 5.8%  
                 Available for Recovery 
               
               
                 combustion 
                   
                   
               
               
                   
                 100%  
                 100%  
               
               
                 Total available 
                 79% 
                 76% 
               
               
                 for recovery: 
               
               
                   
               
            
           
         
       
     
     The heat rejection rate to the coolant changes under different operating conditions. In an automobile at low speeds and loads (Table 2), the coolant heat transfer rate is much greater, amounting to as much as 2-3 times the brake power. 
     Determination of Energy Recovery 
     For a four cylinder spark ignition four stroke automobile engine operating as set forth in Table 1 and assuming an I.C. engine rated at 100 I.C. HP, the brake I.C. power produced under highway conditions would be 26 HP with 54% of the fuel heating value being available for recovery. Assuming the steam generator is 85% efficient and the steam engine operates as a high-pressure superheated condensing engine having an actual brake power efficiency of 24% (see  Heat Engines , Allen Bradley, page 407), the combined efficiency is therefore 20%×54 HP or 10.8 HP for an improvement on the order of 41.5%. Using the lost energy percentage values of Table 2 derived from a vehicle traveling at either 43 or 72 MPH, the potential recovery is 20%×79%=15.8% which amounts to an 87% improvement in gas mileage at 43 MPH. At 72 MPH with the energy available for recovery of 76%×20% efficiency=15.2% of the thermal energy available for a brake power improvement of 72%. Consequently, the improvement in gas mileage that can be achieved through the use of the invention based on empirical test data varies from about 41% to about 87% above the gas mileage otherwise achieved. 
     Recovery of Unburned Fuel Energy 
     As already noted, unburned fuel contributes about 3-9% to the waste exhaust gas enthalpy. Burning it can raise the temperature of the exhaust gas as much as 200° K. Running at high speed, engine exhaust from a typical vehicle engine will range from about 400° C.-900° C. 
     As seen in  FIG. 9A , an inlet pipe  147  connected to the inlet of the air pump  148  is in a countercurrent heat exchange relationship with the exhaust pipe  103  for recovering exhaust heat and transferring it to the air that is forced by the blower  148  through the air injector line  146  into each of the exhaust passages  141 - 144  to supply oxygen for burning hydrocarbons within the superheater  104 . The exhaust passages  141 - 144  enter the superheater  104  through tangential ports  145  which cause the exhaust gases to swirl as they flow through the superheater  104 . The swirling action is sustained by the pitched swirl plates  105  which act like a helix to help ensure complete mixing of the hot secondary air so as to achieve total combustion as well as reducing the emission of pollutants. Thus, the tangential inlets  145  begin the swirling motion and swirl plates  105  promote both swirling and agitation so as to assure complete mixing of the secondary air which cooperates with the large (6″ to 8″ diameter) size of the superheater to oxidize the unburned constituents thereby raising the temperature of the exhaust to between 600° C.-900° C. or more. This temperature is well above that required for virtually complete combustion of both unburned hydrocarbons (requiring about 600° C. for 50 m.s.) and CO (requiring about 700° C. for about 100-150 m.s.). By placing the steam coils  130  within it, the superheater  104  serves as a burner or furnace due to the injection of hot secondary air through air inlet line  146  causing the steam in the last coils  130  to reach a higher temperature than it would in an ordinary engine exhaust manifold thereby further improving Rankine engine efficiency in the engine expansion chamber  44  due to the higher temperatures and pressures achieved. 
     Thus, running at a speed of about 70-75 MPH with the exhaust gas in the superheater at a temperature of around 900° C.-1000° C. due to the additional heat provided by combustion of unburned fuel, steam at the throttle T at designed flow rates can be heated to over 500° C. (932° F.). It is apparent, therefore, that high steam temperatures and pressures necessary for efficient Rankine engine operation are readily obtained by means of the invention. 
     Recovering Momentum of Vehicle 
     Refer now to  FIG. 12  which illustrates the recuperation of kinetic energy during braking in accordance with the invention. A four cylinder automobile engine  150  of this invention e.g.  FIGS. 9-9B  is shown connected by a drive shaft  151  to a drive wheel  152  resting on the ground. The illustration shows a solenoid operated selector valve  153  in steam outlet line  52  and a solenoid valve  158  in the steam line leading to the steam generator. Also in line  49  is a solenoid selector valve  159  that is connectable via a first airline to a check valve  154  for receiving ambient air and a check valve  155  coupled to compressed air tank  156 . The selector valve  159  can also connect line  49  via a second airline through check valve  157  to the compressed air tank  156 . When the brakes are applied, the poppet valves  48  inside the engine  150  are held open by the engine management computer and selector valve  159  connects tank  156  to line  49  via valves  154  and  155  so that the changing volume of the steam expansion chambers  44  ( FIGS. 1 and 2 ) forces air under pressure into tank  156  until the vehicle stops thereby storing kinetic energy in the form of compressed air. When the accelerator is depressed by the driver, the solenoid operated selector valve  159  connects tank  156  to line  49  through the check valve  157  while valve  48  operates normally as it does during steam operation thereby propelling the vehicle ahead due to the expansion within the steam chamber  44  of the compressed air that was stored during braking. Compressed air is vented through valve  153 . In this way, the invention provides a vehicle that is propelled by a combination I.C. and steam power that was derived from thermal energy recovered from waste I.C. engine heat and momentum by selectively connecting a steam expansion chamber of the engine to a compressed air storage tank through valving that directs the flow of air from the expansion chamber either into a storage tank during braking of the vehicle or to move ahead, connects the steam expansion chamber to the air tank for directing compressed air from the air tank into the steam expansion chamber. With a cold engine and no steam pressure, the compressed air is able to provide a fast start even before raising steam as well as enhanced fuel efficiency during start up. It can therefore be seen that the invention provides an energy storage unit arranged such that the brake is operatively connected to the wheels for transferring momentum from the wheels  152  of the vehicle during braking (when engine power is not applied to the wheels) to the energy storage unit such as the compressed air tank  156  or any other energy storage device for later application to the wheels for moving the vehicle forward. 
     Stepped Piston Alternative 
     Refer now to  FIGS. 10 and 11  which illustrate an alternative embodiment of the invention that employs a stepped piston  80 . While this variation of the invention makes use of a different piston construction, it is also able to recover power from waste I.C. heat. The modified engine  79  shown in  FIGS. 10 and 11  operates to achieve the same general objectives already outlined; better efficiency and gas mileage, but instead of having a steam expansion chamber inside the piston, the stepped piston  80  is provided with compression rings  80   c  at its upper end and an enlarged diameter  80   a  in the skirt area at its lower end that is provided with compression rings  80   b . The combustion chamber  34  as well as the cylinder head  35  and its components are the same as already described above. The piston  80  fits sealingly for sliding motion in a cylinder  82  that has an enlarged cylindrical lower bore  84  to accommodate the enlarged diameter  80   a , thus providing an annular steam expansion chamber  86  in the enlarged bore section  84 . Both its combustion chamber  34  and the steam chamber  86  are adjacent the piston and chamber  34  is located adjacent the bottom portion of the piston  80 . Lubricating oil is supplied under pressure through lines  9   a  and  9   b  to the inside wall of the cylinder. In operation, steam enters the steam expansion chamber  86  through an inlet valve  92  and port  91  from high-pressure valve chest  94 . When the piston reaches bottom dead center and uncovers openings in the cylinder, steam is exhausted through a steam manifold  88  provided in the part of the engine cylinder block  89  that encircles the lower bore  84  from which it flows through a closed circuit like that described above including a condenser (not shown) through a check valve e.g. reed valve  9   c  via a low-pressure steam return line  90 . The piston  80  located as shown between the combustion chamber  34  above the piston and the steam chamber  86  is connected to a crankshaft  87  by a wrist pin  83  and connecting rod  85 . Waste combustion heat from the I.C. chamber  34  is recovered in a boiler and steam circuit as shown and described above in connection with  FIGS. 9-9B  to provide steam to chamber  86  for driving the piston  80  downwardly each revolution of the crankshaft  87 . This is not a preferred embodiment in part because the large surface to volume ratio of the annular steam expansion chamber  86  will promote cooling resulting in reduced steam pressure. Flow restriction around the piston will also produce greater breathing losses, longer rings  80   b  result in increased mechanical losses and there is no heated surface adjacent steam outlet  88 . 
     Description of FIGS.  18  to  25   
     Refer now to drawing  FIGS. 18 through 25  wherein the same numerals refer to corresponding parts described above. The engine  10  has one or more cylinders  12  each with a combustion piston  14  slideably mounted therein and sealed by piston compression rings  54 ,  56 , a combustion chamber  34  outward of the piston  14  and a steam expansion chamber  44  in the cylinder  12  inward of the piston, i.e. between the piston and the cylinder cap  20 . In general, the engine shown is constructed and operates as described above in connection with  FIGS. 1-8 . Differences in construction and operation will now be described. Mounted within the cylinder cap  20  to control the flow of steam from the steam chest  46  through the cap to the steam expansion chamber  44  above its upper surface are two series connected steam admission valves  200  and  202  which it will be noted are enclosed within the piston  14 . The space between the crosshead guide  20   a  which supports cap  20  and the cylinder  12  defines the steam chest  46  as described above which contains high-pressure, high temperature steam at substantially throttle pressure that is admitted to the steam expansion chamber  44  below the piston  14  when both of the valves  200  and  202  are in the open position thereby driving the piston  14  outwardly. Valve control for regulating the supply of steam to the expansion chamber  44  during each expansion stroke is accomplished in this example by changing the phase of one of valves  200  or  202  as will be described more fully below. Valve  200  is ported through the cylinder cap  20  about midway between the piston rod  24  and the cylinder  12  ( FIG. 18 ). During operation, the skirt of the piston  14  reciprocates as already described in the annular space  11  ( FIG. 20 ) between the cylinder wall  12  and the cap  20 . 
     In the manner described in connection with  FIGS. 1-8 , a conventional internal combustion chamber  34  above the upper face  14   a  of the piston  14  is enclosed at the top of the cylinder by a cylinder head  35  which has an inlet valve  36 , an exhaust valve  38 , a steam jacket  12   b ,  39  (shown in  FIGS. 1 and 2 ) for coolant circulation between the cylinder and the head with a spark plug  40  operating as a four stroke (Otto) cycle or two-stroke I.C. engine that burns gasoline or other fuel in the combustion chamber  34  all as described above. The internal combustion section of the engine can run as a spark or compression ignition engine or combination of both wherein spark ignition is used for starting the latter. The combustion chamber  34  is cooled by a coolant circulated through the cooling jacket  12   b  ( FIGS. 1 and 2 ) and then through  39  ( FIG. 1 ). 
     Within the wall of the cylinder  12  and extending around it nearly in alignment but slightly above the top of cap  20  is the steam exhaust manifold  51  ( FIG. 19 ) which communicates with the interior of the cylinder  12  through circumferentially spaced steam exhaust ports  50  as described in more detail concerning  FIGS. 1 and 2 . It can be seen in  FIG. 19  that the steam inlet valves  200  and  202  and steam exhaust ports  50  are located in approximate lateral alignment but the exhaust ports are at a slightly higher elevation outward of the cap  20 . It is also important to notice that by exhausting through the cylinder wall  12 , the invention makes it possible to keep low-pressure exhaust steam away from the heated area below cap  20  where it could reduce the enthalpy of steam in the steam chest and in the incoming steam. The steam cylinder head or cap  20  has a peripheral collar  19  that is slideably and sealingly engaged with the inside wall of the piston. The steam exhaust valve also includes one or more ports  14   b  in the skirt of the piston  14  that are each spaced from the free lower edge of the piston by a skirt portion  18  ( FIG. 19 ) which is large enough to overlap the collar  19  of the cylinder cap and maintain a seal when the piston is at the top center position shown in  FIG. 1  as well as in application Ser. No. 12/075,042 filed Mar. 7, 2008, now U.S. Pat. No. 7,997,080 which is incorporated herein by reference. 
     As in  FIGS. 1-8 , the cap  20  of  FIGS. 18-23  serves as a lower steam cylinder head for the steam expansion chamber  44 , seals the chamber, and in this embodiment provides support within piston  14  for both of the two series related steam inlet valves  200  and  202  as well as establishing the clearance volume of steam chamber  44  which is purposely kept small to insure efficient operation (see  FIGS. 2 and 19 ). 
     In one form of the invention, the entire lower end of the steam expansion chamber  44  is steam jacketed including the steam inlet valves  200  and  202  and the top surface of the cap  20  which are therefore kept close to the elevated temperature of the steam chest  46  e.g. @ 850° F. thereby preventing loss of power due to steam condensation on those parts within chamber  44 . It will be noted that the steam exhaust ports  50  unlike uniflow steam exhaust ports of a conventional uniflow steam engine are in this case located on the cylinder wall adjacent to an engine surface that can be heated, namely, the fixed cylinder cap  20 , all of which except the center part close to piston rod  24 , can be heated externally, if desired, throughout operation by the high pressure steam in the steam chest  46 . Steam jacketing of the cylinder end cap  20  in accordance with the invention is beneficial in keeping the inner wall of the piston hot and can also be beneficial especially in small bore engines and under reduced loads with earlier cutoffs or at lower-range steam temperatures and pressures, e.g. during idling as well as start and stop driving when steam is wetter. Low-pressure steam is exhausted through line  52  as before. As illustrated, the exhaust valve will begin to open and will close fully when chamber  44  is about 89% fully expanded and is fully open at the top center position. Consequently, steam recompression will begin on the down stroke following steam exhaust as the piston  14  leaves the upper end of its stroke, i.e. the top dead center position. 
     The engine of  FIGS. 18-22  produce a marked improvement in Rankine efficiency compared to a conventional counterflow steam engine in which steam enters and leaves through the same valve. When port  51  closes, steam is recompressed substantially throughout the remaining inward stroke of the piston bringing the pressure and temperature of residual steam up to admission values. In this way condensation of incoming steam by residual steam is avoided as well as in a steam-only uniflow engine. Efficiency, however, can be better than a uniflow steam engine because unlike a standard uniflow steam engine, where the piston surface adjacent the exhaust valve cannot be heated, here the entire adjacent cap  20  ( FIGS. 1 ,  2 , and  18 - 22 ) above steam chest  46  can be steam jacketed in any engine application that would benefit from it and thus heated continuously by the steam chest  46  so as to prevent chilling the incoming charge of steam from producing a loss in power. The steam exhaust valve, piston, cylinder and cap  20  are dimensioned, constructed and arranged to provide an effective zero clearance in chamber  44  and a gain in the mean Rankine cycle temperature as will be further described below. 
     The mechanism for operating valves  200  and  202  will now be described with reference to  FIGS. 18-20  and  22 . These Figures show how steam admission poppet valves  200  and  202  are placed in series relationship and are enclosed within piston  14  at the upper and lower ends of inlet passage  46   a  that extends through the cylinder cap  20  with valve  200  at its upper end and valve  202  at its lower end so that steam is admitted from the steam chest  46  into the steam expansion chamber  44  only when both of the valves  200  and  202  are open. The stems of valves  200  and  202  extend inwardly through the steam chest  46  within valve guides  204  and  206  ( FIG. 20 ) respectively, the former being threaded into the lower end of the inlet passage  46   a  by screw threads  6   b  ( FIG. 20 ). Both guides  204 ,  206  are not shown in  FIGS. 18 and 19  so that the valves can be clearly seen. The guides  204  and  206  are sealed at their lower ends within openings provided in the crankcase  21  as shown at  208  and  210  ( FIG. 20 ). Guide  206  extends into the steam supply line at  49   c  ( FIG. 23 ). The stems of valves  200  and  202  can be provided with shallow vertically spaced apart circular grooves  201  to serve as a labyrinth seal. It should be noted that the valves  200  and  202  have beveled valve face seals that are smaller in diameter at the outer end of each valve, providing distal seals, so that the valves open by being withdrawn inwardly, away from the steam expansion chamber  44  toward the crankshaft  30 . Therefore, instead of acting as push rods, the stems act as traction rods to open the valves. By using series-related inwardly opening poppet valves  200  and  202 , a relatively short cutoff is made possible with very little throttling while avoiding excessive G forces and cam stress at high RPM&#39;s. Consequently, the valve arrangement within the cap located inside of the combustion piston  14  as described makes it possible to accomplish a short steam cutoff in a high RPM combined cycle engine that has a piston speed compatible with the piston speed commonly experienced in an ordinary internal combustion car or truck engine that lacks thermal power recovery. At 3000 RPM each stroke lasts 0.01 second so that a 10% cutoff requires steam admission valves to open and close in 1/1000 second. However, by placing a pair of series-related inwardly retractable steam inlet valves in a cylinder cap that is slideably enclosed within the piston, it is possible to provide a variable steam cutoff even with short cutoff periods of 10% or less in a double-acting combustion/steam dual cycle engine in which steam is recompressed to admission pressure. 
     Operation of the valves  200  and  202  is accomplished by camshafts  212  and  214  through the action of centrally pivoted valve rockers  216  and  218  which open the valves by retracting them, i.e. moving them proximally (away from the steam expansion chamber  44 ) so that during operation steam enters the steam expansion chamber  44  from the steam chest  46  which is at a throttle pressure of say 1,000 p.s.i. Thus, steam is admitted when valves  200  and  202  are withdrawn responsive to a downward movement of the central ends of the rockers  216  and  218  against spring retainers  220  and  222  connected to the stems or traction rods of valves  200  and  202  which are normally held in the closed position by steam pressure and compression springs  224  and  226 . The distal face seals of valves  200  and  202  can also permit the valves to open for relieving excess pressure whenever steam in chamber  44  is recompressed enough to exceed the closing force on valves  200  and  202  caused by steam pressure within steam chest  46  plus the spring force. As described below and shown in  FIG. 24 , an auxiliary clearance volume chamber  352  similar to that in  FIG. 2  is provided in the cylinder cap  20 . The pressure balancing ability of valves  200 ,  202  in cooperation with the auxiliary clearance volume chamber  352  prevent excessive recompression counter-torque on the crankshaft during starting and idling. It will also be noticed that the steam inlet valves  200  and  202  are easily moved by the camshafts  212 ,  214  due to the tendency for recompression pressure from above to open them, thus helping to balance the closing pressure from the steam chest  46 . The steam admission valves  200  and  202  can therefore be opened with a force in the same range as that in a conventional internal combustion engine even when steam exerts a closing force of 500 lbs. or more on the valves. 
     The control of one or more steam inlet valves in accordance with the invention is used to continuously regulate the charge of steam admitted into the clearance volume at the beginning of each power stroke. While engine valve timing (the angle from the bottom center position of the crankshaft to the point at which the steam inlet valve opens or closes) and valve lift can be varied in any of several known ways in the present invention, whatever method is used should provide a regulated change in the mass of steam admitted. Therefore, the terms “valve control” or “valve cutoff” are used broadly herein to include valve phase shifting, valve lift changing, as well as changing the valve timing either separately or together for regulating the mass of steam that is admitted each cycle of operation. 
     Valve control for regulation the mass of steam admitted each stroke by means of valve phase angle control in place of a three-dimensional cam  64  ( FIG. 2 ) will now be described with reference to  FIGS. 18-23 . The left camshaft  212  runs at crankshaft speed through its connection by drive chain  230  and a cooperating sprocket  30   a  at one end of the crankshaft  30  and an equal size sprocket  232  at the end of camshaft  212 . The right camshaft  214  is also driven via a sprocket  246  and a shaft  244  rotating at crankshaft speed, in this case through a variable valve timer, specifically, a phase shift control  234  or other suitable valve timing device, variator or phaser of known construction for regulating the mass of steam admitted during each outward stroke of the piston. While two series related valves are preferred, the control  234  can be connected to a single valve in place of two valves  200  and  202  arranged to control the quantity of steam admitted each stroke. In  FIG. 18  an electric servomotor  236  or other actuator is connected for shifting a positioning fork  238  parallel to camshaft  214  any selected distance so as to slide a helical gear  240  axially of a cooperating helical gear  242  at the end of camshaft  214  which is engaged with the gear  240 . It will be seen that the left end of the positioning fork  238  extends into a circumferential groove in a boss at one end of gear  240  so that the helical gear  240  can rotate freely as the positioning fork  238  slides the gear  240  during operation to any selected position from one end of helical gear  242  to the other. It will also be seen that the gear  240  is supported for sliding movement on the axially splined shaft  244  which is driven at crankshaft speed by the chain  230  via the sprocket  246  so that gear  242  turns slightly relative to gear  240  as gear  240  moves axially thereby operating valve  202  earlier or later in the cycle. The electronic engine management computer or controller  305  ( FIGS. 14 ,  18 , and  25 ) is wired to control the operation of servomotor  236  to regulate the position of gear  240  and thereby provide the optimum steam charge, i.e. cutoff so as to achieve the lowest specific fuel consumption as previously described in connection with  FIGS. 1-17 . The electronic motor controller  305  itself is described in more detail hereinabove. The I.C. valves  36  and  38  can be operated by an overhead camshaft (not shown) or in a lower cost engine, they can be operated from steam camshaft  212  running at half crankshaft speed by providing each steam cam on camshaft  212  with two similar steam lobes 180° apart. The timing of valve  36  can also be coordinated with valve  202  by an I.C. pushrod from camshaft  214  to a valve rocker (not shown) for valve  36 . 
     Refer now to the graphs shown in  FIG. 21  which illustrate valve lift vs. time to depict the opening and closing of valves  200  and  202 . During operation, when the electronic engine management controller  305  signals the servomotor  236  to shift the gear  240  a selected distance in a direction that spaces the opening of valves  200  and  202  further apart, there is an incremental rotation of shaft  214  due to the axial movement of gear  240  causing the phase of shaft  214  to be shifted, thereby altering the overlap of the valves so as to provide a short steam cutoff A as seen in the upper graph. Delaying the opening of the valve  202  as shown in the lower graph will provide a longer steam cutoff B by spacing the opening and closing of valves  200  and  202  closer together. In this way, by advancing or retarding the opening and closing of valve  202 , a continuous infinitely variable steam cutoff is provided to control the charge of steam supplied to each cylinder for optimizing thermal power recovery and specific fuel consumption of the combined cycle engine  10  throughout operation. 
     During operation, the valves  200  and  202  are normally held shut by the operating steam pressure acting on the lower faces of the valves plus the spring force. However, it is desirable to have the recompression pressure in chamber  44  developed by the downward movement of the piston be the same as the operating pressure even when the steam operating pressure is varied by changing the throttle setting. The maximum operating pressure, i.e. the generator or boiler pressure of the power plant can be selected first, for example, 1000 p.s.i. The clearance volume in the chamber  44  is then set so that the recompression pressure that results when the piston descends equals the pre-selected operating pressure of the steam generator, namely, 1000 p.s.i. However, when the throttle pressure is reduced below 1000 p.s.i., power is wasted during the recompression stroke. Consequently it is desirable to keep the recompression pressure in the clearance space equal to whatever the throttle pressure happens to be. 
     To accomplish this, in case excessive recompression occurs in the clearance volume of chamber  44 , a resulting drop in efficiency can be prevented by an optional pressure-regulating valve  360  ( FIG. 24 ) which will now be described. Threaded into opposite ends of a passageway  361  that extends through the cylinder cap  20  from chamber  44  to chamber  46  is an annular valve seat  362 , and an annular spring retainer  363  enclosing a relatively light spring  364  with enough force to reliably seat a frustoconical valve element  365  onto the seat  362 . The clearance volume between the cap  20  and the piston  14  at bottom dead center is determined so as to recompress residual steam up to the maximum operating pressure, i.e. the boiler pressure, e.g. 1000 p.s.i. However, throughout operation, whenever the throttle pressure is less than 1000 p.s.i., the valve  360  will open near the end of the recompression stroke equalizing the pressure by allowing excess steam to pass out of the clearance space thereby preventing power losses due to work performed in recompressing residual steam above the throttle pressure. The valves  200  and  202  will then be opened only by the valve retractors and not by a pressure differential across them. 
     During operation, the effective clearance volume within the steam expansion chamber  44  can also be varied as explained above by the auxiliary clearance volume chamber  45  ( FIG. 2 ) or  352  ( FIG. 24 ) and if valve  360  is used, the maximum recompression pressure that can be developed will also be controlled by the regulating valve  360  so that when the piston reaches the end of its inward stroke, the recompression pressure will be equal or almost equal to the throttle pressure in chamber  46  whatever its value. Thus, at the opening of the admission valves  200  and  202  at or near BDC, no steam flows into chamber  44  of the cylinder because the cylinder is already filled. Consequently, no steam mass is consumed just to fill the clearance volume. The result is an effective zero clearance. When steam does flow into the cylinder, its mass is totally consumed by admission and expansion work. Steam is therefore more efficiently utilized, thus improving efficiency of the engine. Also, as recompression occurs, the temperature of the recompressed steam will rise up to or above the admission supply temperature. The recompressed steam mixes with the supply steam admitted through valves  200 ,  202  resulting in a steam temperature at cutoff that is most preferably greater than the supply temperature thereby producing a gain in the mean cycle temperature and when the mean cycle temperature is elevated, the efficiency of the engine is enhanced. These two events of course occur at the expense of the work of recompression. However, thermodynamic analysis indicates that there is a net improvement in efficiency due to an effective zero clearance and an increase in the mean cycle temperature which produces an increase in output that is greater than the fraction of the recompression work that cannot be recovered during the expansion stroke. It can therefore be seen that the present invention is able to provide a dual cycle internal combustion steam engine having an effective zero clearance in the steam expansion chamber  44  as well as the capacity for achieving a mean cycle temperature gain thereby assuring a higher level of Rankine efficiency. It should be noted that if valve  360  is used, it will open whenever the pressures in chamber  44  is slightly above that in chamber  46  while in the case of valves  200 ,  202 , the opening force will be significantly greater than the net closing force whenever the throttle is partly closed. 
     The retractable series valve arrangement of the valves  200  and  202  in the cap  20  which is in turn enclosed within of the internal combustion piston  14  brings steam valve acceleration and operating rates to reasonable levels even if a short cutoff period is required as optimum efficiency is achieved while at the same time the closing force on the valves is balanced in large part through the recompression pressure developed as the piston descends acting in cooperation with the auxiliary clearance chamber  352  ( FIG. 24 ). The series-related valves  201  and  202  are, moreover, effective in overcoming the valve acceleration and stress problems within the cutoff range (5% to 12%) that is of interest because it will guarantee a steam use rate which is commensurate with the water evaporation rate of the steam generator. 
     EXAMPLE 
     Calculation of Power Recovered 
     A one-cylinder 564 cc (34.4 cubic inches), 4-cycle internal combustion engine (bore 96 mm×stroke 78 mm) producing 13.5 horsepower (572.6 Btu/min) at 3000 rpm and exhibiting a brake efficiency of 21% will require an energy input rate of 2526.7 Btu/min and will reject 2154.1 Btu/min to the steam generator  104 . For a boiler efficiency of 70%, which is merely average for modern monotube steam generators, 1507.8 Btu/min will be transferred to heat the feed water. The sustained evaporation is the ratio of the waste heat recovered to the enthalpy change Δh as the feed water (or steam) passes through the steam generator. At 800 psia and 800° F. with saturated feed water at 14.7 psia and 212° F., the enthalpy change is 1218.5 Btu/lb (1398.6-180.07). The resulting sustained evaporation rate for supply steam m s  is then 1.24 lb/min.: 
                     m   s     =       waste   ⁢           ⁢   heat   ⁢           ⁢   recovered       Δ   ⁢           ⁢   h                   =       1507.8   ⁢           ⁢   Btu   ⁢     /     ⁢   min       1218.5   ⁢           ⁢   Btu   ⁢     /     ⁢   lb                   =     1.24   ⁢           ⁢   lb   ⁢     /     ⁢   min                 
Rankine cycle analysis based on the internal energy changes of non-flow process within a 24 cubic inch (399 cc) displacement high compression uniflow steam expansion chamber  44  (e.g.  FIGS. 18-25 ) with a 7% cutoff will yield a brake efficiency of 18.9% with supply conditions at 800 psia and 800° F. This level of performance is consistent with an engine friction torque of 0.10 foot pounds per cubic inch displacement and pump work necessary to raise the feed water pressure from 14.7 psia to an operating pressure of 800 psia. Steam consumption under these constraints is 1.11 lb/min. This is consistent with the evaporation rate of 1.24 lb/min. Power delivered by steam=0.189×1507.8 Btu/min/42.41 Btu/min/hp=6.72 horsepower. The combined performance of both internal combustion and steam engine therefore represents a 49% increase over the 13.5 horsepower internal combustion engine acting alone. Regenerator use and heat recovery from unburned fuel provides a still greater increase. At a 75% boiler efficiency consistent with monotube steam generators tested in cars, the brake Rankine efficiency would be 20.4% producing 7.25 HP from steam which is a 54% increase in power under the same conditions. When used in a hybrid electric installation, even greater economies are obtained.
 
     Consolidated Valves 
     Refer now to  FIG. 22  which illustrates a modified form of the invention having valves that operate in a manner similar to valves  200  and  202  except that in this example a pair of admission poppet valves  200   a  and  202   a  are concentrically arranged so that the valve  200   a  slides within a central bore in a tubular poppet valve  202   a . The lower valve  202   a  is mounted to slide within a valve guide  260  which is secured at  262  to the crankcase  21  to provide a steam-proof seal. Valves  200   a  and  202   a  are normally held in the closed position within the cap  20  inside of the combustion piston by compression springs  207  and  209 . In this case, the valves  200   a  and  202   a  are operated by vertically spaced rockers  270  and  272  respectively, which engage vertically spaced apart cams of camshafts  212   a  and  214   a , the timing of which is controlled in the same manner as described in connection with  FIGS. 18-21 . Thus, the phase of the camshaft  214   a  is advanced or retarded with respect to camshaft  212   a  to thereby regulate the cutoff of steam through the sequential operation of valves  200   a  and  202   a  which together permit the admission of steam through an intervalve passage  203  into the steam expansion chamber  44  when both admission valves  200   a  and  202   a  are open. This enables the steam cutoff to be varied throughout operation as determined by the electronic engine management controller  305  through variable cam positioning, namely by changing the phase angle of shaft  214   a  relative to shaft  212   a  as described in connection with  FIGS. 18-21 . The concentric valves provide the advantage of minimizing the size of passage  203  within casing  205  thereby assuring better control of the volume of steam admitted, especially at a short cutoff as well as a straight passage  302  and enlarged steam chest volume since only one valve guide is needed. 
     Engine Installations and Steam Production 
     The engine  10  can be installed and used in various ways. For example, the engine can be connected directly to the wheels of a vehicle as described above (see  FIG. 12 ). When mechanically connected to the wheels to power the vehicle, the engine will operate at varying speeds and loads that result from continuously changing driving conditions. In such an installation, the invention provides operational flexibility in spite of rapidly changing driving conditions as well as an ability to function at I.C. engine speeds, and a way of matching the engine displacement with the changes in steam generator output as described hereinabove and in the prior related application Ser. No. 12/075,042 (Publication No. US 2008/0216480 A1), published Sep. 11, 2008 which is incorporated herein by reference, now U.S. Pat. No. 7,997,080. However, instead of powering the wheels, the engine can also be used in a hybrid vehicle as a constant RPM, reduced size, battery charging module to increase the range of a vehicle, in this application, the engine  10  is operated at an optimum fixed RPM and load while connected to an electric generator and is run for extended periods of time to recharge a battery and/or an ultracapacitor, i.e. as a recharging module and/or to power an electric drive motor that is coupled to the wheels of the vehicle. This enables the engine to operate as efficiently as possible at a higher speed for extended periods with the dimensions of steam engine components and their operating parameters chosen to provide the lowest specific fuel consumption for the particular internal combustion assembly components used in any given engine. 
     A power plant installation especially useful as a battery charging module to extend the driving range of a hybrid I.C./electric vehicle but which could alternatively be connected mechanically to power the drive wheels is shown in  FIG. 25  wherein the same numerals designate corresponding parts described above and in application Ser. No. 12/075,042 filed Mar. 7, 2008. For simplicity and clarity of illustration, the complete engine coolant circuit within the engine and the steam generator  100  of application Ser. No. 12/075,042 has not been shown in  FIG. 25  but both can, if desired, be constructed as previously described. In  FIG. 25  it will be seen that the engine  10  is connected mechanically by shaft  548  to an electric generator  550  which is wired at  552  to a power supply  554  that provides electric current to storage batteries  557  and/or ultracapacitors  559  through conductor  556  under the control of the electronic central engine management computer  305 . Current from the power supply  554  can also be provided through conductor  558  to an electric motor generator  560  which is connected by shaft  562  to the drive wheels  561  of a vehicle such as an automobile, truck, locomotive, or propeller of an aircraft. Thus, during operation, the engine  10  is run at an optimum speed and load which is typically at a fixed RPM selected for recharging the ultracapacitor  559  and battery  557  when required and/or to provide electric power to the motor  560  which can be supplemented by power from the ultracapacitor  559  and/or battery  557  whenever additional power is needed. When the battery is charged above a set level, the engine  10  can be turned off by the motor controller  305  and the electric motor  560  then operated by the battery and/or ultracapacitor either separately or together. In such an installation, the vehicle is run initially on current from the battery  557  and/or ultracapacitor  559  while the engine  10  is used primarily as a back-up battery recharging device to increase the range of the vehicle. 
     During braking, electric motor  560  acts as a generator for recovering momentum by charging the battery and/or capacitor under the control of the CEM computer  305  for later moving the vehicle ahead. 
     In place of an ordinary liquid coolant system used in a conventional I.C. car engine, heat can optionally be removed from the combustion chambers of the engine  10  by boiling the coolant, if desired, i.e. by evaporative cooling to produce steam in the cooling jacket  12   b  and  39 . This can be accomplished, for example, by spray cooling each cylinder to generate steam. Evaporative spray cooling can be carried out as disclosed by D. A. Arais, et. al.,  SAE Technical Paper,  2006-01-1605 in which the cylinder is cooled by a spray of liquid coolant from several small parallel vertical pipes (not shown) within the jacket  12   b  surrounding the cylinder to produce steam. Compared to a conventional water-cooled engine, evaporative cooling absorbs 970 additional Btus of heat per pound of water evaporated in the production of steam; the heat of vaporization. The resulting steam is able to accomplish much more efficient heating when the coolant is fed to a steam generator as steam rather than as hot water. This is explained by the better match between the temperatures of the energy sources; steam from the I.C. engine block (in place of hot water) and the engine exhaust gas used to power the steam generator. Evaporative cooling is carried out within the engine cooling jacket in a manner that maintains nucleate boiling so as to avoid exceeding a critical heat flux which can result in the formation of an insulating vapor blanket layer within the liquid at the hot metal surface allowing the temperature of the metal to jump suddenly as runaway heating takes place with potentially harmful results such as engine knock (detonation). Spray cooling is one way of avoiding hot spots. Another way is to impart vibratory movement to the liquid by attaching an ultrasonic vibrator to the cooling jacket. Kwon, et. al., were able to substantially increase the critical heat flux using a 40 kHz ultrasonic vibrator (see  Experimental Study On CHF Enhancement In Pool Boiling Using Ultrasonic Field , J. Ind. Eng. Chem., Vol. 11, No. 5 (2005 pg. 631-637). Evaporative cooling can also be carried out as described in U.S. Pat. Nos. 3,731,660; 4,565,162; and 7,421,783 or as described in Ap, et. al.,  New Components Development for New Engine Cooling System  VTMS4, 1999, Paper C 543/047/99. See also SAE Paper by Chamfreau, et. al., No. 2001-01-1742. 
     Refer again to  FIG. 25  which illustrates an example to show how the invention can be installed and used as a constant speed, high RPM battery recharging module. In this example of the invention, engine cooling and final steam production are integrated in series by circulating a single fluid in a closed loop to serve as an engine coolant as well as a working fluid in the engine. Thus, the fluid is heated first in the combustion chamber cooling jacket ( 12   b  and  39   FIG. 1 ) preferably to form steam by evaporative cooling as described above. The steam then flows to the generator/superheater  104   b - 104  where it is heated further by combustion exhaust gas to provide superheated steam under high pressure that is supplied through the throttle T to the steam expansion chambers  44  of the engine  10  below the pistons  14 . By running the cooling chambers  39 ,  12   b  ( FIG. 1 ) at a high enough temperature to evaporate the coolant within the cooling jacket itself, steam collects at a controlled pressure above atmospheric pressure in the chamber  500  just above the combustion chambers  34 . In operation, the steam flows out through a steam duct  504  to a pressure regulator valve  506  which maintains a predetermined pressure within the engine  10 . For example, at 25 psia, saturated steam produced in the engine will be at a temperature of 240° F. Once the steam has reached the predetermined pressure established by valve  506 , it will then pass through supply line  508  to countercurrent flow heat exchanger or regenerator  106  where low-pressure steam exhausted from the steam expansion chambers of the engine  10  through line  52  to line  114  enters the heat exchanger  106 , flowing in the opposite direction thereby transferring a part of its heat load to the low temperature steam formed in the engine cooling jacket  39 ,  12   b  ( FIG. 1 ). Pressure in the steam generator and superheater  104  is maintained by a feed pump  511  in line  510 . From the heat exchanger  106 , the steam which has now been heated to a temperature approaching the temperature of exhausted steam, flows through pump  511  into the superheater  104  which has been extended by a pre-heater section  104   b  to a total length of about 6 feet or more and contains additional heater coils  130  that in the figures are depicted as a single spiral but which can consist of a total of 58 or more pancake coils  512 , e.g. of ⅝″ steel tubing connected end to end and spaced about 1¼ inches on centers. Each pancake coil  512  can be about 60 inches long to provide a total of about 290 feet of tubing (52 sq. ft. of heating surface) providing a 24 HP steam generator in which little power is lost due to backpressure. Superheated steam that is formed in the superheater  104  flows as described above through the throttle T, then through the high-pressure steam supply line  49  and valves V to the steam chest  46  or directly to valve  202  (see  FIG. 23 ) then to the steam expansion chambers  44  to power the engine as described previously. The low-pressure exhaust steam from the heat exchanger  106  after having transferred its heat load to the steam from the engine cooling jacket is pumped from line  514  by a compressor  516  through line  518  to a condenser  520  which is maintained by the compressor  516  at an elevated pressure substantially above atmospheric pressure so as to achieve a high rate of cooling by the condenser  520  owing to a substantial temperature difference between the ambient air passing through the condenser and the pressurized steam entering the condenser. Condensed steam collects at the bottom of the condenser  520  where it drains into a storage tank  164 . The pressurized condensate in the storage tank  164  flows through a line  522  to a pressure regulator valve  524  which maintains the high pressure in the condenser  520  and in storage tank  164 . From valve  524 , condensate flows at a relatively low pressure through a feedwater line  526  to a countercurrent flow heat exchanger  528  where it can be preheated under certain operating conditions by diverting the flow from line  518  by valves  530  and  532  through the heat exchanger  528  when steam in line  518  is at a significantly higher temperature than the feedwater entering through line  526 . From the heat exchanger  528 , the feedwater is pumped by a feedwater pump  534  through line  536  back to the engine cooling jacket  12   b  to complete a closed circuit where it is again evaporated to form steam within the cooling jacket  12   b  and  39  of the engine  10 . 
     During operation, the I.C. exhaust gases passing through exhaust pipes  141 - 144  into the exhaust manifold  104 - 104   b  which functions as a superheater, pass out through exhaust pipe  103 . As noted above, spent steam exhaust from engine  10  is carried by pipe  52  through line  114  to the regenerator  106 , then to condenser  520  and through line  536  to the cooling jacket of engine  10 . Coolant leaving the engine as steam through duct  504  picks up the residual heat from the exhausted steam in regenerator  106  before entering the generator/superheater  104 - 104   b . Superheated steam from the superheater section  104  passes through the throttle T to the high-pressure steam line  49  into the engine  10  while the steam cutoff is regulated by engine controller  305  to maximize efficiency as described above and in application Ser. No. 12/075,042, now U.S. Pat. No. 7,997,080. In  FIGS. 18-25  the steam charge cutoff is controlled as previously described by changing the phase angle of camshaft  214  to optimize the specific power output recovered from steam. One or more engine operating variables including the fuel consumption rate can be used as inputs to electronic computer  305  for controlling the operation of the throttle T and the cutoff servo  236  ( FIG. 18 ) as previously described. Rankine cycle operation is most effectively optimized by regulating both steam cutoff and throttle control. 
     As noted above, operating conditions experienced by the engine vary greatly depending upon how the engine is used and applied to the load, whether connected to drive the wheels of a vehicle or run at a constant RPM for extended periods as in powering an electric generator that is used to charge a battery. In the second application, and particularly when accompanied by the use of an afterburner for consuming unburned exhaust constituents as shown in  FIGS. 9A ,  9 B and  25 , the engine  10  may produce relatively high temperature exhaust gas, e.g. at 700° C. to 900° C. for long periods of time. When run continuously in this manner, the temperature of the steam being supplied to the engine may reach a level sufficiently high that the cylinder cap  20  will become overheated, that is to say, if a high degree of superheat is provided over an extended period, it is possible to heat the upper surface of the cap  20  enough so that heat carried away in the steam exhausted from the cylinder outweighs the saving provided by heating the cap  20  to prevent the cap from chilling and thus reducing the enthalpy of each fresh charge of high-pressure steam. In such a case, where there is excessive heat loss from the cap, the cap can be provided with either no external heating or a controlled degree of external heating. One way this can be accomplished is through the use of a heat insulating layer inside the cap such as an optional porous mineral liner  17  ( FIGS. 19 and 20 ) having relatively low thermal conductivity to insulate and thereby limit the heat flux from steam chest  46  to the upper surface of the cap  20  to a degree that optimizes heat transfer to chamber  44 . Thus, according to this feature of the invention, the rate of heat flow from the steam chest  46  through the cap  20  is limited, i.e. controlled. It can be seen that the optional insulating layer  17  of  FIGS. 19 and 20  reduces heat transfer through the cylinder cap  20  while the valve compartment  201  containing valves  200  and  202  is not covered by the optional insulating layer  17  and therefore remains at the temperature of the steam chest  46 . The controlled heating rate can be determined by selecting the thickness and thermal properties of the insulating layer  17  to optimize the transfer of heat to the top of the cap  20  as judged by the power output or specific fuel consumption of the engine. Accordingly, it is an optional feature of the invention to provide a cylinder cap inside an internal combustion piston with either no external heating or controlled external heating of the cylinder cap  20 . Thus, heat control is accomplished in this case by optionally providing a heat source, e.g. the steam at  46  in heat-conductive relationship with the cylinder cap through the heat transfer barrier, e.g. layer  17 , between the cap and the heat source for reducing heat flow through the cylinder cap to the steam expansion chamber  44  to a level below that produced by steam jacketing the cylinder cap as in  FIGS. 1-8 . On the other hand, in applications when the operation of the engine  10  is typically intermittent as in a hybrid gas engine/electric vehicle such as the Toyota Prius™ car where the engine is mechanically connected to the drive wheels, heat flow to the cap  20  can be uncontrolled so as to maximize heating of the cap by high-pressure steam in the steam chest  46 . However, if the engine  10  is connected instead only to drive an electric generator at a constant relatively high speed for recharging batteries, etc., as in the G.M. Volt™ car or any other application in which overheating of the cap could reduce steam efficiency, heating from a source of heat such as the steam chest  46  can be completely removed or reduced in any suitable way by controlling heat flow to the top of the cap  20  to an optimal level based on power output. 
     Refer now to  FIG. 23  which shows the engine  10  constructed without the steam chest  46 . Instead, steam from the superheater  104  flows through a feed pipe  49   a  directly to valve  202 . In accordance with the optional feature of the invention shown in  FIG. 23 , the cap is either not heated externally at all or, if desired, limited heat is optionally transferred in a different way to the cap  20  at a controlled rate. In this embodiment, steam flows from supply line  49  through the vertical pipe  49   a  directly to the valve  202 , i.e. without being allowed to enter the chamber inside cylinder  12  below cap  20 . The space  46  inside the cylinder  12  below the cap  20  can be sealed at the lower end of the cylinder  12  as shown in  FIGS. 19 and 20  or open at  51  and  53  ( FIG. 23 ) to the interior of the crankcase at  31 , if desired with the crosshead guide  20   a  held securely in place, e.g. by a brace at  55   a  and by pipe  49 . Consequently, there is no significant direct heating of the cap; only incidental heating in the area of the steam inlet valves. However, to accomplish controlled heating when some heat is desired, limited heat can optionally be supplied to the top of cap  20  through a small steam pressurized supply passage  57  having an inlet  67  connected to steam supply pipe  49   b  and fed via distribution channel  59   a  within the cap to a few small dead ended radial chambers  161  connected to the cap or within the cap  20 . The radial chambers  161  provide heat at a controlled rate to the top of the cap; the temperature gradient and maximum flux in Btu&#39;s/hr/ft 2  being significantly less than when the entire lower surface of the cap is steam jacketed by the steam chest  46  as shown in  FIGS. 1-4 . The size and number of the radial chambers  161  is chosen to provide a heat flux that maximizes the specific power output of the engine  10 . The pressure-regulating valve  360  (not shown in  FIG. 23 ), if used, is placed in this case between chamber  44  and pipe  49   a.    
     Refer again to  FIG. 24  which illustrates an alternate optional auxiliary clearance volume chamber at  352 . Except for the removal of condensed steam, the auxiliary clearance volume  352  of  FIG. 24  functions in the manner of the auxiliary clearance volume chamber  45  of  FIG. 2  as described above and in application Ser. No. 12/075,042, now U.S. Pat. No. 7,997,080 by admitting steam through a throttling duct  350  of selected length and diameter. The auxiliary clearance volume chamber  352  is located in the cylinder cap  20  so that the throttling duct  350  communicates with the steam expansion chamber  44  at the top of the auxiliary clearance volume. The auxiliary clearance volume  352  like  45  ( FIG. 2 ) reduces the pressure in steam chamber  44  at lower engine speeds as previously described. During operation when the throttle pressure is lowered, engine speed is, of course, reduced. Hence the auxiliary clearance chamber  45  or  352  can be used to automatically lower cylinder pressure to the reduced throttle pressure thereby eliminating the need for valve  360 . In  FIG. 2 , gravity will drain condensate (if any) from chamber  45 . Because of the high operating temperatures, no condensate should accumulate in chamber  352 . However, if condensate does tend to form, a suitable thermostatic drain valve  356  can be used to remove the condensate through a drain  354  by opening when the engine is cold and closing when the engine is hot. 
     Characteristics and Unexpected Results 
     From the description of  FIGS. 1 and 2  it can be seen that the invention is capable of providing even better protection against the chilling of the metal surfaces by low-pressure exhaust steam than a conventional steam-only uniflow engine. A uniflow steam engine exhausts steam adjacent to the piston head and there is no way to heat the surface of the uniflow piston head positioned adjacent to the ports through which steam is released. By contrast, in the present invention low-pressure steam is exhausted at the cap  20  comprising the steam cylinder head, exactly where heat can be supplied to the steam expansion chamber by the adjacent steam chest  46 . Consequently, for certain applications, especially if start and stop operation and idling is essential, the present invention is able to provide better heat loss protection and therefore greater Rankine efficiency than that in a standard uniflow steam engine. The invention can provide better protection against power losses during operation in part through enhanced control of the steam mass admitted each stroke, e.g. by the provision of one or a pair of steam admission valves in the cap that open into the steam chest and in part through special exhaust valving which in one preferred form comprises a double aperture automatic exhaust valve having ports in both the piston skirt as well as in the cylinder wall which are covered when steam is admitted but which open adjacent the cylinder cap when aligned with one another while the steam chamber is in an expanded state. Additionally, the invention provides a combination I.C./steam engine in which residual steam within the piston can be recompressed so as to provide as effective zero clearance with a gain in mean Rankine cycle temperature. Moreover, low-pressure exhaust steam need not be ducted below the cylinder cap where it could cool the cap or the steam chest which is therefore able to jacket the entire lower surface of the steam cylinder cap in any installation in which it is advantageous to do so. In addition, the invention provides an oil ring on the piston for stripping combustion products and excess oil from the cylinder and depositing it in an annular collection channel that is built into the wall of the cylinder at a point located in alignment with the oil ring when at bottom dead center and a passage for carrying excess oil and blow-by combustion products to the sump. Optionally, the collection channel holds one or more wiper rings that press centrally against the outer wall of the piston for capturing excess oil and blow-by combustion products and ducting them to the engine sump before they can reach the steam exhaust manifold. 
     Besides sealing the steam expansion chamber  44 , the stationary cylinder cap also provides support for one or a pair of steam inlet valves, reduces the steam clearance volume between its upper surface and the confronting inner wall of the piston, defines the top of the steam chest, can heat the steam exhaust area and supports packing around the piston rod to prevent the escape of steam. By providing a piston with a skirt that is in sealing and sliding relationship between both the steam cylinder head and the cylinder walls, the added length of the cylinder needed to accommodate steam is minimized since the steam chamber and I.C. chamber occupy the same space. In addition, the invention provides an improved system and sequence of heat transfer devices for efficiently recovering waste combustion heat from the I.C. engine assembly. 
     In summary, the invention provides the following benefits and unexpected results among others: 1) efficiency in a combined cycle engine as good or better than a uniflow steam engine while adding as little as possible length to the engine cylinders, 2) the steam expansion chamber occupies the same space as the combustion chamber of the I.C. engine, 3) the steam expansion chamber is heated by direct thermal transfer from the I.C. engine combustion chamber, 4) the burnt oil from the I.C. chamber as well as blow-by combustion gasses are kept separate from the steam expansion chamber and the exhausted steam, 5) the exhaust valve need not exhaust low-pressure steam below the steam cylinder head where it could cool incoming steam or interfere with steam jacketing of the steam cylinder head, 6) clearance volumes can be as small as desired since the opposing surfaces of the piston and cylinder cap are both flat, 7) the exhaust valve when opening sweeps adjacent steam and moisture if any out of the cylinder, then closes so that the cylinder pressure is brought up to or very close to the steam admission pressure thereby preventing steam at atmospheric pressure from washing heat from the cylinder walls and head, which if it occurred could reduce power due to the condensation of incoming steam, 8) piston walls are exposed to exhaust steam pressure only for the short period that the exhaust port is uncovered, whereupon the pressure and temperature immediately begin to rise so that at the end of the down stroke the temperature and pressure is such that an effective zero clearance is achieved with a gain in mean Rankine cycle temperature whereby efficiency is improved and the incoming steam meets relatively hot surfaces thereby preventing cooling of the incoming charge, 9) unlike a standard uniflow steam engine, the metal surface at the end of the steam chamber adjacent the exiting steam can be externally heated when it is advantageous to prevent exhaust steam at atmospheric pressure from chilling or condensing the incoming charge of steam, 10) a short steam admission cutoff can be provided without excessive valve and cam stress, 11) evaporative cooling improves steam production efficiency, 12) controlled heating or no heating of the cylinder cap reduces thermal loss in the exhausted steam, 13) steam recompression pressure can be limited to throttle pressure, 14) the engine can be mechanically connected to the wheels of a vehicle or used to charge a battery, and 15) momentum energy of a vehicle can be stored and used later. 
     Many variations of the present invention within the scope of the appended claims will be apparent to those skilled in the art once the principles described herein are understood.