Abstract:
A cogeneration system for generating electricity and process steam. The system includes an internal combustion engine having a shaft and a cooling system comprising a cooling fluid adapted to circulate through the engine and to cool the engine under conditions of nucleate boiling in which at least 10 percent of the coolant exits the engine in a vapor phase. It includes a vapor separator adapted to separate the coolant that exits the engine into a vapor phase coolant and a liquid phase coolant. The engine shaft drives an electric generator to provide electric power. A hot vapor line directs hot vapor exiting the vapor separator to a hot vapor process load. A coolant circulation pump is provided to force the cooling fluid through the engine, and a hot water line is provided to return hot water exiting the vapor separator to the coolant circulation pump. In preferred embodiments the system further includes an excess steam condenser for to collecting and condensing excess steam not needed by the hot vapor load, a condensate return tank adapted to store condensate from the hot vapor load and the excess steam condenser, and a condensate return line adapted to return condensate to the coolant recirculation pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Patent Application Ser. No. 61/958,798, filed Aug. 6, 2013. 
     FIELD OF THE INVENTION 
     The present invention relates to internal combustion engines and in particular to such engines used for the generation of electricity. 
     BACKGROUND OF THE INVENTION 
     Reciprocating Engines 
     Reciprocating engines are desirable in cogeneration applications due to their high electrical efficiency. However the relatively low temperature of the heat generated as a byproduct of producing electricity is simply not hot enough to be useful, and hence the heat is wasted through a heat rejection system such as a cooling tower or radiator. In some applications, the heat may be useful for space or hot water heating, but may require an expensive hydronic or low-pressure steam system to distribute the heat to where it is needed. 
     Combustion temperatures of natural gas fired engines are substantially higher than the boiling points of the engine coolants (typically water, a water alcohol mixture or a commercial antifreeze product which may be a mixture of alcohol and ethylene glycol). So coolant boiling in the engines could lead to a condition of uncontrolled boiling in the coolant passages of the engines, especially in proximity of exhaust valves. This condition can drastically reduce the heat flux being carried away by the cooling system. This, in turn, can potentially produce a catastrophic effect on the internal metal parts of the engine. For this reason internal combustion engines are typically designed to be cooled with convective liquid cooling, mostly with water. 
     Nucleate Boiling 
     There is, however, a condition between normal liquid coolant flow conditions and uncontrolled boiling that provides an optimum heat flux from the parts to be cooled by the liquid cooling system. This is known as nucleate boiling in which bubbles are generated on a tiny or microscopic scale. This allows significant increases in heat flux, but this condition in many cases is a momentary transition between sub-boiling conditions and uncontrolled damaging. 
     Ebullient Cooling 
     Ebullient cooling of internal combustion engines has a long history and is a well-known, proven and increasingly practiced art. It has been utilized in some makes of large industrial and stationary engines to produce low-pressure steam as a cogenerated thermal product along with mechanical or electrical power and has been the subject of many patents. A 1983 Evans patent (U.S. Pat. No. 4,367,699) describes a boiling liquid cooling system for the engine of a passenger car. It cites no less than 49 related U.S. patents, five foreign patents and six publications dating back to 1911. 
     Ebullient cooling refers to the process of boiling a fluid in contact with the surfaces of a heated structure for the purpose of controlling its temperature to maintain structural integrity and/or to control heat losses. Ebullient cooling differs substantially from convective liquid cooling. The thermal capacity of the coolant is derived from its latent heat of vaporization rather than from its much lower sensible heat capacity. The consequent reduction in flow rates, pumping power and temperature changes makes it possible to produce nearly isothermal cooling with nearly uniform material temperatures and substantially reduced parasitic pumping power. 
     Almost without exception, modern liquid-cooled piston engines provide for coolant entry into the cylinder block and exit from the cylinder head. Coolant passage from the block to the head is typically internal to the engine via the head gasket and matching ports provided in the decks of the block and head castings. The occurrence of ebullient phenomena in the cooling systems of these conventional, typically upward-flowing, liquid-cooled engines operated under high output conditions is commonplace, although usually unintentional. It frequently occurs locally at high heat-flux points in the neighborhood of the engine combustion chamber where flow, temperature and pressure conditions may become unfavorable for the intended convective heat transfer. When it occurs under these conditions, it is usually considered to be adverse to engine durability by virtue of the development of cavitation erosion and hot-spots. Vapor bubbles formed locally on a superheated surface may subsequently condense as they are transported across cooler surfaces, resulting in minute but intense localized implosive shocks to the surface. Also depending on the flow, pressure and surface conditions prevailing at these superheated areas, vapor bubbles attached to the surface may grow to such a size that appreciable surface area is occluded from the circulating liquid, thereby defeating intended convective heat transfer. This condition, known as film boiling or departure from nucleate boiling (DNB), sharply reduces the local heat transfer rate which, for a given heat flux, requires large temperature differences. This cause or contribute to cooling-system failure. 
     Conventional ebullient cooling approaches rely on natural circulation of the coolant by the thermo-siphon effect. In this approach, the liquid coolant is introduced into the cylinder block and flows upward into the cylinder head and out of the engine. The coolant flow paths are almost identical to that which occurs in the conventional liquid-cooled engine and in many cases the fittings, gaskets and cooling systems are physically unchanged for ebullient operation. The main difference is in the method of coolant circulation. In the liquid-convective cooling system a coolant pump forces the circulation as determined by pressure, flow and geometrical considerations. 
     Some systems utilizing ebullient cooling may permit natural circulation of the coolant. Natural circulation ebullient cooling conditions are permitted by the lift and drag created by the vapor bubbles which form as heat transfer occurs. The large density difference between the bubbles and the liquid produces a strong buoyancy effect on the bubbles, and the relative motion of the bubbles in the confined liquid gives rise to the viscous drag that lifts the liquid upward and out of the engine as an entrained mixture with the vapor. When, external to the engine, the vapor is separated from the liquid and the density of the liquid is sufficiently great to cause the liquid to return to the engine block by gravity. A pump is required only to supply any make-up fluid required and/or to scavenge liquid from a remote condenser if used. 
     This approach, while practical for many applications, suffers from the same incipient film boiling and distribution problems mentioned in connection with conventional upward-flow liquid cooling. Because the gravity-motivated vapor lift type circulation is weak, coolant flow distribution in the critical high-flux zones about the cylinder head at the upper end of the flow path may be poor. Without internal control of this weak circulation, vapor/liquid distributions in the head where the heat flux is the greatest may be unfavorable for the heat transfer required. 
     Since the rate of bubble formation is greatest where the heat flux is highest, there is a tendency for the high-flux zones of a confined cooling jacket to be deprived of the liquid that provides the latent cooling effect. For this reason, some engine manufacturers de-rate their engines for ebullient-cooled operation. Since it supplies virtually all of the thermal capacity, the liquid must wet the surface to be cooled in order to obtain the full benefit of the ebullient cooling effect. This cannot be assured when the coolant flow path is from the low-flux to the high-flux zones of an engine, i.e. upward in a conventional automotive engine. Excessively large vapor bubbles and/or excessive vapor fractions sharply reduce the boiling heat transfer rate because of impaired liquid contact with the heated surface. 
     Jacketed engines are almost always designed to be cooled by the processes generally known as forced-convection heat transfer. The regimes of forced-convection heat transfer and the rates of heat transfer associated with these regimes are depicted qualitatively in  FIG. 1 . For a first approximation, velocity and temperature gradients are neglected in this presentation. In the ebullition regime, three forms of boiling may occur, each achieving widely different heat transfer rates. These are known as surface boiling, nucleate boiling and film boiling, listed in order of the level of heat-transfer-rate attainable. 
     Surface boiling, illustrated in  FIG. 2A , achieves the highest rate of heat transfer known in the art. However, these high rates are obtained with little or no net vapor generation, since the phenomenon occurs largely in entrance regions when the bulk of the liquid phase is in a subcooled condition. Nucleate boiling occurs at the surface, but the small bubbles that form are quickly swept into the subcooled bulk where they condense back to liquid, giving up their latent heat of condensation to the bulk liquid. The high heat transfer rate attained in surface boiling is largely due to this latent transport mechanism and the vigorous mixing that accompanies it. This process is very useful for spot-cooling intensely heated areas but is difficult to implement throughout an engine jacket because of the narrow range of the bulk-fluid temperatures which sustain it. It is most useful when applied as an entrance region transient to be followed by a more general boiling technique. If heat recovery in the form of saturated vapor is desired, other more general forms of boiling, or ebullition, must be employed. It is also difficult to exploit usefully in conjunction with single-phase, forced conventional cooling, since it occurs, if at all, toward the exit regions of the jacket and, as indicated above, can quickly lead to film boiling with sharply reduced heat transfer and cooling system failure. 
     Nucleate boiling, illustrated in  FIG. 2B , is the preferred mechanism for producing vapor simultaneous with high heat transfer rates at isothermal fluid conditions and minimal temperature gradients. Nucleate boiling can be established and maintained up to fairly high vapor/liquid ratios provided certain design constraints are observed. Representative heat-transfer coefficients in nucleate boiling of various fluids are given in  FIG. 3 , showing the effects of temperature difference and fluid pressure. Fluid velocity also has a significant effect (not shown), which can be used to enhance heat transfer. However, the viscous-pressure losses that accompany increased velocities reduce the vapor pressure and therefore the boiling temperature which, in turn, reduces the thermodynamic availability of the vapor generated. The upper terminals of the nucleate boiling curves of  FIG. 3  indicate the approximate limits of nucleate boiling. Fluxes in excess of these limiting values result in a transition to the film boiling mechanism accompanied by sharply increased temperature differences required to compensate for the sharply reduced heat-transfer coefficients. 
     Heat transfer coefficients attained in nucleate boiling are at least an order of magnitude higher than forced convection liquid values at the same temperature difference. As a result, the use of the nucleate boiling mechanism in engine jackets can result in the over-cooling of certain engine parts, leading to excessive heat losses and reduced thermal performance. Thus, the successful application of the nucleate boiling method of engine cooling emphasizes temperature control rather than cooling per se in order to gain the full advantage of its high heat-transfer potential and characteristically low temperature gradients. With proper coolant distribution and flow control, a high degree of temperature uniformity at optimum temperature levels can be obtained in the engine structure. For comparison, the region of experience for forced convection, single-phase liquid heat-transfer attained in conventional engine-cooling jackets is also shown in  FIG. 3 . 
     The choice of working fluids and operating conditions for ebullient cooling of engines involves a number of material and thermodynamic considerations. These are listed in Table 1. 
     Since all of these factors are intrinsic to the fluid itself, its selection will require compromises and compensation in the determination of proper operating conditions. The magnitude of the latent heat of vaporization determines the coolant heat capacity in ebullient cooling. This in turn governs the coolant flow-rate schedule required to maintain a stable engine heat balance. The interfacial tension depends on the surface-wetting properties of the coolant. It determines the vapor bubble contact angle under boiling conditions which, in turn, determines the surface area effective in boiling heat-transfer (see  FIG. 2 ). 
     
       
         
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Latent Heat of Vaporization 
               
               
                 Interfacial Tension with Engine Materials and Jacket Internal Surfaces 
               
               
                 Vapor/Liquid Densities 
               
               
                 Specific Heat 
               
               
                 Thermal Conductivity 
               
               
                 Viscosity: Liquid and Vapor 
               
               
                 Vapor pressure 
               
               
                 Corrosiveness, Solvent Power and Dielectric Properties 
               
               
                 Critical Pressure/Temperature 
               
               
                 Cost 
               
               
                   
               
             
          
         
       
     
     The ratio of vapor and liquid densities, together with the latent heat, determines the volume of liquid displaced by the vapor formed for a given rate of heat transfer. It also relates to the bubble size and rate of growth which, together with the surface tension, determines the loss of effective heat-transfer surface area tending to diminish the heat transfer coefficient. These fluid-related effects are strongly dependent on the critical pressure. 
     The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature. Maximum nucleate boiling heat-transfer coefficients for a given fluid are attained when the operating pressure is maintained at about one-third the critical pressure. Thus, there is an optimum operating pressure for heat transfer, but this may not be reconcilable with structural, material and system constraints, so that compromises may be required. Water, for example, has a critical pressure of 3,206.2 psia at a critical temperature of 705.4 F. Maximum boiling heat transfer rates can be obtained at pressures in the neighborhood of 1,070 psia and saturation temperatures of about 550 F. While these design conditions are acceptable—even desirable—for stationary power and marine propulsion boilers, they are excessive for existing reciprocating-engine cooling jackets. 
     Among the compromises that must be made to maintain nucleate boiling under lower-than-optimum pressure conditions is the degree of vaporization utilized in the high-flux zones of the jacket. This requires that an excess of liquid be pumped over and above that which would provide the minimum latent heat capacity for heat transfer, the excess being required to compensate for excessive vapor displacement. In low-pressure and natural circulation evaporators, this is known as flooding. In forced-circulation, once-through boilers or engine jackets this excess liquid is referred to as transport flux. 
     A variety of alcohol, hydrocarbon and halocarbon materials having somewhat lower critical pressures than water are available. Some of these materials will operate in engine jackets at nearly optimum pressure levels for heat transfer and have other properties providing advantages in some applications. 
     What is needed in the art therefore is a cooling system which effectively maintains nucleate boiling in an engine cooling system to maximize heat removed from the engine combustion chamber while providing much higher temperatures in the coolant discharged from the cooling system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cogeneration system for generating electricity and process steam. The system includes an internal combustion engine having a shaft and a cooling system comprising a cooling fluid adapted to circulate through the engine and to cool the engine under conditions of nucleate boiling in which at least 10 percent of the coolant exits the engine in a vapor phase. It includes a vapor separator adapted to separate the coolant that exits the engine into a vapor phase coolant and a liquid phase coolant. The engine shaft drives an electric generator to provide electric power. A hot vapor line directs hot vapor exiting the vapor separator to a hot vapor process load. A coolant circulation pump is provided to force the cooling fluid through the engine, and a hot water line is provided to return hot water exiting the vapor separator to the coolant circulation pump. 
     In preferred embodiments the system further includes an excess steam condenser for to collecting and condensing excess steam not needed by the hot vapor load, a condensate return tank adapted to store condensate from the hot vapor load and the excess steam condenser, and a condensate return line adapted to return condensate to the coolant recirculation pump. In preferred embodiment the system further includes a computer driven control system and temperature and flow meter components to permit automatic control of the system to maintain a desired degree of nucleate boiling in the engine. In preferred embodiments the coolant exiting the engine is saturated with a quality of between 2 and 30 percent. A wide variety of cooling fluids can be used. Typically they will be at least 90 percent water, but in special cases cooling fluids that are not water based may be preferred. 
     The hot vapor of the present invention can be advantageously utilized in a great variety of processes including many industrial, commercial and residential processes including space heating. The electrical output can provide a base load or be used to supply peaking power. 
     In preferred embodiments of the present invention the temperature of lower quality vapor generated in an engine jacket is increased by an exhaust to coolant heat exchanger, after which vapor is separated from saturated liquid for use in various industrial or commercial processes. In other words, it is desired to extract the engine jacket heat as dry vapor. It is a principal object of the present invention, therefore, to provide an improved boiling liquid cooling system for an internal combustion engine in which the heat transfer is accomplished by nucleate boiling maintained by the pressure drop across cooling jets. Preferred embodiments of the present invention provides an improved boiling liquid cooling system for an internal combustion engine in which a series of liquid nozzles are positioned to impinge areas of highest heat flux with cooling liquid at or its near saturation pressure with velocity sufficient to maintain nucleate boiling conditions while preventing film boiler through a constant predetermined pressure drop between the nozzle entrance and exit under all engine operating conditions. These and other objects of the invention are also achieved in a boiling liquid, cooling system for an internal combustion engine including a coolant inlet and coolant outlet, the cooling system including a separation tank coupled to the coolant inlet and coolant outlet for separating vaporized coolant from liquid coolant, a makeup system coupled to the separation tank for replacing the vaporized coolant flowing from the separation tank to an external heat sink. 
     In one embodiment of the invention, the coolant is boiler feedwater and the vaporized engine coolant supplements steam needed of feedwater deareator. Saturated liquid from a deareator is fed from a feedwater pump through a control valve to maintain a predetermined pressure drop across the engine coolant nozzles. Low quality steam from the internal combustion engine is then returned to the dearator. In another embodiment of the invention, the coolant is water and the vaporized coolant from the engine provides steam for a laundry or other commercial or industrial process requiring low pressure steam. 
     Another embodiment of the invention, involves the induction of vapor in the form of steam produced in the engine jacket into the air intake of the engine for the purpose of controlling oxides of nitrogen emissions. It is well known that the generation of nitrogen oxide is reduced by adding water in the combustion process of an internal combustion engine. This is due to the cooling effect by the added water. Actually, water injection to a reciprocating engine has been done by two different methods, i.e. direct injection of water into the combustion chamber, or introduction of water into the combustion chamber by way of intake air passage. Water injection adversely affects engine efficiency as the phase change requires substantial energy which reduces the force of the engine expansion stroke. The use of steam generated in the engine jacket for induction into the air inlet of the reciprocating engine reduces nitrogen oxide emisisons without the reduction in engine efficiency. 
     The foregoing objects of the invention are also achieved in a boiling liquid coolant system for an internal combustion engine having a cylinder block with at least one cylinder, a cylinder head, at least one inlet per cylinder, each coolant inlet comprising a jet or series of jets for directing high velocity coolant to impinge on areas of high heat flux arranged so to maintain nucleate boiling conditions on the engine heat transfer surfaces. 
     The objects of the inventions maintain stable nucleate-boiling heat-transfer conditions having the following attributes:
         Radically reduced coolant flow-rates and parasitic pumping power.   Extremely short engine-warm-up transients.   Orderly coolant behavior over a wide range of operating conditions including shutdown.   Excellent engine structural temperature control featuring good temperature uniformity in high-heat-flux zones during engine operation from idle to maximum continuous power and also upon sudden shutdown.   Reduced combustion-chamber and piston heat losses without compromise to material structural margins, seal integrity, knock-limited torque development, or fuel economy.   Brake mean effective pressures approaching 300 PSI with brake specific fuel consumptions below 0.48 Lbs per HP-Hr.       

     The foregoing and other additional objects, features, and advantages of the present invention are more fully described in the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts regimes of forced-convection heat transfer and rates of heat transfer associated with these regimes. 
         FIG. 2  is a graphic description of surface boiling, nucleate boiling and film boiling. 
         FIG. 3  shows the regime of conventional water jacket cooling heat transfer.\ 
         FIG. 4  is a general layout of a preferred embodiment of the present invention. 
         FIGS. 5, 6 and 7  show a technique for cooling a standard V-8 engine head and block. 
         FIG. 8  shows an approximate temperature of the components of the V-8 engine utilizing embodiments of the present invention. 
         FIG. 9  is the experimental data of valve seat metal and exhaust gas temperatures distribution of a conventionally cooled 454cid V-8 engine operating at wide open throttle at 3600 rpm. 
         FIG. 10  is the experimental data of valve seat metal and exhaust gas temperatures distribution of a 454cid V-8 engine modified for ebullient cooling operating at wide open throttle at 3600 rpm. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The design of a specific embodiment of the present invention is represented in  FIG. 4  and in Tables 2 and 3. The system features an ebulliently-cooled, production-type, spark-ignition automotive engine fueled by natural gas driving a state-of-the-art induction generator and managed by a state-of-the-art microprocessor-type process automation system. 
     A prototype embodiment has been built and tested by Applicant. For it he utilized a General Motors V-8 engine with a displacement of 454 cubic inches. The specific engine parts are in general those of this engine. In the prototype Applicant&#39;s coolant was water.  FIG. 4  shows a boiling liquid cooling system based on Applicant&#39;s prototype. The internal combustion engine  10  includes an oil pump  4 , an oil cooler  5 , a vapor separation tank  13 , a circulation pump  14 . These components are arranged in a circuit, the discharge of the circulation pump  14 , flowing counter flow through an engine oil cooler  5 , wherein engine oil pumped by the engine oil pump  4  is cooled and reintroduced to the engine  10 , the coolant discharge from the engine oil cooler  5  feeds coolant injection nozzles  25 , arranged so to impinge high heat flux areas within the engine cylinder head  17  (shown in  FIG. 5 ) with high velocity coolant. Engine shaft  40  drives electric generator  41  to provide electric power. 
     
       
         
               
             
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 FEATURED CHARACTERISTICS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Compact, Light-Weight, Small-Foot-Print Package Plant Based on Use of High Specific Power Prime 
               
               
                 Mover. 
               
               
                 Reduction in Cost Based on Use of Production Automotive Engine Subject to Large-Scale Manufacturing 
               
               
                 Economies. 
               
               
                 High Thermal Efficiency Maintained Under Widely Variable Electric/Thermal Load Ratios Using 
               
               
                 Thermal-Load-Matching Automation to Conserve Fuel, Minimize Excess Steam Production and Minimize 
               
               
                 Start-Stop Cycles which Adversely Affect System Reliability and Engine Durability. 
               
               
                 Improved Efficiencies Available with Concurrent Hierarchical Thermal Outputs, e.g. Hot Water, Low- 
               
               
                 Pressure Steam, High-Pressure Steam, Hot Gas, etc.: High Efficiency Both Qualitatively and 
               
               
                 Quantitatively. 
               
               
                 Improved Durability/Rating/Flexibility Trade-Offs With Dual Speed Options, e.g. 1,800 rpm for 
               
               
                 Continuous Base Loads, 3,600 rpm for Periodic Peak Loads. 
               
               
                 Improved Durability, Shaft Rating and thermal Performance with Forced-Downflow Ebullient Engine 
               
               
                 Cooling. 
               
               
                   
               
             
          
         
       
     
     Coolant flows across the interior of the engine cylinder head  17  down through selected passages between the head and engine block, flowing as partial quality saturated vapor out of the engine block  10  as shown at  27  in  FIGS. 5 and 6 . The partial quality saturated vapor is collected in a discharge header feeding a coolant line to the vapor separator  13 . Vapor is fed from the vapor separator to a hot vapor distribution line  9  as shown in  FIG. 4  to feed a hot vapor load (referred to as “load” in  FIG. 4 ). The level of the vapor separator  13  is maintained by a level controller (not shown) which actuates a feed valve  20  based on a predetermined set-point coolant level measured by a level transmitter  18 . Coolant and make up coolant in the vapor separator are fed to the circulation pump  14  thus completing the circuit. 
     Separation tank  13  as shown in  FIG. 4  has one inlet and two outlets. A liquid coolant outlet  19  at or near the bottom of the tank connects through a conduit such as a hose  21  to the circulation pump and then the oil heat exchanger, lastly entering the engine through the coolant nozzles  25 . The second liquid coolant outlet  8  is located at the bottom of the tank  13  as a blow down. A vapor inlet  23  in the side of tank  13  receives a mixture of hot coolant liquid vapor delivered through a conduit such as hose  24  from a discharge  27  at the front of the engine; then running through the jacketed exhaust manifolds  29  and exhaust heat recovery boiler  22 , thus completing the engine coolant circuit. 
     Condensate from the hot vapor load is returned to a condensate receiver tank  30  as shown in  FIG. 4 . In addition the preferred embodiment includes a bypass valve and an air cooled excess vapor condensate tank  3  adapted to condense hot vapor not needed by the hot vapor load. Condensate from these two components is pumped by a feed pump shown in  FIG. 4  through a flow meter to recirculation pump  14 . Make up cooling fluid is provided through makeup valve  6  which preferably is automatically controlled to maintain a desire level of coolant fluid in the system. 
       FIGS. 5 and 6  show the side and front of the standard V-8 engine head  17  and engine block  10  and  FIG. 7  depicting a head  17 , four coolant entrance ports are drilled and tapped into the side of head  17 , with threading to mate to the coolant supply nozzles  25 . The coolant supply nozzles  25 , are arranged to provide specific directional flow  26  of high velocity coolant for impinging the high heat flux surfaces inside the engine head, the direction typically arranged in a series of jets which are fixed to a conduit supplying coolant at constant pressure for maintaining constant velocity. 
       FIG. 5  shows a cross sectional circulation pattern of flow to maintain nucleate boiling conditions throughout the engine, the head gasket sealing the interface between the head  17 , and the engine block  10 , is provided so that coolant port openings between the head  17  and engine block  10  are sealed with the exception of a head exit ports located opposite the coolant entrance ports  25 , creating a passage for partially saturated liquid coolant flowing across the head and into the engine block  10 . The coolant passing into the block flow transverse out of the engine block through coolant exit ports  27 , originally reserved for a water pump of a conventional engine. In order to remove any entrained air in the saturated liquid, engine coolant vents  28  are provided at the end of the intake manifold which communicate with the engine coolant passages. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 EBULLIENT-COOLING SYSTEM 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1.  
                 REVERSED-FLOW PATH 
               
             
          
           
               
                   
                   
                  a.  
                 Aggressive surface impingement and boiling at high-flux zones 
               
               
                   
                   
                  b. 
                 Stable nucleate boiling with once-through, forced-flow zones 
               
               
                   
                   
                  c.  
                 Excess liquid circulation with external vapor separation 
               
               
                   
                   
                  d.  
                 Cross-flow in head from exhaust to intake side 
               
               
                   
                   
                  e.  
                 Cross-flow in block from ends to center 
               
               
                   
                   
                  f.  
                 External head-to-block connection 
               
               
                   
                   
                  g.  
                 Head vent to standpipe 
               
             
          
           
               
                   
                 2. 
                 JET-INDUCED CENTRIFUGAL CIRCULATION PUMP 
               
             
          
           
               
                   
                   
                  a.  
                 Electrically driven, constant head and flow 
               
               
                   
                   
                  b.  
                 Low power consumption 
               
               
                   
                   
                  c.  
                 Pulsation isolated from boiler 
               
             
          
           
               
                   
                 3. 
                 MINIMUM TEMPERATURE CONTROL 
               
             
          
           
               
                   
                   
                  a.  
                 Back-pressure override on vapor delivery pressure 
               
               
                   
                   
                  b.  
                 Accelerated warm-up 
               
               
                   
                   
                  c.  
                 Stand-by oil heater, thermostat-controlled 
               
             
          
           
               
                   
                 4. 
                 MAXIMUM TEMPERATURE CONTROL 
               
             
          
           
               
                   
                   
                  a.  
                 Automated load management 
               
               
                   
                   
                  b. 
                 Pressure-relief dump to waste-vapor condenser 
               
               
                   
                   
                  c. 
                 External oil cooler, thermostat-controlled 
               
               
                   
                   
                  d. 
                 Under piston cooled oil impingement 
               
               
                   
               
             
          
         
       
     
     In this down-flow forced-circulation arrangement, feed coolant enters the exhaust side of the heads  17 , as shown at  25 , transits the exterior of the combustion-chamber roofs in a cross-flow direction  26 , exits the heads and enters the cylinder block along the intake side as shown at  29  in  FIG. 7 , cross-flows the cylinders and exits the block at the center on each side  27 . The flow rates, pressures and temperatures are managed such that, together with the prevailing heat-flux distributions, nucleate boiling occurs at the heated surfaces contacted by the coolant. The fluid temperature remains virtually constant throughout the jacket, with the vapor fraction and velocity increasing progressively from inlet to outlet. 
       FIG. 7  shows a cross-section of the head at one combustion chamber and the location of the coolant-entry port, the twin-jet orifice producing liquid impingement at the spark-plug boss and exhaust-valve seat boss. In this design, the total coolant flow to the engine is represented by 64 units of coolant, 32 units in each side of the engine jacket. Each head-inlet nozzle  25  (one for each cylinder, four in each head) receives eight flow units, which it delivers into the head jacket via the twin jets, one axial and one radial. Six units of flow are directed-axially at the valve boss with a velocity of 49 feet-per-second. This velocity is produced with a pressure difference across the orifices of approximately 19 psi. Two units of flow at the same velocity are directed radially at the spark-plug boss. The total inlet flow (sub-cooled liquid) handled by the eight inlet fittings is approximately 9.918 cubic feet per second. The axial orifice is approximately 7/64 ths of an inch in diameter, and the radial orifice is approximately 1/16 th of an inch in diameter. 
     The fluid leaving the heads and entering the block is approximately 10% vapor by mass, having a total volume flow of approximately 2.92 cubic feet per second. In this representative design, five matching ports provided in the decks of the heads and block, allow the fluid to pass into the block and circulate there through. Special cylinder-head gaskets are used to prevent flow except at these five ports in each deck (ten in all), which are sized for approximately 100 feet-per-second velocity at a pressure difference of about 9.5 psi. This pressure drop results in a temperature reduction of about one-degree F. Deflector vanes installed in each block-side port can be used to enhance the cross-flow distribution in favor of the top-end of the cylinder. The special cylinder-head gaskets differ from stock gaskets only in the number and size of coolant ports punched. 
     Following a short, single-phase entrance region, the vapor fraction increases progressively as the fluid transits the engine jacket. This process is illustrated in  FIG. 8 , showing representative heat transfer, vapor fraction and temperature distributions throughout the system. 
     The vapor quality leaving the engine jacket is a relatively low 15%. This results from using high liquid transport fluxes to maintain the most favorable conditions for nucleate boiling with liquid at low pressures. Subsequent to the engine jacket, the two-phase fluid is passed through an exhaust-heat recovery boiler and then to the vapor separator where the vapor and liquid phases are separated. The saturated vapor is then piped to the heat load, and the saturated liquid is circulated to the engine via the separately driven (electric) centrifugal pump, aided by a variable-area jet inducer (eductor). 
     For variable load and speed applications, the feed pump and eductor are automated as an energy conservation measure. The pump speed is modulated to schedule its output as a function of the fluid vapor fraction entering the vapor separator. This is accomplished by a state-of-the-art, signal-following induction-motor control that modulates the pump speed to maintain a given ratio of recirculated flow-to-feed flow as measured by appropriately placed flow meters and calculated by the microprocessor. The eductor primary nozzle area is modulated by a state-of-the-art position control which maintains a given primary-flow-to-total-flow ratio as the pump output varies, so that adequate flow rate through the engine maintains nucleate boiling. 
     The proof-of-concept of the invention consisted of an experimental evaluation of the effects of the nucleate cooling scheme disclosed on a back to back basis with the same engine prior to the nucleate cooling modification. The approach capitalized on the relative ease of retrofitting the novel ebullient cooling system to the conventional engine to facilitate such back-to-back testing. A Chevrolet V-8 engine with 454 cubic inch displacement was prepared for natural gas service. The engine was instrumented with temperature probes to measure head metal temperature near the exhaust ports. The engine was connected to a variable speed dynamometer and run at wide open throttle at 3600 and 1800 rpm. The first run of the back-to-back test was with the stock engine as conventionally cooled with 30 gallons per minute of 125° F. water entering the engine block, exiting the engine from the intake manifold.  FIG. 9  is the valve seat and exhaust gas temperatures resulting from the first run. The second run was with the same engine modified for nucleate cooling with 12 gallons per minute of 240° F. water entering the engine head through 8 separate jets and existing the engine block at 255° F. saturated temperature and pressure.  FIG. 10  represents the valve seat and exhaust temperature distribution of the same engine modified for ebullient cooling. 
     The valve seat temperature distribution of the ebullient cooled engine was within 20° F. of the same engine conventionally cooled although the cooling water supply for the ebullient cooled engine was 115° F. higher than the conventionally cooled engine. Engine performance was found to be equal or better with the ebullient cooling scheme compared to conventional cooling, the ebullient cooled variation yielding higher power output at the same rpm and using the same amount of fuel input. 
     Applicant has built and tested prototype versions of his invention as described above and the prototype described above provides the following features representing important technical advances in the prior art:
         Engine boiling is universally known to be unacceptable requiring immediate engine shutdown and precluding improved performance resulting from nucleate boiling in internal combustion engines.   Exceptional heat transfer and temperature control.   Surface and nucleate boiling—high heat transfer rates, small temperature gradients.   Temperature uniformity in coolant and engine structure, permitting improved engine performance and durability.   Heat-transfer rate inherently matched to heat-flux distribution.   Temperature control—maximum and minimum with short warm-up and starting transients.   Latent cooling capacity less dependent on flow rates and velocities.   Reduced parasitic pumping power by virtue of latent heat capacity.   Reduced life-cycle cost by virtue of automotive-technology adaptation.   Reduced application complexity by virtue of compact size and light weight.   Increased application flexibility with two-speed operation arid load-matching controls.   Increased application potential by virtue of the hierarchy of thermal outputs and dual ratings (baseload and peaking).   Reduced nitrogen oxide emissions from the induction of vapor in the form of steam generated in the engine jacket into the air inlet.       

     Utility 
     The usefulness of the method is found in terms of the following factors:
         Reduced capital cost by virtue of the retrofit utilization of automotive engines.   Improved performance, efficiency and durability with rapid pay-back potential.   Steam cogeneration with high electric and thermal availability and high electric and thermal efficiencies.   Both base-load and peak-shaving modes of service can be utilized, maximizing payback potential.   Thermal outputs suited to a variety of commercial, industrial and domestic utility-service applications can be provided. Hot fluid byproduct of electric generation has substantially increased usefulness as compared to hot water from prior art systems.   Increased availability of heat from engine by virtue of constant temperature latent heat exchange.       

     FIGURE NOMENCLATURES 
     
         
           1 . Pressure relief valve 
           2 . Sparge for makeup preheating 
           3 . Air cooled vapor condenser for bypass 
           4 . Oil pump 
           5 . Oil Cooler 
           6 . Makeup 
           7 . Hot coolant supply 
           8 . Blow Down Outlet 
           9 . Dry Vapor line 
           10 . Engine Block 
           11 . Gas supply 
           12 . Air supply 
           13 . Vapor separator 
           14 . Circulation pump 
           15 . Engine cooling distribution header 
           16 . Crank case vent 
           17 . Engine Head 
           18 . Level transmitter 
           19 . Tank outlet to circulation pump 
           20 . Feed Valve 
           21 . Return line from separater 
           22 . Exhaust heat recovery boiler 
           23 . Vapor separation tank inlet 
           24 . Engine coolant discharge header 
           25 . Coolant entrance nozzle 
           26 . Coolant supply flow pattern 
           27 . Coolant exit ports 
           28 . Engine Coolant vents 
           29 . Head exit ports 
           30 . Deareator and condensate return tank. 
       
    
     Variations 
     Preferred embodiments of the present invention have been describe in detail above but these embodiments are not to limit the present invention. Persons skilled in this are will recognize that there are many obvious additions and modifications that can be made to the versions of the present invention as specifically described above. Therefore, the scope of the invention are to be determined by the appended claims and not by the specific embodiments described above.