Abstract:
A cooling system for a liquid cooled internal combustion engine having coolant passages and a heat exchanger selected to operate the engine cooling system in the region of nucleate boiling. A sensor detect the presence of nucleate boiling and a pump and pressure relief valve responsive to the sensor maintain the coolant system pressure at a level marinating optimum nucleate boiling to increase heat flux from the engine and reduce overall size of the system.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to internal combustion engine systems and more specifically to coolant systems and methods for such systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    One of the principle sources of parasitic losses, complications and bulk in an internal combustion engine has to do with the waste heat generated by the internal combustion engine process. Attempts have been made to manage heat flux from the material surrounding combustion chambers by paying careful attention to flow passages, coolant flow rates and temperatures through such passages. Typically the internal combustion engines are liquid cooled so as to maximize the heat flux to the cooling system, particularly in the region closely adjacent the combustion chamber. When cooling systems operate under off design conditions because of duty cycle or component malfunction, it can lead to a condition of uncontrolled boiling in the coolant passages for the engine. This condition causes complete loss of liquid to metal contact and drastically reduces the heat flux carried away by the cooling system. When this is left uncontrolled, the pressure relief for the system, usually a radiator cap, is opened to release pressure and allow even greater generation of steam. This, in turn, has a potentially catastrophic affect on the temperature of the internal metal parts of the engine. 
         [0003]    There is, however, a condition between normal liquid 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 microscopic scale. This allows significant increases in heat flux, but this condition, at best, is a momentary transition between sub-boiling conditions and uncontrolled or macro-boiling. 
         [0004]    What is needed in the art therefore is a cooling system which effectively maintains nucleate boiling in an engine cooling system to maximize heat flux from the engine combustion chamber. 
       SUMMARY OF THE INVENTION 
       [0005]    In one form, the invention is a cooling system for a liquid cooled internal combustion engine. The system includes coolant passages formed at least around a combustion chamber for the engine. A heat exchange device is fluidly connected to the passages for dissipating heat from at least around the combustion chamber. A pump for circulating coolant through the passages and the heat exchanger is selected to promote nucleate boiling at least around the combustion chamber. A sensor is provided for indicating the presence of nucleate boiling in the system and a device responsive to the sensor maintains the pressure in the system at a level permitting controlled nucleate boiling to increase heat flux from at least around the combustion chamber. 
         [0006]    In another form, the invention is a power system including a liquid cooled internal combustion engine having at least one combustion chamber, the engine having coolant passages at least around the one combustion chamber. A heat exchange device has internal flow passages and is fluidly connected to the coolant passages. A pump is provided for circulating coolant through the passages and the heat exchange device for removing heat from at least around the combustion chamber. The coolant passages heat exchange device and the pump are selected to promote nucleate boiling at least around the combustion chamber. A sensor is provided for indicating the presence of nucleate boiling of coolant in the system and a device responsive to the sensor maintains the pressure in the system at a level permitting nucleate boiling to increase the heat flux from at least around the combustion chamber. 
         [0007]    In still another form, the invention is a method of operating a liquid cooled internal combustion engine having at least one combustion chamber. The method includes the steps of circulating liquid coolant at least around the combustion chamber such that the coolant is operating in the region of nucleate boiling. The presence of nucleate boiling is sensed around at least the combustion chamber and the pressure of the liquid coolant in response to the sense pressure of nucleate boiling is maintained at a level providing an optimum nucleate boiling level. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic view of a power system having an internal combustion engine with a coolant system embodying the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    Referring to  FIG. 1 , there is shown a power system  10  having an internal combustion engine, generally indicated by reference character  12 . Internal combustion engine  12  may be one of a number of types of engines in terms of combustion process but is usually a liquid cooled internal combustion engine  12  having a block  14  and a head  16 , both of which have internal surfaces exposed to a combustion chamber of variable volume provided by reciprocating pistons all connected to an output crankshaft to provide a rotary power output. Details of the internal portions of block  14  and head  16  are not shown to simplify the understanding of the present invention. Engine  12  has an exhaust manifold  18  receiving products of combustion and delivering them through an exhaust conduit  20  to a turbine  22  of a turbocharger  24  and ultimately to an exhaust conduit  23  leading to ambient. The turbine  22  drives a compressor  26  through a common shaft  28 . The compressor  26  receives ambient air from an inlet  30  and delivers it through inlet line  32 , usually past an aftercooler  34 , and line  36  to an intake manifold  38 . 
         [0010]    The engine  12  is an air breathing, fuel consuming internal combustion engine in which a hydrocarbon based fuel is burned to provide a rotary power output. Many other features such as exhaust gas recirculation (EGR) and exhaust aftertreatment may be employed as appropriate. However, these are not shown to further simplify the discussion of the present invention. 
         [0011]    The engine  12 , as stated previously, is a liquid cooled engine in which internal coolant passages within the block  14  and head  16  carry away the waste heat generated from the combustion process. The coolant is pressurized by a pump  40  through passage  42  to the engine  12  where it is circulated through appropriately sized and positioned passages to carry heat away from engine  12 . Pump  40  is usually mechanically driven by engine  12 . The coolant, with the additional heat input passes through line  44  to a heat exchanger  46  to dissipate the increase in heat. Heat exchange device  46 , in usual fashion, may be a radiator of the liquid to air type in which the coolant passing through line  44  traverses multiple internal flow passages (not shown). In heat exchange device  46 , ambient air is forced over the exterior of the passages, usually with extra heat exchange surfaces to carry away the heat to the ambient air. A return line  48  is connected from the outlet of heat exchange device  46  and feeds the inlet to pump  40 . The heat exchange device  46  may have a top tank (not shown) but, in addition, it has a reservoir  50  exposed to ambient pressure at  52  and having a cap  54  for replenishment of fluid. A valve  56  is interposed in a line  58  extending from heat exchange device  46  to reservoir  50 . Valve  56 , as herein shown, is electrically actuatable by an ECM  60  via a signal line  62 . ECM  60  also controls a pump  62  receiving coolant from reservoir  50  via line  64  and connected via line  66  to the engine  12 , illustrated herein as connecting to the head  16 . Pump  62  is preferably electrically powered and controlled by a signal from line  68  extending from ECM  60 . A sensor  70  is connected to ECM  60  via a line  72 . Sensor  70  preferably is connected to the head  16  of engine  12  so as to determine conditions closest to the engine combustion chambers. Sensor  70  is a sensor enabling the detection of nucleate boiling. This may be accomplished by making sensor  70  a pressure sensor that senses differential pressure versus differential time or another words the rate of change of pressure versus time. This would determine that the conditions are approaching nucleate boiling and can determine effectively whether the conditions have gone beyond nucleate boiling to macro-boiling or an out of control situation. Another, alternative measurement would be to provide sensor  70  in the form of a temperature sensor sensing the differential temperature versus differential time. Again this is an indicator of going beyond nucleate boiling and into the macro-boiling conditions. Still other sensor forms for  70  may take the form of bubble detectors such as an optical device calibrated to respond to bubbles of a given size or a sonic sensor also calibrated to determine the size of bubbles. 
         [0012]    The component parts of the engine  12  and more specifically the coolant passages within engine  12  and heat exchanger  46  are selected with due regard to the duty cycle of the engine so that the engine  12 , in combination with its cooling system operates, in the region of and promotes nucleate boiling. In order for the engine condition to be controlled within a relatively tight range of nucleate boiling, the sensor  70  determines the presence of nucleate boiling and sends a signal to ECM  60  which in turn actuates pump  62  to pressurize the cooling system within engine  12  to maintain nucleate boiling conditions. The pump  62  does not have to be a high volume pump since it is pressurizing a liquid within rigid confines so that brief actuation is sufficient to raise the pressures to appropriate levels. A typical pressure for maintaining nucleate boiling is between three and four bars. In order to control the upper level of pressure, valve  66  responds to signals from the ECM  60  via line  62  to release pressure to reservoir  50  maintained at essentially ambient pressure. The valve  66  preferably is electrically controlled and a fast responding valve so that a tight control may be maintained over the conditions that produce nucleate boiling. 
         [0013]    The ultimate effect of such a cooling system is to enable higher system operating temperatures up to 150 C and a more compact engine envelope because of a higher potential heat flux of waste heat from the combustion process. 
         [0014]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.