Abstract:
A piston crown for a diesel engine in which the crown has an annular recess coaxial with an injector injecting fuel in a radiated, non-swirl pattern. The recess has an internal central crown portion approximately parallel to the angle of the fuel injected and a curved outer section to curve air compressed by the piston significantly enough that it is directed back toward the central axis and mixes with the fuel injected along the internal central crown portion to promote mixing and reduction in soot formation.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to internal combustion engines and, and, more specifically, to pistons for such engines. 
     The configuration of pistons in internal combustion engine has been the subject of design and development for decades. Particularly in the field of compression ignition, or diesel engines, the configuration of the portion of the piston exposed to the combustion process has been highly developed. The reason for this is that the compression ignition engine relies on the heat of compression to ignite fuel that has been injected in measured and timed quantities to provide the appropriate combustion which results in maximum efficiency and power. With the advent of regulations placed on emissions from internal combustion engines by the EPA, the design of the combustion chamber has received increased attention. 
     It is common to provide a diesel engine combustion chamber within a cylinder having reciprocating pistons. The pistons are displaced from a maximum volume to a minimum volume during which the air that has entered the combustion chamber is compressed and its temperature increased. In the vicinity of the minimum volume or top dead center (TDC), fuel is injected into the compressed air and the resultant mixture ignited to provide the expansion stroke for the piston. There are two major systems for orienting the fuel injection relative to the piston. The first is a high swirl system in which the fuel is injected and the air flows in a circular motion around the crown of the piston. The other is a quiescent or zero swirl arrangement in which the fuel is injected from a central location in a uniform radial pattern and distribution. To enhance the mixture of the compressed air and fuel, a so called Mexican hat has been proposed for the piston crown. This involves a central peak with a curved annular outer section to promote mixture within the molecules of air and the fuel. 
     However, for ever decreasing emissions limitations, particularly in the area of soot formation, the traditional crown configurations impose a limit on the reduction of soot and oxidization. 
     What is needed in the art, therefore, is a piston having a configuration for minimizing soot and increasing combustion efficiency. 
     SUMMARY OF THE INVENTION 
     In one form, the invention is a piston for an internal combustion (IC) reciprocating engine. The piston includes a cylindrical form having a connection to provide reciprocating motion in response to a combustion event involving air and an injected fuel quantity from an injector providing fuel injection from a central location in a radiated, substantially non-swirl pattern. A crown is formed on the end of the cylindrical form, the crown having an annular recess with a center of rotation substantially coaxial with the central location for the injector. A central peak is in the recess and forms an angle with respect to the central axis that is approximately parallel with the injected fuel. A substantially curved outer section directs air compressed by the piston around the curve and toward the central axis to mix with and be directed along the peak by the injected fuel. 
     In another form, the invention is an internal combustion engine including a cylinder block having at least one cylinder for receiving a piston. A cylindrical piston is reciprocable within the cylinder in response to a combustion event involving air and an injected fuel quantity from an injector providing fuel injection from a central location in a radiated, substantially non-swirl pattern. A fuel injector injects fuel into the combustion chamber in a measured and timed quantity. The piston has a crown formed on the end thereof facing the combustion chamber, the crown having an annular recess with a central axis substantially coaxial with the central location for the injector and a internal central crown portion forming an angle with respect to the central axis that is approximately parallel with the injected fuel and a substantially curved outer portion directing air compressed by the piston around the curve and toward said central axis to mix with and be directed along the peak by the fuel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a cross sectional view of an engine having a piston embodying the present invention; and, 
         FIG. 2  is an expanded detailed view of the piston incorporated in  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates one embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an engine  10  of the reciprocating internal combustion engine type. Engine  10  operates on the principal of reciprocating pistons moved in response to a combustion event in a combustion chamber. As illustrated herein, the reciprocating motion of the pistons is converted into rotary motion through the means of a crankshaft. However, it should be apparent to those skilled in the art that the reciprocating motion of the pistons may be utilized in the form of a linear electrical generator in which movement of pistons and ferromagnetic materials induces an electrical power output. 
     Engine  10  includes a block  12  having a plurality of bores  14  for receiving reciprocating pistons  16 , only one of which is shown. The cylinder bores  14  may be cast integral with the block  12  or, as illustrated herein, may be separate liners so as to enhance the rebuilding process. 
     The piston  16  includes a cylindrical form  18  having a pivotal connection  20  for receiving a wrist pin  22  connected to a connecting rod  24 . Connecting rod  24  is rotatably connected to a crank throw or crankpin  26  on a crankshaft  28  suitably journaled within block  12  to provide a rotary power output in response to reciprocation of piston  16 . It should be noted that a plurality of pistons may be provided depending upon the requirements and duty cycle of the engine  10 . 
     Piston  16  reciprocates within cylinder  14  to define a combustion chamber  30  bounded by the cylinder  14 , a crown  32  of piston  16 , and a head  34 . Head  34  has intake passages  36  and exhaust passages  38 . Combustion air passes through intake passage  36  past intake valve  40  for entry into combustion chamber  30 . Products of combustion exit combustion chamber  30  past exhaust valve  42  to exhaust port  38 . 
     The intake air, as is apparent to those skilled in the art, may be pressurized by a compressor of a turbocharger and cooled by means of an after cooler. The exhaust gasses passing from exhaust port  38  typically pass through a turbocharger turbine and then to exhaust after treatment devices. It is also common to provide exhaust gas recirculation which provides a portion of the exhaust gas to the intake port  36 , either cooled or uncooled, to reduce the combustion temperatures and reduce the oxides of nitrogen. 
     Engine  10 , as illustrated, operates on a compression ignition cycle in which air that has entered combustion chamber  30  past intake port  36  and valve  40  is pressurized to such an extent that fuel injected from an injector nozzle  44  via line  46  from fuel injection system  48  at the appropriate time and in the appropriate quantity is ignited by the heat of compression. Injection from nozzle  44  may be from a variety of systems including high pressure common rail, distributor pump, and direct injection in which pressure is generated at the nozzle. Control of fuel injection system  48  is from an ECM  52  via interconnection  50 . 
     In any of the systems, the fuel is injected from an axis A coaxial with the axis of the injector  44  in a radiated pattern so as to permeate the combustion chamber  30 . As is well known to those skilled in the art, the number of discrete holes provided in injector  40 , their cross sectional flow area and the angle they make with respect to the central axis A of injector  44  is selected according to the design requirements of engine  10 . Although the preferred location of injector  44  is coaxial with the axis of combustion chamber  30 , it should be apparent to those skilled in the art that the injector  44  may be offset from the central axis. 
     In accordance with the present invention, piston  16  has a crown  32  that improves the combustion process. The configuration of crown  32  is shown in expanded detail in  FIG. 2 . Piston crown  32  has an upper surface  54  connecting with the piston body  18 . It should be noted that piston body  18  has circumferential grooves  56 ,  58 , and  60  for appropriate compression and oil scraper rings (not shown). 
     Upper surface  54  has an annular recess  62  defined by an outer diameter  64 . The annular recess  62  is coaxial with the axis of injector  44  whether the injector  44  is on the center line of the combustion chamber  30  or elsewhere. The recess  62  has a central crown portion  66  with a peak  68  coaxial with axis A. The central crown portion  66  blends into an annular curved portion  70  having a substantial curve to outer diameter  64  such that air compressed within recess  62  curves around portion  70  and is directed towards central axis A. 
     The configuration of central crown portion  66  is such that it is approximately parallel to the angle of injection  72  from a point  74  on injector  44 . The range of angles .PHI.-.beta. as shown in  FIG. 2  with respect to the axis A is between 0.degree. and 5.degree. The included angle the surface of the crown portion makes with the axis A is between approximately 50.degree. and 80.degree. The outer diameter  64  of the opening to recess  62  is no greater than 40% of the piston diameter thus giving an aggressive swish motion within recess  62 . The configuration of the outer curved portion  70  relative to the central crown portion is such that it turns the fluid through greater than 180.degree. 
     In operation, the piston  16  moves from bottom dead center towards the head  34  to decrease the volume of the combustion chamber  30  and thus pressurize and increase the temperature of the air within combustion chamber  30 . As the piston moves towards top dead center, the central crown portion  66  from the peak  66  causes the air to be moved down the peak and around the curved section  70  onto itself. When the injection event is initiated, the high pressure of injection adds to the motion of the air to enhance and increase the mixture. The net result of this is substantially lower soot formation. Furthermore, the increased turbulence of the fuel/air mixture leaving the relatively small bowl enhances the oxidization of soot to prevent a generation of particulates. It should be noted in  FIG. 2  that the outer diameter  64  and peak  68  are curved so as to prevent the occurrence of sharp corners and, thus, localized hot spots and stress generators. It should be noted that the fuel injected from injector  44  cannot have swirl relative to the central axis A in order to promote the efficient entrainment of fuel particles within the air. It is also to be noted that the recess  62  may be offset from the central axis of piston  16  so long as the central axis of the recess  62  is coaxial with the axis of a fuel injector. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.