Abstract:
A toroidal combustion chamber shape with side injectors is being developed for an opposed-piston engine. Favorable combustion characteristics of such configuration are transferred to a conventional engine, i.e., one with a combustion chamber delimited by a piston, a cylinder wall, and a cylinder head. At least one injector is disposed in the cylinder head at the periphery. The fuel is injected substantially along the plane of interface between the cylinder head and the cylinder block. The intake system is configured to provide a swirling flow in the combustion chamber. The fuel is injected in an angle that is displaced from the central axis of the cylinder and directed along the swirl. In some embodiments, a substantially torus-shaped volume is formed between the piston and the cylinder head when the piston is at top center. The injector or injectors spray fuel into the toroidally-shaped volume substantially tangent to the torus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefit from U.S. provisional patent application 61/568,787 filed 9 Dec. 2011. 
     
    
     FIELD OF INVENTION 
       [0002]    The present disclosure relates to shape of the combustion chamber and injector orientation in internal combustion engines. 
       BACKGROUND 
       [0003]    Thermal efficiency and engine-out emissions from an internal combustion engine are determined by many factors including the combustion system design and the mechanical design. Combustion system design includes combustion chamber shape, the fuel injection nozzle, and the fuel injection pressure, intake manifold and exhaust manifold, etc. All of these together are optimized to achieve mixing quality that leads to effective combustion. 
         [0004]    An unconventional engine that is being developed to exploit its high power density and other positive characteristics is an opposed-piston engine. Conventional direct-injection diesel combustion chamber geometry does not work for the opposed-piston engine because the centrally-located injector in conventional engines is not feasible in an opposed-piston engine because the combustion chamber is contained between two piston faces. In the opposed piston engine, the only position in which a conventional injector can be installed to have access to the combustion chamber is in the cylinder wall. It has been found that a toroidally-shaped combustion chamber provides a very favorable combustion characteristic. It would be desirable to obtain such desirable combustion and emission characteristics in other engine architectures. 
       SUMMARY 
       [0005]    It has been found that a toroidal combustion chamber with side injection provides favorable emission characteristics in an opposed-piston engine. Such favorable characteristics may present advantages in an engine with a cylinder head. Disclosed herein is an internal combustion engine having a block defining a cylinder wall and a cylinder head affixed to the block. The cylinder head has two intake ports with first and second intake valves disposed therein and two exhaust ports with first and second exhaust valves disposed therein. The cylinder head has an intake geometry that promotes a swirl flow of gases flowing through intake ports. A piston is disposed within the cylinder wall with a central axis of the piston substantially coincident with a central axis of the cylinder wall. A top of the piston has a raised outer ring near the periphery of the piston that squishes gases inwardly toward the central axis when the piston travels toward the cylinder head. A first injector is disposed in the cylinder head at a location proximate the cylinder wall. The injector has at least one orifice through which at least one fuel jet emanates when the orifice is open. The injector is disposed in the cylinder wall with an axis of the injector angled such that a tip of the injector is pointed downward toward the block. One fuel jet exits at an angle to direct the jet upward with respect to an axis of the injector and along the direction of the swirl flow. The piston top also has a raised central region and an inner ring disposed between the raised central region and the outer ring thereby defining a substantially toroidal volume in the piston top. The piston top in the raised central region nearly meets the cylinder head when the piston is at a top center position of its travel within the cylinder wall. The intake and exhaust valves are situated in such a manner in the cylinder head to preclude accommodation of a standard fuel injector pocket in the center of the cylinder head. The standard fuel injector pocket includes a fuel injector, the material into which the injector is secured, and cooling water passages provided around the fuel injector. In some embodiments, the cylinder head has a centrally-located raised region that is substantially oval-shaped as considered in a plane parallel to a deck of the block. Alternatively, the raised region can be circular. In some embodiments, a second fuel injector is disposed in the cylinder head at a location approximately diametrically opposed from the first fuel injector. The second injector has at least one orifice through which at least one fuel jet emanates when the orifice is open. The second injector is disposed in the cylinder wall with an axis of the second injector angled such that a tip of the injector is pointed downward toward the block. One fuel jet of the second injector exits at an angle to direct the jet upward with respect to an axis of the second injector and along the direction of the swirl flow. 
         [0006]    Also disclosed is an internal combustion engine having a block defining a cylinder wall, and a cylinder head affixed to the block. The cylinder head has at least one intake port with an intake valve disposed therein and at least one exhaust port with an exhaust valve disposed therein. The piston has three regions: a center, an outer ring near the periphery of the piston, and an inner ring that is recessed in relation to the center and outer ring. The three regions each have a geometric center that is substantially coincident with a central axis of the cylinder wall. An injector is disposed in the cylinder head proximate the cylinder wall. The injector has at least one orifice through which a fuel jet exits when the orifice is open. The fuel jet is substantially directed into the recess associated with the inner ring. 
         [0007]    The piston is adapted to reciprocate within the cylinder wall between top center and bottom center positions. When the piston is at the top center position, the piston top and the cylinder head are displaced by a small gap in the regions of the outer ring and the center and, most of the volume between the cylinder head and the piston is within the inner ring of the piston. When the piston is at top center position, the volume between the cylinder head and the piston top is substantially a toroidal volume proximate the inner ring with a geometric center of the toroidal volume substantially coincident with the central axis of the cylinder wall. 
         [0008]    In some embodiments, the engine also has a second fuel injector disposed in the cylinder head at a location approximately diametrically opposed from the first fuel injector. The second injector has at least one orifice through which at least one fuel jet exits when the orifice is open. The at least one fuel jet from the second injector is directed into the recess associated with the inner ring. The at least one fuel jet from the first injector is directed along a first side of the inner ring and the at least one fuel jet from the second injector is directed along a second side of the inner ring opposite from the first side. The cylinder head has two intake ports, two exhaust ports, two intake valves, and two exhaust valves. The fuel injector is disposed between adjacent valves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an isometric representation of a portion an OPOC engine; 
           [0010]      FIG. 2  is a cross section of a combustion chamber in an opposed-piston engine; 
           [0011]      FIG. 3  is a sketch of the regions on the top of the intake piston of  FIG. 2 ; 
           [0012]      FIG. 4  is a plot of heat release for a conventional combustion chamber and an opposed-piston, toroidal combustion chamber with side injection; 
           [0013]      FIG. 5  is a cross section of a toroidal combustion chamber for an engine with one piston in the cylinder and a cylinder head; 
           [0014]      FIG. 6  is an illustration of a piston top of a piston similar to that shown in  FIG. 5 ; 
           [0015]      FIG. 7  is a cross section of a toroidal combustion chamber for an engine with one piston in the cylinder and a cylinder head; 
           [0016]      FIG. 8  is an illustration of a piston top of a piston similar to that shown in  FIG. 7 ; and 
           [0017]      FIG. 9  is a cross section of a toroidal combustion chamber for an engine with one piston in the cylinder and a cylinder head. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0019]    An example of an opposed-piston, opposed-cylinder engine is disclosed in U.S. Pat. No. 6,170,443, which is incorporated herein by reference. An isometric representation of one end of an opposed-piston, opposed cylinder engine  10  is shown in  FIG. 1 . An intake piston  12  and an exhaust piston  14  reciprocate within the cylinder (not shown to facilitate viewing of the connecting rods). An exhaust piston  14  couples to a journal (not visible) of crankshaft  20  via a pushrod  16 . An intake piston  12  couples to two journals (not visible) of crankshaft  20  via pullrods  18 , with each intake piston  12  having two pullrods  18 . The engine in  FIG. 1  has a combustion chamber formed between the piston top of intake piston  12  and the piston top of exhaust piston  14  and the cylinder wall (not shown). Pistons  12  and  14  are shown are at an intermediate position in  FIG. 1 . Combustion is initiated when the pistons are proximate each other. 
         [0020]    A cross-sectional representation of a combustion chamber shape that shows promise based on analytical results is shown in  FIG. 2 . An intake piston  40  and an exhaust piston  42  are shown at their closest position. Piston  40  has grooves  44  and  45  and piston  42  has grooves  46  and  47  to accommodate piston rings (not shown). Pistons  40  and  42  reciprocate within cylinder wall  50 . The combustion chamber is the volume enclosed between the tops of pistons  40  and  42  and the cylinder wall  50 . Pockets  62  are provided in cylinder wall  50 . Injectors  60  pierce cylinder wall  50  leading into pockets  62 . 
         [0021]    A top of intake piston  40  is shown in  FIG. 3 . The piston is shown having three regions: outer ring  52 , inner ring  54 , and center  56 . Exhaust piston  42  has three corresponding regions: an outer ring, an inner ring, and a center. The majority of the volume of the combustion chamber, when the pistons are in close proximity, is contained in the volume between the inner ring surface of the intake piston and the inner ring surface of the exhaust piston. 
         [0022]    The cross section of the combustion chamber volume, as shown in  FIG. 2 , shows two roughly oval areas  64 . The shape of the combustion chamber in the inner ring region is a surface of revolution generated by revolving oval area  64  in space about a central axis  66  of cylinder  50 . Strictly speaking, a torus is the result of rotating a circle around an axis. However, in the present disclosure, the term torus is used to apply to any 2-dimensional shape rotated about central axis  66 . As shown in  FIG. 3 , the cross-sectional area of areas  64  varies slightly through the rotation about central axis  66  because center  56  is longer along horizontal axis  32  than along vertical axis  34 , i.e., center  56  is ovoid. The term torus is applied to all of these variants within the present disclosure. 
         [0023]    A typical heat release rate curve  66  for diesel combustion is shown in  FIG. 4 . Initially, the heat release rate dips below zero due to the effect of the vaporization of the injected fuel. The heat release rapidly rises upon ignition, the spike commonly referred to as the premixed combustion phase and the tail in the later portion referred to as the mixing-controlled combustion phase. The premixed combustion phase is predominantly responsible for the production of NOx. The height of the premixed combustion phase may be reduced by reducing the ignition delay by using multiple injections. However, there is still a need to reduce the impact of the initial high spike in the heat release rate. Heat release rate in a combustion system such as that illustrated in  FIGS. 2 and 3  is shown as dashed curve  68  in  FIG. 4 , which yields NOx production about one-third to one-half that of the heat release rate curve  66  for typical diesel combustion. Such a fundamental change in combustion characteristics provided by the combustion chamber shape in  FIGS. 2 and 3  can be translated into a conventional engine combustion chamber as well. 
         [0024]    A piston and cylinder head arrangement to exploit the advantages of seen in the opposed-piston configuration is illustrated in cross section in  FIG. 5 . A piston  70  is disposed in a block  72 . Piston  70  has a squish region  74  at the periphery. When piston  70  is at its closest position to cylinder head  76 , the volume in the combustion chamber is largely contained in substantially ovoid regions  80  in the piston top. The combustion chamber is defined by a cylinder wall  78 , the top of piston  70 , and the bottom of cylinder head  76  that opposes piston  70 . The cylinder head extends beyond the cylinder wall and may cover multiple cylinders. The portion of cylinder head  76  that encloses the combustion chamber is that portion within a projection of cylinder wall  78  or, put another way, that portion that opposes the piston top. Cylinder head  76  has a plurality of ports or openings therein into which poppet valves  84 ,  86  are disposed. In most modern engines, two intake valves and two exhaust valves are provided. The cross section is taken so that two valves  84 ,  86  are illustrated. Also included in cylinder head  76  is an injector  88 . It is likely, instead, that injector  88  would be installed into head  76  at a location that is rotated from the widest part of valve  86 . However, simply for illustrative convenience, injector  88  is shown in the cross-sectional view in  FIG. 5  as well. As injector  88  is located at the periphery of the cylinder and the typical fuel injector is centrally located, the fuel from injector  88  travels farther to reach the farthest reaches in the combustion chamber compared with a central injector. To overcome this, a second injector (not shown) can be installed in the cylinder head substantially diametrically opposed to injector  88 . The axis of injector  88  is installed at an acute angle with respect to the portion of cylinder head  76  that mates with a deck  90  of block  72 . Such angle is driven by the interface between deck  90  and cylinder head  76 , meaning that injector  88  is installed in either head  76  or cylinder wall  78 , i.e., displaced from that interface. Orifices in a tip of injector  88  are defined in a manner so that fuel jet or jets  94  exit at an angle displaced from the axis of injector  88 . A pocket  92  is provided for jets  94  of injector  88  to access regions  80  in piston  70 . 
         [0025]    Although it would present other complications, in an alternative embodiment, the injector could be placed in the cylinder wall with the injector tilting upward toward the cylinder head and the jets aiming downward into regions  80  in piston  70 . 
         [0026]      FIG. 6  is an illustration of a piston  100  that is similar to piston  70  of  FIG. 5 . The squish region  102  is at the periphery. A dashed circle  104  indicates the reentrant edge associated with squish region  102 . The center  106  is raised upward from the piston top with the dashed oval  108  indicating another reentrant edge associated with center  106 . Pockets  110  are provided for fuel injectors. The poppet valves in the cylinder head are shown projected onto piston  100 . Intake valves  112  are slightly larger than exhaust valves  114 . In some embodiments, dishes (not shown) in the piston top may be provided to avoid collision of the valves  112 ,  114  in the piston top. These are often called eyebrows. 
         [0027]    In  FIG. 6 , the projection of the intake and exhaust valves  112 ,  114  overlaps pockets  110  in piston  100 . As pockets  110  are in piston  100  and the valves are in the cylinder head. However, the space needed to accommodate the injector in the cylinder head including the injector, the material into which the injector is installed, and cooling passages, may be greater than can be accommodated in the configuration as shown for some embodiments. In such a situation, the orientation can be adjusted such that fuel injectors are arranged between pairs of adjacent valves. In such a case projections of the intake valves and exhaust valves are rotated with respect to the top of piston. 
         [0028]    An advantage of the combustion chamber as shown in  FIG. 5  is that the intake and exhaust valves can be larger than with a cylinder head that accommodates a central injector. Cooling raised central portion  73  on piston  70  is a challenge as pistons are cooled by conduction through piston rings and due to oil cooling on the underside. Cylinder heads are water cooled and thus less of a challenge to cool due to forced flow. 
         [0029]    In  FIG. 7 , an alternative combustion chamber shape is shown in which the raised center portion is applied to the cylinder head rather than the piston. A piston  170  reciprocates with a cylinder wall  178  that is part of a block  172 . Piston  170  has a squish region  174  at the periphery. When piston  170  is at its closest position to cylinder head  176 , the volume in the combustion chamber is largely contained in substantially ovoid regions  180 . The combustion chamber is defined by cylinder wall  178 , the top of piston  170 , and the bottom of cylinder head  176  that opposes piston  70 . Cylinder head  176  has a plurality of ports or openings therein into which poppet valves  184 ,  186  are disposed. Also included in cylinder head  176  is an injector  188 . A pocket  192  is provided for jets  194  of injector  188  to access air compressed in regions  180  in piston  170 . 
         [0030]      FIG. 8  is an illustration of a piston  200  that is similar to piston  170  of  FIG. 7 . The squish region  202  is at the periphery. A dashed circle  204  indicates the reentrant edge associated with squish region  202 . An oval  206  at the center is a projection of the center region of cylinder head (related to a raised portion  173  of  FIG. 7 ). Pockets  210  are provided for jets exiting the injectors. 
         [0031]    Such an alternative has the advantage of having the raised portion  173  being part of cylinder head  176  which can be water cooled. However, a disadvantage of the alternative in  FIG. 7  is that raised portion  173  limits the size of valves  184  and  186 . 
         [0032]    In yet another alternative in  FIG. 9 , the combustion chamber is very similar to combustion conventional combustion chambers except that one or more injectors are side mounted rather than a central injector. 
         [0033]    The embodiments described in relation to  FIGS. 5 ,  6 , and  9  allow for larger valves than a cylinder head with a central injector. The additional valve area can be applied to the intake valves to allow for: improved breathing, increased swirl, or a combination thereof. 
         [0034]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.