Patent Publication Number: US-7210448-B2

Title: Internal combustion engine producing low emissions

Description:
This application is a continuation-in-part of application Ser. No. 10/814,332, filed Apr. 1, 2004, now U.S. Pat. No. 6,966,294, the contents of which are incorporated herein by reference, which is a continuation of application Ser. No. 10/166,051, filed Jun. 11, 2002, now Pat. No. 6,732,703. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates to an improved engine capable of minimizing emissions. 
   2. Description of the Related Art 
   Internal combustion engine designers continue to confront an ever more demanding set of governmentally mandated emissions standards and performance objectives. Modifications made to meet one standard may lead to increased emissions of a type that cause another standard to be exceeded. Thus designers are often confronted with not only the challenge of meeting a newly imposed emission standard but to do so in a way that does not cause other emissions standards, previously met or newly imposed, to be exceeded. The engine designers must also necessarily consider and preferably minimize the adverse effects of modifications on engine performance and fuel economy. 
   An example of the difficulties created for engine designers is that created by a new set of diesel engine emissions standards/limits mandated by the Environmental Protection Agency for application in the U.S. market. These standards require diesel engines to produce extremely low levels of emissions below specific limits based upon fuel consumption. Specifically, for example, new on-highway regulations require diesel engines complying with the regulations to maintain nitrogen oxide (NOx) emissions combined with unburned hydrocarbons below 2.5 grams/b-hp-hr and particulates below 0.1 grams /b-hp-hr. 
   Changes in any one of a variety of engine design variables or engine operating variables such as engine compression; combustion chamber shape; rate of combustion chamber heat rejection and/or fuel injection spray pattern, pressure, timing and/or flow rate may be used to positively affect the control of one or more emissions. However, such changes can often adversely affect one or more other emissions possibly causing the emissions to exceed the acceptable limit. For example, as the brake mean effective pressure (bmep) is desirably increased, a tendency arises for NOx emissions in the engine&#39;s exhaust to increase. This problem is accentuated by the need to achieve other critical engine operating characteristics such as fuel economy, high torque output, low operating costs and/or reduced maintenance. As one example, the amount of soot that is entrained in the engine&#39;s lubrication oil can have a profound effect on the cost of operation and the length of service before a major overhaul is required. Soot is very abrasive and can cause high wear if allowed to become entrained in the engine&#39;s lubrication oil to any substantial degree. The amount of soot entrained in the engine&#39;s lubrication oil can be affected by a number of factors such as combustion chamber shape and fuel injection spray angle but changes in these variables can have the undesired effect of actually increasing emissions entrained in the engine&#39;s lubrication oil. 
   Many attempts have been made to produce an ideal flow pattern for the charge air and fuel within the combustion chamber of an internal combustion chamber. For example, provision of a combustion bowl in the upper region of a piston to cause, among other things, fuel/charge air mixture within a direct injection engine is well known as disclosed the article entitled “Future Developments . . . ”, Automotive Industries, Oct. 15, 1952. While most of the combustion bowl designs disclosed in this article appear to be symmetric about a central axis, the article does not address the critical relationship of the combustion bowl shape and the fuel injection path, nor other combustion chamber features, on the specific problems addressed by the subject invention. 
   A variety of piston designs have been disclosed including symmetrical bowl shaped recesses formed in the upper surface of the piston crown to achieve desired flow patterns within the combustion chamber formed in part by the piston. These bowl configurations are often referred to as “Mexican-hat” designs. For example, U.S. Pat. No. 4,377,967 discloses an articulated piston assembly including a crown containing a symmetrical combustion bowl in the top surface defined by a cone shaped central floor section which connects at its base to an arcuate surface of revolution coaxial with the central axis of the cone surface wherein the surface of revolution flares upwardly to join with the uppermost surface of the piston. The base of the cone shaped central floor section extends over no more than approximately 50% of the diameter of the bowl. Other similar piston designs are disclosed in U.K. Patent Application No. 2,075,147; and U.S. Pat. Nos. 1,865,841; 3,508,531; 4,242,948 and 5,029,563. However, none of these references disclose any critical size ranges or ratios for the disclosed combustion bowl and chamber designs, suggest the importance of the angle of the fuel spray from the spray orifices in relationship to the combustion bowl shape and specific distances between the piston and both the cylinder head and spray orifices. Thus, these patents fail to disclose that the combustion chamber and piston bowl have crucial dimensions and dimensional relationships that are required to achieve specific engine functionalities including low emissions. 
   U.S. Pat. No. 5,868,112, assigned to the assignee of the present invention, discloses a piston having a crown containing a combustion bowl shaped to complement the injection fuel spray plume in a manner to maintain very low entrainment of soot in the lubrication oil of the engine and to maintain other engine emissions within acceptable ranges. However, this patent does not appreciate the specific combination of features and dimensions necessary to produce both NOx and particulates below the new regulated limits. 
   U.S. Pat. No. 4,781,159 to Elsbett et al. discloses a composite piston for use in a cylinder of a diesel engine where the composite piston has a crown with “Mexican-hat” design with additional features that enhance strength and improve cooling of the piston. Various cross-sectional figures of the Elsbett et al. reference appear to show an angled chamfer on the composite piston. However, this reference does not appreciate the significance of such a feature, the importance of the dimensional parameters of the chamfer, or the specific combination of the chamfer together with dimensions of other features of the piston which is necessary to produce both NOx and particulates below the new regulated limits. 
   Despite the many examples of combustion chamber arrangements, including piston designs, contained in the prior art, the prior art does not appear to suggest an arrangement that creates the appropriate cooperation between the piston and an injector spray plume to minimize NOx emissions while effectively promoting the oxidation of particulates during combustion by controlling and directing combustion gases in a manner to achieve acceptably low exhaust emissions relative to the new regulated limits. A need, thus, exists for an engine and combustion chamber arrangement that is capable of achieving this combination of functionality. 
   SUMMARY OF THE INVENTION 
   It is, therefore, one object of the present invention to overcome the deficiencies of the prior art and to provide an internal combustion engine containing a combustion chamber arrangement designed to reduce undesirable engine emissions sufficiently to meet new regulated limits. 
   Another object of the invention is to provide a combustion chamber arrangement which reduces undesirable engine emissions sufficiently to meet new regulated limits while also minimizing soot in the engine lubrication oil and maintaining other engine performance requirements, such as fuel economy, at acceptable levels. 
   Still another object of the present invention is to provide a diesel engine capable of meeting the new NOx and particulate emission regulations while maintaining acceptable fuel consumption and lube oil soot contamination. 
   Another object of the present invention is to provide a diesel engine capable of operating below 2.5 gramslb-hp-hr of NOx emissions plus unburned hydrocarbons and below 0.1 grams/b-hp-hr of particulates while also satisfying mechanical design constraints for a commercially acceptable engine. 
   A more specific object of the subject invention is to provide an engine including a combustion chamber arrangement having dimensions and dimensional relationships to minimize the amount of fuel exposed to oxygen in the chamber during the initial portion of the injection to minimize NOx emissions while ensuring oxidation of sufficient particulates during combustion to minimize both particulates available for entrainment in the engine&#39;s lubrication oil and particulates available for discharge to the exhaust system. 
   A still more specific object of the subject invention is to provide a key combination of combustion chamber design parameters that together result in a combustion recipe that produces lower NOx emissions than conventional engines. 
   According to the invention, the above objects and other more detailed objects may be achieved by providing an engine with a combustion chamber arrangement having certain predetermined combinations of combustion chamber design parameters, including specific combustion chamber dimensions and dimensional relationships. For example, in the preferred embodiment, an internal combustion engine containing a combustion chamber is provided the engine comprising an engine body including an engine cylinder, a cylinder head forming an inner face of the combustion chamber and at least one intake port formed in the cylinder head for directing intake air into the combustion chamber. The engine also includes a piston positioned for reciprocal movement in the engine cylinder between a bottom dead center position and a top dead center position, the piston including a piston crown including a top face facing the combustion chamber, the piston crown containing a piston bowl formed by an outwardly opening cavity. In one embodiment, the piston bowl includes a projecting portion having a distal end, an inner bowl floor section extending inwardly, an outwardly flared outer bowl section having a concave curvilinear shape in cross section, and a chamfer extending toward the top face at an angle δ in the range of 30 to 75 degrees from an axis of reciprocation of the piston. An injector is further provided which is mounted on the engine body adjacent the projecting portion of the piston bowl to inject fuel into the combustion chamber, the injector including a plurality of orifices arranged to form a spray plume. 
   In accordance with another embodiment of the present invention, the inner bowl floor section extends inwardly at an inner bowl floor angle α from a plane perpendicular to the axis of reciprocation of the piston, and each of the plurality of orifices have a central axis oriented at a spray angle β from a plane perpendicular to the axis of reciprocation of the piston, so that the spray angle β minus the inner bowl floor angle α (β−α) is in the range of −7 to 19. 
   In still another embodiment of the present invention, the chamfer extends toward the top face a vertical distance K in the range of 1 to 17 mm. In yet another embodiment, the piston bowl may include a transition radius R 4  between an end of the outer bowl section and the chamfer in the range of 1.5 to 7 mm. Moreover, in yet another embodiment, the plurality of orifices include an outlet opening having a center, the center being a distance L 1  in the range of 0.5 to 12 mm from the distal end of the projecting portion. 
   In the above embodiments, the injector may have 8 or less orifices, and a distance L 2  between the center of the outlet opening and the inner face of the cylinder head forming the combustion chamber is in the range of −0.5 to 3 mm. In addition, the intake air preferably undergoes a swirling effect during operation to provide a swirl ratio in the range of 0.5–2.5. Moreover, the concave curvilinear shape of the outwardly flared outer bowl section has a radius of curvature R 1  in the range of 8 to 20 mm, and the distance BH between the top face of the piston crown and the center of the outlet opening is in the range of 0.5 to 8 mm. 
   Of course, other specific combinations of the design parameters taught herein are also deemed to be within the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cutaway view of a portion of the internal combustion engine of the present invention employing the combustion chamber arrangement of the present invention with the piston in the top dead center position; 
       FIG. 2  is an enlarged view of a portion of  FIG. 1  showing various dimensions; 
       FIGS. 3   a – 3   c  are cutaway cross sectional views similar to  FIG. 1  showing sequentially the progress of the spray plume during an injection event as the piston moves from the top dead center position toward the bottom dead center position; 
       FIG. 4  is an enlarged cutaway, cross sectional view taken through the end of the injector nozzle assembly of  FIG. 1  which contains the injection orifices; 
       FIG. 5  is a graph illustrating normalize data showing the emissions results of the present invention relative to emissions levels of current production engines; 
       FIG. 6  is a graph illustrating the effects of varying distance L 1  with the engine of the present invention; 
       FIG. 7  is a graph illustrating normalized data showing the emissions results of the present engine relative to emissions levels of current production engines; 
       FIG. 8  is an enlarged cutaway of a portion of an internal combustion engine employing the combustion chamber arrangement in accordance with another embodiment of the present invention with the piston in the top dead center position; and 
       FIG. 9  is a schematic view of the piston bowl profile of  FIG. 8  with details of the chamfer in accordance with one embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , the present invention is directed to an internal combustion engine, a portion of which is shown in a cutaway cross sectional view and generally indicated at  10 , capable of producing emissions, e.g. NOx and particulates, at levels significantly lower than emissions levels produced by conventional engines and below recent government regulated limits. As discussed hereinbelow, engine  10  includes various precise configuration parameters resulting in a combustion process which achieves desired combustion characteristics for producing acceptably low emissions satisfactory to meet newly adopted engine operating standards applicable to diesel engines including both low noxious emissions and low particulates, while achieving desirable fuel economy and efficiency. 
   Engine  10  includes an engine block, only a small portion of which is illustrated at  12 , and at least one combustion chamber  14 . Of course, the engine may contain a plurality of combustion chambers, typically four to eight, which may be arranged in a line or in a “V” configuration. Each combustion chamber is formed at one end of a cylinder cavity  16  which may be formed directly in engine block  12 . The cylinder cavity  16  may be arranged to receive a removable cylinder liner  18  which is only partially shown in  FIG. 1 . As is also common, one end of the cylinder cavity is closed by an engine cylinder head  20 . The engine  10  further includes a respective piston  22  mounted in a corresponding liner  18  associated with each combustion chamber. Although only a top portion of piston  22  is shown in  FIG. 1 , piston  22  may be any type of piston so long as it contains the features identified hereinbelow necessary for accomplishing the present invention. For example, piston  22  may be an articulated piston or a single piece piston design. The upper surface or top face of piston  22  cooperates with head  20  and the portion of cylinder liner  18  extending between head  20  and piston  22  to define combustion chamber  14 . Although not specifically illustrated, piston  22  is connected through a connecting rod to a crankshaft of the internal combustion engine which causes the piston to reciprocate along a rectilinear path within cylinder liner  18  as the engine crankshaft rotates.  FIG. 1  illustrates the position of piston  22  in a top dead center (TDC) position achieved when the crankshaft is positioned to move the piston to the furthest most position away from the rotational axis of the crankshaft. In the conventional manner, the piston moves from the top dead center position to a bottom dead center (BDC) position when advancing through intake and power strokes. For purposes of this disclosure, the words “outward” and “outwardly” correspond to the direction away from the engine crankshaft and the words “inward” and “inwardly” correspond to the direction toward the crankshaft of the engine or bottom dead center position of the piston. 
   Engine  10  of the present invention is a four-cycle compression ignition (diesel) engine employing direct injection of fuel into each combustion chamber of the engine. An intake passage  24  selectively directs intake air into combustion chamber  14  by means of a pair of poppet valves  26 , only one of which is illustrated in  FIG. 1 . Similarly, an exhaust passage  28  selectively directs exhaust gas from combustion chamber  14  by means of a pair of exhaust poppet valves  30 , only one of which is illustrated in  FIG. 1 . The opening and closing of valves  26  and  30  may be achieved by a mechanical cam or hydraulic actuation system or other motive system in carefully controlled time sequence with the reciprocal movement of piston  22 . 
   At the uppermost, TDC position shown in  FIG. 1 , piston  22  has just completed its upward compression stroke during which the charge air allowed to enter the combustion chamber  16  from intake passage  24  is compressed thereby raising its temperature above the ignition temperature of the engine&#39;s fuel. This position is usually considered the zero position commencing the 720 degrees of rotation required to complete four strokes of piston  22 . The amount of charge air that is caused to enter the combustion chambers may be increased by providing a pressure boost in the engine&#39;s intake manifold. This pressure boost may be provided, for example, by a turbocharger, not illustrated, driven by a turbine powered by the engine&#39;s exhaust, or maybe driven by the engine&#39;s crankshaft. 
   Engine  10  also includes an injector  32  securely mounted in an injector bore  34  for injecting fuel at very high pressure into combustion chamber  14  when piston  22  is approaching, at or moving away from, the TDC position. Injector  32  includes, at its inner end, an injector nozzle assembly  36  which is held to the remainder of the injector assembly, not illustrated, by a means of a nozzle retainer  38 . Injector  32  includes a plurality of small injection orifices  40 , formed in the lower end of nozzle assembly  36  for permitting the high pressure fuel to flow from the nozzle cavity of injector  32  into the combustion chamber at a very high pressure to induce thorough mixing of the fuel with the high temperature, compressed charge air within combustion chamber  14 . It should be understood that injector  32  may be any type of injector capable of injecting high pressure fuel through a plurality of injector orifices into combustion chamber  14  in the manner described hereinbelow with respect to the spray angle of the fuel. For example, injector  32  may be a closed nozzle injector or an open nozzle injector. Moreover, injector  32  may include a mechanically actuated plunger housed within the injector body for creating the high pressure during an advancement stroke of the plunger assembly. Alternatively, the injector  32  may receive high pressure fuel from an upstream high pressure source such as in a pump-line-nozzle system including one or more high pressure pumps and/or a high pressure accumulator and/or a fuel distributor. The injector  32  may include an electronically actuated injection control valve which supplies high pressure fuel to the nozzle valve assembly to open the nozzle valve element, or controls the draining of high pressure fuel from the nozzle valve cavity to create a pressure imbalance on the nozzle valve element thereby causing the nozzle valve element to open and close to form an injection event. For example, the nozzle valve element  36  may be a conventional spring-biased closed nozzle valve element actuated by fuel pressure, such as disclosed in U.S. Pat. No. 5,326,034, the entire contents of which is hereby incorporated by reference. The injector  32  may be in the form of the injector disclosed in U.S. Pat. No. 5,819,704, the entire contents of which is hereby incorporated by reference. 
   The engine of the present invention includes combustion chamber components and features sized, shaped and/or positioned relative to one another, as described hereinbelow, to advantageously reduce both NOx emissions and particulates to levels at or below new regulatory standards while maintaining acceptable fuel economy. Specifically, the dimensions, shape and/or relative positioning of the combustion chamber components and features reduce the exposure of the fuel to oxygen in combustion chamber  14  during the initial portion of an injection event thereby reducing NOx emissions while ensuring sufficient oxidation of particulate matter later in the combustion event and minimizing interaction between the combustion gases and the cylinder walls. The dimensions, shape and/or relative positioning of the combustion chamber components and features as described hereinbelow results in a combustion chamber capable of forming, directing, controlling and creating a pattern of injected fuel and gaseous flow within the combustion chamber  14  during both the initial stages of fuel injection and during the initiation of combustion and expansion of the resulting gases during the power stroke of piston  22  so as to achieve optimum emission reductions. 
   To understand the unique physical characteristics of combustion chamber  14 , attention is initially directed to  FIGS. 1 and 2  illustrating the various physical characteristics or parameters, at least two, and preferably all, of which are required to achieve the unexpected emission reduction advantages of the present invention. While the general shape of the combustion chamber has antecedence in the prior art, it is the specific configuration, and more importantly, the critical dimensions and dimensional relationships described hereinbelow which result in the improved functional performance of the present invention. More particularly, the upper portion of piston  22  may be referred to as the piston crown  50 . This area of the piston includes a depending cylindrical wall having a plurality of outwardly opening, annular grooves  52  for receiving corresponding piston rings designed to form a relatively tight combustion gas seal between the piston and the surrounding walls of cylinder liner  18 . Piston crown  50  includes a top face  54  partially forming combustion chamber  14  and a piston bowl  56  formed by an outwardly opening cavity. Piston bowl  56  includes a projecting portion  58  preferably positioned at or near the center of bowl  56 . Projecting portion  58  includes a distal end  60  positioned, in the preferred embodiment shown in  FIG. 1 , at the center of piston bowl  56  and thus positioned along the axis of reciprocation of piston  22 . Projecting portion  58  also includes an inner bowl floor section  62  extending from projecting portion  58  inwardly (toward the BDC position of piston  22 ) at an inner bowl floor angle α in the range of 16–40 degrees from a plane perpendicular to an axis of reciprocation of piston  22  as shown in  FIG. 1 . As will be explained hereinbelow, the inner bowl floor angle α is designed to be relatively steep and also designed relative to a spray angle β so as to cause desirable interaction between a fuel spray pattern or plume  63  ( FIG. 3   a ) and piston bowl  56  necessary for optimized engine emissions reductions. Preferably, a more specific and desirable range for inner bowl floor angle α would be between 18 and 30 degrees. 
   Piston bowl  56  also includes an outwardly flared outer bowl section  64  having a generally concave curvilinear shape in diametric cross section. Outer bowl section  64  effectively shapes and directs the flow of fuel and the fuel/air mixture within the combustion chamber. Outer bowl section  64  is designed with a particular radius R 1  and a particular location for a center of radius CR 1  so as to ensure the spray plume interacts with an inner face  65  of cylinder head  20  in an appropriate manner to ensure proper mixing and burning without interaction with the walls of cylinder liner  18 . Specifically, R 1  may range between 8 and 20 mm, and preferably within the range of 12–16.5 mm. For each of the dimensional ranges provided herein, a value within the higher end of the range will likely be more appropriate for larger engines having larger piston diameters and a value falling within the lower end of the range will more likely to be more desirable for smaller engines having smaller diameter pistons. Also, the location of the center of radius CR 1  for R 1  is preferably positioned on a plane extending through top face  54  of piston  22 , or within piston bowl  56 , and thus it is less desirable for R 1  to be positioned above top face  54  shown in  FIG. 1 . By combining the magnitude of R 1  and the location of CR 1  as described herein, the present invention creates outer bowl section  64  with an outward flare capable of controlling the momentum of spray plume  63  as it follows outer bowl section  64  to optimize combustion. An important objective of the subject invention is to minimize the amount of soot which actually reaches and becomes entrained in the lubrication film formed on the cylinder walls of liner  18  by promoting efficient combustion of the fuel within combustion chamber  14  while creating and constraining the flow of gases within the combustion chamber  14  to further minimize the possibility of soot entrainment within the film by ensuring the complete burning/oxidation of the particulates formed during the combustion process. Specifically, the position of CR 1  and the magnitude of R 1  ensures that the spray plume and fuel/air mixture rolling off the upper edge  66  of bowl  56  has sufficient momentum to be directed into cylinder head  20  resulting in the proper degree of mixing and oxidation of particulates. Outer bowl section  64  is specifically designed to prevent inadequate momentum of the spray plume and fuel/air mixture which would cause undesirable stagnation of the plume and air fuel mixture without interaction with the cylinder head thereby resulting in inadequate mixing and burning of particulates. This is achieved by having an R 1  that is sufficiently large resulting in a curvature in outer bowl section  64  to create and maintain the momentum in the spray plume and fuel/air mixture. Outer bowl section  64  is also designed to prevent excessive momentum in the spray plume and fuel/air mixture which would cause the spray plume and fuel/air mixture to interact with the cylinder head with an excessive velocity causing the spray plume/fuel/air mixture to impact cylinder head  20  and spread or rebound toward the cylinder walls formed by cylinder liner  18 . The fuel interacting with the lube oil film on the cylinder walls of combustion chamber  14  causes the unburned particulates in the fuel/air mixture to become entrained within the lubrication film resulting in soot which eventually works its way below the piston rings where it may become intermixed with the engine lubrication oil. The amount of fuel and particulates interacting with oil on the cylinder wall is at least partially minimized by using an R 1  that is sufficiently small to create a curvature which avoids excessive momentum in the spray plume and fuel/air mixture. Thus, R 1  is designed to modulate the momentum of the combustion plume to ensure the plume has sufficient momentum to interact with the cylinder head and reflect back into the open space of the combustion chamber  14 . Decreasing R 1  tends to decrease the momentum of the combustion plume. 
   The upper surface of outer bowl section  64  adjacent edge  66  preferably extends vertically parallel to the axis of the piston, or slightly inward toward the axis of reciprocation of piston  22 . That is, if this upper surface of outer bowl section  64  at edge  66  has a center of radius CR 1  then CR 1  is preferably positioned on a plane extending through top face  54  or positioned with bowl  56 . The curvilinear shape of outer bowl section  64  may be formed by a surface having a radius of curvature R 1  which terminates before edge  66  while a vertical upper portion of outer bowl section  64  extends tangentially from the surface having a radius of curvature R 1 , vertically to edge  66 . Preferably, as noted above, CR 1  is not positioned above top face  54 , and preferably the upper portion of outer bowl section  64  adjacent edge  66  does not intersect edge  66  in a manner which directs gases outwardly toward the cylinder walls formed by cylinder liner  18 . In this manner, proper control of the spray plume and fuel/air mixture and control of the interaction with the cylinder head is enhanced while preventing interaction with the cylinder walls thereby minimizing emissions and reducing soot. 
   As shown in  FIG. 3 , spray or injection orifices  40  of injector  32  extend through the injector nozzle  36  to deliver fuel to combustion chamber  14 . An important aspect of the subject invention involves orienting the central axis of each orifice  40  in a relatively steep spray angle β measured between a plane perpendicular to the axis of reciprocation of the piston and a central axis of each spray orifice  40  ( FIGS. 1 and 4 ). Therefore, β is the angle of spray emanating from fuel injection orifices  40 . Spray angle β may be equal to a value causing the spray angle β minus the inner bowl floor angle α to be in the range of 0–19 degrees, but preferably within the range of 1–13 degrees. This dimensional relationship results in the fuel spray plume  63  being directed toward the upper portion of projecting portion  58  near the upper edge of inner bowl floor section  62  as shown in  FIG. 3   a . Although it is possible that the fuel spray may be directed in a parallel direction along inner bowl floor section  62  under certain conditions where the movement of piston  22  and swirling of the air causes the spray plume to be forced into impingement with inner bowl floor section  62 , preferably the central axis of the spray plume  63 , which is also the central axis of each spray orifice  40  passing through the center C of each outlet opening  68  ( FIG. 4 ) of each spray orifice  40 , is angled slightly toward inner bowl floor section  62  at some angle such as any degree greater than 0 and less than 13 degrees. As a result, spray plume  63  engages projecting portion  58  soon after exiting outlet opening  68  and spreads out over inner bowl floor section  62  of projecting portion  58  as it flows downwardly as shown in  FIGS. 3   a – 3   c . By forming α and β such that the dimensional relationship between β and α, i.e. β minus α, causes spray plume  63  to be directed toward the top portion of projecting portion  58 , the present invention maximizes the amount of fuel in contact with inner bowl floor section  62  thereby minimizing the exposure of the fuel to oxygen in the combustion chamber  14  during the initial portion of the injection event/combustion. As a result, the formation of NOx and particulate emissions is desirably minimized.  FIG. 5  illustrates normalized data showing the emissions results of the present invention at β−α=8 degrees relative to emissions levels of current production engines.  FIG. 5  illustrates that key benefit of the present invention in reducing both NOx and particulate emissions, not just one type of emissions. 
   Another important combustion chamber parameter of the present invention critical to ensuring that fuel spray plume  63  contacts projecting portion  58  quickly and properly interacts with inner bowl floor section  62  is the vertical distance L 1  from the distal end  60  of projecting portion  58  to the center C of outlet openings  68  of injection orifices  40  as shown in  FIG. 2 . The combustion chamber arrangement of the present invention specifically includes the dimension L 1  having a magnitude in the range of 0.5–4 mm, and preferably in the range of 1.5–3 mm. An L 1  value within this range has been found by applicants to effectively enhance and ensure the interaction of spray plume  63  with inner bowl floor section  62  and minimize the length of the flow path of spray plume  63  between the outlet opening  68  and the impingement point of the spray against inner bowl floor section  62  thereby minimizing the opportunity for oxidation of the fuel and thus minimizing NOx emissions. Also, with each data point representing a different injection timing, a greater distance L 1 , for the arrangement illustrated in  FIG. 1 , results in significantly increased NOx emissions and decreased particulates as shown in  FIG. 6 . 
   Another important combustion chamber parameter significantly affecting emissions is the number N of injection or spray orifices  40 . In accordance with the present invention, no more than six injection orifices are used to deliver fuel to combustion chamber  14 . Preferably, less than six injection orifices, such as four or five, are used. The number of injection orifices N is critical for the following reason. One object of the present invention is to minimize NOx emissions by minimizing the exposure of fuel to air in the combustion chamber during the initial portion of the injection event/combustion as the spray plume travels from outlet openings  68  of injection orifices  40  to inner bowl floor section  62 . The greater the number of injection orifices, the greater the number of spray plumes flowing through the combustion chamber resulting in a larger surface area of fuel exposed to oxygen in the combustion chamber. Thus, the amount of fuel exposed to oxygen in the combustion chamber can be reduced by reducing the number of injection orifices. However, this reduction in injection orifices must be balanced with the need to promote proper distribution of the fuel within combustion chamber  14  and effective mixing of the fuel and air during the entire combustion process. Although many conventional injectors use more than six injection orifices, applicants have found that preferably no more than six orifices would be used and preferably four or five to minimize the exposure of the fuel to oxygen as it travels toward inner bowl floor section  62  and as it flows across the various surfaces of bowl  56  thereby reducing NOx emissions. 
   Another important combustion chamber parameter beneficial in controlling emissions is the swirl ratio of the air flow that is generated by the intake ports  24 . The swirl ratio SR is a ratio of the tangential velocity of the air spinning around combustion chamber  14  divided by the engine speed. That is, the swirl ratio is a measure of the tangential motion of the air as it enters the engine cylinder from the intake port(s) of the cylinder head. Precisely, the term swirl ratio refers to the average in-cylinder angular velocity of the air at intake valve closing divided by the cylinder piston angular velocity. For example, an engine running at 1800 rpm with a head generating an air motion with a swirl ratio of 2 implies that the air in the cylinder at intake valve closing is rotating with an average angular velocity of 3600 rpm. The higher the swirl ratio, the greater the swirling effect of the air or air fuel mixture, while the lower the swirl ratio, the lower the swirling effect. The swirling effect is a generally tangential motion that upon compression by piston  22  creates turbulence and assists in the combustion process. However, an increased swirling effect or swirl ratio generally tends to increase NOx emissions. The reason for this increase in NOx emissions is that the swirling effect tends to undesirably deflect the plume and cause a decay in the momentum of the combustion plume exiting the piston bowl. As a result, the ability of the plume to exit the piston bowl and desirably interact with the combustion head ( FIG. 3   c ) is disadvantageously impeded possibly causing the plume to remain in the piston bowl thereby hindering complete combustion by preventing maximum exposure to free oxygen. Applicants have found that maintaining a swirl ratio in the range of 0.5–2.5, and preferably within the range of 0.7–1.5, in combination with one or more of the other combustion chamber parameters, maintains the swirling effect at a sufficiently low level to enhance the reduction in NOx emissions while still permitting sufficient turbulence for combustion. By maintaining a swirl ratio within the preferred range, the combustion plume is permitted to advantageously interact with the cylinder head ( FIG. 3   c ) to optimize exposure to free oxygen in the combustion chamber thereby enhancing the reductions in particulates and NOx emissions. 
   Another combustion chamber parameter which can be set to assist in reducing emissions is the vertical distance L 2  from the center C of the outlet openings  68  of injection orifices  40  to the inner face  65  of cylinder head  20  facing combustion chamber  14 . That is, L 2  represents the distance the injection orifices  40  protrude into the combustion chamber below cylinder head  20 . Applicants have found that the range of L 2  should preferably be −0.5–3 mm, wherein the negative value of L 2  occurs when the center C of the outlet opening  68  is positioned just inside of the bore  34  of cylinder head  20 . 
   Another important combustion chamber parameter is the distance BH from the piston top face  54  to the inner face of cylinder head  20  when piston  22  is in the top dead center position as shown in  FIG. 2 . Applicants have found that the preferred range for BH is 0.5–8 mm. Of course, the lower end of the BH value is limited by mechanical clearance issues while the important upper limit assists in confining the combustion gases more to the interior of the combustion chamber or piston, i.e. the piston bowl  56 . Applicants have found that BH significantly affects the interaction of the combustion plume with the cylinder head. Also, it has been found that a BH outside the preferred range is more likely to increase soot in the lubrication oil on the cylinder walls. BH is especially effective in combination with one or more of the other combustion chamber parameters discussed herein to enhance the reductions in emissions. It should be noted that the top face  54  of piston  22  is considered the outer most surface of the piston and therefore BH is not measured from a recessed surface such as those surfaces formed by valve pockets for providing clearance from open intake and exhaust valves. 
   Another critical combustion chamber parameter is the radius of curvature R 2  at the lip or edge  66  of combustion bowl  56  as shown in  FIG. 2 . Although the radius R 2  is only shown at  FIG. 2  at one point along edge  66 , it should be understood that R 2  is formed along the entire edge  66  around the circumference of piston bowl  56 . R 2  is preferably in the range of 0.5–1.5 mm. The upper limit of 1.5 mm is important to maintaining the control over the direction of flow of the combustion plume as it flows off of outer bowl section  64 . Applicants have found that an R 2  having a greater value than approximately 1.5 mm undesirably permits a significant amount of combustion gases to flow toward the cylinder walls of liner  18  thereby undesirably increasing the level of particulates/soot developed in the lube oil film on the cylinder wall. Moreover, a smaller radius R 2  at edge  66  permits more control over the direction of flow of the combustion gas in the vertical direction toward cylinder head  20  and thus ensures a continuation of the momentum and desired interaction with the cylinder head, i.e. reflecting back into the free air space of the combustion chamber in a desirable manner. The objective is to form R 2  with the smallest radius possible while maintaining the structural integrity of the piston. 
   Finally, the size of combustion chamber  14  can be adjusted to control emissions. The cylinder bore diameter CD is preferably in the range of 95–140 mm. The precise cylinder bore diameter within this range depends greatly on the desired size and power output of the engine. Similarly, the piston bowl diameter BD shown in  FIG. 1  is preferably of a magnitude that causes the ratio of the bowl diameter to the cylinder bore diameter BD/CD to be in the range of 0.5–0.9. Essentially, applicants had found that it is beneficial to form a BD/CD ratio which is as high as the structural limits of the piston permit. Applicants have found that a larger piston bowl diameter BD improves fuel economy by exposing more of the combustion plume to more free oxygen after the initial bum as the plume interacts with the cylinder head ( FIG. 3   c ) resulting in improved combustion. Thus, applicants have found it to be very beneficial to achieve a BD/CD ratio between 0.8–0.9. 
   Combinations of the above described combustion chamber parameters selected within the specified ranges provided advantages in reducing emissions in comparison to conventional engine designs, including specifically meeting new emissions standards relative to NOx emissions and particulates, and also in reducing lube oil contamination by particulates. Combustion chamber  14  specifically includes a spray angle β relative to an inner bowl floor angle α that maximizes the amount of fuel in contact with the inner bowl floor section  62 , in combination with one or more of the following dimensions and dimensional relationships hereinabove with respect to: the vertical distance L 1  from the distal end  60  of the piston bowl  56  to the center C of the outlet openings  68  of the injection orifices  40 ; the number N of injection orifices; the swirl ratio SR; the vertical distance L 2  from the injection orifices  40  to an inner face  65  of the cylinder head  20 ; the distance BH from the piston top face  54  to cylinder head  20 ; the radius of curvature R 1  of an outer bowl section  64 ; a radius of curvature R 2  at an edge of piston bowl  56 ; the ratio BD/CD of the piston bowl diameter to the cylinder diameter; and the cylinder diameter CD.  FIG. 7  illustrates normalized data showing the emissions results of the present invention relative to emissions levels of current production engines. For example, the data point farthest to the left on the graph shows that with the right combinations of the engine parameters as discussed hereinabove, diesel particulate matter can be reduced to approximately 36% of the level typically produced by a conventional diesel production engine, while NOx was reduced to approximately 62% of typical conventional diesel engine levels. Thus, the NOx vs DPM tradeoff curve is radically different from a conventional engine in that both the NOx and particulates can be reduced simultaneously to levels within regulated standards. 
     FIGS. 8 and 9  show a piston bowl  156  in accordance with another embodiment of the present invention,  FIG. 8  showing a partial cutaway of a portion of a combustion chamber for internal combustion engine  100 , while  FIG. 9  shows a partial schematic view of the piston bowl profile of  FIG. 8 . The piston bowl  156  of engine  100  is optimized for injector nozzle  140  in which the number of injection orifices N is eight or less. Thus, whereas the previously described piston bowl profile discussed above relative to  FIGS. 1 and 2  were optimized for injector nozzles with six or less injection orifices, the present piston bowl profile of engine  100  allows for higher number of injection orifices. 
   In the illustrated implementation, some of the various parameters discussed above still apply. In this regard, various parameters of the engine  100  corresponds to the engine  10  discussed above, and thus,  FIGS. 1 ,  2 , and  4  apply in defining such parameters with respect to engine  100 . The swirl ratio SR of engine  100  is maintained in the range of 0.5 to 2.5, and is preferably within the range of 0.7 to 1.5 in the illustrated embodiment. The swirl ratio SR, in combination with one or more of the other combustion chamber parameters described in further detail below, maintains the swirling effect at a sufficiently low level to enhance the reduction in particulates and NOx emissions where the injector nozzles  140  are implemented with eight or less injection orifices. 
   In addition, the vertical distance L 2  from the center C of the outlet openings of injection orifices  140  to the inner face  165  of cylinder head  120 , which represents the distance the injection orifices  140  protrude into the combustion chamber below cylinder head  120 , is in the range of −0.5 to 3 mm. The outer bowl section  164  of the illustrated piston bowl  156  has radius R 1  in a range between 8 and 20 mm, and preferably, within the range of 12 to 16.5 mm. This radius R 1  ensures that the spray plume interacts with an inner face  165  of cylinder head  20  in an appropriate manner to ensure proper mixing. In particular, the radius of curvature R 1  of the outer bowl section  164  is optimized to modulate the amount of time required for the combustion plume to move along the contoured surface, the contour of the piston bowl  156  helping to redirect the combustion plume. The time required for the combustion plume to move along the bottom contour of the piston bowl  156  is increased as the radius is decreased, correspondingly slowing down the combustion which results in lower NOx emissions. 
   Moreover, the distance BH from the piston top face  154  to the inner face  165  of cylinder head  20  when piston  122  is in the top dead center position is preferably in the range of 0.5 to 8 mm. As described previously, applicants have found that BH significantly affects the interaction of the combustion plume with the cylinder head, and that a BH outside the preferred range is more likely to increase soot in the lubrication oil on the cylinder walls. 
   The piston bowl  156  of engine  100  shown in  FIGS. 8 and 9  relies on the combustion plume contact with the piston bowl surface to help control nitrous oxide emissions. By optimization of the spray angle β and the bowl floor angle α, the combustion plume contacts the piston  122  as illustrated in  FIG. 8 . Correspondingly, the combustion plume that impinges on the piston bowl  156  reduces the amount of hot gases, and reduces the amount of diffusion flame surface area which contributes to NOx emissions formation. In this regard, in the piston bowl  156  of the engine  100  shown, the dimensional relationship between the bowl floor angle α and the spray angle β is such that β minus α is between −7 to 19 degrees (β−α=−7 to 19), the negative angle occurring when the spray angle β is less than the bowl floor angle α. Thus, in contrast to the embodiment of the present invention described relative to  FIGS. 1 and 2 , the piston bowl  156  of combustion chamber  100  may be implemented such that there is reduced impingement of the injected fuel on the inner bowl floor section  162 . 
   In addition, in the engine  100  of  FIGS. 8 and 9 , the vertical distance L 1  from the distal end  160  of projecting portion  158  to the center C of the outlet openings of injection orifices  140  is optimized so that L 1  is in the range of 0.5 to 12 mm, which is substantially larger than the range of 0.5 to 4 mm for the previously described embodiment of  FIGS. 1 and 2 . The vertical distance L 1  from the distal end  160  of projecting portion  158  to the center C of the outlet openings of injection orifices  140  is increased to prevent excessive liquid fuel from impinging on the piston crown  150 , such impingement of liquid fuel being caused in part, by unburned fuel and carbon particulates. 
   Correspondingly, to minimize the formation of NOx and particulate emissions, the piston bowl  156  of engine  100  is provided with a chamfer  170  that is defined by various parameters δ, R 4 , and K which are discussed in detail below. Referring to  FIG. 8 , it should be evident that the chamfer  170  is provided at the end of the outer bowl section  164 , the chamfer  170  extending upwardly toward the top face  154  of the piston  122 . 
   As most clearly shown in  FIG. 9 , the end of the outer bowl section  164  transitions to the chamfer  170  at transition radius R 4 . The transition radius R 4  is preferably in the range of approximately 1.5 to 7 mm. The chamfer  170  is angled δ in the range of approximately 30 to 75 degrees from the axis of reciprocation of the piston  122  toward the top face  154  of the piston  122  and terminates at the top face  154 . In addition, the chamfer  170  extends approximately a distance K in the range of approximately 1 to 17 mm toward the top face  154  of the piston  122  and terminates at the top face  154 . 
   The above described chamfer  170  provided in the piston bowl  156  of engine  100  as shown in  FIGS. 8 and 9 , reduces the likelihood of the combustion plume from separating from the piston bowl  156 , and contacting the cylinder head  120 . The illustrated piston bowl profile allows a portion of the combustion plume to remain in contact with the piston bowl  156  which allows further reduction in NOx emissions. The fuel injection timing can then be adjusted to achieve a more fuel efficient thermodynamic cycle which results in better fuel economy at a prescribed NOx value. In addition, the described chamfer  170  provides less heat flux to the cylinder head  120 . Furthermore, the chamfer  170  reduces particulate matter that is confined to the region along the top of the cylinder head  120  so as to reduce the likelihood of poor particulate oxidation which may occur when soot is confined near the cylinder head  120  due to the lack of available oxygen. 
   While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the detail shown and described previously, but also includes all such changes and modifications. 
   INDUSTRIAL APPLICABILITY 
   It is understood that the present invention is applicable to all reciprocating piston internal combustion engines. This invention is particularly applicable to diesel engines and specifically heavy duty diesel engines, used in truck and automotive vehicles as well as industrial applications, for example stationary power plants and others.