Abstract:
A combustion chamber bowl is defined in a crown of a piston for use in a cylinder of a diesel engine. The combustion chamber bowl includes a center convex spherical portion, first and second annular concave portions and an annular convex portion. The center convex spherical portion is elevated relative to a bottom plane of the combustion chamber bowl and smoothly transitions into the first concave annular portion which transitions smoothly into the second concave annular portion. The second concave annular portion smoothly transitions into the convex annular portion which smoothly transitions into the top surface of the piston crown.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]    The present invention relates to a combustion chamber for use in a diesel internal combustion engine. 
       BACKGROUND OF THE INVENTION  
       [0002]    Many attempts have been made to produce an ideal flow pattern for the charge of air and fuel within the combustion chamber of a diesel internal combustion engine. Considerations that must be taken into effect include, but are not limited to, providing for adequate power generation, minimizing the NOx entrained in the engine exhaust, and minimizing the amount of soot particulate also entrained in the engine exhaust. 
         [0003]    It is known that changes in any one of a variety of engine design variables, such as engine compression ratio, combustion chamber shape, fuel injection spray pattern, and other variables can have an affect on both emissions and the fuel economy. Unfortunately, in the past, engine designs that have reduced emissions have also had worse fuel economy, and designs with a better fuel economy have had increased emissions. 
         [0004]    The amount of soot that is expelled with the engine&#39;s exhaust is unsightly and generates public pressure to clean up diesel engines. Further, the amount of soot that is entrained in the engine&#39;s lubrication oil can have a deleterious effect on engine reliability. Soot is very abrasive and can cause high engine wear. 
         [0005]    There is additionally a great deal of pressure to reduce the NOx emissions from the engine. Ever increasing regulatory demands mandate reduced levels of NOx. Typically, a combustion chamber design that is effective at reducing NOx levels has been found to increase the levels of soot and vice-versa. Additionally, doing either of the aforementioned typically reduces engine torque and power outputs. 
         [0006]    There are numerous examples of combustion chambers formed in the crown of a piston. Notwithstanding all these prior art designs, the present inventor has recognized the need for reduction both in NOx and entrained soot while at the same time maintaining or enhancing engine torque and power outputs without adversely affecting the fuel economy of the engine. 
       SUMMARY OF THE INVENTION  
       [0007]    The present invention provides a piston for a diesel engine wherein the piston includes an improved combustion chamber bowl formed into the piston crown. The present invention provides a diesel engine which operates with reduced NOx and soot emissions, and with an increased fuel economy. 
         [0008]    The combustion chamber bowl comprises several concave and convex surfaces. The shape and size of the bowl is advantageously configured to create a combustion chamber that compresses and ignites fuel in the chamber in such a way as to increase fuel economy and reduce emissions. 
         [0009]    The combustion chamber bowl defined in the crown of the piston has been shown to both reduce soot entrainment and NOx and soot emissions while at the same time slightly increasing engine power output. The piston will function effectively with heads having two or more valves. A further advantage of the combustion chamber of the present invention is that by being symmetrical with respect to a combustion chamber central axis the combustion chamber is relatively easily formed in the crown of the piston. 
         [0010]    The present invention comprises a combustion chamber assembly for use in a diesel engine and includes a combustion chamber bowl being defined in a crown of a piston, the piston having a central axis, the combustion chamber bowl having a center portion being elevated relative to a bottom plane of the combustion chamber bowl. The center portion is defined in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the combustion chamber bowl central axis. 
         [0011]    The combustion chamber bowl further has an outer margin, the outer margin being defined in part by two concave annular surfaces. The uppermost of the concave annular surfaces transitions into a convex annular surface near to the top surface of the piston crown. 
         [0012]    The plurality of curved surfaces of the combustion chamber bowl have smooth tangential transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion, the concave annular surfaces and the convex annular surface. 
         [0013]    The present invention further encompasses a piston having the aforementioned combustion chamber bowl and method of forming the aforementioned combustion chamber bowl. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]      FIG. 1  is a side cross-sectional view of the combustion chamber bowl of the present invention; and 
           [0015]      FIG. 2  is a bar graph showing results of the combustion chamber bowl of the present invention design vs. a prior combustion chamber bowl design in terms of BSFC, NOx emissions, and soot. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
         [0017]    The piston of the present invention is shown generally at  10  in  FIG. 1 . A combustion chamber  12  of the present invention is defined in part by a crown  14  having a top surface  15 . The crown  14  of the piston  10  defines in part the upper margin of the piston  10 . 
         [0018]    It should be noted that the combustion chamber bowl  12  is rotationally symmetrical about a longitudinal axis A 1  that is coincident or at an offset with a center axis A 2  of the piston  10 . 
         [0019]    The various radii (R), diameters (D), and heights (H) that will be described below are clearly indicated in the depiction of  FIG. 1 . 
         [0020]    The piston  10  of the present invention is designed primarily for use in heavy duty diesel engines but would also be applicable to lighter duty diesel engines. The piston  10  may be utilized with two-valve or multiple-valve heads. It is desirable that the fuel be injected proximate the center of the combustion chamber bowl and that the injection pattern be radially symmetrical. 
         [0021]    The combustion chamber bowl  12  defined in the crown  14  of the piston  10  is comprised of a plurality of curved surfaces, being both spherical and annular surfaces. The combustion chamber bowl  12  has no flat surfaces. There is a smooth, tangential transition between the various curved surfaces that define the combustion chamber bowl  12 , as described in greater detail below. 
         [0022]    Generally, the combustion chamber bowl  12  is comprised of a convex spherical surface  20 , a first concave annular surface  22 , a second concave annular surface  24  and a convex annular surface  26 . 
         [0023]    There are a number of parameters that control the geometry of the combustion chamber bowl  12  and thereby control the diesel engine combustion performance as well as NOx and soot emissions. A portion of a spherical surface, defined by the spherical radius R 20 , is located in the center portion of the combustion chamber bowl  12 . The origin O 1  of the spherical surface is located on the center axis A 1  of the combustion chamber bowl  12 . As depicted in  FIG. 1 , the origin O 1  is below the point of intersection of the axis A 1  of the combustion chamber bowl  12  and the bottom plane  27  of the combustion chamber bowl  12 . 
         [0024]    The first concave annular surface  22  has a first concavity radius R 22  and is located outside of the spherical surface  20  and has an extent that defines in part an outer margin of the combustion chamber bowl  12 . The first concavity radius R 22  of the first concave annular surface  22  has an origin O 2 . 
         [0025]    The second concave annular surface  24  has a second concavity radius R 24  and is located above and generally to the outside of the first concave annular surface  22  and defines in part the outer margin of the combustion chamber bowl  12 . The second concavity radius R 24  of the second concave annular surface  24  has an origin O 3 . 
         [0026]    A convex annular surface  26  is formed at the top of the sidewall of the combustion bowl  18 . The convex annular surface  26  transitions into the top surface  15  of the piston crown  14 . The convex annular surface  26  has a convexity radius R 26 . 
         [0027]    The combustion chamber bowl  12  as indicated above is comprised of combined spherical and annular surfaces. It is noted that the transition between surfaces  20  and  22  is smooth and tangential, the transition between surfaces  22  and  24  is smooth and tangential, the transition between surfaces  24  and  26  is smooth and tangential and the transition between surfaces  26  and  15  is smooth and tangential. In this manner, there are no flat surfaces that define the combustion chamber bowl  12 . The curves and smooth transitions as previously described promote smooth flow in the combustion chamber bowl  12  and act to reduce the thermal loading in the combustion chamber bowl  12 . Further, the combustion chamber bowl  12  being rotationally symmetrical about the axis A 1 , it is much easier to turn the combustion chamber bowl  12  as compared to an asymmetrical combustion chamber bowl defined in a piston. 
         [0028]    It should further be noted that the convex annular surface  26  defines a reentrant combustion chamber bowl  12  at the intersection with the top surface  15  of the crown  14 , as distinct from an open combustion chamber bowl as depicted in some of the prior art. 
         [0029]    The piston  10  has diameter D 1 , the combustion chamber bowl  12  has maximum diameter D 2 , and the convex annular surface  26  of the combustion chamber bowl  12  has diameter D 3 . The combustion chamber bowl  12  has a depth H 1  and a center axis A 1 , and the convex spherical surface  20  has a height H 2 . The piston  10  has a center axis A 2  that is a distance H 3  away from the combustion chamber bowl center axis A 1 . The distance H 3  should be between 0 and 0.08D1, and is preferably 0. 
         [0030]    The spherical radius R 20  of the convex spherical surface  20  has the origin O 1  located a distance H 4  below the point of intersection of the combustion chamber bowl axis A 1  with the bottom plane  27  of the combustion chamber bowl  12 . The distance H 4  should be between 0 and 0.35D1, and is preferably 0.164D1. 
         [0031]    The ratio of D 2 /D 1  should be greater than 0.44 and should be less than 0.84, and is preferably 0.626. 
         [0032]    The ratio of D 3 /D 2  should be greater than 0.69 and should be less than 0.999, and is preferably 0.984. 
         [0033]    The ratio of R 20 /D 2  should be greater than 0.18 and should be less than 0.68, and is preferably 0.417. 
         [0034]    The ratio of H 1 /D 2  should be greater than 0.14 and should be less than 0.44, and is preferably 0.242. 
         [0035]    The ratio of H 2 /D 2  should be greater than 0.11 and should be less than 0.41, and is preferably 0.156. 
         [0036]    The ratio of R 22 /D 2  should be greater than 0.06 and should be less than 0.36, and is preferably 0.121. 
         [0037]    The ratio of R 24 /D 2  should be greater than 0.16 and should be less than 0.66, and is preferably 0.413. 
         [0038]    The ratio of R 26 /D 2  should be greater than 0.01 and should be less than 0.11, and is preferably 0.034. 
         [0039]      FIG. 2  shows by experimental data the effects of these configurations on BSFC, NOx emissions, and soot emissions. The Brake Specific Fuel Consumption (BSFC) is a measure of fuel consumption of the engine divided by its power (Consumption/Power). Since higher efficiency is correlated with a lower BSFC, lower BSFC numbers mean higher quality engines and better fuel economy. 
         [0040]    It is shown that the BSFC is reduced by 0.4%, the NOx emissions are reduced by 4.3%, and the soot emissions are reduced by 14.1%. 
         [0041]    It will be obvious to those skilled in the art that other embodiments in addition to the ones described herein are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto.