Abstract:
A swirl chamber used in association with a combustion chamber for diesel engines, includes a pair of sub-nozzle holes on the opposite sides of a main nozzle hole to supply a secondary air into the swirl chamber, the sub-nozzle holes being positioned such that the secondary air ejected therethrough is fully utilized for the combustion in the swirl chamber, thereby securing the complete combustion and the reduction of environmental contaminants such as NOx and fumes.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a combustion chamber for diesel engines, and more particularly, to improvements upon a swirl chamber used in association with a combustion chamber for diesel engines. 
     BACKGROUND ART 
     In general, diesel engines are notorious as a major source of environmental contaminants such as NOx and fumes. However, no effective measures have been accomplished for solving those problems. It is known that these problems are due to the incomplete combustion in the engine occurring because of inadequate mixing of air and fuel. To solve these problems, swirl-aided combustion systems are commonly used. Here is one example for tackling this problem, which is disclosed in Japanese Patent Laid-open Application No. 07-97924. Referring to FIG. 10, the known combustion chamber fitted with a swirl chamber will be described: 
     In  FIGS. 10A and 10B  the right-hand side (toward the central axis  103 ) is called “rearward”, and the left-hand side (toward the cylinder liner  104 ) is “forward” each as designation for convenience only. The known combustion chamber shown in  FIG. 10A  is provided with a cylinder  101  having a cylinder head  105 , a reciprocating piston  102 , and a combustion chamber  109 . In addition, the cylinder head  105  is provided with a recess  106  in which a mouthpiece  107  is fitted. The mouthpiece  107  is provided with a top-open recess  107   a , and t15he recess  106  includes a bottom-open recess  106   a . The top-open recess  107   a  and the bottom-open recess  106   a  constitute a space  108  functioning as a swirl chamber, hereinafter the space being referred to as “swirl chamber  108 ”. The swirl chamber  108  communicates with the combustion chamber  109  through a main nozzle hole  111  having a center axis  113 . The main nozzle hole  111  is forwardly inclined toward the swirl chamber  108 . The mouthpiece  107  is additionally provided with a pair of sub-nozzle holes  102 , through which a secondary air is forced into the swirl chamber  108  on the compression stroke. The sub-nozzle holes  112  are symmetrically positioned on opposite sides of the central axis  113 - 114  as shown in FIG.  10 A. 
     Under the construction mentioned above, however, a major disadvantage is that the second air ejected through the sub-nozzle holes  112  does not reach the central part of the swirl chamber  108 , thereby failing to bring about effective swirls therein. In this way the conventional sub-nozzle holes  112  are not conducive to the full utilization of the secondary air. 
     The disadvantages mentioned above is due to the following arrangement of the sub-nozzle holes  112 : When a hypothetical sphere  115  is supposed about the center of the open end  107   b  of the top-open recess  107   a , and the radius of the open end  107   b  and that of the sphere  115  are respectively supposed to be 100% and 70%. 
     The sphere  115  having a radius of 70% passes outward, whereas the sphere  115  having a radius of 50% passes inward in  FIGS. 10A and 10B . In this situation, the central axis  112   a - 112   b  of each of the sub-nozzle holes  112  passes outside the sphere  115 . 
     In another aspect, when the mouthpiece  107  is seen from just above, the sub-nozzle holes  112  have their upper openings  112   c  deviated from the center of the swirl chamber  108  so that even if every sub-nozzle hole is oriented vertically, the central axis  112   a - 112   b  of each sub-nozzle hole  112  cannot pass inside the 50% sphere  115 . 
     Accordingly, an object of the present invention is to provide an improved swirl chamber capable of causing effective swirls to help air and fuel being well mixed, and dispersing the fuel well in the swirl chamber. 
     Another object of the present invention is to provide an improved swirl chamber capable of reducing the production of both NOx and fumes, not one or the other under the conventional system. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a swirl chamber used in association with a combustion chamber, wherein the combustion chamber is defined by a piston, a cylinder, and a cylinder head, includes a mouthpiece fitted in a hole of the cylinder head, the hole having a bottom-open recess, and the mouthpiece including a top-open recess, the bottom-open recess and the top-open recess constituting a space for the swirl chamber; a main nozzle hole produced through a base wall of the mouthpiece to allow the swirl chamber to effect communication between the combustion chamber and the swirl chamber; and a pair of sub-nozzle holes which are separated from the main nozzle hole, produced through the base wall of the mouthpiece, the holes being positioned on opposite sides of the central axis of the main nozzle hole when the mouthpiece is seen from just above; wherein each of the sub-nozzle holes is arranged to pass inside a hypothetical sphere depicted around a center of an upper circle of the top-open recess and having a radius of 70% of a diameter of the upper circle of the top-open recess. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is generally a diagrammatic view exemplifying a first embodiment of the present invention;  FIG. 1A  being a plan view,  FIG. 1B  being a cross-sectional view taken along the line B—B of  FIG. 1A ;  FIG. 1C  being a bottom view, and  FIG. 1D  being a cross-sectional view taken along the line D—D; 
         FIG. 2  is generally a diagrammatic view exemplifying the nozzle hole in the mouthpiece shown in  FIG. 1 ;  FIG. 2A  being a vertical cross-sectional side view of the mouthpiece,  FIG. 2B  being a perspective view of the nozzle hole;  FIG. 2C  being a diagrammatic view of the nozzle hole viewed in the direction indicated by the arrow C in  FIG. 2A , and  FIG. 2D  being a bottom view of the nozzle hole; 
         FIG. 3  is generally a diagrammatic view exemplifying the swirl chamber shown in  FIG. 1 ;  FIG. 3A  being a horizontal cross-sectional plan view of a cylinder incorporating a piston, and  FIG. 3B  being a cross-sectional side view of the swirl chamber and the surrounding part members; 
         FIG. 4  is a graph showing NOx content in the exhaust gases under the first embodiment shown in  FIG. 3 , in comparison with a contrasted example  1  having no sub-nozzle holes; 
         FIG. 5  is a graph showing the amount of NOx and fumes exhausted under the first embodiment shown in  FIG. 3 , in comparison with contrasted examples 1 and 2; 
         FIG. 6  is generally a graph showing the relationship between the cross-sectional area of the sub-nozzle holes and the characteristics of gases exhausted from the swirl chamber of  FIG. 3 ;  FIG. 6A  showing variations in the amount of NOx in relation to the cross-sectional area;  FIG. 6B  showing variations in the amount of fumes in relation to the cross-sectional area; and  FIG. 6C  showing variations in the total amount of NOx and fumes in relation to the cross-sectional area; 
         FIG. 7  is generally a diagrammatic view exemplifying the mouthpiece of a second embodiment;  FIG. 7A  being a plan view,  FIG. 7B  being a cross-sectional view taken along the line B—B in  FIG. 7A ;  FIG. 7C  being a bottom view, and  FIG. 7D  being a cross-sectional view taken along the line D—D in  FIG. 7B ; 
         FIG. 8  is generally a diagrammatic view exemplifying the mouthpiece of a third embodiment;  FIG. 8A  being a plan view,  FIG. 8B  being a cross-sectional view taken along the line B—B in  FIG. 8A ;  FIG. 8C  being a bottom view, and  FIG. 8D  being a cross-sectional view taken along the line D—D in  FIG. 8B ; 
         FIG. 9  is generally a diagrammatic view exemplifying the mouthpiece of a fourth embodiment;  FIG. 9A  being a plan view,  FIG. 9B  being a cross-sectional view taken along the line B—B in  FIG. 9A ;  FIG. 9C  being a bottom view, and  FIG. 9D  being a cross-sectional view taken along the line D—D in  FIG. 9B ; and 
         FIG. 10  is generally a diagrammatic view exemplifying a known swirl chamber;  FIG. 10A  being a plan view of the mouthpiece and the piston, and  FIG. 10B  being a vertical cross-sectional side view of a swirl chamber and surrounding part members. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout the drawings like numerals are used to designate like components, and in  FIGS. 1B ,  3 B,  7 B,  8 B,  9 B, and  2 A the right-hand side is “forward”, and the left-hand side is “rearward” for convenience of illustration only. A first embodiment is shown in  FIGS. 1  to  6 , in which a pair of sub-nozzle holes  12  are provided upright in parallel with the central axis  3  of a cylinder  1 . This is the same with a second embodiment shown in  FIG. 7 , but in the third embodiment shown in  FIG. 8 and a  fourth embodiment shown in  FIG. 9  the sub-nozzle holes  12  are slightly converged and slightly diverged toward their top open ends, respectively. The feature common with all the embodiments is that the sub-nozzle holes are spaced from, and positioned symmetrically on opposite sides of, the main nozzle hole. In addition, the sub-nozzle holes are produced on the forward side. 
     In  FIG. 3B  a reciprocating piston  2  is provided inside a cylinder  1  along whose central axis  3  the piston  2  moves up and down. The cylinder  1  has a head  5  having a recess  6  in which a mouthpiece  7  is fitted. The recess  6  includes a bottom-open recess  6   a , and the mouthpiece  7  includes a top-open recess  7   a . The bottom-open recess  6   a  and the top-open recess  7   a  constitute a space  8  that is utilized as a swirl chamber. The cylinder  1  is provided with a combustion chamber  9  having a main nozzle hole  11  passing through the mouthpiece  7 . The combustion chamber  9  and the swirl chamber  8  communicate with each other through the main nozzle hole  11 , which is forwardly inclined toward the swirl chamber  8  from the combustion chamber  9 , as shown in FIG.  3 B. The mouthpiece  7  has an undersurface  7   d  in a plane perpendicular to the central axis  3  of the cylinder  1 . 
     As best shown in  FIG. 3B , a fuel jet nozzle  19  and a heat plug  20  are provided toward the swirl chamber  8 . The piston  1  is provided with a triangular recess  21  adapted to guide a gas flow, wherein the root portion of the recess  21  is positioned immediately below the main nozzle hole  11 , and as best shown in  FIG. 3A , the recess  21  expands progressively far from the main nozzle hole  11 , thereby having a diminishing depth, as best shown in FIG.  3 B. 
     The principle underlying the combustion chamber  9  fixed with the swirl chamber  8  is as follows: 
     On the compression stroke the piston  2  rises, thereby introducing compressed air into the swirl chamber  8  to cause swirls therein. When the piston  2  reaches the top dead point, fuel is ejected through the ejection nozzle  19 . The fuel is mixed with the air in the swirl chamber  8 , and the charge of fuel and air is ignited, and burned in the chamber  8 , and as a result, it expands in volume. The expanded gases pass into the combustion chamber  9  through the main nozzle hole  11 . The fresh charge expands and rises as it goes away from the main nozzle hole  11  in the triangular recess  21 . The fuel-content in the fresh charge mixes with air in the combustion chamber  9 , and the mixture is ignited and burned. 
     The sub-nozzle holes  12  will be described: 
     In  FIGS. 1A  to  1 D, particularly in  FIGS. 1B and 1D , the sub-nozzle holes  12  are provided in pair through a base wall  10  of the mouthpiece  7 . Each of the sub-nozzle holes  12  is away from the main nozzle hole  11  such that they are symmetrically positioned about the central axis  13  of the main nozzle hole  11  or about its extension  14 , depending upon the shape of the main nozzle hole  11 . 
       FIGS. 1A ,  1 B, and  1 D show a hypothetical sphere  15  about a center  7   c  which is the center of the open end  7   b  of the recess  7   a . The radius of the open end  7   b  is supposed to be 100%, and that of the sphere  15  to be 50%. Each of the sub-nozzle holes  12  is positioned such that its central axis  12   a - 12   b  passes through the sphere  15 , or in the drawing, through the sphere  15 . 
     Preferably, the radius of the sphere  15  is 70%; more preferably, 60%, and most preferably, 50%. In  FIGS. 1A ,  1 B, and  1 D the innermost, middle, and outermost sphere  15  are drawn in correspondence to 50%, 60%, and 70%, respectively. It has been demonstrated that this range of angular positioning of the sub-nozzle holes  12  enables a secondary air to gather at the center of the swirl chamber  8 , thereby making the most of the air ejected through the sub-nozzle holes  12  and causing effective swirls in the swirl chamber  8 . 
       FIG. 1A  shows, as a preferred embodiment, that the center  12   c  of the open end of each sub-nozzle hole  12  overlaps the sphere  15  having a radius of 50% when the mouthpiece  7  is seen from just above, thereby enabling the central axis  12   a - 12   b  of each sub-nozzle hole  12  to pass through the center of the swirl chamber  8 . In this case, the radius is preferably 70%, more preferably 60%, and most preferably 50% of that (100%) of the open end of the top-open recess  7   b.    
     In  FIGS. 1A and 1D , a hypothetical reference line  16  extends just upwards. The position of each hole  12  is determined in relation to this hypothetical reference line  16 ; that is, each sub-nozzle hole  12  is positioned such that its central axis  12   a - 12   b  coincides with the reference line  16  in every direction as viewed in  FIGS. 1A  to  1 D. 
     In this way the sub-nozzle holes  12  are positioned at various angles for the reference line  16  (FIGS.  1 B and  1 D). If it is positioned at a relatively small angle to the reference line  16 , the sub-nozzle hole  12  can be short in length, thereby reducing frictional resistance to the flow of a secondary air passing through the sub-nozzle hole. In  FIG. 1B  where the cross-section of the mouthpiece  7  is viewed from the side, and the two sub-nozzle holes  12  appear to be in alignment, the central axis  12   a - 12   b  of the sub-nozzle hole  12  is preferably inclined at 30° or less to the reference line  16 , which will be referred to as “first angle”. In  FIG. 1D  where the cross-section of the mouthpiece  7  is viewed from the back, and the sub-nozzle holes  12  appear to be arranged side by side, the central axis  12   a - 12   b  is preferably inclined at 15° which will be referred to as “second angle”. In another preferred embodiment the first angle is 15° or less, and the second angle is 8° or less; more preferably, 8° or less to 4° or less, and most preferably, 4° or less to 2° or less. 
     In the embodiment illustrated in  FIGS. 1B and 1C  the first angle is 30° and the second angle is 15° each angular relation being indicated by chain lines. 
     The size of each sub-nozzle hole  12  is determined as follows: 
     It has been demonstrated that when the main nozzle hole  11  has an open end having an effective area is supposed to be 100%, the total area of the open ends of the two sub-nozzle holes should be in the range of 3% to 15%; preferably, 4 to 10%; more preferably, 6 to 10%, and most preferably, 7 to 9%. In short, the range of 3 to 15%, or preferably, of 5 to 15% is effective to reduce the production of NOx and fumes evenly. 
     The main nozzle hole  11  is constructed as follows: 
     Referring to  FIGS. 2A  to  2 D, the main nozzle hole  11  includes a main groove  17  and a pair of side grooves  18  communicatively continuous to the main groove  17  through banks (not numbered). In  FIG. 2A , each side groove  18  is formed such that its central axis  18   a  is slightly behind the central axis  17   a  of the main groove  17 . Each side groove  18  is also arranged that its angle of elevation is smaller than 45° of the axis  17   a.    
     As best shown in  FIG. 1A , each of the side grooves  18  gradually but slightly becomes narrower in width toward the depth of the main nozzle hole  11  while the main groove  17  remains the same along its full length. The side grooves are positioned such that the distance between them diminishes toward their forward ends. Each of the side grooves has a progressively diminishing cross-sectional area toward its forward end. When the mouthpiece is seen from just above, each of the side grooves is arranged at a position retreated from an upper opening of every sub-nozzle hole in parallel to a center axis of the main nozzle hole and immediately rearwards thereof. 
     Referring  FIGS. 4 and 5 , the major advantage of the first embodiment is that environmental contaminants such as NOx and fumes are reduced in the exhaust gases, which will be demonstrated, on condition that the applied load is the same: 
     From  FIG. 4 , it will be understood that the first embodiment has less nitrogen oxides (NOx) than a contrasted example ( 1 ) that has neither sub-nozzle holes  12  nor the side grooves  18 . It will be appreciated that the sub-nozzle holes  12  and the side grooves  18  are effective to reduce NOx content. 
       FIG. 5  shows that the first embodiment has less NOx and less fumes than contrasted examples 1 and 2, wherein the contrasted example 2 has sub-nozzle holes corresponding to the sub-nozzle holes  12  but no grooves corresponding to the side grooves  18 . The comparison between the contrasted examples 1 and 2 shows that the addition of the secondary air sub-nozzle holes  12  are conducive to the reduction of NOx and fumes. Likewise, the comparison between the first embodiment and the contrasted example 2 shows that the side grooves  18  are conducive to the reduction of NOx and fumes. 
     The efficiency of reducing exhaust gases depends upon the area of the open end of the sub-nozzle hole  12 . Referring to  FIGS. 6A  to  6 C, each horizontal co-ordinate is the percentage of the total minimum area of the open ends of the sub-nozzle holes  12  to the area of the open end of the main nozzle hole  11 . The vertical co-ordinate of  FIG. 6A  indicates variations in the amount of NOx; in  FIG. 6B  the vertical co-ordinate indicates variations in the amount of fumes, and in  FIG. 6C  the vertical co-ordinate indicates variations in the total amount of NOx and fumes. Each coefficient of variation is calculated, as a reference value, based upon the amount of NOx and fumes produced in the combustion chamber having no sub-nozzle holes  12 . Let the reference value be α, and the amount of variation be β. Then, the coefficient of variation will be (β-α)/α. 
     As shown in  FIG. 6C , the absolute value of the total reduction rate is maximized when the area of the open end of the sub-nozzle holes  12  is 7.7%. Let the absolute value of the reduction rate at this stage be 100%. It has been demonstrated that to increase the rate of reduction of exhaust gases up to 98%, the total area of the open ends of the sub-nozzle hole  12  must be in the range of 7 to 9%, and if it exceeds 95%, the total area can be in the range of 6 to 10%. If it exceeds 60%, the total area can be in the range of 3 to 15%. Among these ranges, when it exceeds 70%, and both NOx and fumes effectively decrease, the total area is in the range of 4 to 10%. As a result, it will be concluded that the total area of the open ends of the sub-nozzle holes preferably in the range of 3 to 15%; more preferably, 4 to 10%, further preferably, 6 to 10%, and most preferably, 7 to 9%. 
     Referring to  FIGS. 7 ,  8  and  9 , a second embodiment, a third embodiment and a fourth embodiment will be described, respectively: 
     In the second embodiment shown in  FIG. 7  the total area of the open ends of the sub-nozzle holes  12  is 8% of the area (100%) of the open end of the main nozzle hole  11 , wherein each sub-nozzle hole has an open end having the same area. This embodiment reduces the production of NOx or fumes or both, as clearly demonstrated by comparison with the contrasted examples  1  and  2 . 
     In the third embodiment shown in  FIG. 8  the pair of sub-nozzle holes  12  are inclined forwardly and upwardly toward the swirl chamber  8  or, in other words, slightly converged toward the swirl chamber  8  from the combustion chamber  9  in contrast to the first and second embodiments where they extend upright between the combustion chamber  9  and the swirl chamber  8 . In  FIG. 8B  the angle of incline is 30° and in  FIG. 8D , the angle of incline is 15° toward each other. 
     In the fourth embodiment shown in  FIGS. 9A  to  9 D, the pair of sub-nozzle holes  12  are inclined rearwardly and upwardly toward the swirl chamber  8 , as best shown in  FIG. 9B , and, as shown in  FIG. 9D , are inclined outwardly or, in other words, slightly diverged toward the swirl chamber  8  from the combustion chamber  9 . In  FIG. 9B  the angle of incline is 30° and in  FIG. 9D , the angle of incline is 15° toward each other.