Abstract:
A method of charging an internal combustion engine with a fuel air mixture, the engine having opposed pistons with a combustion chamber therebetween, wherein the method includes forcing induction air during a compression stroke between a first and a second cylinder via a contraction and expansion or a venturi disposed between the first and second pistons.

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    Not applicable. 
       NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT Not applicable. 
     REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC 
       [0002]    Not applicable. 
       BACKGROUND OF THE: INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a method and means for controlling combustion in internal combustion engines and more particularly in internal combustion engines generally configured as disclosed in WO96/12096 and WO2004/007911, the contents of which are incorporated herein by reference. 
         [0005]    Throughout this description and the claims which follow, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps. 
         [0006]    The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia. 
         [0007]    In this specification an internal combustion engine is defined as an internal combustion engine having opposed pistons with a combustion chamber therebetween as disclosed in WO96/12096 or WO2004/007911. 
         [0008]    As used herein “first” and “second” piston have the same meaning as in WO96/12096. In the environment of an internal combustion engine the first piston may be considered a power piston and the second piston a valving or timing piston associated with the opening and closing of inlet and exhaust gas flows. Typically, the timing piston need only be of sufficient diameter to allow intake and exhaust openings to comply with the well understood design criteria for longevity and good design requirements for 2-stroke induction and exhaust systems. The second cylinder and piston form part of the intake and exhaust manifold and may be treated as such in calculating ram and scavenging effects. 
         [0009]    2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98. 
         [0010]    Prototypes in accordance with the prior art arrangements as shown in WO96/12096 and WO2004/007911 function in an adequate manner but have some deficiencies as regards the quality and efficiency of induction, exhaust and combustion. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    With a view to aiding the performance and efficiency of the related prior art arrangements when operated as an internal combustion engine, the present invention proposes a method and means for controlling induction of an air and fuel mixture into the combustion chamber formed between the first and second pistons. In that regard the present invention is concerned with the characteristics of the passage between the first and second pistons so as to achieve a desired gas flow into and out of that passage. The passage is also adapted to form a significant portion of the combustion chamber in the space between the two pistons. 
         [0012]    In accordance with a first aspect of the present invention there is provided a method of charging an internal combustion engine as disclosed in WO96/12096 or WO2004/007911 with a fuel air mixture wherein induction air, during a compression stroke, is forced between the first and second cylinders via a contraction and expansion between the first and second pistons. 
         [0013]    Preferably, mixing of fuel and intake air occurs within the contraction and expansion between the second and first cylinders. 
         [0014]    It is further preferred that fuel be injected into a zone between the contraction and expansion. 
         [0015]    In accordance with a second aspect of the present invention there is provided an internal combustion engine as disclosed in WO96/12096 or WO2004/007911 wherein a passage incorporating a venturi joins the first and second cylinders such that induction air is compressed in the passage as the first and second pistons move toward each other during a compression stroke 
         [0016]    In a preferred form the passage between the two pistons, commencing from the cylinder of the second piston, leads into a first conical bore contracting toward the first piston to as zone of minimum cross-sectional area and from that zone a second conical bore expands to open into the cylinder of the first piston. The minimum cross-sectional area zone forms a tuning region for the intake fluid flow between the second and first pistons and which zone acts in a manner akin to that of an intake poppet valve of a conventional four-stroke internal combustion engine. The pressure drop across the zone determining a best operating speed of the engine by allowing a maximum ram effect at the predetermined best operating speed. The contraction then expansion of the passage provides a venturi effect which is advantageous to induction. 
         [0017]    The shape of the zone can take any form that is suited to a desired mode of initial combustion for the engine. 
         [0018]    Preferably, the minimum cross-sectional area zone is generally oval shaped as viewed in the direction of gas flow between the pistons. That oval shape has particular advantages when the engine is operated as a diesel engine with direct injection. 
         [0019]    Preferably, the volume of the passage between the two pistons is approximately a third of the compressed volume of the engine when the first piston is at top dead centre (TDC). Such an arrangement is considered to provide benefits when direct injecting liquids so that they premix with a relatively smaller volume of compressed air when compared with the operation of a conventional internal combustion engine. 
         [0020]    Preferably, the oval shaped zone is fitted with a pintle projecting thereinto which is adapted to retain heat and aid combustion in diesel engines. Typically, the pintle can be of stainless steel or any other suitable material. 
         [0021]    In a further preferred embodiment, a direct injection of fuel is provided into the oval, shaped zone in the direction of the major axis of the oval shape. Still further, it is preferred that the pintle projects into the oval shaped region along the major axis but opposite to the direction of injection of fuel. 
         [0022]    Preferably, the head of the first piston is shaped as at least a partial complementary fit within the second conical bore such that varying that shape across a range of alternate pistons leads to readily altering the compression ratio of the engine by a change of first pistons. 
         [0023]    Preferably, the top of the second piston, which is inverted relative to the first piston, is shaped as a frustum of a cone adapted to mate with a. complementary conical shape, preferably being a portion of the venturi, at the top of the second cylinder when the second piston is at its TDC. This relationship assists in allowing a thorough mixing of the air and any entrained atomised fuel. 
         [0024]    A small oval shaped chamber of preferred embodiments also allows for establishment of a desirable flame front before the hot gasses force their way out of the oval shaped chamber into the remaining compressed volume within the combustion chamber. The established flame front expands into the expanding conical shape and then into the adjacent first cylinder, as the bottom or first piston moves away from TDC, creating substantial turbulence which provides good conditions for movement of the flame front into the remaining air within the combustion chamber. 
         [0025]    During an exhaust stroke the spent gasses have to again pass through the venturi space between the first and second cylinders and so generate swirl and turbulence as they flow into the second cylinder on their way to an exhaust port revealed by movement of the second piston away from its TDC. 
         [0026]    In one embodiment a particular type of injector under consideration has a spray angle of 155 degrees; a common rail type 30,000 psi pump is fitted. to spray into the zone or chamber between the contraction and expansion so as to generate a fan shaped spray spreading out into the oval shape. A further advantage of the oval shape is that upon movement of air therethrough or thereinto on a compression stroke of the engine, a double swirl pattern may be generated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The present invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a perspective view of a single cylinder engine in accordance with an embodiment of the present invention; 
           [0029]      FIG. 2  is a front elevation view of the embodiment of  FIG. 1  viewed from the inlet port side thereof; 
           [0030]      FIG. 3  is a section view III-III of  FIG. 2 : 
           [0031]      FIG. 4  is a side elevation view of the embodiment of  FIG. 1  ; 
           [0032]      FIG. 5  is a section view V-V of  FIG. 4 ; 
           [0033]      FIG. 5  A is a magnification of the circled section of  FIG. 5 ; 
           [0034]      FIG. 6  is a section view VI-VI of  FIG. 4 ; 
           [0035]      FIG. 6A  is a magnification of the major part of  FIG. 6 ; 
           [0036]      FIG. 7  is an isometric section view of a portion of the engine of  FIG. 1  through the axis of the gudgeon or wrist pin of the first piston of the engine; 
           [0037]      FIG. 8  is an isometric section view of the engine of  FIG. 1 , similar to but orthogonal to the view of  FIG. 7 ; 
           [0038]      FIG. 9  is a side elevation similar to  FIG. 4  with the first or bottom piston at 40° before to dead centre (BTDC); 
           [0039]      FIG. 10  is the section view X-X of  FIGS. 9 ; and 
           [0040]      FIGS. 11-18  are similar to  FIG. 10  but with the first piston at 30°, 20° and 10° BTDC, TDC, and 10°, 20°, 30° and 40° after top dead centre (ATDC), respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    The embodiment shown in the drawings is of a single cylinder pair, direct injection diesel engine  10  having a lower or first cylinder  11 , an upper or second cylinder  12 , an air intake  13  and exhaust pipe  14  disposed either side of upper cylinder  12 . Sprocket  15  mounted on lower or first crankshaft  16  is aligned with sprocket  17  on upper or second crankshaft  18  which controls the opening and closing of inlet and exhaust ports  19  and  20 , respectively, via motion of second piston  21  and rotary porting discs  22 ,  23 . A drive chain (not shown) runs between sprockets  15  and  17  and the drive ratio therebetween is 2:1 for this 4-cycle engine. 
         [0042]    A fuel injector  24  and pintle  25  are mounted within chamber or passage  26  between cylinders  11  and  12  which house first piston  27  and second piston  21 . Passage  26  includes conical contracting portions  28 ,  29  leading from cylinders  11  and  12 , respectively, toward central one  30  defining the minimum cross-sectional area of passage  26 . In this particular embodiment central zone of passage  26  is of an oval cross-sectional shape, as viewed in the direction of flow between cylinders  11  and  12  ( FIGS. 6 ,  6 A), and has injector  24  and pintle  25  disposed in diametrically opposed positions therewithin along the minor axis of the oval shape. 
         [0043]    As shown in  FIGS. 5 and 5A , the first piston is at TDC within cylinder  11  while inverted second piston  21  is similarly located within cylinder  12 . In this position, a boundary of oval-shaped central one  30  within conical contracting portion  29  is at or near the TDC position of inverted second piston  21 . The positioning of second piston  21  relative to first piston  27  may be varied as desired. It is preferred that the TDC position of piston  21  coincides with an adjacent edge of central zone  30  where frusto-conical head portion  31  of piston  21  mates with conical portion  29  of one contraction/expansion of the venturi between cylinders  11  and  12  to provide an approximate sealed region during commencement of combustion. 
         [0044]    From the views of  FIGS. 7 and 8  the maximum and minimum dimensions  34 ,  35 , respectively, of the depth of oval passage  26  as it extends between conical portions  28 ,  29  can he seen. Those dimensions necessarily arise due to the configuration of the intersection between passage  26  and the conical portions  28 ,  29 . In the case where oval passage  26  is replaced by a circular bore the corresponding depth thereof will, in contrast, be a constant dimension. 
         [0045]    In the depicted embodiment the injector  24  is located at the mid-point of minimum depth dimension of passage  26 . This location corresponds to a position of substantially maximum velocity of the airflow within passage  26  during compression while aiding the creation of turbulent flow as the compressed air flows out of passage  26  into conical portion  28  upon movement of first piston  27  away from passage  26  during the power stroke of piston  27  under the action of combustion. 
         [0046]    The embodiment as shown also incorporates a small compressor  33  formed at the opposite end of cylinder  12  to piston  21  and operated by crankshaft  18 . Compressor  33  may be used for a number of purposes and could be employed to supply, say, up to 5% of the air required for the engine. 
         [0047]    Referring now to  FIG. 10  where piston  27  is shown at 40° BTDC, piston  21  is also proceeding towards its TDC with porting disc  23  having or nearly closed exhaust port  20  while piston  21  is yet to cover port  20 . It will be appreciated that steps required to vary the engine timing are particularly convenient due to the ease of repositioning, of the chain drive between sprockets  15  and  17  and/or adjusting the relative positions of or using alternate rotary porting discs  22 ,  23 . In a preferred assembly, discs  22 ,  23  are slidably mounted on splines on crankshaft  18  and secured by thrust bearings. 
         [0048]    In  FIGS. 11-18  it can be seen that motion of piston  21  lags that of piston  27  in movement towards their respective TDC positions while the dwell of piston  21  at its TDC continues from around 10° to 30° ATDC for piston  27 . 
         [0049]    Embodiments of the present invention lend themselves to use of multi event injectors with, say, up to five injections per power stroke. In operating the present embodiment, injector  24  fires a pilot shot at TDC of piston  27  and up to one more shot until piston  27  is 20° ATDC. 
         [0050]    At 20° ATDC for piston  27 , injector  24  tires its major fuel charge with perhaps an after shot to consume remaining gasses. At this time piston  21  is at its TDC with maximum pressure generated within the combustion chamber so allowing achievement of maximum torque by piston  27  as its associated crank arm  32  moves toward a maximum. 
         [0051]    When piston  27  is 20° before bottom dead centre (BBDC) on the power stroke, piston  21  starts to uncover exhaust port  20  allowing exhaust gasses to flow through the venturi between cylinders  11  and  12 . Exhaust port  20  remains open until piston  27  is again 20° ATDC at which time it is fully closed by rotating disc valve  23 . During this phase the intake port  19  has opened via rotary disk valve  22  and piston  21  to allow intake air to be drawn in across piston  21  to scavenge cylinder  12  of spent gasses. 
         [0052]    Intake port  19  remains open until piston  27  is 20° after bottom dead centre (ABDC) whereupon it is fully closed by disc valve  22 . This timing provides maximum opportunity for use of a ram effect created by the pressure drop across the oval shaped zone of the venturi forming part of the combustion chamber. Thereafter compression and combustion follows as described above. 
         [0053]    In the depicted embodiment the compression ratio is 16:1 but it will be appreciated that this arrangement provides great flexibility in designing engines for a wide range of compression ratios as poppet valves are not employed. 
         [0054]    It is possible to have an air-cooled or liquid-cooled engine in accordance with the present invention. 
         [0055]    Notwithstanding that the engine of the embodiment is naturally aspirated it may be provided with a supercharger or turbocharger. 
         [0056]    When using a spark ignitable fuel it may be preferable to have a circular rather than oval chamber linking the contraction and expansion of the venturi between the first and second cylinders. 
         [0057]    Notwithstanding the embodiment described it will be appreciated by persons skilled in the art that modifications and variations of the invention are possible without departing from the spirit or scope thereof as contemplated by the disclosure.