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 . 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 ( fig6 , 6 a ), and has injector 24 and pintle 25 disposed in diametrically opposed positions therewithin along the minor axis of the oval shape . as shown in fig5 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 . from the views of fig7 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 . 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 . 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 . referring now to fig1 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 . in fig1 - 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 . 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 . 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 . 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 . 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 . 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 . it is possible to have an air - cooled or liquid - cooled engine in accordance with the present invention . notwithstanding that the engine of the embodiment is naturally aspirated it may be provided with a supercharger or turbocharger . 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 . 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 .