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SIX STROKE ENGINE

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					Six Stroke Engine                                                               Seminar ‘05



                                 INTRODUCTION

                We have heard about two and four stroke engines. Two stroke engines
  got its name from the fact that the required strokes are completed in one revolution.
  In short there is one power stroke in one revolution. In the case of four stroke
  engines the four strokes are completed in two revolutions, or there is a power stroke
  in two revolutions. Then how about a six stroke engine. The name of the engine has
  nothing to do with the number of revolutions or anything of that sort. This engine got
  its name due to its construction. A six stroke engine derived its name from the fact
  that it is a mixture of two and four stroke engine. This engine is a radical
  hybridization of two and four stroke engines. This engine combines the top portion
  of two stroke engine and the bottom rather the middle section of a four stroke engine.


                These types of engines have many advantages compared to OHC four
  stroke engines. They are as follows


  1) Increased torque and power output.
  2) Better fuel economy.
  3) Cleaner burning with reduced emission.
  4) Longer service intervals.
  5) Reduced tooling costs.


                Six stoke engines were developed in the year 1998 by Malcolm Beare.
  This technology is undergoing tremendous research works for improving the six
  stroke or Beare technology as it is popularly known. This type of engine is not
  commonly available because of two main reasons


  1. This technology is patented by Ducati.
  2. Research works are going on for improvement of this technology.




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Six Stroke Engine                                                                Seminar ‘05




               CONSTRUCTION AND WORKING

                The six stroke engine basically works just like a four stroke engine. The
  major difference is in the construction. The major drawbacks of conventional
  engines were poppet valves, its basic problems being inertia, and inhibiting flow
  especially the exhaust valve hot-spot in the combustion chamber. So a six stroke
  engine was simplified with the objective of improving efficiency and increasing
  performance compared to a conventional engine by overcoming the drawbacks of
  poppet valves, by means of a rotary valve application to four stroke engine. Of
  course, a two stroke doesn't suffer such problems as it had no poppet valves. So these
  drawbacks were resolved by taking the basic components of a rotary disc induction
  two stroke engine, and grafting them on to a four stroke to produce the best of both
  worlds.


                Below the cylinder head gasket, everything is conventional, so one
  advantage is that the Beare concept can be transplanted onto existing engines without
  any need for redesigning or retooling the bottom end. But the cylinder head and its
  poppet valves get thrown away. To replace the camshaft and valves, Beare has
  retained the cam drive belt and fitted an ultra short-stroke upper crankshaft complete
  with piston, which the belt drives at half engine speed just as it previously drove the
  cam. This piston drives up and down in a sleeve, past inlet exhaust ports set into the
  cylinder wall, very much like on a two-stroke: these are all exposed during both inlet
  and exhaust strokes. This being it's only function, the rotary valve is lightly loaded,
  reducing lubrication and sealing problems.


                During the compression and expansion strokes, the upper piston seals
  off both ports, leaving the pressure contained between the two pistons, with the
  lower one a conventional flat-top three-ring design, while the conical upper one (so
  shaped to aid gas flow during both inlet and exhaust cycles by guiding it towards the
  ports) has two rings - one compression, one oil. In the combustion phase, twin spark
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Six Stroke Engine                                                                 Seminar ‘05
  plugs provide ignition via the stock Ducati CDI and a pair of Harley coils - one per
  cylinder - and not only does the engine run on pure petrol (no need to add oil,


  because all required surfaces are positively lubricated, in spite of the application of
  two-stroke technology), it's also happy on low octane unleaded fuel. Obviously there
  are no valve seats to suffer from lack of lead, and Malcolm says the compression
  ratio can be increased significantly from the Ducati motor's 10.6:1 quite safely
  because of the lack of hotspots, without problems with detonation.


                So now the claimed advantages of all this start to come to light -
  allowing a higher compression while still happy with low octane unleaded make this
  an efficient and cleaner engine. There are no poppet valves to float or bend. This is a
  much more cost-effective way of achieving this than expensively machining a set of
  closing rockers for all the valves in a cylinder head, quite apart from the unwanted
  inertia such a system still entails. But there are other, much more significant apparent
  spin-off benefits from the Beare design.


                First of these is fuel economy: Malcolm Beare claims his engine is 35%
  more economical at low revs/throttle openings than an equivalent conventional
  engine and 13% less thirsty at high rpm/full throttle, in spite of the doubled-up carbs.
  That should mean fewer hydrocarbon and CO2 emissions, because you're using less
  fuel to achieve the same performance. Ducati-based prototypes Beare discovered the
  six-stroke version produced the same torque as a four stroke 1,000 rpm lower down
  the scale, as well as producing exponentially more torque as revs rose.


                But in a commercial application, perhaps the most attractive benefit is
  the reduced number of moving parts, compared to a four stroke design, so the six
  should be cheaper to make. Not as few as a two stroke, but what you appear to be
  getting here is improved performance and torque, coupled with the inherent
  advantages of a four stroke, on the cheap. Finally, as the upper two stroke piston is
  driven at half engine speed, it should have twice the life of the lower four stroke one.



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Six Stroke Engine                                                                 Seminar ‘05


                      DISCUSSION ON THEORY

                According to the theory more torque is derived if the upper piston drive
  is advanced in relation to the main crank. This would be so if all other factors remain
  constant. Advancing the upper piston drive has detrimental effects on valve timing,
  combustion chamber volume and rate of change in volume during the combustion
  period and total engine volume.


       1. Valve Timing. The effect is to open the exhaust port earlier, reduce the
          amount of valve overlap and close the intake port earlier. Opening the
          exhaust port earlier means that the expansion stroke is effectively shortened
          and less energy is extracted. Reducing the amount of overlap does not allow
          enough time for intake to clear the combustion chamber and the exhaust
          extraction effect is reduced. The earlier intake port closing reduces charge
          filling and volumetric efficiency.


       2. Combustion chamber volume. It is effectively increased thus lowering
          compression ratio. The rate of acceleration of expansion is faster in the earlier
          periods, contrary to the ideal of a constant volume during combustion.


       3. Total Engine Volume. The effect is to reduce change in volume during
          intake and compression and increase expansion and exhaust, thus reducing
          volumetric efficiency of intake.


                If we do advance the timing we would have to compensate in the design
  of the engine by
  1)    Reducing combustion chamber volume.
  2)    Raising exhaust port lower lip to provide later exhaust opening.
  3)    Lowering intake port lower lip to provide later intake closing.
  4)    Altering disc timing to allow later exhaust port closing.


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                        NON-PARASITIC DRAG

                In practical tests, actually retarding the upper piston drive has a positive
  outcome on power output and efficiency largely because it effectively increases
  compression ratio, reduces the rate of change in volume during the combustion
  period, opens the exhaust port later, increases the period of valve overlap thus
  utilising the exhaust extraction effect and closes the intake port later. The negative
  effect of this is to increase the amount of energy input to the head, but this is more
  than compensated by the positive outcomes.


                The Sixstroke engine is fundamentally superior to the fourstroke
  because the head is no longer parasitic but is a net contributor to - and an integral
  part of - the power generation within the engine. The Sixstroke is thermodynamically
  more efficient because the change in volume of the power stroke is greater than the
  intake stroke, the compression stroke, and the exhaust stroke. The compression ratio
  can be increased because of the absence of hot spots and the rate of change in
  volume during the critical combustion period is less than in a Fourstroke.The
  absence of valves within the combustion chamber allows considerable design
  freedom.




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              THERMODYNAMIC ADVANTAGES




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                Referring to the graph, the intake begins at 0 degrees on the X-axis. The
  effect of the additional volume changes that the upper piston has on the volume of
  the engine is all positive from a thermodynamic point of view. If the engine were a
  normal 4 stroke the cylinder capacity would be 340cc. Of note - maximum volume at
  the end of the intake stroke occurs at 173 degrees instead of 180 degrees- the change
  in volume is 308cc which is less than a 4 stroke (340cc), yet the total volume at the
  end of the intake stroke is 415cc as opposed to 375cc for a conventional stroke.


                This means that the extra volume is best swept by gas velocities and not
  mechanical movement, and therefore mechanical input energy is less. Also,
  maximum volume is before bottom dead centre 173 deg. Consequently valve timing,
  if the same as a four stroke, is more radical and is of longer duration in relation to
  engine volume and hence volumetric efficiency is considerably improved.


                The change in volume during the compression stroke is slightly greater
  than a four stroke after the ports are closed. The expansion stroke is much greater
  than a four stroke; both from TDC to BDC and from TDC till the exhaust port is
  open. It is possible to leave the opening of the exhaust port later than in a four stroke
  because maximum volume is not reached until after BDC (-548 deg), instead of 540


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  deg. Hence the six stroke system is better from a thermodynamic point of view
  because more energy is extracted from the expansion process.


                During the critical combustion period the rate of change in volume in
  the six stroke is less than a four stroke. Minimum volume is not reached until after
  TDC, at 361 deg. This is because of the phasing of the upper piston. It is retarded in
  reaching its TDC until 20 deg. after TDC (380). This is much better from a
  thermodynamic view in that combustion occurs at a more constant volume; hence
  ignition timing is not as critical as in a four stroke. There is room in the combustion
  chamber for up to four spark plugs and two direct injectors if needed.




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                The change in volume during the exhaust stroke is less than a 4 stroke.
  This means that the negative pumping work is less than a 4 stroke. Extractive gas
  velocity is very important. Easily accomplished at T.D.C. with a fully open exhaust
  port. The design can cope with various runner diameters and lengths because the
  reed valves allow any positive pressure pulses to pass through and cancel any
  negative ones, as well as providing good secondary atomisation. Hence at low revs
  the long thin runners are in tune and at higher revs the shorter fatter ones take over
  with no need to shut down the long thin ones or visa versa as would be necessary
  with a normal 4 stroke. Swirl is in one direction at low revs and moves to tumble
  when the flows are in balance reverting to swirl in the other direction as the short fat
  ones predominate. A good spread of torque is achieved.




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Six Stroke Engine                                                                 Seminar ‘05


                        CONSTRUCTION ISSUES

                The mass of the reciprocating parts in the head is about the same as a 4
  stroke but the accelerations are much slower so energy absorption is less. The piston
  speed of the upper piston is about a quarter of the main piston; therefore its service
  life should be at least twice that of the main piston. There are no service adjustments
  necessary. There are no valves to drop or get hit if a timing belt snaps and the
  effective rev limit is only what the main piston will stand. The design has similarities
  to the Atkins and Miller designs in that the expansion stroke is larger than the intake
  stroke.


                Per single cylinder the number of parts in the Beare design head is
  fifteen compared to a single overhead cam 4 stroke of approx. 40 to 50 parts. The
  design also allows the production of a single piece engine (i.e. head cast with the
  block) further reducing machining and therefore costs. The tips of the reed valves
  are positioned close to the intake port windows, thus achieving a similar result to
  variable cam timing. At low throttle & revs the petals only partly open and keep gas
  velocity high .At full throttle & high revs they fully open to allow maximum flow.
  The exhaust disk does not touch anything and is only subject to sub-atmospheric
  pressure, not gas flow; and therefore its service life is practically infinite. The
  exhaust valve is a piston port.


                The simplest layout for car engines is the flat 4 or V4, with internal
  central chain drive to the heads. This layout allows access to 3 sides of each cylinder,
  with exhaust discs each end of the motor and reed valve blocks both sides of each
  cylinder. For in-line layouts the drive chain or belt is at the end with a row of
  exhaust disks down one side and a row of intake disks or reed blocks down the other
  side. A right angle drive is taken off the drive chain with a very light internal drive
  chain to the disks, or a direct drive is taken off the drive chain with light right angle
  drive at each disk.


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  The design with 4 intake ports fed by 2 reed blocks per cylinder allows the use of
  several different intake manifold types:




    1. 4 separate manifolds fed by 4 carburettors or injector bodies, of various length
        and diameters or all equal length and diameter.
    2. 2 separate manifolds bifurcated to each cylinder so that each has its own
        carburettor or injector body, with various lengths and diameters.
    3. 2 separate manifolds bifurcated to each cylinder in turn, so that each cylinder is
        fed by 2 carburettors in turn even though the system has a total of 2
        carburettors or injectors, with various length and diameter runners.
    4. 3 intake manifolds, with 3 carburettors or injector bodies, 1 bifurcated to each
        cylinder with long small diameter runners, the other 2 with short large diameter
        runners.




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  GRAPHICAL COMPARISON OF FOUR STROKE
                    AND SIX STROKE ENGINES




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                                 ADVANTAGES

  1.    The six stroke engine is fundamentally superior to the four stroke because the
        head is no longer parasitic but is a net contributor to, and an integral part of the
        power generation within the engine.
  2.    The six stroke is thermodynamically more efficient because the change in
        volume of the power stroke is greater than the intake, compression, & exhaust
        strokes.
  3.    The compression ratio can be increased because of the absence of hot spots.
  4.    The rate of change in volume during the critical combustion period is less than
        in a four stroke.
  5.    The absence of valves within the combustion chamber allows design freedom.
  6.    A one-piece engine from crankshaft to upper shaft becomes feasible. No head
        gasket.
  7.    The valving is desmodromic.
  8.    There are no valves to drop or bounce.
  9.    The rev limit is only what the bottom end can stand.
  10.   Gas flow on intake increase of 20%.
  11.   No possibility of engine damage if the timing belt slips or snaps.
  12.   Increased torque and power output.
  13.   Better fuel economy.
  14.   Cleaner burning and reduced emissions.
  15.   Longer service intervals.
  16.   Reduced tooling cost.
  17.   Low cost of manufacturing and machining cost due to absence of valves.
  18.   Higher compression ratio.
  19.   Small size.
  20.   Less number of parts.
  21.   High torque at low rpm.


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                                 CONCLUSION

                From the above given data it can be easily understood the Beare
  technology or six stroke engines are the technology for the future. The project is well
  patented and is undergoing heavy research works. Any product takes time to
  establish itself in the market. Six stroke engines with all the desired qualities of a two
  stroke and four stroke engines will be hitting the market soon. From the above given
  data it is clear that six stroke engines are better compared to two stroke and four
  stroke engines. It is sure that six stroke engines will surely be the main stay of
  automobiles in the near future.




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                                 REFERENCE

               http://www.grc.nasa.gov/WWW/K-12


               http://www.bearetechnology.com


               http://www.sixstroke.com


               http://www.howstuffworks.com


               http://www.wikipedia.com


               Autocar India, 2005 Edition July




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                        ACKNOWLEDGEMENT


                I express my sincere gratitude to Dr. T.C.Peter, Head of Mechanical
  Engineering Department, on this occasion for his suggestions in the selection of this
  topic and the presentation of this seminar.


                I also take this opportunity to express my sincere thanks to
  Mr. Alex Bernard and Mr. Krishna Kumar T.S., for their valuable advice and
  guidance in completion of this seminar in its pristine form.


                At this juncture, I gratefully remember the moral support and co
  operation extended by my classmates on this seminar presentation. Their active
  participation really brought life to my seminar.


                Heartfelt thanks to one and all.




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                                   ABSTRACT

                Six stroke engines as name suggest does not consist of six strokes. It is
  actually a radical hybridization of two stroke and four stroke engines. From this fact
  this engine derived the name Six Stroke Engine.


                A six stroke engine is actually a four stroke engine in working, but not
  so in construction. It is actually a two stroke in the top part and a four stroke engine
  in the bottom rather middle portion. In a six stroke engine the valves are replaced by
  rotary valves like in a two stroke engine. This gives higher compression ratio, greater
  torque, mileage and cleaner burning. Six stroke engines was invented in the year
  1999, it is undergoing tremendous research works. Hence it is not so common in the
  market. Six stroke engines are used in the field of racing due to its high torque at low
  rpm. Six stroke engines will be commercially hitting the market by the year 2006.




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                                   CONTENTS

  (1)       Introduction                                                   1
  (2)       Construction and working                                       2
  (3)       Discussion on Theory                                           4
  (4)       Non-parasitic Drag                                             5
  (5)       Thermodynamic advantages of six stroke engines                 6
  (6)       Construction issues                                            9
  (7)       Graphical comparison of four stroke and six stroke engines     11
  (8)       Advantages                                                     13
  (9)       Conclusion                                                     14
  (10)      Reference                                                      15




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