moto me kinitira 6-stroke [Αρχείο]

Todi

23/02/2004, 14:57

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 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

reducing combustion chamber volume
raising exhaust port lower lip to provide later exhaust opening
lowering intake port lower lip to provide later intake closing.
altering disc timing to allow later exhaust port closing
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.

basizetai ston Kyklo Atkins nomizo.. exei toulaxiston arketes omoiotites.

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Todi

23/02/2004, 15:01

..:hypnotize

Thermodynamic Advantages of the Six Stroke
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 4 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 4 stroke after the ports are closed. The expansion stroke is much greater than a 4 stroke; both from T.D.C. to B.D.C. and from T.D.C. till the exhaust port is open. It is possible to leave the opening of the exhaust port later than in a 4 stroke because maximum volume is not reached until after B.D.C.-548 deg. Instead of 540 deg. Hence the 6 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 6 stroke is less than a 4 stroke. Minimum volume is not reached until after T.D.C., at 361 deg. This is because of the phasing of the upper piston. It is retarded in reaching its T.D.C. until 20 deg. after T. D.C. (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 4 stroke. There is room in the combustion chamber for up to 4 spark plugs and two direct injectors if needed.

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 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.

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.

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.

Market Size
(1) There are 40 auto manufacturers worldwide producing 50 million vehicles annually.
(2) There are approximately 40 million engines produced annually for other applications - everything from model aircraft and lawn mowers to locomotives and cargo ships.
(3) There is also a significant aftermarket for the conversion of existing engines.
(4) It is anticipated that market penetration will begin in a small way in the more specialist sectors e.g.; motorcycles & ultra-light aircraft, leading to quite high penetration in certain sectors. Eventual penetration of the larger market sectors could be considerable over a 10 to 20-year period.

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