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WELCOME BACK TO: THE SIX STROKE ENGINE DISCUSSION PAGE 15 FEB 2011
As you may know; my website has been off line and mute since early 2008, postings on discussion including my latest inventions and findings will soon re-commence as we progress towards finite analysis and testing.
Meanwhile, please note that the below posted commentary is of many years ago and does not include discoveries, inventions, or revelations emerging of recent years.
(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
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.