On Sun, 17 Feb 2008 09:23:24 +0900, Bernd Felsche
<bernie@[EMAIL PROTECTED]
> wrote:
>If an engine is really working at compressing and breathing in, then
>there are some power losses. The valve operation needs to be
>optimised for the cylinders not producing nett power; e.g. opening
>inlet valve during most of the nominal compression stroke keeps that
>power loss to a minimum.
I would have instinctively said that it would be less problematical to
use the exhaust valve, but on reflection, it sounds like some
experimentation is in order to find the answer.
> Another possibility is to simply not open
>inlet or exhaust valves on "idle" cylinders; allowing the contents
>to (ideally) work as "air springs". The problem with that is that
>there will always be some leakage so it won't work for all that many
>consecutive cycles.
I think so. But with full valve control, an optimum sequence of
opening and closing might be found.
>A different regime is to use the compressed air from the idle
>cylinders to super-charge the power cylinders; even to the extent of
>going "two-stroke" on the power cylinders with the idle ones also
>assisting to scavenge by blowing and sucking. The valvetrain to do
>this becomes very complicated; especially in engines where the role
>of each cylinder isn't fixed.
That's a really cunning idea that I hadn't considered.
>Some of the real-world constraints come into play; things like
>keeping the cylinder block at a fairly even temperature so that the
>gaskets don't break. So the cylinders actually producing power need
>to be changed i.e. the "power" cylinders aren't fixed and what is
>an "idle" cylinder can be a power cylinder on the next cycle.
Or use a different construction, with separate pots or sub-blocks for
the different groups. This would be heavier and more complicated,
but might have some advantages, especially if different cylinder sizes
are used for the different roles ( of course, creating other
problems).
--
Cheers
Paul Saccani
Perth, Western Australia.
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