by Bernd Felsche <bernie@[EMAIL PROTECTED]
>
Feb 17, 2008 at 09:23 AM
Snapper <snapper_won@[EMAIL PROTECTED]
> wrote:
>RogerM wrote...
>> invent an engine that say, is 6cyl, when on the highway at
>> cruising speed and not labouring (or liberaling) have some kind
>> of device fitted that drops the fuel inlet to say 2 or 3
>> cylinders to conserve fuel and then when the
>I'm still trying to work out how this would be more economical.
You burn less fuel. Spark ignition engines can only operate over a
limited range of air-fuel ratios.
Engines have to feed the 3-way cataclysmic err.... catalytic
convertor with exhaust gases near (~+/- 5%) the stoichiometric ratio
in order for the convertor to convert. So air from idle cylinders
can't be mixed with those from power cylinders because that would
lean out the mixture and prevent some of the conversion.
>Having a number of pistons being thrown about with them not doing
>any work per se surely would be less efficient than if they were
>working normally.
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. 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.
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.
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.
--
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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