"Clive George" wrote in message
...
On 15/11/2016 11:51, NY wrote:
Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

You don't send fuel to the cylinders unless you have direct injection. So
a rotary diesel isn't going to work, but a carburetted petrol engine as
those old rotaries will be fine. The cylinders pull in fuel/air. Since
it's suck rather than blow for that mix, any leaks will result in more air
coming in rather than fuel leaking out, and that's easy enough to cope
with by making the mix a little richer.

Ah, of course. For some reason I visualising the carb on the rotary part,
but if it's on the static part, then a normally aspirated engine would suck
the mixture and hence any leakage would be inwards, and air-only.

Do supercharged petrol engines compress the mixture, or do they compress the
air and then inject fuel into the stream between compressor and cylinders?
In other words, can you have non-fuel-injected carburettor
super/turbo-charged petrol engines? Presumably for a rotary engine, as long
as the supercharger is on the rotating part, it still sucks in mixture (so
leakage will be inwards) and then compresses it after the leaky joint.

In either case, you've got the problem of not
being able to have a large (and therefore heavy) air reservoir to store
boost pressure for cases where the throttle is opened on a slow engine
and high boost is needed at a time when the engine can't yet generate it.

Turbos and superchargers have been used for years (pre-ww2), and don't use
air reservoirs in the way you describe. Turbo lag is real, but the get
rounds for that aren't air reservoirs, and the lag isn't terribly long
anyway.

I hadn't realised that. I assumed that all charged engines had a reservoir,
and that it was in the exceptional case of very hard acceleration from low
engine speed (and hence low pressure) that the reservoir became exhausted,
and that this was what caused turbo lag.

I've learned something!