Paul Lamar:

On a rotary it is not a good idea to let the raw fuel drain
into the intake as it could cause hard starting and seal
sticking. It is an absolute no no in an RX8 engine as it
is guaranteed it won't start regardless if the apex seals
stick or not.

Would this post-shutdown fuel seepage problem be solved by having the
fuel pumps on their own pullable circuit breaker, and having a shutdown
procedure that involves pulling that breaker while at idle?  This would
permit the fuel rail pressure to be relieved at shutdown, making the
injectors less likely to seep.  It's also very reminiscent of how
Lycosaurs are shutdown; is that good or bad? :-)

Russell Kent

Russell,

I think you would find that the pressure regulator would keep the fuel rail
pressurised so a leaky injector would still present the dripping. A return
to tank fuel line just ahead of the regulator might work though, just open
it at shutdown and close it for start up. A small orifice in the end could
minimise the risk in the advent of accidental opening in flight.

John

I don't think leaky injectors are the real problem. Any injectors
mounted out near the ends of runners are going to have a certain amount
of raw fuel on the inner walls when not running flat out. Particularly
when idling. The air flow is minimal and the tubes are cool due to
evaporation.  This fuel must go somewhere. In rotary you don't want
a lot of it going into the engine after you shut it off. You might as
well accept the fact there will be raw fuel and collect it up and 
drain it back into the fuel tank. The advantages of running the injectors
on the ends of the runners are several. One; BSFC is slightly better. Two;
it is some what trivial to mount the injector in a rectangular
plenum opposite the end of the runners. This is mostly a cost issue.
It is expensive to weld, machine and align the injector holders in the
runner walls. Three; injectors so mounted have a response problem
so they are not used in cars unless the runners are extremely short
as used in 18,000 RPM tiny Formula One engines. Not an issue in
aircraft engines.

On the other side of the coin an injector in the rotor housing pointing
straight down 90 degrees to the runner axis has a problem with
mixing. Mazda got around this to a certain extent in the 2nd gen
primary port  by using a tiny plastic screen in the runner.

They fixed it in the RX8 by mounting the injectors at an acute
angle in the runners them selves.

There will be raw fuel! Deal with it.

Paul Lamar
 
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