Message-ID: <015f01c44c4c$5d73c470$0202a8c0@eric>
From: "Eric Ruttan" <ericruttan@chartermi.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-130075@logan.com>
Subject: Re: [FlyRotary] Re: Turbo boost limits in the EC2
Date: Mon, 7 Jun 2004 01:00:30 -0400

> >>>>Cutting fuel till the MAP comes down is the only workable solution I
can
> >>>>see.
> >>>Yes, I tend to agree. Tracy - are you listening? Does this make sense
to
> >>>you?
> >>>Anyone else care to comment? I'd really like to get something built
into
> >>>the EC2....soon.
> >>>Regards,
> >>>John
> >>Again, - I'm speaking auto use - you have to be very careful using fuel
> >>cut in a boosted rotary, all it takes is a couple of hard knocks
> >>instigated by a transient lean condition to break apex seals. There's
> >>plenty of fuel coating the inside of the manifold, etc., to do this even
> >>if you shut the injectors completely off. It's a very short phenemenon
> >>but it is there. Another thing - hard fuel cuts are scary in a car, I
> >>would imagine the soiled underwear factor is quite a bit higher while
> >>flying when you hit cut. I use hard fuel cut as a rev limiter in my NA
> >>and it STILL gets my attention. That said, I believe Tracy's ECU manages
> >>spark as well as fuel. Random spark cut and/or massive retard may be the
> >>way to cut your boost in those temporary situations.
> >>    -Mike
> >Hi, Mike....my concern is that if you cut spark, and still have fuel
going
> >into the engine, you may end up with a flooded engine, or worse yet, a
> >terrific backfire due to the excessive fuel build-up then reintroducing
> >spark.  I used to take my 1960 Ford, coast down a large hill with the
> >ignition off (standard transmission in gear), then turn the key back on,
and
> >scare everyone with the loud backfire. Did that until I blew my muffler
> >right down the seam one day.  Got too expensive for a 16 year-old
(expensive
> >firecrackers).  Just another consideration.  Paul Conner, MicroTech ECU
with
> >fuel cut boost limiter.
> Good point, Paul. I do know that some aftermarket ECUs do the random
> spark cut thing as a soft rev limit. I have no experience myself with
> that scheme other than getting grounded for a month after doing the key
> off/coast/key on/kablam thing with my father's 1972(?) Torino, blowing
> most of the exhaust system apart. :-) I'm wondering if a closed exhaust
> (cat, restrictive muffler, etc) is necessary for the exhaust backfire
> scenario? The hard fuel cut may be the least worst method of emergent
> excess boost management now that I think about it some more. I would
> think that the lean transients could be minimized if not eliminated by
> injector placement. In the irons, as stock, is a great place to address
> the lean transient thing. I have a 20" intake tract on my car with the
> injectors at the TB - there's enough wall wetting in that system to run
> the engine for a good 2-3 seconds after I kill the FI electronics. The
> stock / near port placement of injectors would not/ does not do this
AFAIK.
>
>      -Mike

First of all if you cut fuel you will not have a "lean transient".  Lean is
still 16:1.  If you got enough fuel in you intake to get that ratio, you
need to fix that first.

Cutting fuel will force an unburnable lean condition, immediatly.  Which is
what you NEED to have happen.  There is simply no other choice but a hard
fuel cut.
Remember this is an emergency situation.  If you get over the max boost
threshold you are already in a all bets are off situation.  A hard cut is
called for.
The thing required before this happens is a knock sensor that retards timing
to cut the detonation off at the pass.
I agree with tracy that he dont need a bunch of gadgets cluttering up his
elegant and simple design, but thats one that turbos need.

If I was Rusty I would now mention that An electronic waste gate controler
would be cool.

But I am not