Oh, one more interesting thing.  Some people, me included,

pretended
that

you could improve the rotary's BSFC by going to aggressively lean

mixtures

(some spoke of 21:1 air/fuel ratio...) Well, tests show clearly

that
BSFC

decreases as you lean the mixture until you hit an optimum, then

it increases again as you lean further. This optimum is not too
bad as we
are

down to 0.455 lb/hp.hr at 75% cruise power and believe we still

have a
few

percent to gain.  Of course, fuel consumption decreases as you

continue leaning but, past this optimum, power drops faster. I
want to do a few
more

tests before I release the optimum A/F ratio.  Let's say that it

is definitely on the lean side of peak, but much less lean than I
personally

anticipated.  I'll elaborate an other time on the two combustion

phenomena

(well.. at least two...) that seem to be at work.

Best regards,  Francois

Oh yeah...  Another question on BSFC.  Is BSFC better when running
extremely lean or with the throttle closed, but less lean?  I assume that
running extremely lean hurts BSFC at the point that the mixture is so
lean that a sizeable percentage doesn't get burned at all.

Have people played with direct injection on a rotary - like many of the
2 strokes have been running?  This is pretty neat stuff...  The fuel can
be squirted in right by the plug, which when done properly means that
it has very little chance being wasted down in the squish areas of the
chamber - where it can't burn anyway.  It also has the potential to make
manifold design easier because you don't have to worry about making
sure the fuel stays with the air.

Regards,

Matt-

I think some work was done but fuel vaporization left a lot to be desired
as I recall. Probably a little intake manifold heat would help
the BSFC but must be turned off when max power is needed.

Paul Lamar

Matt, you are correct. Past the optimum I mentioned, extremely lean mixture
hurts BSFC in a BIG way.  The power management strategy yielding the best
overall fuel economy is as follows:  

1. Keep the mixture at its optimum of

leanness and the RPM at the setting yielding the best economy and control
power with the throttle until WOT. 

2. Keeping the mixture at the same best

economy setting, progressively increase RPM to best power, throttle stays
wide open. 

3. With WOT and RPM at best power setting, then enrich the

mixture from best economy to best power.  Watch EGT while doing this as you
will go over the peak and should not stay there long.

We toyed with direct injection.  With gasoline, its benefits are not worth
its cost.  For jet-fuel it is an absolute must, but then we are talking of
very high-pressure injection, "common-rail" technology.  A whole different
ball game.

Francois

 
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