Fred Writes,
>Here is why I
ask. If you have a good induction air inlet that is getting a high
percentage of the ram air pressure, and smaller cooling air inlet >ports
that do a lesser job at recovering the ram pressure, then it is entirely
possible that your manifold pressure is higher than the cooling air >pressure
surrounding the normally aspirated injectors.
The overwhelming truth
when I made my injector shrouded ram system was consistency. I believe it’s
not a question of how much delta P you are generating but the fact that all
cylinders receive consistent pressure. Remember, #2 on a Lyc is facing
the ram while he #1 injector is blocked by the cylinder, etc. Fred, this
is not a do some testing thing. It is a put it in and cry over how much
leaner and smoother your engine will run. This is the single most
overwhelming improvement to my plane following my Koger canopy shade, Spry
shocks, ok, ok, and my 10:1 pistons, Catto Prop, etc J Trust me I noticed improvement and
I’m not a real analytical guy.
And btw, this requires
no fancy rails or expense. My neighbor just through in a 3/8” tube
feeding a couple reducing T’s to ¼” lines. The ¼”
lines go to the injectors with a little collar and a couple O rings. You
can whittle out the collars or buy’m from Airflow Performance. He’d
like to sell you injectors too but I put my old Lyc injectors in the lathe and
trimmed a few thousandths and it all fits nice.
Larry Henney
2007 SARL Gold J
N360LH
PS: Not an
engineer but stayed at a Holiday Inn Express last night……. No,
really!
From: Fred Moreno
[mailto:fredmoreno@optusnet.com.au]
Sent: Saturday, December 15, 2007
8:00 AM
To: lml@lancaironline.net
Subject: GAMI Injectors - More
questions for Walter
Many thanks to all that
responded to my post. The discussion is most enlightening. And
there is nothing like actual operational experience to correct nebulous
speculations. Thanks also to Walter who pointed out my fuzzy thinking
that was blending atomization and vaporization. They are separate
processes.
More questions:
1) The turbo injectors do
not have screens like the NA injectors do. They have air inlets from an
upper deck reference line. Scott is using those.
Do the turbo injectors
have better air passages that allow them to do a better atomization job than
the normally aspirated injectors, even when installed in a normally aspirated
engine? Said another way, for the same delta P do the screens on the NA
injectors restrict air flow compared to the turbo injectors with their air
shroud and supply line?
2) The delta air pressure is
most important at WOT... A delta P of 3" Hg is adequate to result in
excellent fuel atomization to aid in vaporization. More pressure does not
necessarily make things better.
OK, let’s see what might
be possible with a normally aspirated engine. The ram pressure at 200
KIAS is about 2 inches Hg, give or take. Let’s assume you get 100%
of this for the fuel injector air flow using a nice pitot tube set up like
Scott’s. And let’s assume that the engine induction system
gets about 75% of this for a little manifold pressure boost at WOT, this being
a typical figure for a good diffuser taking in induction air. Then the
difference of 0.5 inch Hg is available for atomization. This is clearly
better than zero, but a lot less than 3” Hg. So might one make
further improvements in atomization by somehow boosting the injector air flow?
(The mind boggles….) Or is 0.5 inches Hg enough at WOT
cruise?
3) Mark wrote: I cobbled together a similar arrangement to
supply ram air to the injector shrouds. I can't say I see a bunch of speed improvement as I'm not one for
careful analytical testing. I can say - the improvement in engine
smoothness when running LOP in high altitude cruise is DRAMATIC.
Please tell us more
about your set up, Mark. Is your engine induction air coming from a
separate scoop than the cooling air? Does your cooling air come through
small inlet ports in the cowl? Which engine?
Here is why I ask.
If you have a good induction air inlet that is getting a high percentage
of the ram air pressure, and smaller cooling air inlet ports that do a
lesser job at recovering the ram pressure, then it is entirely possible that
your manifold pressure is higher than the cooling air pressure surrounding the
normally aspirated injectors.
This “reverse
pressure delta P” would reverse the injector air flow, and may cause the
blue staining that was mentioned around the NA injectors. It would also
cause poor atomization that becomes most evident operating LOP.
But if you now add a
pitot set up like Scott’s, you get more air pressure fed to the
injectors, and you restore the injector air flow to the way it should be
– air flowing into the intake manifold instead of out of it.
Atomization improves and your ability to lean further improves as a
result. Do you think that may have been happening on your plane?
The reason I persist on
this topic is that for those of us using IO-550’s in Legacy or ES (or
rare birds like me, in an LIV) where induction air is coming from inside the
cowl, there may be a lot to learn that could improve our cruise efficiency,
particularly worthwhile with 5 buck avgas.
I see another test
program looming on the horizon…..
Still Curious Fred