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That is all good stuff. I just did all that on my own plane. We're
all talking Fuel Injected engines, that's for sure. I just did this
write-up of my own experience doing the lean test and all:
http://www.myrv10.com/N104CD/upgrades/20090822/index.html
The problem is, there is one guy in particular who's a friend
of mine and I flew his plane, and analyzed his GAMI curves
and his are probably better than mine (and mine are < .2)
and yet he still can't get even all the way TO peak without
it stumbling. So I'm trying to learn what other effects
to worry about. Timing, Compression, Exhaust, and whatever
else. My compression is 8.5:1, his is 10:1. We have different
exhaust, but both are supposed to be good at exhaust scavenging
and good flowing. Timing he's got to check and verify yet.
The interesting thing is, there are a few other people I'm
talking to who have plenums and circular inlets by
coincidence and they're all having the same problem...stumbling
as they get to 13gph or so...and considering I know the one
guys injectors are flowed well and peak together, I'm getting
curious as to how much of an effect things like Plenum air
pressures and the like will have on injector performance.
Looking for the things OTHER than the gph spread in the
EGT peaks that could cause things not to run at peak EGT or
leaner.
I sure hear you though....LOP can definitely be faster than
ROP when you start dropping off extra fuel stops from the
equation!!!
Tim
Sky2high@aol.com wrote:
Listen up Grasshopper,
1. If the engine is carbureted, you may be out of luck as there is no way to control the F/A ratio in each cylinder. However, you can try step 3 for informational purposes if you have the equipment listed in step 2. 2. You must have an engine monitor and sensors that display (or record) EGT for each Cyl and the fuel flow.
3. Injected engines must perform the GAMI lean test before a "next step." At 75% power (that means at or above 6500 MSL, 7500 if using ram air and KIAS is less than 190, or higher), WOT (necessary to control air distribution when running LOP) . a. Starting sufficiently ROP, lean in small steps (less than .3 gph) and record the EGT for each step for Cyl 1. Continue past peak EGT for that Cyl for about 50F degrees LOP or until ugly roughness.
b. repeat "a" for each cylinder.
c. Check the gph for each cyl peak EGT. If the spread in .3 gph or less, you are done and you should be able to run LOP 20F, 30F, 40F depending on the spread).
4. If the spread is GT .3 gph, you must fix the A/F ratio. A cheap way to start is to provide equal air pressure to each injector - a wee plenum distribution to each shrouded injector) and repeat the Lean Test.
5. if the lean test shows the proper spread, go fly LOP (less than 75% power)...................
6. If the lean test fails (GT .3 gph spread), consider different sized injector nozzles (either GAMI or others) for the rich/lean cyls.
Grayhawk can fly a 320 at 8500 MSL, ROP, 9.5 gph and see 195 KTAS or LOP, 7.5 gph and 186 KTAS (all things being equal) thus eliminating a fuel stop at 3.5 hours cause he could go another hour. 195 x 3.5 = 683, 186 x 4.5 = 837, 837/195 = 4.3 + 1 (re-fuel stop time) = 5.3 Duh!
Grayhawk
In a message dated 8/24/2009 2:40:57 P.M. Central Daylight Time, Tim@5000feet.com writes:
Hey guys, I am remembering a long time ago reading about
how the air pressure surrounding the injector can affect how
well the injector works. If I'm not mistaken, turbocharged
engines even use some pressure manifold around the injector
to accommodate for the increased Manifold Pressure.
What gets me curious is that I'm having a discussion with some
folks right now who are all having problems running Lean of Peak
and their engines stumble before they get to peak EGT. Between
the group, there are a variety of ignitions such as 2 mags
or 1 lightspeed and one mag, and varieties such as 8.5:1,
9:1, and 10:1 compression ratios, but the one constant is that
they all have what is purported to be a more effective cowl...
the Sam James cowl with a plenum. So I'm wondering if the
knowledge base some of you have would provide any insight
to the issue. I originally was worried that the 10:1 pistons
might make LOP operation harder to accomplish, but perhaps
there is just too much air pressure on the outside of the
injector? The cowl is known to often have too little exit
area, so it could be that the pressure differential is
even too high between the top and bottom half of the
cowl.
Any insight you can give?
Thanks,
Tim
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