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I don't see any problem with the term "vapor lock" itself
- because when the pressure on the pump inlet gets low enough, that is exactly
what happens - sufficient fuel enters a gaseous state to interfere
with the pumping of liquid fuel to the high pressure side. So the term is
not that bad a description so long as we all realize it happens on the Low
pressure (inlet) side of the pump and NOT the high pressure side.
My experience with "vapor lock" showed that by turning my
boost pump on (adding pressure to the "suction " side of the EFI high pressure
pump) eliminated the condition - which again indicates the problem is low
pressure on the inlet side of the EFI pump. If there were liquid
there, it would be pumped, so must be vapor - so the pump is "vapor locked" but,
- not on the high pressure side.
Perhaps we should refer to a more technical accurate
descriptive name , how about "Pump Suck Lock" {:>) - just kidding.
Ed
Sent: Wednesday, August 31, 2011 3:07 PM
Subject: [FlyRotary] Re: CG Products Intake
Manifold
Data point: One of the big aviation engine/fuel injection
suppliers installs -4 lines everywhere in front of the firewall up to the
'spider', on all 4 cyl Lycs (up to 200+ hp) and if memory serves, even on the
6cyl engines (230+ hp). The individual lines from the 'spider' to the cylinders
are so small you'd be hard pressed to get safety wire through them. This is on a
Bendix style injection system using a diaphragm type fuel pump and no return
line after the pump. These systems run at between 15 & 30 psi. Logic is that
minimum diameter line minimizes quantity of fuel that can boil on the engine
side of the firewall.
With minimum diameter lines, as long as the pump
can provide pressure it won't take long to clear any vapor as soon as cranking
begins, or you hit Tracy's 'cold start' button a couple of times. (Vapor in the
combustion chamber is a good thing anyway, right?) :-)
As Al Wick pointed
out, the only place vapor should be a problem is at the inlet to the pump
itself.
Charlie
On 08/31/2011 07:35 AM, CozyGirrrl@aol.com wrote:
Interesting Chad.
The people flying Subes and using autogas were also guessing that
altitude was a factor in vaporlock. We won't be using autogas due to variable
formulation eating up epoxy tanks.
We were thinking that if the regulator was the last item in the chain and
that the rails were hooked up serially that it would minimize vaporlock and
also a few seconds of the pump running before a hot restart would cool and
clear the rail.
Chrissi
& Randi
www.CozyGirrrl.com
CG Products, Custom Aircraft
Hardware
Chairwomen, Sun-N-Fun Engine Workshop
I recently researched EFI regulation a bit and found something
interesting. Many modern (post-1995) vehicles have "returnless" EDI systems
where the regulator is in or near the tank, not the engine compartment.
It turns out this isn't for complexity reasons, though it does save a
bit. It's for emissions. The heating of the fuel in the engine compartment
transfers heat back to the tank. The tank's emissions do count even though
they're not huge. It's also one less part, hose, and set of fittings to
fail- and get warranty calls on.
To deal with vapor lock they just crank up the pressure to 65 or more
psi. Very effective.
Not at all saying we should do the same, but the purpose is interesting,
no? As well as the vapor lock" solution"...
Regards,
Chad
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