Heat soaked vapor lock is a problem in any closely cowled engine. There are 3 possible solutions, let the heat
out, flush the heat out, or don't let the heat in.
Let
the heat out - I have seen internal hinged flapping louvers on the top of cowls
that fall open from gravity when the engine is at rest. Internal high pressure
forces them closed when the aircraft is in motion. One easy solution you might
try is to open your oil dip stick access door and leave it open during your
turn around.
Flush
the heat out - A metered fuel return line, from the fuel servo back to the main
tank, metered to flow about 4-6 GPH will flush the
fuel system of high temp fuel. And the lower temp wing fuel flow through the
system will cool the servo, lines, and pump.
Don't
let the heat in - The last possible solution is to insulate the fuel lines and
servo. All should be doing this by wrapping the fuel lines in fire sleeve. I
don't know how one could insulate the fuel servo. I also don't know the heat
transfer characteristics of fire sleeve in a heat soaked environment.
Bruce
www.Glasair.org
-----Original Message-----
From: Lancair Mailing List
[mailto:lml@lancaironline.net] On Behalf Of Sky2high@aol.com
Sent: Tuesday, April 10, 2012 4:07 PM
To: lml@lancaironline.net
Subject: [LML] Re: Engine
"surge" issue
Check
for induction system air leaks.
During
the surging, does your fuel pressure display indicate changes in
pressure? How about fuel flow? Fuel flow is typically sensed in the
line that feeds the spider, thus nearer the end of the fuel's trip to the
cylinder. Fuel pressure is typically sensed between the engine pump and
throttle body.
In some
cases you may want to investigate the route from the firewall to the
fuel pressure sensor. That is, thru gascolator/filter, boost pump
and engine pump. The area betwixt the firewall and rear engine baffling
can build up quite a bit of heat because of dead air. You may want to
consider a blast tube on one or more of these components. Fire shielding
all fluid lines is a good thing and protects from radiated heat, but also
retains heat not dissipated by a slow flow of fresh cool fuel (idle
flow). Usually, heat-soaking of the engine pump can occur after a
shut-down and it may cavitate a bit until cooled by the fuel flow.
Usually, turning on the boost pump raises the fuel pressure enough to eliminate
vapor bubble formation or forces such bubbles back into the
fuel. It is serious if that doesn't resolve surging.
Consider
these possibilities and investigate further.
In a
message dated 4/9/2012 10:55:38 A.M. Central Daylight Time, randylsnarr@yahoo.com writes:
Berni,
100 octane fuel boils at a very low temp. Fuel is boiling in the injection
lines when the engine is hot when you are idling. When you are above idle there
is enough fuel traversing the fuel lines to keep them under the boiling point
which is why you only get this this at idle when the engine is hot.
This was explained to me by don Rivera at airflow performance, he designed the
bendix injection system and is the guy who designed the airflow performance
system as well so he knows what he is talking about. This same reason is
responsible for the hot start issues in our fuel injection set ups.
This is normal...
Randy Snarr
N694RS
Sent from my iPad
On Apr 8, 2012, at 8:37 PM, Berni Breen <bbreen@cableone.net> wrote:
> Whenever my GAMI injected IO360 powered Lancair 360 is really heated up,
following a flight and only a short time to cool down (less than 30 minutes)
and restarted, the engine will surge during idle and taxi. Again this
only happens when the engine is hot, has been shut down and restarted.
The issue never occurs when the airplane (engine) is started for the first time
on any given day (super hot day or super cold day).
>
> Since I feel the issue is fuel related I tried leaning and use of the
electronic fuel pump during idle and taxi with zero improvement. The
engine runs very badly with a pronounced surge. If I get on the runway
and give the engine full throttle, the engine will develop good power and lift
off as if there were no issue...that is until yesterday when the engine just
about quit 2000' into my takeoff roll. I aborted the takeoff, did some
high speed taxiing and then took off 3 minutes later (no shutdown).
>
> Today I took off, climbed aggressively to get the engine good and hot and
landed. I shutdown, let the engine sit for about 10 minutes, restarted
and once again experienced the surge during idle and or taxiing. I
removed the upper and lower cowl but am still not able to identify the cause of
my issue.
>
> Clearly I have an issue that is caused by heat affecting fuel. All
of my fuel lines are heat shielded. Can anyone offer suggestions or ideas
that I can try?
>
> Berni
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