 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
frans(at)privatepilots.nl
Guest
|
 Posted: Tue Jul 31, 2012 5:08 am Post subject: Proposal fuel system enhancement for mogas |
 |
|
Ok everyone,
After my recent problems with mogas I digged into this subject and it
looks like that with some minor changes the Rotax 914 fuel system can be
made more suitable for mogas.
There are two problems with the use of mogas concerning the Rotax 914:
1) Vapor pressure.
The boiling point of mogas is often lower than that of avgas. With
higher temperatures and lower pressures (altitude) the fuel vaporizes
inside the fuel system. It starts with small bubbles, but eventually it
leads to a complete stoppage of the fuel flow (vapor lock).
2) Ethanol.
Ethanol in the fuel can bind water and keep it in suspension. At lower
temperatures (like after climbing to altitude) the water can precipitate
out of the fuel. Eventually this can lead to freezing or other water
related problems.
For both problems there are solutions:
1) In the 914, the fuel system is pressurised, and there is a high
return flow of fuel. The pumps are located outside the engine bay.
Consequently, there is almost no heating of the fuel, and bubbles are
transferred back to the fuel tank because of the return flow and
pressure regulator.
There is one weak point, and that is the fuel pump inlet. The suction of
the fuel pump causes a pressure drop in the inlet, especially if the
inlet system contains a fuel filter. The drop of pressure invites the
fuel to vaporize instantly. Once vaporized, it will not easily revert
back to a liquid state, even if the pressure is increased again.
In cars, to minimeze vapor lock problems, fuel pumps are often located
inside the tank, to eliminate/minimize the suction (low pressure) area.
In the 914, I think a good solution would be to install a high flow/low
pressure pump at the main tank outlet, combined with a bypass check
valve. Such a pump will eliminate the flow resistance of the fuel valve,
the filters, the hoses, the various joints, and thus eliminate the low
pressure area. If the pressure in the entire fuel system is kept higher
than in the tank, the fuel will not vaporize.
Should the pump fail, the bypass check valve will allow the system to
operate as before.
I found this on ebay:
http://www.ebay.com/itm/320954771747
"THIS PUMP IS A FREE FLOW the solenoid pump uses a piston actuated by
an electromagnetic coil to generate fuel pressure and flow. By using
only short pulses of electricity, the solenoid pump is very
energy-efficient. It is also long-lasting, with no internal rubber parts
or bellows to wear out."
2) The precipitation of water out of the fuel can be prevented by
keeping the fuel on its initial temperature. If, before the flight, no
water can be found at the bottom of the tank, no water will form if the
fuel is kept at the same temperature.
For the Rotax 914, the fuel return line flows at least 30 liters per
hour. Heating this fuel should be sufficient to prevent the fuel from
cooling down at altitude, especially if the return line enters the tank
at the bottom. The easiest way is to install an electrical fuel heater
with thermostat as often found on diesel engines. Another way would be
to use the coolant as a heat source, via a thermostatic valve and heat
exchanger.
Heating the fuel may look a contradiction to 1) where we want to prevent
vapor lock. However if the fuel is not heated but merely kept on the
take off temperature, vapor lock should not be an issue. It the fuel
temperature was good enough for a full power take off, it certainly is
enough for maintaining cruise power.
On Ebay I found this:
http://www.ebay.com/itm/120928913405
Any comments or further ideas on this subject?
Frans
| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Europa-List |
|
|
|
| Back to top |
|
 |
JonathanMilbank
Joined: 14 Apr 2012
Posts: 391
Location: Aberdeen area
|
| Posted: Tue Jul 31, 2012 2:10 pm Post subject: Re: Proposal fuel system enhancement for mogas |
|
|
An apposite saying "If it ain't broke, don't fix it !"
The UK CAA advice for use of mogas has worked very well for me for more than a decade:
1) Don't fly above 6000 ft p.a. with mogas
2) Don't fly if the temperature of fuel inside the tank exceeds 20C
3) Don't use mogas if alcohol can be detected in it
| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Europa-List |
|
|
|
| Back to top |
|
|
neveyre(at)aol.co.uk
Guest
|
| Posted: Wed Aug 01, 2012 12:11 pm Post subject: Proposal fuel system enhancement for mogas |
|
|
Jonathon's point 3]
No chance of that where he lives [Scotland], the natives would never put anything in fuel that could be drunk !
--
| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Europa-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
