[Diy_efi] returnless and air bubbles
Stewart Prince
sprince at csun.edu
Mon Jul 7 00:15:16 GMT 2003
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We recently tried a returnless system based on the Ford idea, but didn't
have much success on our FSAE car. The Gearotor pump is really hard to
servo control at low flow rates due to friction and the turbine pump
leaks by design (we mounted the pump externally). We then tried a
pump/regulator with a tee between the pump and the regulator which went
to the fuel rail, a return type system with only one line going to
injectors. We put another tee in front of the pump which went to the
low pressure side of the regulator: we did this to avoid welding a
return bung to the fuel tank. Of course, this is not a good idea as the
fuel is continuously circulating through the pump/regulator and never
returns to the tank, thus putting excessive heat into the fuel. The
experiment was a bust, but we did learn (observe) something: one
student swore he heard "bubbles" in the fuel lines even after we purged
the system and to prove it to me he used clear lines for both high and
low pressure. He was right!! Even when there was no air in the line
going into the fuel pump, the line exiting the regulator ALWAYS had air
bubbles in it. I'm still not sure why this happens....nevertheless,
we're back to a conventional return type system.
Stewart Prince
Professor, Mech Eng
Cal State Northridge
Perry Harrington wrote:
>That's far different than conventional returnless designs.
>
>The conventional design does fuel pump control via closed loop with a fuel
>pressure transducer.
>
>This is how Ford does it.
>
>The way you prime a rail is to hold the injectors open and pump until you see
>pressure.
>
>--Perry
>
>On Fri, Jul 04, 2003 at 08:54:57AM +0100, bill SHURVINTON wrote:
>
>
>>Not per se, just how the rail primes. 'dry' the bypass spring is down, so
>>fuel wont go to the rail.
>>
>>
>>>On Thu, Jul 03, 2003 at 11:56:32PM +0100, bill SHURVINTON wrote:
>>>
>>>
>>>>They've also gone returnless on the fuel rails now. When there is no gas
>>>>
>>>>
>>in
>>
>>
>>>>the system it really looks as if it will never work.
>>>>
>>>>
>>>You mean, if the rail gets air in it?
>>>
>>>
>
>
>
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We recently tried a returnless system based on the Ford idea, but didn't
have much success on our FSAE car. The Gearotor pump is really hard to servo
control at low flow rates due to friction and the turbine pump leaks by design
(we mounted the pump externally). We then tried a pump/regulator with a
tee between the pump and the regulator which went to the fuel rail, a return
type system with only one line going to injectors. We put another tee in
front of the pump which went to the low pressure side of the regulator: we
did this to avoid welding a return bung to the fuel tank. Of course, this
is not a good idea as the fuel is continuously circulating through the pump/regulator
and never returns to the tank, thus putting excessive heat into the fuel.
The experiment was a bust, but we did learn (observe) something: one student
swore he heard "bubbles" in the fuel lines even after we purged the system
and to prove it to me he used clear lines for both high and low pressure.
He was right!! Even when there was no air in the line going into the fuel
pump, the line exiting the regulator ALWAYS had air bubbles in it. I'm still
not sure why this happens....nevertheless, we're back to a conventional return
type system.<br>
<br>
Stewart Prince<br>
Professor, Mech Eng<br>
Cal State Northridge<br>
<br>
Perry Harrington wrote:<br>
<blockquote type="cite" cite="mid20030704011650.A6055 at scarab.apsoft.com">
<pre wrap="">That's far different than conventional returnless designs.
The conventional design does fuel pump control via closed loop with a fuel
pressure transducer.
This is how Ford does it.
The way you prime a rail is to hold the injectors open and pump until you see
pressure.
--Perry
On Fri, Jul 04, 2003 at 08:54:57AM +0100, bill SHURVINTON wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Not per se, just how the rail primes. 'dry' the bypass spring is down, so
fuel wont go to the rail.
</pre>
<blockquote type="cite">
<pre wrap="">On Thu, Jul 03, 2003 at 11:56:32PM +0100, bill SHURVINTON wrote:
</pre>
<blockquote type="cite">
<pre wrap="">They've also gone returnless on the fuel rails now. When there is no gas
</pre>
</blockquote>
</blockquote>
<pre wrap="">in
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">the system it really looks as if it will never work.
</pre>
</blockquote>
<pre wrap="">You mean, if the rail gets air in it?
</pre>
</blockquote>
</blockquote>
<pre wrap=""><!---->
</pre>
</blockquote>
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