Yesterday my neighbor had to show off his new diesel pickup. It has one of
those trip computers that displays MPG and range so I was interested in
seeing how the fuel flow sensors were set up. By tracing the supply line
from the injector pump it was easy to find the supply side sensor but the
return line, instead of going back to the tank went through a finned cooler,
then into a heat exchanger cooled by the new fuel and back into the supply
line after the flow sensor. That eliminated the need for a second sensor on
the return line which simplifies the net flow calculations, maintains the
fresh and recycled fuel at the same temperature so the density is constant
which further improves the accuracy of the flow measurement and reduced the
load on the filter.

Anyone seen this setup on a boat?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

My Perkins seems to have something similar. The returns from the injectors
go back to the fuel filter. Then another line from the fuel filter goes back
to the
tank. Not sure what is happening but it does seem that the returned fuel is
being
mixed with fresh fuel. The Perkins actually returns very little fuel
according to
the Entec folks. When I was having some initial problems with my genset, the
Entec folks said the Farymann engine is a "full flow return" system and it
returns
alot of fuel (gallons per hour). He said that the genset makes a pretty good
fuel polishing system but filters will clog much quicker than I was used to
if
I have dirty fuel. He said that the Perkins may only return a few
tablespoons of fuel
per hour. Last fall I tried to empty one of my tanks by drawing fuel from
one and returning
it to the other. After an hour of running the engine, there was no
detectable difference
in fuel level in the tanks.

Doug
s/v Calista

"Glenn Ashmore" wrote in message
news:mbNae.33637$Zr.18735@lakeread08...
Yesterday my neighbor had to show off his new diesel pickup. It has one
of those trip computers that displays MPG and range so I was interested in
seeing how the fuel flow sensors were set up. By tracing the supply line
from the injector pump it was easy to find the supply side sensor but the
return line, instead of going back to the tank went through a finned
cooler, then into a heat exchanger cooled by the new fuel and back into
the supply line after the flow sensor. That eliminated the need for a
second sensor on the return line which simplifies the net flow
calculations, maintains the fresh and recycled fuel at the same
temperature so the density is constant which further improves the accuracy
of the flow measurement and reduced the load on the filter.

Anyone seen this setup on a boat?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Glenn Ashmore" wrote in message
news:mbNae.33637$Zr.18735@lakeread08...

Anyone seen this setup on a boat?


My Volvo Penta MD2B, albeit rather primitive and basic in it's design has no
fuel return to the tank either. There is no fuel cooler, the excess fuel
just returns to the outlet side of the filter. All the MD1,2,3 series
engines are this way.

This is my second engine of this Volvo series and initially I found it
surprising and thought there might be problems with the injector pump
handling the returned fuel due to heat and foaming usually found in the
return fuel in other engines.


--
My experience and opinion, FWIW
--
Steve
s/v Good Intentions

Glenn,

I have never seen this on a boat and I might be a tad leary. The fuel
retuen usually stitches along the injectors and then gets the top of the
injection pump and then head back tot he tank.

In the engine test labs that I have run over three plus decades, we have
seen non-condensable gasses (little bubbles) coming back to the the
float controlled level tank typically used in such facilities. I will
not go into what problems that might cause if not removed.

By the By,
Two flow instruments and approriate totalizing equipment is unreliable
largely becuase of the temperature differential of the two streams. It
can be done (we did do it - once), but it requires really expensive mass
flow sensing transducers.

Matt Colie

Glenn Ashmore wrote:

Yesterday my neighbor had to show off his new diesel pickup. It has one of
those trip computers that displays MPG and range so I was interested in
seeing how the fuel flow sensors were set up. By tracing the supply line
from the injector pump it was easy to find the supply side sensor but the
return line, instead of going back to the tank went through a finned cooler,
then into a heat exchanger cooled by the new fuel and back into the supply
line after the flow sensor. That eliminated the need for a second sensor on
the return line which simplifies the net flow calculations, maintains the
fresh and recycled fuel at the same temperature so the density is constant
which further improves the accuracy of the flow measurement and reduced the
load on the filter.

Anyone seen this setup on a boat?

On Sun, 24 Apr 2005 09:30:04 -0400, "Glenn Ashmore"
wrote:

Yesterday my neighbor had to show off his new diesel pickup. It has one of
those trip computers that displays MPG and range so I was interested in
seeing how the fuel flow sensors were set up. By tracing the supply line
from the injector pump it was easy to find the supply side sensor but the
return line, instead of going back to the tank went through a finned cooler,
then into a heat exchanger cooled by the new fuel and back into the supply
line after the flow sensor. That eliminated the need for a second sensor on
the return line which simplifies the net flow calculations, maintains the
fresh and recycled fuel at the same temperature so the density is constant
which further improves the accuracy of the flow measurement and reduced the
load on the filter.

Anyone seen this setup on a boat?


On a boat no: - but I remember the notes of a fellow who converted a
(Fuel Injected) subaru for an experimental airplane. He returned the
excess fuel to the feed line, and was hit by problems that turned out
to be due to the return fuel [GASOLINE not diesel] bubbling when it
hit the low pressure feed. He returned the fuel to the tank, and lived
happily ever after, which was formerly in doubt....

Brian W