Actually, both Meihdert and Glen are correct.
And, if you were to try to subtract the return flow from the supply,
there is a good chance you will get negative fuel flow at low loads
unless the temperature correction is Perfect...(Somebody tried it - Once)

What he can do is get or build a little tiny cooler. Put it in the
return line and then route the return line to the lift pump's fuel
filter and put an upside down empty filter housing after that to collect
bubbles.

This is substantially what we did in any number of diesel engine labs
over the last multiple decades. Or maybe we used a cooler and a
float/level tank (like a giant carburetor float bowl) but this would be
most unsuitable for a boat.

Matt Colie (a Detroit lab rat for a couple of decades)
Lifelong Waterman, Licensed Mariner and Congenital Sailor

Meindert Sprang wrote:
"Franz Eckert" wrote in message
. dk...

Hi there.

Nope, if you make a T piece on the return fuel, you won't need more that
one.
The return fuel is only there because you need a way to get the air out of
your system, once it is out, you can simply return the (return) to your

fuel

system.


I beg to differ. It is my understanding that the return fuel MUST be
returned to the tank, because it is used for lubrication and _cooling_ of
the injector pump. If you return it the way you describe, you'll end up with
a very hot diesel loop.

Meindert

"Glenn Ashmore" wrote in message
news:1pMOe.30$dm.3@lakeread03...
I should add:
As the injectors heat up beyond their design temperature they deliver less
fuel which leans out the mixture. Lean engines run hotter which heats up
the injectors more which heats up the fuel more.

Aren't you mixing up diesel and gas engines now? As far as I know, you
regulate the power of a diesel with the amount of injected fuel, as opposed
to the intake valve of a gas engine. So you cannot have a lean diesel
engine, right?

Meindert

"Meindert Sprang" wrote in message
...
"Glenn Ashmore" wrote in message
news:1pMOe.30$dm.3@lakeread03...
I should add:
As the injectors heat up beyond their design temperature they deliver
less
fuel which leans out the mixture. Lean engines run hotter which heats up
the injectors more which heats up the fuel more.

Aren't you mixing up diesel and gas engines now? As far as I know, you
regulate the power of a diesel with the amount of injected fuel, as
opposed
to the intake valve of a gas engine. So you cannot have a lean diesel
engine, right?

I don't think so. An injector is very precisely machined. As it heats up
the plunger expands. Because it is longer than wide its displacement
decreases so less fuel gets injected. Unless the engine has a sophisticated
EDC that compensated for temperature you will get a leaner mixture. It
can't lean out as much as tightening down a gas carburetor but it does
reduce fuel flow while the same amount of air is being introduced into the
cylinder.

--
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:suOOe.41$dm.31@lakeread03...
I don't think so. An injector is very precisely machined. As it heats
up
the plunger expands. Because it is longer than wide its displacement
decreases so less fuel gets injected. Unless the engine has a
sophisticated
EDC that compensated for temperature you will get a leaner mixture.

I don't understand this. If the injector gives less fuel, won't the engine
simply go down in revs?

Meindert

"Meindert Sprang" wrote
I don't understand this. If the injector gives less fuel, won't the engine
simply go down in revs?

Oops! Small brain fart. You are right. It will reduce power, not increase
the combustion temperature.

--
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:Jb_Oe.513$dm.386@lakeread03...


"Meindert Sprang" wrote
I don't understand this. If the injector gives less fuel, won't the
engine
simply go down in revs?

Oops! Small brain fart. You are right. It will reduce power, not
increase
the combustion temperature.

Phew! For a brief moment I thought I'd lost my understanding of diesels...
:-))

Meindert

In article ,
"Franz Eckert" wrote:

Hi there.

Nope, if you make a T piece on the return fuel, you won't need more that
one.
The return fuel is only there because you need a way to get the air out of
your system, once it is out, you can simply return the (return) to your fuel
system.

If only you had a "clue" about the technology your spewing about.....
The Return line isn't there to bleed air out of the injector lines...
ALL Diesel Injectors are Fuel Cooled, and the Injector Pump ALWAYS
puts more fuel up the Injector lines than the Injector puts into the cyl.
The difference is drained back to the fuel tank via the Return Line.
If you don't have a Return line your going to be spilling the extra fuel
somewhere. Just try this experiment, if you think different....Take
your Return Line and plug it off, to say 60Psi...when your Return Line
fills up, one of two things will happen. Either your engine will stop
running due to overpressure on the injecter Returns, or you will burst
the plugged off Return Line and spew fuel out the break.

Me

Me wrote in
:

In article ,
"Franz Eckert" wrote:

Hi there.

Nope, if you make a T piece on the return fuel, you won't need more
that one.
The return fuel is only there because you need a way to get the air
out of your system, once it is out, you can simply return the
(return) to your fuel system.

I've been watching this thread in amusement wondering when someone would
point out that you need dual flow meters to compensate for the return fuel
flow. From past discussions I seem to recall that it's very difficult to
accurately measure the flow rates as the fuel pulses rapidly as the
injectors open/close which leads to inaccurate readings. I believe that
this is a much more complex problem than it seems from the outset.

-- Geoff

In article ,
Geoff Schultz wrote:

Me wrote in
:

In article ,
"Franz Eckert" wrote:

Hi there.

Nope, if you make a T piece on the return fuel, you won't need more
that one.
The return fuel is only there because you need a way to get the air
out of your system, once it is out, you can simply return the
(return) to your fuel system.

I've been watching this thread in amusement wondering when someone would
point out that you need dual flow meters to compensate for the return fuel
flow. From past discussions I seem to recall that it's very difficult to
accurately measure the flow rates as the fuel pulses rapidly as the
injectors open/close which leads to inaccurate readings. I believe that
this is a much more complex problem than it seems from the outset.

-- Geoff

Actually, it isn't all that complicated, one just has to understand the
mechanics of the diesel fuel system of the engine. I run a 2.5Mwatt
Powerhouse during the summers, and we monitor the fuel useage of all our
BIG Yellow KittyCATS. Years ago I installed calibrated flowmeters in
all the fuel supply lines to each engine, as well as calibrated
flowmeters in each return line just before the checkvalve that leads
back to the Fuel Return Manifold. Each flowmeter has a Electronic
Instrument Output, that feeds a Network Node Processor. Our Monitoring
System reads the pulses out of each meter and subtracts the Return
Flow for each engine from the Input flow to each engine and logs it
on an Hourly Cycle. Not hard to do, it just takes money.

Bruce in alaska who proved to Mgmt that a 3516 uses less than
80% the fuel as two 398's when all are running
at 90% Load.....
--
add a 2 before @

Okay okay okay.
Cool down guys, i stand corected about the return line.

But there has also been some misunderstandig in this thread.

I have at no time mentioned anything about simply closing the return line,
as one mentioned.

As i see it there is two solutions at hand.

1. Getting two flow sensors, where the one mounted on the return line count
negative (if you get my drift).

2. Taking the return line for a spin in some copper pipe to cool it down,
and then letting it reenter right after the flow sensor from the tank.

Tank ---(Flow Sensor)----------------------------Pump
|
|
----Return---With cooling----

But what i don't really understand. How come that many smaller boats
(Diesel) have fairly small tank's, and yet the Diesel does not seem to get
hotter?

I believe you guys, don't misunderstand me.
But it must be possible to do there measuring like i draw in the schematic.

Anyways, i found a counter schematic from vellerman, that can use two
flowsensors. And it is not that expensive, all in all i think the system
would cost me 60 $, lot cheaper that the ready made systems out there.

Unless somebody really has a cheap offer.

Man, i love theese quests for solutions :-)

Wkr
Franz