multi fuel 101

[hummin2london]

I'm looking for a primer on the multi fuel. Could somebody explain exactly how the FDC, etc. work? I did a bone head thing; trusted the fuel gauge. The truck stopped abruptly with a 1/4 tank showing. Open the lid and viola!, about 1/2 inch in the bottom of the can. No diesel on the base so I put in about 20gals of petrol. It started right up (ran a little funny but okay) and then put 25 gals of diesel in it.

THis is the kind of thing that should go in m35 faq.

Cheers!

 

[cranetruck]

Cole, how is this for an explanation:

The fuel viscocity compensator is located on the top rear portion of the IP.
A piston within the unit moves in accordance with the fuel pressure acting on it. The fuel pressure in turn varies as its viscocity varies. A lighter fuel (gasoline) will produce a lower pressure as some of the less viscous liquid will easily bypass the piston. A heavier fuel (diesel #2), will produce a higher pressure as less is bypassing the piston.
The piston sets the maximum fuel delivery to the injection pump.
The end result is that a fuel with lower heating value (BTU/gallon) will be delivered in higher quantity keeping the power output of the engine constant for a given position of the throttle.
The size of the orifices will change as the temperature of the fuel changes, so heating the fuel to lower the viscocity wil not alter the end result.
This works well for the four fuels specified in the manuals, diesel #2, Diesel #1, kerosene and gasoline. For these fuels, the BTU/gallon is directly proportional to the viscosity of it.
A common misconception is that ANY fuel can now be used and since the engine has a FDC the power output stays constant. Not so, biodiesel, for example has a lower heating value than diesel #2, but is more viscous, therefore the FDC works against biodiesel, delivering less fuel when it actually should deliver more for a constant power output.

Hoping this will help,
Bjorn

 

[hummin2london]

Cole, how is this for an explanation:

A common misconception is that ANY fuel can now be used and since the engine has a FDC the power output stays constant. Not so, biodiesel, for example has a lower heating value than diesel #2, but is more viscous, therefore the FDC works against biodiesel, delivering less fuel when it actually should deliver more for a constant power output.

Hoping this will help,
Bjorn

That is the best explanation I've seen after much searching. Thank you very much indeed! I've had lots of questions as the viability of biodesiel and now I have a better understanding. So, here in the land of fish and chips, free used chip fat wont do me much good I see

Oh well. Out of curiousity, do you know if the IP is man enough to deal with veg oil (read: free chip fat) without the compensator? I'm not that wrapped around the idea but I know folks who are.

Cheers!

 

[cranetruck]

Absolutely. The IP works just fine w/o the FDC. The FDC only finetunes the fuel delivery. When using veggie oil, the ambient temp becomes a BIG factor (actually for biodiesel too). Veggie oil and BD will begin to cloud at 40F. Must be heated or mixed with diesel. gasoline or kerosene for colder temps.
I'm playing with mixtures of gasoline and/or kero to lower the viscocity and to fool the FDC.

Bjorn

 

[SixBuy]

Bjorn, I'll bet you know the answer to this one also. My IP is tagged that the FDC has been disconnected to avoid oil dilution. How does the fuel wind up in the crankcase? Is that a universal problem worth being concerned about? And if it's a problem, I wonder if the unwashed BD is detrimental to the seals...

 

[ken]

I've had to run gasoline when i couldn't find diesel. It works, but it's not something i would like to do often. You do what you have to in a emergency. I sudjest you get a jerry can and keep it full of diesel. And if you have to use gas, then you can mix it with 5 gal of diesel. Your engine will be much happier!

 

[cranetruck]

I think there is a greater chance for fuel to end up in the crankcase by it sneeking by cold piston rings. I have had two lab oil analyses (pl?) done over the years and no fuel has been detected in the oil (My fdc in not bypassed).
The fdc is sealed from the rest of the IP governor housing except for the 1/4" piston rod shown in the image below. Any fuel leaking past the rod would end up in the governor housing below it. The IP itself has no direct connection with the crankase oil, it's lubricated by the fuel.
Guess I don't know what they are talking about, look at the image and see for yourself.

Bjorn

 

[SixBuy]

Makes sense to me! Looks like the piston rod is well sealed. Here's the decal Tooele put on the oil filter can: