Plantoil/diesel conversion basics
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danalinscott

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Reply with quote  #1 
The basic configuration I suggest is





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danalinscott

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The three way valves

This configuration allows the existing diesel fuel supply to the engine to remain nearly untouched. The areas in this closeup show where the two three way valves are connected in the diesel fuel supply and return lines so VO can be routed to (and from) the IP and injectors.



Since the three way valves are located where hot VO is present the least expensive three way valves should not beused. They are not engineered for high temperatures and so a long useful life cannot be expected. Hydraulic valves such as Hydraforce valves should be used instead.  Make certain that the seals and o-rings in these valves are Viton.


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danalinscott

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A restriction must be placed in the line highlighted by the red circle. This prevents an excessive amount of VO from flowing back to the VO tank. 



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danalinscott

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In the diagram below you can see the two 3-port valves.
The one which controls which fuel is supplied to the IP is labeled "A" and the one which controls the the flow of return fuel from the IP and injectors is labeled "B".


The "default" state for both valve A and B is "power off".  That is to say when no power is supplied to the valves the fuel system will "default" to running on diesel fuel.

The diagram below illustrates fuel flow when the valves are in the "default state". Red circles indicate the "non-energized" state of each valve and red arrows indicate direction of diesel fuel flow.

This diagram illustrates fuel flow when the valves are energized. Green circles indicate power being supplied to the valves. Yellow arrows indicate the direction of VO fuel flow.

And this diagram illustrates the flow of diesel fuel (red arrows) and the blend of VO and diesel fuel (blue arrows) that is created during the purge cycle in a two tank conversion.




 


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danalinscott

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Fuel Pumps
 
This conversion has two fuel pumps.
One is the mechanical fuel pump that comes stock with the Mercedes fuel system. This pump operates regardless of which fuel is being used but only supplies diesel fuel to the IP when three way valve "A"  is in a "default" (non-energized) state. The rest of the time diesel fuel is slowly circulated back to the diesel tank.

The other is an electric fuel pump which only provides VO to the IP when both three way valves are energized.


The electric (VO fuel) pump is located close to the VO fuel tank to help prevent air from being drawn into the VO fuel system. Air can ONLY be drawn into the fuel system in sections of the fuel system where a partial vacuum exists and so by operating the majority of  the VO fuel circuit under positive pressure the probability of this occurring is very low. This nearly eliminates the most common problem associated with newly installed VO conversions.


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danalinscott

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Flat Plate Heat Exchanger (FPHE)

The VO fuel system is designed to accomplish two things, heat VO and deliver it to the Injectors. Flat Plate Heat Exchangers are capable of heating VO to very close to the temperature of engine coollant(140-160F) for a very low initial cost. The majority of the heat added to the VO fuel in this conversion is transferred from the coolant (which has been heated by the engine). When operating properly the engine will create more than enough heat to accomplish this as well provide heat to the cabin, heated fuel pickup, and heated VO fuel lines.





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Heated fuel line
 
Because VO is too thick (sometimes solid) in low ambient termperatures the lines that carry it from the tank to the engine (and back) must be heated. By providing as little as 90F of heat to VO fuel supply and return lines any very thick or solid VO present easily flows through them.

There are three options to accomplish this.
Two basic designs of heated VO/PO fuel lines are in common use today:

HOH - Hose On Hose- Lines that hot coolant flows through are bundled with the line(s) that VO/PO flows through.


and

HIH - Hose In Hose- A line through which VO/PO flows is completely encased in a large line that hot coolant flows through.  
 
Often both HOH and HIH lines are sheathed in insulation to conserve coolant heat. 
 
Of these first two options HOH is usually simpler to fabricate and install and so provides a "cleaner" looking installation for those without experience in bending aliuminum line without kinking it.

The third option uses low wattage resistance wire inside flexible fuel line.  This is significantly easier to install than either HOH or HIH heated fuel line.





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danalinscott

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Heated Filter



As is the case with VO in fuel lines the VO in filters upon start up may be solid ad must therefor be heated so it is liquid enough to easily pass through the filter element. Heated filters designed for use with diesel fuel are not well suited to this task as they usually are thermostatically limited to around 65F. However most "spin on element" filters can be cheaply and easily modified to increase their heat capacity sufficiently for this use by adding a "coolant wrap" around their filter cartridge. This is essentially a coolant heated cylinder that fits tightly around the replaceable spin on element. When an element needs to be changed the "coolant jacket" is slid off the old element and slid onto the one replacing it. A PDF file on how to make a coolant jacket that will fit nearly any spin on filter element can be found HERE.



Many other more expensive options exist some which use coolant heat and some which use electrical resistance heat.



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danalinscott

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Reply with quote  #9 
Heated fuel pickup



Because VO fuel can be too thick (even solid) to flow from a fuel tank at cool ambient temperatures a heated fuel pickup must be empoyed to liquify it. This can be done using either coolant heat or electrical resistance heat. Electrical resistance heat is the best option IMO since it makes installation much easier and can be regulated to prevent the contents of the VO fuel tank from getting hot enough to cause rapid polymerization.

A simple coolant heated fuel pickup can be made from commonly available copper plumbing fittings. The HotRod design has been used for half a decade with no reported failures or polymerization problems but if cost is not a concern you can have a "HotRod" fabricated from aluminum tubing. This design is available for purchase HERE.

Other more expensive options are available.




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danalinscott

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Reply with quote  #10 
VO fuel tanks

The best VO fuel tanks are made of plastic.
And the least expensive tanks tend to be Marine OutBoard Motor Tanks.
There are a lot of options and sizes but I find the 6gallons tanks tend to be easy to find on sale and fit easily into the forward area of Mercedes trunks.


I prefer to use them in a standing position snugged up against the diesel tank using quick release hold down straps..but they can be located nearly anyplace in the trunk and used in either a vertical or horizonatal position.

Since filling them in the trunk inevitably leads to a VO spill (and the bad smell lasts long after the initial mess is cleaned up) I advise leaving a long enough section of heated fuel line to allow the tank to be removed form the trunk and filled while laying on the ground.


There are a lot of other more expensive options.

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danalinscott

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Injector Line Heaters
(and injector line insulation)
 

While the FPHE will raise VO fuel temperatures to around 160F some of that heat is lost as the fuel passes through the IP and Injector Lines. To minimize that loss insulation can be placed around the injector lines. The most flexible foam insulation similar to but much smaller than the foam insulation that is often used to keep home plumbing lines from losing heat.


A more effective approach is to use injector line heaters to significantly raise the temp of the VO in the injector lines. This significantly improves combustion and so will tend to increase the useful life of your engine, stretch your supply of fuel, and create lower tailpipe emissions.




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Under construction
Parts list:
2 - 12v Three way valves (Hydraforce)
1 - 12v Electric fuel pump (4-7psi)
1 - 16 plate FPHE
1 - Heated fuel filter
1 - Heated VO fuel pickup
1 - VO fuel tank
1 - three way dash switch
1 - 12v relay
20-25' heated fuel line w/return
20' 18g insulated wire
Misc. rubber grommets, wiring connectors, and high quality hose clamps

Optional but recommended:
4-6 - injector line heaters
1 - injector line wiring harness
Fuel temp gauge/sensor
Fuel pressure gauge/sensor
Purge buzzer


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danalinscott

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Coolant plumbing

This is what the basic plumbing for the coolant circuit looks like:

The lower loop in the above diagram shows a FPHE installed. This should be done using heater hose so flow is sufficient to allow maximum heating of VO as it passes through the FPHE. The upper loop is the circuit which is plumbed to the heated filter (wrap) and the coolant heated fuel line (if used) and coolant heated fuel pickup (if used). 


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danalinscott

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Reply with quote  #14 
Where to get the parts:

12v Electric fuel pump:
Any auto parts store
(add link) 

16 plate FPHE:
The best prices I have found for FPHEs are at: http://www.dudadiesel.com/heat_exchangers.php

The heated filter:
The simplest and cheapest way to add heat to any diesel fuel filter to adapt it to VO fuel is to use a coolant jacket wrap.
An example of a simple coolant jacket wrap can be downloaded from:
http://vegoilconversions.netfirms.com/newpage1.htmIt can be combined with a CimTek series 200 (10 micron) filter and filter head to make a fairly good heated filter for around $40. These can be purchased together HERE for around $20. 

Heated VO fuel pickup:
Coolant heated fuel pickups can be made using the "HotRod" how to file.
12v heated pickups can be purchased. (add link) 
 
VO fuel tank:**
Plastic marine outboard motor fuel tanks.
Heavy plastic 5 gallon "cubees" that restaraunts get soap and sanitizer in.

The 12v relay**
Any auto parts store


Three way dash switch**
Any auto parts store
A two way (on/off) switch can easily be changed to a (on/on) switch by using a 12v relay.



**Denotes a part that can be "scrounged" or salvaged.


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soshea00

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Reply with quote  #15 
Hi Dana,
I noticed on #3 you mentioned a restriction must be placed on that portion of the loop.  Are you referring to a fuel grade check valve or is there something cheaper/easier?
Thanks,
steve
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