Plantoil/diesel conversion basics
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danalinscott

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Modern diesel engines are designed to use diesel fuel. 
Many are durable enough to run on "off spec" fuels but their useful life will be shortened by doing so. VO and WVO are clearly very different from petrodiesel and must therefore be considered VERY "off spec" fuel.  Even when  converted using the best information and conversion components available SOME engines are more likely to have significantly shortened useful life.  

So pick which engines you convert wisely. This is especially true for your first conversion.  Below are some guidelines to help...

1. If possible choose an InDirect Injection (IDI) type engine to convert. These engines have a small "pre-injection chamber" into which the Fuel Injectors inject the fuel. This thimble size chamber is kept very hot once the engine is running by the combustion gasses and so helps prevent large droplets of fuel from entering the main combustion chamber located directly above the piston.  This in turn help prevent partially burned droplets of VO fuel from reaching the cylinder walls and being scraped into the piston ring lands (and turning to "coke") each time the piston rises and falls. 

Using an engine with pre-combustion chambers won't guarantee  that piston ring coking won't occur .. but it will help significantly compared to an engine that does not.

This is one of the main reasons that older Mercedes engines have faired better than most other engines after conversion to VO fuel.   *Even very crude conversions work longer when an IDI engine is used but eventually the pre-combustion chamber fills with carbon and ceases to work properly. This can be avoided by either using a state of the art conversion or periodically removing the engines head and cleaning the accumulated carbon from the pre-combustion chamber. 

2. If it is not possible to use an IDI engine choose a Direct Injection (DI) engine that has large diameter cylinder bore and NO electronic fuel controls. Since a DI engine has not pre-combustion chamber fuel droplets have only the amount of time it takes them to travel from the fuel injector tip to the cylinder wall to fully combust.  The larger the cylinder bore the longer the fuel droplet has to combust before it strikes the cylinder wall.  Engineers that design IDI engines attempt to create as much turbulence or "swirl" in the combustion chamber to help the fuel injected evenly mix with the air charge but since they all do that bore size remains the most critical measure of a DI engines ability to survive use of VO fuel for a long time.  Large bore diesel engines also tend to run at a lower RPM. This means that for every mile traveled the engine makes fewer revolutions. Fewer revolutions translate to fewer times the fuel injectors squirt fuel into the combustion chamber and fewer times the piston moves up and down. And this in turn translates to fewer times partially combusted droplets of fuel reach the cylinder walls and are scraped off by the piston rings. A good example of a large bore low RPM engine is the Cummins 12v diesel engines found in Dodge Ram truck prior to 1997.


*3. The engines least likely to survive use of VO fuel long term are small diameter bore DI engines that run at high RPM AND have electronic fuel control systems.  If you are contemplating your first conversion AVOID THESE ENGINES or expect  shortened engine life when you use VO fuel in them. Not only do they have the problem of very short time for fuel droplets to burn up before striking the cylinder wall they have a computer trying to inject exactly the right amount of DIESEL FUEL into the combustion chambers and you will be tasking them with injecting the right amount of VO  FUEL. 

Early efforts to trick the computer controls involved tricking the computer into ignoring the temperature of the fuel being injected. That helped significantly...but to eliminate the problem caused by a computer that "thinks" it is injecting diesel fuel when it it is really injecting VO fuel the entire fuel control program needs to be re-programmed.  The cost of doing the research required to do that would be total well over $100,000 ...which is why no one has attempted to do so yet. 

4. Don't try to add a conversion to an engine that has a high performance package. 

Diesel high performance packages generally increase power by injecting more fuel per stroke. This may increase available horsepower but it also increases the amount of unburned  fuel that reach the cylinder walls and end up carbonizing on the piston rings. 
 
*This is the authors opinion based on "post mortem" examinations of VO fuel damaged engines and discussions with engineers that design diesel engines.
 

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Dana danalinscott@yahoo.com
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