SVO, not biodiesel:
The use of drying oils or sem-drying - with linseed and tung being
the most drying (although few would use them in a diesel engine,
given how much more expensive they are that WVO frying oils) and
walnut and soy being less so - is reported to cause polymerization
of lube oils if they migrate into the crankcase. And, as you point
out, any straight vegetable oil can do this if unheated.
Poor atomization of WVO or SVO is the main mechanism that leads to
dilution/contamination of the lube oil - if the fuel-air charge
isn't atomized well enough, the resulting larger droplets don't
combust, and can run down the cylinder walls and into the crankcase
- and if the WVO or SVO is a drying or semi-drying oil,
polymerization will occur. Also, the uncombusted fuel can,
reportedly, cause deposits in the ring lands - the piston ring
grooves - preventing the rings from expanding and contracting as
designed, resulting in an even greater tendency of any uncombusted
fuel to get into the crankcase, and, if the compression rings are
also effected, poor compression results, with even worse combustion.
The vicious circle phenomenon.
And, direct-injection engines are more subject to all of this, since
the pre-chamber in an indirect injection engine helps with
combustion with less-than-perfect fuels.
So, the best way(s) to prevent polymerization of lube oils, are, in
rough order of priority (and in my opinion:)
1. Heat the WVO/SVO. The hotter the better - which is why we use
both coolant and 12V electric. This is even more critical in
direct-injection (DI) engines. 2. Use a synthetic motor oil - they
are less prone to polymerization. 3. Especially with a genset, and
even more especially with a DI genset, don't use drying or
semi-drying oils. 4. As Anton pointed out, run the genset at full
load. Add load if necessary. 5. Use a two-tank system, and purge
well. Bioidiesel is better for purging/cleaning than diesel, so use
that. 6. Pay for periodic lube oil analysis to check for uncombusted
veggie oil. 7. Change the lube oil more frequently with the $ you've
saved by running the thing on free fuel.
Or, in the case of a genset, just run it on good biodiesel.
Craig Reece
Neoteric Biofuels
http://www.biofuels.ca
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