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Diesel engines require very
little modification to run on waste vegetable oil (WVO).
At room temperature, WVO is thicker than regular diesel, which means
that it has to be heated before it can flow easily through an engine.
WVO gathered from restaurants also contains tiny contaminants left over
from cooking that can clog and damage engine parts. Therefore a
successful WVO system must have a means of both heating and filtering
the WVO.
We use a combination of
electric heaters and coolant routing to warm WVO up to the required
70°C. Our WVO vehicles start up on regular diesel fuel and allow the
engine to warm up. Coolant lines, which carry heat away from the
engine, are used to heat WVO that is stored in a second tank. When the
WVO gets hot enough, the driver flips a switch, and the engine begins
pumping hot WVO instead of diesel. For small cars in warm climates, the
WVO can heat fast enough to allow switching after only a few minutes of
driving on diesel. However, for a larger engine that operates in cooler
climates, the engine may take a long time to heat up and may never even
reach a full 70°C. Although the vehicles can run on slightly
cooler WVO, the added viscosity puts more stress on the fuel pumps and
injection system and therefore shortens the engine's life.
To speed up heating and
therefore reduce the diesel startup time, we fit a
Webasto coolant heater to our large truck to keep it at full
temperature. This has proven itself down to -25C. We use a Hotfox
combined fuel heater and pickup in the storage tank. It concentrates
energy right where it is needed, melting enough WVO to be easily pulled
into the fuel lines. A coil warms the filter element to minimize the
WVO's resistance through the filter membrane. The filter is placed near
the engine so that the oil has little time to cool before it reaches
the fuel injectors. Nevertheless, another in-line vegtherm heater warm
the WVO along the final fuel path just prior to the engine.
As the vehicle runs,
coolant captures waste energy from the engine and transfers it to
maintain the high WVO temperature. Coolant lines normally route excess
heat from a vehicle engine to the radiator, which dissipates the energy
into the air and prevents the engine from overheating. That radiated
heat is energy lost to the environment and a major source of engine
inefficiency. Our vehicles recycle that energy by routing hot coolant
through various components of the WVO fuel system before allowing
what's left to escape through the radiator. For example, hot coolant
warms the fuel pickup, which makes the oil flow from the tank more
easily and extends the life of the bus's fuel pumps. Similarly, coolant
warms the WVO filter and also passes through a heat exchanger that
transfers energy from the coolant to the WVO before it reaches the
engine. Finally, all WVO lines are bundled with coolant hoses and are
insulated to maximize the area of heat transfer.
Our vehicles still have the
original (bio)diesel fuel system. It not only affords a backup, should
the WVO system malfunction, but diesel is also crucial to purging the
system before the engine is shut off. Over time WVO will gum up the
small openings and moving parts inside an engine if it is allowed to
cool. Therefore, the vehicle is run on diesel for a few minutes before
shutdown to "purge" the system of WVO.
The second major consideration for running WVO is ensuring that it is
properly filtered. During its former life as a cooking agent, WVO picks
up particulates that can damage the finished surfaces inside an engine.
When WVO is collected, it passes through a series of filters and a
centrifuge that block anything larger than 5 microns or 0.0002 inches
in size. The filtering extends the life of components in the fuel
system, especially the primary oil filter, which removes water and
anything larger than 10 microns from the oil. This onboard filter
greatly extends the life of the engine and gets clogged/needs
replacement less often because of the 5 micron filtering before it. Why
does it ever get clogged if the oil is filtered to smaller than the
primary filter? The size rating on most filters is "nominal," which
basically represents an average-- some particles above the rating will
get through. Moreover, the fuel tanks themselves may have some
contaminants from previous life. The onboard WVO filter is the last
defense against these particles.
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The systems used in the following vehicles can be adapted to other diesel cars and trucks. Conversion kits vary from $600 up to $3000 and more, take a look at the diagrams on following pages to see the flexibility.
1994 Ford E350
1994 Ford L7000
1989 Dodge D250
1981 Mercedes 300SD
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