of electric heaters and coolant routing to warm WVO
up to the required 70°C. Most 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 (like The Big Green Bus),
the engine may take a long time to heat up and may never
even reach a full 70°C. Although the bus can run
on slightly cooler WVO, the added viscosity puts more
stress on the fuel pumps inside of the engine and therefore
shortens the engine's life.
, The Big
Green Bus has four high-power electric heaters that
run off of deep-cycle batteries. One heater warms WVO
in the storage tank in the area just around the fuel
pickup. It therefore concentrates energy right where
it is needed, melting enough WVO to be easily pulled
into the fuel lines. A second, flexible pad heater warms
the filter element to minimize the WVO's resistance
through the filter membrance. The filter is placed near
the engine so that the oil has little time to cool before
it reaches the fuel injectors. Nevertheless, two more
in-line heaters warm the WVO along the final fuel path
just prior to the engine. The concentrated electric
heating has the potential to allow the bus to start
without diesel, as long as the heaters are
given a few minutes to warm the oil prior to startup.
Once the engine is running, a 215 watt SunPower solar
module tops of the heater batteries.
(sound like an oxymoron?) captures waste energy from
the engine and maintains the high WVO temperature.
Coolant lines normally route excess heat from a car’s
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. The
Big Green Bus recycles 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 to maximize
the area of heat transfer.
the original (bio)diesel fuel system. It not only affords
a backup, should the WVO system malfunction, but diesel
is also crucial to cleansing 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 bus is run on diesel for a few
minutes before shutdown to "purge" the system
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 pumped onboard on the
bus, it passes through a series of Rosedale
filters that block anything larger than 5 microns
or 0.0002 inches in size. The initial 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 tank
itself has some contaminants from when it sat in a salvage
yard. The onboard WVO filter is the last defense against