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VEGETABLE OIL
Overview
Into The Engine
Make It Hot
Using Waste Oil
Advantages
Disadvantages
Conclusion
Links
Overview
Few people realize that vegetable oil can be used for more
than frying fast food! Indeed, Rudolph
Diesel's first public exhibition of the internal combustion
technology that was to later bear his name featured an engine running
on peanut oil. He envisioned freeing small businesses from the
monopolistic coal and steam power of the day by using organic fuels in
his engine. Unfortunately, it turned out that his engine also lent
itself to burning low-grade fractions of petroleum, and the rest is
history -- diesel engine manufacturers optimized the design for lighter
oils, and the use of vegetable oil never really got a chance.
But experimenters throughout the world have been reviving Diesel's
vision, and "Straight Vegetable Oil" (SVO) is finding increasing use,
particularly in the US, UK, Germany, and Australia.
Into The Engine
Because of this legacy, the fuel injection pump and the fuel
injectors in modern diesel engines won't work on room temperature
vegetable oil, which is too thick. There are three common ways to thin
vegetable oil so it can be used in diesel engines:
- Blend the vegetable oil with a lighter fuel,
- Change the chemical composition of the vegetable oil, or
- Heat the vegetable oil until it becomes thin enough.
Blending (#1) is fraught with problems, and although some
enthusiasts swear by it, others end up swearing at it, as they
damage expensive injection pumps with the heavier fluid. Some have
suffered explosions when trying to mix extremely lighter fuels, like
gasoline, with vegetable oil. Those reporting success seem to be
limited to a mix no more than 50/50 with petro-diesel at no colder than
"shirt sleeve" temperatures, on a few engines that have very robust
injection pumps.
Changing the chemical composition, (#2) also known as biodiesel, is safe, reliable, reduces
pollution, and will work in almost any diesel engine without
modification. On the other hand, creating it requires processing with
dangerous chemicals, and although the methanol commonly used to make
biodiesel can be made in a sustainable manner, most of it comes from
fossil fuel today. So today's biodiesel is not completely
sustainable.
When you heat vegetable oil (#3) to about 80°C (or about
180°F), it's viscosity is only a bit above that of normal diesel
fuel, and so can make its way through pumps and injectors without
damaging them. This strategy is called "Straight Vegetable Oil" (SVO).
But how to heat the oil?
Make It Hot
Fortunately, those wishing to use SVO for fuel generally have a
large, hot object nearby -- the engine inself! The most efficient
diesel engine still produces a lot of waste heat, and has nicely
packaged it in a readily available form. All you have to do is insert a
"T" into the lines going to the passenger compartment heater, and route
the engine coolant to a heat exchanger to warm up the SVO. Most
typically, this uses two tanks, one for your "start/purge" (S/P) fuel
that you run until the engine is hot, and the other tank for the
SVO.
Many SVO enthusiasts supplement engine coolant heat
with an electric boost (pictured), just before the fuel hits the
engine. This ensures it is really hot enough!
Fluid heat exchangers take many forms. To be efficient, the
exchanger needs a large surface area shared between the two fluids.
This has led to embedding the fuel line inside the coolant line, or
"Hose In Hose" (HIH). This design is fraught with peril if not done
carefully; if there is a leak, you've got a mess in your radiator, or
worse yet, water in your fuel -- even a tiny bit can cause expensive
engine damage.
For this reason, many tightly bind their fuel lines to the coolant
lines, using a "Hose On Hose" (HOH) approach, which transfers less
heat, but makes it impossible for the two fluids to mingle.
If it is inconvenient to run thick bundles of hoses around, they can
be run separately to a manufactured or home-built heat exchanger, which
can be as simple as a spiral of small copper tube for the SVO soldered
to a thicker copper pipe for the coolant.
The thermally-coupled fuel and coolant lines have to go to the same
place -- how convenient! Because the next thing to do is heat the fuel
tank. This is generally done by sending the coolant through a coil of
copper or aluminum tubing inside the fuel tank, or by using a
commercially-made tank heater. In colder weather, this may be a
requirement, as some SVO may solidify at fairly high temperatures
(compared to diesel fuel), but some report success without a tank
heater.
Finally, you need a way to switch between the S/P fuel and the SVO.
This takes the form of an electric valve and a toggle switch on the
dash. You start your engine on S/P fuel (hopefully, biodiesel), wait
for the temperature gauge to come up to normal, then flip the switch to
run on pure vegetables! A few minutes before your destination, flip the
switch back to your S/P fuel to ensure easy starting once the engine
cools down. (Leaving SVO to cool in the engine may make it impossible
to start without heating up the engine by some means.) Some commercial
kits feature timers and buzzers to remind you to purge.
Using Waste Oil
As with biodiesel, waste vegetable oil can be recovered
for engine fuel use, in which case, SVO is commonly called "WVO." But
the similarity ends there!
The process of making biodiesel isolates contaminants as a
side-benefit. Food particles have multiple opportunities to leave the
fuel, during separation of glycerin, during washing, during filtering.
But to use WVO in a diesel engine, you must explicitly remove
contaminants that get removed as a side-benefit of biodiesel
processing.
Most WVO enthusiasts use a combination of gravity settling and
pumped filtering. If you let the WVO sit for days to weeks, the heavier
food particles settle to the bottom, and you can suck the clean oil off
the top. But it still isn't ready for use, and must be cleaned even
more. Diesel engines want fuel that has been filtered to ten microns or
less -- it can take a lot of work to get something that has been
sitting in a dumpster behind a restaurant that clean!
Some report success with a filter-only strategy, by using
progressively finer filters to avoid heavily loading -- and replacing
-- the finer filters. For example, a 100 micron strainer keeps out the
cigarette butts, a 30 micron filter catches most food particles, and a
final 10 micron filter makes it engine-ready. Such a strategy can be
used "on the road" when you don't have time for days to weeks of
gravity settling.
Since restaurants currently pay to have their WVO disposed, what
works best is to develop a relationship with a restaurant, whereby you
agree to remove it on a regular schedule, and they agree to put it back
in the original containers and keep it from getting contaminated with
other waste. Some even report that they are able to talk restaurants
into pouring their waste oil through a paper filter before putting it
back in containers! Having such a "contract" with the restaurant also
dodges the issue of ownership and theft -- some grease recyclers
consider the oil "theirs" once it goes in the dumpster they provide,
even if you have permission from the restaurant to take the oil.
Advantages
SVO shares most of the advantages of biodiesel: better engine
lubrication, high energy content, improved safety, comparable
performance to petro-diesel, and reduced pollution.
Although SVO's emissions have not had as much study as biodiesel's,
SVO appears to have similar emission characteristics: no sulphur, much
lower unburnt hydrocarbons, somewhat lower carbon monoxide and
particulates, and slightly elevated nitrogen oxides.
An additional advantage is that an SVO vehicle can be more easily
justified as being a "Zero CO2" vehicle, since it doesn't have even the
small amount of petroleum-derived methanol that commercial biodiesel
has, except when starting or purging. An organic farm that used SVO in
its tractors to produce oil crops to produce SVO could truly be called
"CO2-neutral," since today's engine emissions are consumed by
tomorrow's oilcrop plants. There are very few transportation fuels that
can claim that!
Few disposables are produced. The filtered bits of food from WVO
make great fireplace starters! Biodiesel production has by-products
that must be further processed or recycled carefully, since burning
them at fireplace temperatures produces toxic chemicals.
An additional benefit over biodiesel is that once the engine
conversion is paid for, there are no extra chemicals to pay for. You're
down to the cost of the oil itself, which may be free.
Disadvantages
Like biodiesel, SVO use is limited to diesel engines, which hold a
tiny market share in BC. Diesel vehicles tend to be more expensive than
gas engines, but this is offset by their longer life.
Vegetable oil, whether made into biodiesel or not, cannot replace
petroleum at current consumption levels. The ethics of switching food
producing cropland to transportation fuel when there are hungry people
in the world must be questioned. However, the current waste oil stream
could supply as much as 10% of all diesel fuel, or perhaps 1% of total
current petroleum use. Given that future energy sources may be
distributed and diversified, SVO/WVO could be an important niche energy
source.
Today, WVO can be harvested for free from restaurants, but if
biodiesel and WVO become popular fuels, this "waste" product may in
fact approach the cost of diesel fuel.
If you're going to "roll your own" one way on the other, and you
have more than one diesel vehicle, biodiesel may be the way to go,
because you'll have to modify each car to run SVO. On the other hand,
you can probably commercially modify two vehicles to burn SVO for the
cost of one commercially available biodiesel processor.
SVO/WVO is considered an experimental fuel, and is not without some
risk to the engine. Almost without exception, those who have had
trouble with SVO don't get it hot enough, or use poor-quality WVO. Just
because the engine temperature gauge says it's up to temp doesn't mean
the oil is hot! Sometimes, the hot oil flows into a cooler injection
pump (which are often mounted away from the engine, and thus thermally
isolated), where it cools down and gels, causing damage.
Even if your injection pump doesn't self-destruct, cool or dirty oil
may be causing hidden damage. Injectors can collect carbon deposits
("coke") as can the piston ring lands on the cylinder wall. Coking
eventually causes poor dispersal from the injectors, which can lead to
premature wear or even piston failure.
Some injection pumps seem to be better suited for SVO than others.
People report good results with Bosche pumps, but tend to have problems
with Lucas or Standyne pumps. Also, older direct-injection (DI) engines
seem to have more problems than indirect-injection (IDI) engines. But
with properly heated and cleaned oil, essentially any diesel engine
will work with SVO.
Conclusion
This all may sound scary, but if you install a commercial kit
according to directions, and stick to high-quality oil, there is little
potential for engine damage. If you do choose to "roll your own" from
scratch, it may be worth it to buy a temperature probe to make sure
things are as hot as they are supposed to be, since the engine may
appear to be running fine, yet still getting coked-up.
And by all means, educate yourself about the process! There are
thousands of Internet resources on SVO/WVO; a few starting
points are below. The information on this web page is an
introduction, and is not intended to be enough for you to do a
conversion!
Keeping in mind some risk of engine damage, there is nothing quite
like pulling up to a stop light, having your exhaust catch up to you,
taking a deep breath, and smiling and thinking "ahhh... that smells
good!" and knowing there is absolutely no fossil fuel in that
exhaust!
Links
Credits
Written by Jan Steinman, for the BC Sustainable Energy Association
Text updated December 22, 2004
Links updated September 7, 2007
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