Vegetable oil is an alternative fuel for Diesel engines and
for heating oil burners. For engines designed to burn diesel fuel, the
viscosity of vegetable oil must be lowered to allow for proper atomization of
the fuel, otherwise incomplete combustion and carbon build up will ultimately
damage the engine.
History
Rudolf Diesel
Rudolf Diesel was the
father of the engine which bears his name. His first attempts were to design an
engine to run on coal dust, but later designed his engine to run on vegetable
oil. The idea, he hoped, would make his engines more attractive to farmers
having a source of fuel readily available. In a 1912 presentation to the
British Institute of Mechanical Engineers, he cited a number of efforts in this
area and remarked, "The fact that fat oils from vegetable sources can be
used may seem insignificant today, but such oils may perhaps become in course
of time of the same importance as some natural mineral oils and the tar
products are now."
Periodic petroleum
shortages spurred research into vegetable oil as a diesel substitute during the
1930s and 1940s, and again in the 1970s and early 1980s when straight vegetable
oil enjoyed its highest level of scientific interest. The 1970s also saw the formation
of the first commercial enterprise to allow consumers to run straight vegetable
oil in their automobiles, Elsbett of Germany. In the 1990s Bougainville
conflict, islanders cut off from oil supplies due to a blockade used coconut
oil to fuel their vehicles.
Academic research
into straight vegetable oil fell off sharply in the 1980s with falling
petroleum prices and greater interest in biodiesel as an option that did not
require extensive vehicle modification.
Application and
usability
Modified fuel systems
Most diesel car
engines are suitable for the use of straight vegetable oil (SVO), also commonly
called pure plant oil (PPO), with suitable modifications. Principally, the
viscosity and surface tension of the SVO/PPO must be reduced by preheating it,
typically by using waste heat from the engine or electricity, otherwise poor
atomization, incomplete combustion and carbonization may result. One common
solution is to add a heat exchanger and an additional fuel tank for the
petrodiesel or biodiesel blend and to switch between this additional tank and
the main tank of SVO/PPO. The engine is started on diesel, switched over to
vegetable oil as soon as it is warmed up and switched back to diesel shortly
before being switched off to ensure that no vegetable oil remains in the engine
or fuel lines when it is started from cold again. In colder climates it is
often necessary to heat the vegetable oil fuel lines and tank as it can become
very viscous and even solidify.
Single tank
conversions have been developed, largely in Germany, which have been used
throughout Europe. These conversions are designed to provide reliable operation
with rapeseed oil that meets the German rapeseed oil fuel standard DIN 51605.
Modifications to the engines cold start regime assist combustion on start up
and during the engine warm up phase. Suitably modified indirect injection (IDI)
engines have proven to be operable with 100% PPO down to temperatures of −10°C.
Direct injection (DI) engines generally have to be preheated with a block
heater or diesel fired heater. The exception is the VW Tdi (Turbocharged Direct
Injection) engine for which a number of German companies offer single tank
conversions. For long term durability it has been found necessary to increase
the oil change frequency and to pay increased attention to engine maintenance.
Unmodified indirect
injection engines
Many cars powered by
indirect injection engines supplied by in-line injection pumps, or mechanical
Bosch injection pumps are capable of running on pure SVO/PPO in all but winter
temperatures. Indirect injection Mercedes-Benz vehicles with in-line injection
pumps and cars featuring the PSA XUD engine tend to perform reasonably,
especially as the latter is normally equipped with a coolant heated fuel filter.
Engine reliability would depend on the condition of the engine. Attention to
maintenance of the engine, particularly of the fuel injectors, cooling system
and glow plugs will help to provide longevity. Ideally the engine would be
converted.
Vegetable oil
blending
The relatively high
kinematic viscosity of vegetable oils must be reduced to make them compatible
with conventional compression-ignition engines and fuel systems. Cosolvent
blending is a low-cost and easy-to-adapt technology that reduces viscosity by
diluting the vegetable oil with a low-molecular-weight solvent. This blending,
or "cutting", has been done with diesel fuel, kerosene, and gasoline,
amongst others; however, opinions vary as to the efficacy of this. Noted
problems include higher rates of wear and failure in fuel pumps and piston
rings when using blends.[3]
Home heating
When liquid fuels
made from biomass are used for energy purposes other than transport, they are
called bioliquids.
With often minimal
modification, most residential furnaces and boilers that are designed to burn
No. 2 heating oil can be made to burn either biodiesel or filtered, preheated
waste vegetable oil (WVO). If cleaned at home by the consumer, WVO can result
in considerable savings. Many restaurants will receive a minimal amount for
their used cooking oil, and processing to biodiesel is fairly simple and
inexpensive. Burning filtered WVO directly is somewhat more problematic, since
it is much more viscous; nonetheless, its burning can be accomplished with
suitable preheating. WVO can thus be an economical heating option for those
with the necessary mechanical and experimental aptitude.
Combined heat and
power
A number of companies
offer compressed ignition engine generators optimized to run on plant oils
where the waste engine heat is recovered for heating.
Properties
The main form of
SVO/PPO used in the UK is rapeseed oil (also known as canola oil, primarily in
the United States and Canada) which has a freezing point of -10°C.[citation
needed] However the use of sunflower oil, which gels at around -12°C,[6] is
currently being investigated as a means of improving cold weather starting.
Unfortunately oils with lower gelling points tend to be less saturated (leading
to a higher iodine number) and polymerize more easily in the presence of
atmospheric oxygen.
Material
compatibility
Polymerization also
has been consequentially linked to catastrophic component failures such as
injection pump shaft seizure and breakage, injector tip failure leading to
various and/or combustion chamber components damaged. Most metallurgical
problems such as corrosion and electrolysis are related to water based
contamination or poor choices of plumbing (such as copper or Zinc) which can
cause gelling- even with petroleum based fuels.
Temperature effects
Some Pacific island
nations are using coconut oil as fuel to reduce their expenses and their
dependence on imported fuels while helping stabilize the coconut oil market.
Coconut oil is only usable where temperatures do not drop below 17 degrees
Celsius (62 degrees Fahrenheit), unless two-tank SVO/PPO kits or other
tank-heating accessories, etc. are used. Fortunately, the same techniques
developed to use, for example, canola and other oils in cold climates can be
implemented to make coconut oil usable in temperatures lower than 17 degrees
Celsius.
Availability
Recycled vegetable
oil
Recycled vegetable
oil, also termed used vegetable oil (UVO), waste vegetable oil (WVO), used
cooking oil, or yellow grease (in commodities exchange), is recovered from
businesses and industry that use the oil for cooking.
As of 2000, the
United States was producing in excess of 11 billion liters (2.9 billion U.S.
gallons) of recycled vegetable oil annually, mainly from industrial deep fryers
in potato processing plants, snack food factories and fast food restaurants. If
all those 11 billion liters could be recycled and used to replace the energy
equivalent amount of petroleum (an ideal case), almost 1% of US oil consumption
could be offset. Use of used vegetable oil as a direct fuel competes with some
other uses of the commodity, which has effects on its price as a fuel and
increases its cost as an input to the other uses as well.
Virgin vegetable oil
Virgin vegetable oil,
also termed pure plant oil or straight vegetable oil, is extracted from plants
solely for use as fuel. In contrast to used vegetable oil, is not a byproduct
of other industries, and thus its prospects for use as fuel are not limited by
the capacities of other industries.[citation needed] Production of vegetable
oils for use as fuels is theoretically limited only by the agricultural
capacity of a given economy. However, doing so detracts from the supply of
other uses of pure vegetable oil.
Legal implications
Taxation of fuel
Taxation on SVO/PPO
as a road fuel varies from country to country, and it is possible the revenue
departments in many countries are even unaware of its use, or feel it too
insignificant to legislate. Germany used to have 0% taxation, resulting in it
being a leader in most developments of the fuel use. However SVO/PPO as a road
fuel began to be taxed at 0,09 €/liter from 1 January 2008 in Germany, with
incremental rises up to 0,45 €/liter by 2012. However, in Australia it has
become illegal to produce any fuel if it is to be sold unless a license to do
so is granted by the federal government. This is a chargeable offense with a
fine of up to 20,000 dollars but this bracket may alter circumstantially. Also
a jail term may result if offenders are aware of the illegality of selling the
fuel.
UK
Before 2011: In the
UK it is legal once duty on the fuel is paid, or, in the case of using or
producing less than 2,500 litres per year, no duty is necessary.
In the UK, drivers
using SVO/PPO have in the past been prosecuted for failure to pay duty to Her
Majesty's Revenue and Customs. The rate of taxation on SVO was originally set
at a reduced rate of 27.1p per litre, but in late 2005, HMRC started to enforce
the full diesel excise rate of 47.1p per litre.
HMRC argued that
SVOs/PPOs on the market from small producers did not meet the official
definition of "biodiesel" in Section 2AA of The Hydrocarbon Oil
Duties Act 1979 (HODA), and consequently was merely a "fuel substitute"
chargeable at the normal diesel rate. Such a policy seemed to contradict the UK
Government's commitments to the Kyoto Protocol and to many EU directives and
had many consequences, including an attempt to make the increase retroactive,
with one organization being presented with a £16,000 back tax bill. This change
in the rate of excise duty effectively removed any commercial incentive to use
SVO/PPO, regardless of its desirability on environmental grounds; unless waste
vegetable oil can be obtained free of charge, the combined price of SVO/PPO and
taxation for its use usually exceeded the price of mineral diesel. HMRC's
interpretation is widely challenged by the SVO/PPO industry and the UK pure
Plant Oil Association (UKPPOA) was formed to represent the interests of people
using vegetable oil as fuel and to lobby parliament.
Following a review in
late 2006,[10] HM Revenue & Customs has announced changes regarding the
administration and collection of excise duty of biofuels and other fuel
substitutes (Veg Oil). The changes came into effect on June 30, 2007. There is
no longer a requirement to register to pay duty on vegetable oil used as road
fuel for those who "produce" or use less than 2,500 litres per year.
For those producing over this threshold the biodiesel rate now applies.
In 2011, the Duties
associated with the use of Biodiesel changed to reflect a flat rate of 20 pence
per litre of biodiesel used. No lower threshold now exists.
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