Vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fat ...

can be used as an

alternative fuel Alternative fuel, known as non-conventional and advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels like; '' fossil fuels'' (petroleum (oil), coal, and natural gas), as well as nuclear mat ...

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

s and in

heating oil Heating oil is any petroleum product or other oil used for heating; a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers use for home heating and in other buildings. Home heating oil is often a ...

burners. When vegetable oil is used directly as a fuel, in either modified or unmodified equipment, it is referred to as straight vegetable oil (SVO) or pure plant oil (PPO). Conventional diesel engines can be modified to help ensure that the

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

of the vegetable oil is low enough to allow proper

atomization Atomization refers to breaking bonds in some substance to obtain its constituent atoms in gas phase. By extension, it also means separating something into fine particles, for example: process of breaking bulk liquids into small droplets. Atomizati ...

of the fuel. This prevents incomplete combustion, which would damage the engine by causing a build-up of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

. Straight vegetable oil can also be blended with conventional diesel or processed into

biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat (tallow), soybean oil, or some other vegetable oil with ...

, HVO or

bioliquids Bioliquids are liquid fuels made from biomass for energy purposes other than transport (i.e. heating and electricity). Bioliquids are usually made from virgin or used vegetable and seed oils, like palm or soya oil. These oils are burned in a po ...

for use under a wider range of conditions.

History

Rudolf Diesel Rudolf Christian Karl Diesel (, ; 18 March 1858 – 29 September 1913) was a German inventor and Mechanical engineering, mechanical engineer who is famous for having invented the diesel engine, which burns diesel fuel; both are named after him. ...

was the father of the engine which bears his name. His first attempts were to design an engine to run on coal dust, but he 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 The Institution of Mechanical Engineers (IMechE) is an independent professional association and learned society headquartered in London, United Kingdom, that represents mechanical engineers and the engineering profession. With over 120,000 member ...

, 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 Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fat ...

in their automobiles,

Elsbett The Elsbett engine is an 89 HP, direct-injection diesel engine designed to run on straight vegetable oil. The engine is also known as Elko engine (for "Elsbett Konstruktion") and was invented by Ludwig Elsbett. The design limits the loss of ener ...

West Germany West Germany is the colloquial term used to indicate the Federal Republic of Germany (FRG; german: Bundesrepublik Deutschland , BRD) between its formation on 23 May 1949 and the German reunification through the accession of East Germany on 3 O ...

. In the 1990s

Bougainville conflict The Bougainville conflict, also known as the Bougainville Civil War, was a multi-layered armed conflict fought from 1988 to 1998 in the North Solomons Province of Papua New Guinea (PNG) between PNG and the secessionist forces of the Bougainvill ...

, islanders cut off from oil supplies due to a blockade fueled their vehicles with

coconut oil frameless , right , alt = A cracked coconut and a bottle of coconut oil Coconut oil (or coconut butter) is an edible oil derived from the wick, meat, and milk of the coconut palm fruit. Coconut oil is a white solid fat; in warmer climates duri ...

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 certain modifications. Principally, the

and

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...

of the SVO/PPO must be reduced by preheating it, typically by using

waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...

from the engine or electricity; otherwise, poor atomization, incomplete combustion, and

carbonization Carbonization is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation. Complexity in carbonization Carbonization is a pyrolytic reaction, therefore, is considered a complex process ...

may result. One common solution is to add a

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

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 were developed largely in Germany and are now 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 engine's cold start regime assist combustion on start up and during the engine warm up phase. Suitably modified

indirect injection Indirect injection in an internal combustion engine is fuel injection where fuel is not directly injected into the combustion chamber. Gasoline engines equipped with indirect injection systems, wherein a fuel injector delivers the fuel at some po ...

(IDI) engines have proven to be operable with 100% PPO down to temperatures of . Direct injection (DI) engines generally have to be preheated with a

block heater A block heater is used in cold climates to warm an engine prior to starting. They are mostly used for car engines; however they have also been used in aircraft engines. The most common design of block heater is an electrical heating element embed ...

or diesel fired heater. The exception is the VW TDI (

Turbocharged Direct Injection TDI (Turbocharged Direct Injection) is Volkswagen Group's term for its current common rail direct injection turbodiesel engine range that have an intercooler in addition to the turbo compressor. TDI engines are used in motor vehicles sold by th ...

) engine for which a number of German companies offer single-tank conversions. For long-term durability it has been found necessary to decrease the oil change interval and pay increased attention to engine maintenance.

Unmodified indirect injection engines

Many cars powered by

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. The most popular of these are the OM616 and OM617 engines found in the Mercedes-Benz W123 and W124 vehicles manufactured from 1980 through 1985. Indirect injection

Mercedes-Benz Mercedes-Benz (), commonly referred to as Mercedes and sometimes as Benz, is a German luxury and commercial vehicle automotive brand established in 1926. Mercedes-Benz AG (a Mercedes-Benz Group subsidiary established in 2019) is headquartere ...

vehicles with in-line injection pumps and cars featuring the

PSA XUD The PSA XUD is a diesel engine designed and built by PSA - Peugeot and Citroën. It is an Indirect injection (IDI) engine, that uses a version of the Ricardo Consulting Engineers ''Ricardo Comet V'' prechamber cylinder head design. The engine c ...

engine tend to perform reasonably, especially as the latter is normally equipped with a coolant heated

fuel filter A fuel filter is a filter used to screens out foreign particles or liquids from the fuel. Most internal combustion engines use a fuel filter, in order to protect the components in the fuel system. Filters for foreign particles Unfiltered fuel m ...

. 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 In chemistry, cosolvents are substances added to a primary solvent in small amounts to increase the solubility of a poorly-soluble Chemical compound, compound. Their use is most prevalent in chemical and biological research relating to pharmaceuti ...

blending is a low-cost and easy-to-adapt technology that reduces viscosity by diluting the vegetable oil with a low-molecular-weight

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. This blending, or "cutting", has been done with diesel fuel, kerosene, and gasoline, among 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.Pacific Islands Applied Geoscience Commission: "Coconut Oil Fuel Research in the Republic of the Marshall Islands"
/ref>

Home heating

When liquid fuels made from biomass are used for energy purposes other than transport, they are called bioliquids or biofuels. 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). New standard oil burners are certified to operate on 20% biodiesel (B-20). Higher blends are possible with care, since biodiesel tends to liberate existing tarry deposits in fuel tank, which may tend to clog one or more filters. Conventional oil burners tend to clog and char if more than a smaller fraction of vegetable oil is mixed with conventional oil fuel. If the vegetable oil is 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 a biofuel is fairly simple and inexpensive. Making the oil into biodiesel involves some toxic and hazardous chemical transformations. Burning filtered WVO directly is somewhat more problematic, since it is more viscous and has a higher ignition temperature; nonetheless, its burning can be accomplished with suitable preheating or burners designed to operate on it. 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

compression ignition engine Compression may refer to: Physical science * Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression *Gas compression * Compression ratio, of a ...

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 Rapeseed (''Brassica napus ''subsp.'' napus''), also known as rape, or oilseed rape, is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed, which naturally contains a ...

oil (also known as

canola oil Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, i ...

, primarily in the United States and Canada) which has a freezing point of . However the use of sunflower oil, which gels at around , is currently being investigated as a means of improving cold-weather starting. However, oils with lower gelling points tend to be less saturated (leading to a higher

iodine number Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

) and

polymerize In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many for ...

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

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 , unless two-tank SVO/PPO kits or other tank-heating accessories, etc. are used. 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

Availability

Recycled vegetable oil

Recycled vegetable oil, also termed used vegetable oil (UVO), waste vegetable oil (WVO), used cooking oil (UCO), or

yellow grease Yellow grease, also termed used cooking oil (UCO), used vegetable oil (UVO), recycled vegetable oil, or waste vegetable oil (WVO), is recovered from businesses and industry that use the oil for cooking. It is used to feed livestock, and to manufa ...

(in

commodities In economics, a commodity is an economic good, usually a resource, that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them. The price of a comm ...

exchange), is recovered from businesses and industry that use the oil for cooking. , the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

was producing in excess of 11 billion liters (2.9 billion U.S. gallons) of recycled vegetable oil annually, mainly from industrial

deep fryer A deep fryer (also referred to as a deep fat fryer), is a kitchen appliance used for deep frying. Deep frying is a method of cooking by submerging food into oil at high heat, typically between temperatures of . While commonly used in commercia ...

s in

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

processing plants,

snack food A snack is a small portion of food generally Eating, eaten between meals. Snacks come in a variety of forms including packaged snack foods and other processed foods, as well as items made from fresh ingredients at home. Traditionally, snack ...

factories, and

fast food restaurant A fast-food restaurant, also known as a quick-service restaurant (QSR) within the industry, is a specific type of restaurant that serves fast-food cuisine and has minimal table service. The food served in fast-food restaurants is typically ...

s. If all those 11 billion liters could be

recycled Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

and used to replace the energy equivalent amount of petroleum (an ideal case), almost 1% of US oil consumption could be offset.See

Greenhouse gas emissions by the United States The United States produced 5.2 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2020, the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenho ...

Utilizing recycled vegetable oil as a replacement for standard petroleum-derived fuels like gasoline would reduce the price of gasoline by preserving the supply of petroleum.

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. 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. It is possible that the revenue departments in many countries are even unaware of its use or consider it too insignificant to legislate. Germany used to have 0% taxation, resulting in it being a leader in most developments of the fuel use.

References

{{Palm oil Biofuels DIY culture Food waste Vegetable oils