Technically, biodiesel is Vegetable Oil Methyl Ester. It is formed by
removing the triglyceride molecule from vegetable oil in the form of
glycerin (soap). Once the glycerin is removed from the oil, the remaining
molecules are, to a diesel engine, similar to petroleum diesel fuel. There
are some notable differences. The biodiesel molecules are very simple
hydrocarbon chains, containing no sulfur, ring molecules or aromatics
associated with fossil fuels. Biodiesel is made up of almost 10% oxygen,
making it a naturally "oxygenated" fuel.
Biodiesel is the name for a variety of ester-based oxygenated fuels made
from soybean oil or other vegetable oils or animal fats. The concept of
using vegetable oil as a fuel dates back to 1895 when Dr. Rudolf Diesel
developed the first diesel engine to run on vegetable oil. Diesel
demonstrated his engine at the World Exhibition in Paris in 1900 using
peanut oil as fuel.
Key Advantages of Biodiesel:
is the only alternative fuel that runs in any conventional,
unmodified diesel engine. It can be stored anywhere that petroleum
diesel fuel is stored.
can be used alone or mixed in any ratio with petroleum diesel fuel.
The most common blend is a mix of 20% biodiesel with 80% petroleum
diesel, or "B20."
the lifecycle production and use of biodiesel produces approximately
80% less carbon dioxide emissions, and almost 100% less sulfur
dioxide. Combustion of biodiesel alone provides over a 90% reduction
in total unburned hydrocarbons, and a 75-90% reduction in aromatic
provides significant reductions in particulates and carbon monoxide
than petroleum diesel fuel.
provides a slight increase or decrease in nitrogen oxides depending
on engine family and testing procedures. Based on Ames Mutagenicity
tests, biodiesel provides a 90% reduction in cancer risks.
is 11% oxygen by weight and contains no sulfur. The use of
biodiesel can extend the life of diesel engines because it is more
lubricating than petroleum diesel fuel, while fuel consumption, auto
ignition, power output, and engine torque are relatively unaffected by
is safe to handle and transport because it is as biodegradable as
sugar, 10 times less toxic than table salt, and has a high flashpoint
of about 300 F compared to petroleum diesel fuel, which has a flash
point of 125 F.
can be made from domestically produced, renewable oilseed crops
such as soybeans.
is a proven fuel with decades of use
When burned in a diesel engine, biodiesel replaces the exhaust odor
of petroleum diesel with the pleasant smell of popcorn or french
Biodiesel is a better lubricant than modern low-sulfur petroleum diesel
fuels, and it also has a much higher cetane rating. Cetane rating for
diesel fuels is the equivalent of “octane rating” for petrol. The use of
biodiesel generally reduces friction and wear on vehicle fuel
systems. As well, biodiesel increases the lifespan of diesel engines
with high-pressure injection pumps, fuel injectors or unit injectors which
rely on fuel for lubrication in those parts.
At room temperature, biodiesel is a free-flowing liquid. Depending upon
the feedstock, its color varies between golden yellow to dark brown. It is
very slightly miscible in water. It has a low vapor pressure and a high
boiling point. Biodiesel’s flash point is at 130°C/266°. 28 This is
significantly higher than the flash point of either petroleum diesel or
The density of biodiesel is around 0.88 g/cm³, which is slightly higher
than that of petroleum diesel. Biodiesel generally has very little sulfur,
so it is frequently added to Ultra-Low Sulfur Diesel fuels (ULSD) to
provide lubrication, since sulfur compounds are responsible for most of
the lubrication in petroleum diesel.
If biodiesel fuel is cooled to a certain temperature, some of its
molecules clump together and become crystals. Biodiesel begins to appear
cloudy when these crystals become bigger than one-quarter the size of
visible light’s wavelengths. This is called the “cloud point” (CP). With
further cooling of the biodiesel, the crystals grow larger.
As measured by the standard tests mentioned earlier, the “cold filter
plugging point” (or CFPP) is the lowest possible temperature at which
biodiesel fuel can still pass through a filter with 45-micrometer mesh
size. If cooled further, biodiesel will gel and eventually solidify. As
mentioned previously, CFPP requirements depend upon the climate region
where the biodiesel fuel is to be sold.
The gelling temperature for pure biodiesel (B100) varies widely depending
upon the exact mix of esters, which in turn depends on the feedstock from
which the biodiesel was produced.
As an example, biodiesel fuel produced from canola seed containing low
levels of erucic acid begins to gel at about 14°F (−10 °C). In contrast,
biodiesel made from tallow or yellow grease containing animal fat begins
to gel at about 61°F (+16 °C).
There are several commercially-available additives which serve to
counteract gelling by lowering the CFPP and the temperature at which
biodiesel can be poured. Even during winter in northern climates,
biodiesel is still viable as a fuel when blended with other fuel oils such
as Number 2 low-sulfur diesel and Number 1 diesel-kerosene.
Another method for using biodiesel fuel under cold conditions is by
installing a second fuel tank for biodiesel to be used in conjunction with
a standard petroleum diesel fuel source. This second tank is insulated,
and the biodiesel inside is warmed with a heating coil fed by engine
Once the already-operating engine has warmed the biodiesel enough to flow
properly, the fuel source can be switched over from petrodiesel to
biodiesel. Likewise, pre-heating can also be used to fuel diesel engines
by using virgin vegetable oil or waste vegetable oil (WVO) instead of
One of the major advantages is the fact that it can be used in existing
engines and fuel injection equipment (no modification required) without
negative impacts to operating performance.
Fuel availability / economy
Virtually the same L/100Km rating as petrodiesel and the only alternative
fuel for heavyweight vehicles requiring no special dispensing and storage
Readily blends and stays blended with petrodiesel so it can be stored and
dispensed wherever diesel is stored or sold.
Biodiesel has a very high flash point (300°F) making it one of the safest
of all alternative fuels.
The only alternative fuel that can boast of a zero total emissions
The only alternative fuel that can actually extend engine life because of
its superior lubricating properties.
The only renewable alternative diesel fuel that actually reduces a major
greenhouse gas components in the atmosphere .
The use of biodiesel will also reduce the following emissions:
The first four alcohols, (in order of carbon content) methanol,
ethanol,propanol, and butanol, are of greatest interest for fuel use as
their chemical properties make them useful in internal combustion engines.
One of the problems with alcohols is that they have lower energy densities
Fuel Energy Density(megajoules/liter)
Average Octane (AKI rating/RON) petrol ~33 85-96/90-105
Methanol ~16 98.65/108.7
Ethanol ~20 99.5/108.6
Propanol ~24 108/118
AKI - Anti-Knock Index:
This octane rating is used in countries like Canada and the United States.
RON - Research Octane Number: This octane rating is used in Australia and
most of Europe
Besides reducing knock, higher octane values are indicative of a fuel that
burns slowly. In general, the slower a fuel burns, the more efficient it
is to extract energy from it. Thus, a higher octane also reveals a more
energy efficient fuel. The fact that alcohols have higher octane values
than petrol helps to offset some of the difference in energy density. The
net result is that the loss of fuel economy (how far a car can travel on a
volume of fuel) is not as drastic as it would be if the octane numbers
were the same.
It is true that any of the alcohols above can be generated from fossil
fuels. However, it is easier and more efficient to derive these products
from biomass or even carbon dioxide and water than to refine petroleum. It
is also the case that petroleum-derived alcohols tend to be less pure
(ethanol is contaminated with methanol for instance) and often cannot be
purified through simple distillation.
Methanol is closely related to methane. In fact, there is only one
atom different between these two chemicals (Oxygen shown in blue, carbon
in black, hydrogen in red)
Though these molecules are remarkably similar, their properties could not
be more different. To begin, methane is a gas at standard temperature and
pressure. Methanol, on the other hand, is a liquid. Methane has an energy
density of 55 MJ/kg while methanol has an energy density of only 23 MJ/kg
at best. Burning methane produces twice the amount of carbon dioxide per
kilogram as burning methanol does (2.74 kg CO2/kg methane
versus 1.37 for methanol).
Ethanol is standard drinking alcohol, so we know it isn't poisonous.
Already we're off to a better start than methanol. It also has a higher
energy density than methanol and is still a liquid, which makes it an
attractive alternative. Ethanol is only one atom different than ethane.
Like methane and methanol, the differences between these molecules are
Ethanol is a common additive to fuels in many countries. Globally,
the average ethanol content in petrol is roughly 5.4%, though some
countries supply 25% or even 100% ethanol for vehicle fuel.
Ethanol has some benefits as a fuel or as a fuel additive. First, because
it has a higher octane number than ethane and even many of the larger
hydrocarbons, ethanol can be used to boost the octane of a fuel. Beyond
that, it burns cleaner than most hydrocarbon fuels and, if created from
biomass rather than petroleum, contains little or no contamination to
damage vehicle parts
The drawbacks to ethanol as a fuel, however, have prevented its widespread
adoption. First of all, it takes about 1.5 times more ethanol than petrol
to get the same energy. That means you need a fuel tank 1.5 times larger
if you want to travel the same distance on ethanol that you do on petrol.
Another problem with ethanol is that it is corrosive to the rubber.
Finally, ethanol absorbs water from the environment, which dilutes its
concentration and makes it impossible to ship it through pipelines.
So, ethanol isn't the optimal standalone fuel, but it does seem to make
for a great fuel additive
Propanol is the forgotten alcohol fuel, but for good reason.
Propanol is the most difficult and expensive alcohol to produce.
Butanol is more similar to petrol than ethanol or methanol. This
similarity is a consequence of its longer hydrocarbon chain, which means
there is more carbon in relation to the single oxygen and thus the
molecule is less polar.
The similarity of butanol to petrol means that it can be used in a
standard vehicle without the need for modifications. Also, because of its
size, butanol has an energy density similar to that of petrol. In fact,
butanol is so close to petrol in energy content that its octane rating
nearly makes up for the difference in energy density. In other words, a
liter of butanol will get your car about as far as a liter of petrol, with
the difference only being about 10%. It is also true that butanol only
produces about 2.03 kg of carbon dioxide per kilogram of butanol while
petrol produces 3.3 kg of carbon dioxide per kilogram of petrol.
Three Reasons Why Butanol Has Not Replaced Petrol:
Butanol actually produces more carbon dioxide than what arises just
from burning it. The reason for this discrepancy is that producing the
biomass, harvesting it, and processing it all requires energy which
Butanol's health effects are not well understood
Butanol is very difficult to produce.
Comparing amount of carbon dioxide that each alcohol produces to the
carbon dioxide production of an equivalent amount of the fossil fuel that
most closely resembles, structurally, the alcohol can be misleading.
A better way to compare carbon dioxide production is in terms of energy
produced per kilogram of carbon dioxide expelled. This is a better example
because even though a quantity of ethanol produces less carbon dioxide
than the same quantity of gasoline, it also produces less energy. The
result is that it is necessary to burn more of the alcohol to get the same
amount of energy as the fossil fuel. The chart below contains a few
examples that help to clarify the point.
This measure compares an alcohol to its closest
The value of carbon produced is arrived at by determining how many
kilograms of alcohol are needed to derive the same amount of energy
as the hydrocarbon.
This number is multiplied by the CO2 production in kg/kg
to determine how many kilograms carbon dioxide are produced for when
energy production is kept the same.
Energy Density (MJ/kg)
Carbon Dioxide production (kg/kg)
Carbon Dioxide production (MJ/kg)
Carbon Dioxide* (kg/Equivalent)
Longer Chain Alcohols Would Make Alcohol a More Viable Alternative to
So it would appear that alcohols, no matter how they are produced, are not
likely to be viable alternatives to fossil fuels until they start to get longer
Methanol and ethanol are not great fuel sources because they produce more
carbon dioxide than their equivalent hydrocarbons for the same amount of
Butanol, however, begins to show a difference.
Butanol produces LESS carbon dioxide than petrol for the same amount of
energy but is currently difficult to produce in large quantities.
If we can produce butanol in large quantity and avoid impact on the
food chain, then it may become a viable alternative to hydrocarbon fuels.
A method of genetic engineering has revealed that bacteria may be the key
to producing long-chain alcohols.