Description
Petroleum diesel, also called petro diesel or fossil diesel is the
most common type of diesel
fuel. It is produced from the fractional distillation of crude
oilbetween **0 °C (**2 °F) and
**0 °C (**2 °F) at atmospheric, resulting in a mixture of carbon
chains that typically contain
between 8 and *1 carbonatoms per molecule.
Synthetic diesel
Synthetic diesel can be produced from any carbonaceous material,
including biomass, biogas,
natural gas, coal and many others. The raw material is gasified
into synthesis gas, which after
purification is converted by the FischerTropsch process to a
synthetic diesel.[9]
The process is typically referred to as biomass-to-liquid (BTL),
gas-to-liquid (GTL) or coal-toliquid
(CTL), depending on the raw material used.
Paraffinic synthetic diesel generally has a near-zero content of
sulfur and very low aromatics
content, reducing unregulated emissions of toxic hydrocarbons,
nitrous oxides and particulate
matter (PM).
Biodiesel
Biodiesel made from soybean oil
Fatty-acid methyl ester (FAME), more widely known as biodiesel, is
obtained from vegetable
oil or animal fats (biolipids) which have been transesterified with
methanol. It can be produced
from many types of oils, the most common being rapeseed oil
(rapeseed methyl ester, RME) in
Europe and soybean oil (soy methyl ester, SME) in the USA. Methanol
can also be replaced with
ethanol for the transesterification process, which results in the
production of ethyl esters. The
transesterification processes use catalysts, such as sodium or
potassium hydroxide, to convert
vegetable oil and methanol into FAME and the undesirable byproducts
glycerin and water, which
will need to be removed from the fuel along with methanol traces.
FAME can be used pure
(B**0) in engines where the manufacturer approves such use, but it
is more often used as a mix
with diesel, BXX where XX is the biodiesel content in percent. FAME
as a fuel is regulated
under DIN EN ****4 and ASTM D***1]
FAME has a lower energy content than diesel due to its oxygen
content, and as a result,
performance and fuel consumption can be affected. It also can have
higher levels of NOx
emissions, possibly even exceeding the legal limit. FAME also has
lower oxidation stability than diesel, and it offers favorable
conditions for bacterial growth, so applications which have a
low
fuel turnover should not use FAME. The loss in power when using
pure biodiesel is 5 to 7%.
Fuel equipment manufacturers (FIE) have raised several concerns
regarding FAME fuels: free
methanol, dissolved and free water, free glycerin, mono and
diglycerides, free fatty acids, total
solid impurity levels, alkaline metal compounds in solution and
oxidation and thermal stability.
They have also identified FAME as being the cause of the following
problems: corrosion of fuel
injection components, low-pressure fuel system blockage, increased
dilution
and polymerization of engine sump oil, pump seizures due to high
fuel viscosity at low
temperature, increased injection pressure, elastomeric seal
failures and fuel injector spray
blockage.
Unsaturated fatty acids are the source for the lower oxidation
stability; they react with oxygen
and form peroxides and result in degradation byproducts, which can
cause sludge and lacquer in
the fuel system.
As FAME contains low levels of sulfur, the emissions of sulfur
oxides and sulfates, major
components of acid rain, are low. Use of biodiesel also results in
reductions of unburned
hydrocarbons, carbon monoxide (CO), and particulate matter. CO
emissions using biodiesel are
substantially reduced, on the order of *0% compared to most petro
diesel fuels. The exhaust
emissions of particulate matter from biodiesel have been found to
be *0 percent lower than
overall particulate matter emissions from petro diesel. The exhaust
emissions of total
hydrocarbons (a contributing factor in the localized formation of
smog and ozone) are up to *3
percent lower for biodiesel than diesel fuel.
Biodiesel also may reduce health risks associated with petroleum
diesel. Biodiesel emissions
showed decreased levels of polycyclic aromatic hydrocarbon (PAH)
and nitrated PAH
compounds, which have been identified as potential cancer-causing
compounds. In recent
testing, PAH compounds were reduced by *5 to *5 percent, except for
benz(a)anthracene, which
was reduced by roughly *0 percent. Targeted nPAH compounds were
also reduced dramatically
with biodiesel fuel, with *-nitrofluorene and *-nitropyrene reduced
by *0 percent, and the rest of
the nPAH compounds reduced to only trace levels.
3.3 Hydrogenated oils and fats
This category of diesel fuels involves converting the triglycerides
in vegetable oil and animal fats
into alkenes by refining and hydrogenation, such as H-Bio. The
produced fuel has many
properties that are similar to synthetic diesel, and are free from
the many disadvantages of
FAME.
3.4 DME
Dimethyl ether, DME, is a synthetic, gaseous diesel fuel that
results in clean combustion with
very little soot and reduced NOx emissions.
3.5 Storage
In the US, diesel is recommended to be stored in a yellow container
to differentiate it from
kerosene and gasoline, which are typically kept in blue and red
containers, respectively. In the
UK, diesel is normally stored in a black container, to
differentiate it from unleaded petrol (which
is commonly stored in a green container) and leaded petrol (which
is stored in a red container).
