Bio-Diesels in Perkins' Engines
With concern growing
about possible climate change, and the implications of the Kyoto Treaty coming
into force, interest in alternative (and hopefully CO2-neutral) fuels grows.
As well as CO2, emissions of NOx, particulates, CO and others need to be reduced
to meet future environmental legislation.
History
A number of variations
on the biodiesel theme have been used in the past, with unrefined vegetable
oils being particularly popular. The high viscosity of these fuels at low
temperatures proved to be a significant problem, as did the variation in
the fuels themselves. These early fuels caused other significant problems,
particularly with the coking of the injectors. The switch to transesterified
biodiesel and the introduction of the EN14214 standard in Europe has largely
eliminated this problem.
The Present
Day
At present, most biodiesel
is produced using the transesterification process, producing fatty acid methyl
esters (FAME). At the molecular level, biodiesel is made up of straight chain
molecules, whilst mineral diesel fuel is primarily made up of a combination
of branched chain aliphatic hydrocarbons and aromatic ring molecules. The
most common raw materials for the production of FAME are rapeseed or soybean
oils. Recycling used cooking oil by converting it to biodiesel is also an
option. Alternative biomass derived fuels to these refined vegetable oils
are being developed. These fuels are referred to as biomass-to-liquid (BTL)
fuels and rely on the well-established Fischer-Tropsch (FT) process. The FT
process was used in Germany during the Forties for liquid fuel production
to compensate for the scarcity of crude oil, and has been used extensively
in South Africa for many years to produce petrol and diesel from coal. Using
farming, forestry or household waste, or almost any other carbonaceous material,
a variety of synthetic liquid biomass derived fuels can be produced, suitable
for either spark- or compression-ignition engines.
Under current
European law, a diesel fuel may contain up to 5% biodiesel before
the manufacturer is required to declare the fuel's content. The warranties
on all of Perkins' engines remain valid at this level of biodiesel
content, though for certain engines this limit may be as high as 30%.
The company has also initiated a project in Germany to monitor 1106C-powered
machines running on 100% biodiesel. This is particularly important
in the Water Protection areas in this market, where 100% biodiesel
use is mandatory. To help increase the adoption of biodiesel, the
German government has made biodiesel duty-free. Across the EU, the
Commission has set targets of biofuel use, as a proportion of all
petrol and diesel, of 2% by 2005, and 5.75% by 2010. In the USA, interest
in biodiesel and bioethanol is mostly driven by security of energy
supply and the farming lobby. Biodiesel has also been advocated as
an additive to ultra low sulphur diesel (ULSD) to improve the lubricity
of ULSD.
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"The
warranties on all of Perkins' engines remain valid at a level of 5%
biodiesel content..."
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For all its potential
environmental benefits, there are inevitably downsides to biodiesel, in particular
the energy content of these fuels, which tends to be lower (by around 8-10%)
than that of mineral fuel. This results in a typical drop in engine power
of 6%, with an expected increase in Specific Fuel Consumption (SFC) in the
region of 6 to 8%. As well as being closer to CO2 neutrality, running engines
on biodiesel reduces all other emissions except NOx, which tends to increase
by around 10%. In terms of chemical compatibility, the main requirement is
the use of Viton rubber seals in the fuel system, since nitrile and natural
rubbers can degrade in the presence of biodiesel. Some Perkins fuel systems
already use such seals, but as of today this is dependant on our suppliers'
capability.
The Future
The
two most significant issues with biodiesel use are the drop in power when
using 100% biodiesel and the consequent increase in specific fuel consumption
as well as the increase in NOx emissions. The increase in fuel viscosity
at low temperatures, which is large compared to conventional diesel, can have
a negative impact on the cold-startability of diesel engines. The availability
of the biological raw material is also an issue; at present, the EU estimates
that 1.5% of Europe's fuel needs could be met by European-produced biofuels.
However, the FT process, which can accept a multitude of biomass as raw
materials, could potentially increase this figure significantly. Ultimately,
studies have shown that "well-to-wheel" emissions of CO2 could be reduced
by up to 78% for FAME and by more than 80% for BTL fuels and consequently
these fuels will have a key role to play in meeting CO2 emission reduction
targets.
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