25-09-2012, 12:58 PM
Renewable and Alternative Energy Fact Sheet Using Biodiesel Fuel in Your Engine
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Introduction
Biodiesel is an engine fuel that is created by chemically reacting
fatty acids and alcohol. Practically speaking, this usually
means combining vegetable oil with methanol in the presence
of a catalyst (usually sodium hydroxide). Biodiesel is much
more suitable for use as an engine fuel than straight vegetable
oil for a number of reasons, the most notable one being its
lower viscosity. Many large and small producers have begun
producing biodiesel, and the fuel can now be found in many
parts of Pennsylvania and beyond either as “pure biodiesel” or
a blended mixture with traditional petroleum diesel (e.g., B5 is
5 percent biodiesel, 95 percent petroleum diesel).
The process of making biodiesel is simple enough that
farmers can consider producing biodiesel to meet their own
needs by growing and harvesting an oil crop and converting
it into biodiesel. In this way, farmers are able to “grow”
their own fuel (see the Penn State Cooperative Extension
publication Biodiesel Safety and Best Management Practices for
Small-Scale Noncommercial Production). There are many possible
reasons to grow or use biodiesel, including economics,
support of local industry, and environmental considerations.
However, there is also a great deal of concern about the
effect of biodiesel on engines. Many stories have been circulating
about reduced performance, damage to key components,
or even engine failures that are blamed on biodiesel. Some
manufacturers are wary about honoring their warrantees on
engines if biodiesel is used, while others are encouraging the
use of biodiesel. Given the wide array of confusing reports,
understanding the truth of the matter is not easy.
Engine Performance Using Biodiesel
While we don’t know everything about its performance, it is
safe to say that good-quality biodiesel fuel generally performs
well in engines. Several of the more important points to keep
in mind are as follows:
• Engine power: engine power and torque tend to be 3 to 5
percent lower when using biodiesel. This is due to the fact
that biodiesel fuel has less energy per unit volume than
traditional diesel fuel.
• Fuel efficiency: fuel efficiency tends to be slightly lower
when using biodiesel due to the lower energy content of
the fuel. Typically, the drop-off is in the same range as the
reduction in peak engine power (3–5 percent).
• Engine wear: short-term engine wear when using biodiesel
has been measured to be less than that of petroleum diesel.
While long-term tests have not been published, engines
are expected to experience less wear in the long run when
using biodiesel.
• Deposits and clogging: deposits and clogging due to biodiesel
have been widely reported but are generally traceable
to biodiesel that is either of low quality or has become oxidized.
If fuel quality is high, deposits in the engine should
not normally be a problem.
Biodiesel Quality Is Vital
It is important not to confuse the performance of high-quality
biodiesel with the performance of low-quality biodiesel. The
difference can be tremendous, and producers that do not pay
careful attention to their process are almost guaranteed to end
up with poor-quality biodiesel. Proper fuel quality and care are
vital for all engine fuels, and this is certainly true for biodiesel.
The most common problems with fuel quality are (1) the
biodiesel may contain some “unconverted” vegetable oil (incomplete
processing), (2) traces of chemicals from the making
of the biodiesel (e.g., methanol, lye) can remain in the biodiesel,
(3) products of the reaction (e.g., glycerin, soaps) may not
be completely removed from the biodiesel, (4) excess water
that is used to “wash” the fuel may be left in the biodiesel fuel,
and (5) the fuel can polymerize/oxidize due to long-term
storage or exposure to moderate to high temperatures.
Engine Care When Running on Biodiesel
Generally, biodiesel fuel should be able to be used interchangeably
with traditional diesel. However, some manufacturers
recommend that you reduce the maintenance interval
(often by 50 percent) to ensure that filters remain unclogged
and the lubrication oil remains in good shape. However, it
is important to consult the manufacturer of your engine for
specific recommendations.
Also, because of biodiesel’s tendency to oxidize, you
should exercise care if you are planning to store your engine
for any period of time. It may be appropriate to drain the
engine of all fuel before storage, change back to petroleum
diesel before storage, or alternately add a fuel stabilizer.
Summary
High-quality biodiesel fuel that is properly cared for should
result in a lifetime of excellent performance. In general, it can
be used in exactly the same manner as petroleum diesel fuel.
The one notable exception is during cold-weather conditions,
when biodiesel tends to “gel up” sooner than traditional diesel
fuel. Many additives are available on the market that can help
safeguard the quality and improve the cold-weather performance
of biodiesel, and their use is one option for improving
the performance of the fuel when using biodiesel. However,
using a “winter fuel blend” is the recommended approach for
the severe winter conditions experienced in Pennsylvania.