Engine
Suitability
1 The Diesel Engine
2 Theory of Vegetable Oil Use as a
Fuel
3 Engine suitability
4 Heating the Oil
5 Biodiesel
6 Micro Emulsions and Blends
7 Vegetable Oil Engine Design
8 Vegetable Oil Furnaces and Heaters
9 Oil Types and Filtering
10 Taxation
11 Implications of Vegetable Oil
Fuel Use
12 Sources
There are many variations on diesel engine design.
Some engines are more suited to vegetable oil fuel use.
Combustion Chamber
Direct Injection (DI)
Found in commercial vehicle engines but also used since the
late eighties in light vehicles. If fuel oil with a greater
viscosity to that for which the engine was designed is used
the injector will not produce the suitable fine mist and the
fuel oil will not burn efficiently leaving carbon / oil deposits.
For this reason great care has to be taken to make sure only
sufficiently heated oil is burnt in this type of engine.
Hemmerlein et al.[28] tested three
unmodified DI engines, one 2.6 litre air cooled and two larger,
6.6 litre and 12 litre, turbo charged and intercooled with
liquid cooling, running rapeseed oil. All three engines failed
durability tests due to problems caused by carbon build ups.
Karaosmanoglu et al.[30] tested
a Panccar Motor 1 litre single cylinder DI engine running
sunflower oil. The engine successfully completed long term
engine testing when it was started and shut down for 5 minutes
with diesel fuel. The engine was run at a constant low speed
under partial load.
Indirect Injection (IDI)
Found in cars and light commercial vehicles. The fuel is
injected as a jet and atomised in the separate combustion
chamber before it enters the cylinder and completes combustion.
The atomisation processes in IDI units make them less prone
to problems from using thicker fuel oil.
Hemmerlin et al. [28] tested three
unmodified IDI engines running on rapeseed oil. A small 1.6
liter swirlchamber engine failed durability testing due to
carbon build up within the engine. Two larger IDI engines,
a 6.2 litre prechamber engine and a 5.7 litre swirlchamber
engine completed the durability testing.
Fuls et al.[31] found that
an unmodified IDI engine in a tractor successfully completed
extended service tests using sunflower oil as a fuel
Togashi et al. [29] found that
a small Yanmar IDI engine could be reliably operated on refined
or deacified rapeseed oil.
Mercedes prechamber engines have been operated on refined,
food grade rape oil for extended periods without problems
[10]
Injector Pump (IP)
Most injector pumps have an integral transfer pump to pull
the fuel into the injector pump from the fuel tank, others
are supplied by a separate lift pump, many have both. There
are two basic designs of injector pump.
In-Line Pump
An in-line pump has a small plunger to supply fuel to each
cylinder of the engine. This plunger pushes the fuel oil up
the high pressure fuel lines to the injector. These pumps
have proved to be very reliable when fuelled with vegetable
oil. In fact Mercedes IDI engines with in-line pumps have
been run on vegetable oil for extended periods without conversion.
Rotary Pumps
These pumps use a single pumping mechanism which pumps through
a rotating valve into all cylinders. They look similar to
a petrol engines distributor. On a four cylinder engine the
pump mechanism is working four times as hard as it’s
in-line equivalents.
Due to the high stress these pumps encounter at their given
work load they should be run only with oil at a similar viscosity
to diesel fuel in order to maintain longevity.
There are also two general designs of rotary pump mechanisms
Lucas/CAV Type : Uses two plungers that are flung outwards
by the rotor, they are pushed inwards by a cam to expel the
fuel
Bosch Type : The entire rotating valve system moves backwards
and forwards pumping the fuel.
The Lucas/CAV units has been found to be susceptible to malfunctions
when running on vegetable oil, thought to be caused by their
less rugged construction and a possible build up of dirt in
the rotor which is cleared by the backwards and forwards motion
of the Bosch unit.
These units come with either metal or fibre vanes in the
transfer pump which pulls the fuel into the IP. Damage has
been caused by a suspected swelling of the non-metal vanes
these however can be replaced with the metal vanes. Another
possible cause of problems is expansion or contraction caused
by fuel of a radically different temperature suddenly being
introduced. Great care should be taken when using this type
of pump. The fuel should be filtered very thoroughly and vegetable
oil heated carefully.
Injector pumps can be modified to allow them to function
more reliably with vegetable oil. As previously stated Lucas/CAV
pumps that have fibre vanes in their transfer pump can be
up rated with metal vanes. Also the main pumping mechanism(s)
can be modified by using lapping paste on the pump plunger(s)
so that it requires a similar force to move when pumping SVO
as when using diesel. This will reduce stresses on the pump
but in many cases may be unnecessary. Injector pumps are very
precise systems and such operations should only be attempted
by a suitably experienced technician.
Injectors
Injectors with a pre injection have been found to be superior
when fuelled with vegetable oil as the bulk of fuel is injected
into a burning fuel/air mixture providing superior combustion.
Glow Plugs
Some vehicles glow plugs have an after glow function where
the glow plugs stay on after starting for a few minutes to
smooth cold running. This function will greatly help when
starting on vegetable oil fuels with a cold engine.
Upgrade kits are available for some vehicles from both Bosch
and Buru. The plugs are heavy duty to withstand the extended
heating times. Buru plugs are marked GV for Vorglueh (pre-glow)
or GN for Nachglueh (post-glow).
1 The Diesel Engine
2 Theory of Vegetable Oil Use as a
Fuel
3 Engine suitability
4 Heating the Oil
5 Biodiesel
6 Micro Emulsions and Blends
7 Vegetable Oil Engine Design
8 Vegetable Oil Furnaces and Heaters
9 Oil Types and Filtering
10 Taxation
11 Implications of Vegetable Oil
Fuel Use
12 Sources
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