Heating
The Oil
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
As previously stated vegetable oil can be used in a diesel
engine if it is heated to reduce its viscosity so that it
will perform in a similar fashion to diesel fuel. By adding
fuel heaters a vehicle can be operated on vegetable oils.
A number of studies have shown that the use of such systems
can give operating characteristics similar to when running
diesel fuel. Emissions and power have been shown to be comparable
or improved.[2][23]
When environmental, production, social and economic considerations
of the use of biofuels or transportation fuels has been considered,
studies have found straight vegetable oil to be the most suitable
energy source.[16][17][24]
Vegetable Oil Conversion Design
When designing a fuel heating system a number of factors
need to be considered to ensure reliable operation:-
direct / indirect fuel injection
rotary / inline injector pump
ambient temperatures encountered
type of oils to be used
computer / mechanical controlled injection
The time when problems are most likely to occur is when
the engine is being started from cold. The engine does not
have the latent heat that would aid combustion and the engine
may not fire at all. Elsbett offer conversion kits and a conversion
service that allow vegetable oil to be poured into the tank
instead of diesel. There is however an alternative solution
to this single tank solution that is widely utilised.
The Twin Tank or Duel Fuel System
An effective way to safely run on vegetable oil is to run
a duel fuel system. The engine is started on petro-diesel
(or bio-diesel etc) and the heat created by the engine is
used to heat the vegetable oil. This avoids running vegetable
oil through a cold engine at start up. A temperature gauge
in the fuel line allows you to see when the oil is hot enough
for the fuel supplies to be switched.
The fuel supply is switched by a three way valve. Before shutting
down for extended periods the fuel supply is switched back
and the engine is allowed to run for a few minutes (approx
3-5mins depending on set-up)so that the vegetable oil is flushed
from the fuel system. The vehicle is then ready to be restarted
on diesel fuel. Placing the fuel selection valve as close
to the injector pump as possible reduces the flushing time.
Fuel Return
In most engines the injector pump is supplied by the transfer
pump with more fuel than is required. The excess fuel is generally
returned to the fuel tank although some engines recycle the
excess back to the injector pump.
When running a duel fuel system a ‘return to tank’
system will require modification. Getting vegetable oil returned
into the diesel tank is undesirable as it may accumulate and
could cause problems with cold starts and blocked filters.
Getting diesel in the vegetable oil is not a problem mixing
diesel into vegetable oil improves its performance.
Having a three way valve in the return line allows fuels to
be sent to the appropriate tank. Care should be taken to feed
back to the diesel tank only after vegetable oil has been
purged from the system avoiding diesel tank contamination.
Although when using oils with low melt points this has proven
to be less of an issue.
Having a single return to the vegetable oil tank is another
possibility but a lot of diesel would be pumped into the vegetable
oil tank when the vehicle was running on diesel, in the wrong
circumstances this could lead to an overflowing tank.
Another option is to run this fuel, by using a T connector,
into the injector pump intake line. There is however the possibility
of a build up of air due to slight leaks and the closed circuit
giving the air nowhere to vent. This could lead to the engine
cutting out as if it had run out of fuel, as well as the possibility
of the injector pump which uses the fuel oil for lubrication
being damaged. A valve that let this air escape could be introduced
to this closed loop which would solve this problem. Many people
use this system without problems. Extra care should be taken
to make sure all pipe connections, filter seals etc. are tight
so that air cannot be sucked into the fuel system.
This method offers the advantage of mixing the fuel returned
from the injectors, which has been heated through compression
in the injector pump and contact with the engine, with the
fresh fuel supply. Upon switching the vegetable oil is gradually
mixed with the hot diesel, the vegetable oil percentage increasing
as the diesel content of the loop is gradually injected into
the engine. A mixture of fuels will be more likely to combust
completely at lower temperatures allowing a degree of leniency
with the temperature of the vegetable oil when switching.
Assessing exactly when to switch fuel sources takes trial
and error. Experimentation preferably with a vacuum gauge
will show when it is safe to switch. When using this looped
return the transfer pump does not have to work as hard as
it is not pulling the same volume of fuel from the fuel tank.
Heating Methods
Cold weather is a problem for diesel fuel as it can begin
to solidify below –7 deg C and will block the fuel filter
[11]. Products to aid diesel fuel flow in cold weather are
available and many are suitable for application in a SVO system.
Sometimes it may be appropriate to ‘tune’ these
products as they are often designed to heat to a temperature
below that which is desirable with an SVO system. Heating
systems specifically designed to be used in SVO systems are
available or can be fabricated.
Engine Coolant Heat
Only available with liquid cooled engines. The hot engine
coolant fluid is used to heat the vegetable oil. The coolant
in an engine generally runs between about 75 and 90 deg C
(158-203 deg F) so it is at a suitable temperature to heat
the oil via a heat exchanger. There are many examples of successful
coolant heated vegetable oil fuel systems.
Engine Oil Heat
Hot engine oil is used to heat the veg oil. Engine oil will
heat to above 100 deg so may be a better option than coolant
in some applications. Leaks in the oil system are much more
likely to be terminal for the engine. Great care should be
taken to avoid engine oil leaks.
Exhaust Heat
A source of heat available for any application. The hot
gasses from the engine exhaust system are utilised.
A reported system used metal fuel line wrapped around the
exhaust system of a genset. As a generator engine runs at
a steady rate using a steady fuel flow heat was regulated
by the number of turns around the exhaust. The unit was not
dual fuel and there were some problems with cold starting.
Using this heat source in a dual fuel system could lead to
problems overheating the oil before switching.
Systems have been proposed using a valve to allow a regulated
exhaust gas flow away from the existing exhaust system and
into other piping where the hot gasses are used to heat the
vegetable oil. The valve opening could be regulated to give
the required amount of heating. An idea with potential considering
the very quick heating times that could be achieved.
Returned Fuel Heat
As mentioned above the fuel returned from the injectors
has been heated through compression in the injector pump and
high pressure lines as well as from contact with the hot injector.
This heat can be used by T-ing the return into the fuel supply
as described or by sending it to the veg oil tank.
Electrical Heat
An electrical heating element is used to heat up the oil
to suitable temperatures. In a vehicle application care has
to be taken not to have a power demand that would be excessive
for a given electrical system. Rapid heating is possible with
an electric heater. A suitably modified engine equipped with
electrical heaters can be started on veg oil and run on SVO
alone.
Injector Pump Heating
Assessment of the first vehicle converted using a dual fuel
system showed the possibility of insufficiently heated oil
running through the engine and causing crud build ups in the
cylinders and on the injectors. The perceived problem was
when the fuel supply was switched from petro-diesel to vegetable
oil. The hot vegetable oil would rush into the fuel injection
pump, which was considerably cooler than the oil, cool down
and then get injected into the engine at a temperature below
that which would be desirable.
The engine was equipped with a delicate CAV rotary pump and
there was a perceived problem of possible damage from unequal
expansion due to sudden temperature changes within the injector
pump.
A method of heating the injector pump was devised. Both fuel
supplies were heated with coolant before the injector pump.
This way the injector pump would be gradually warmed by the
heated diesel fuel before switching to vegetable oil. Care
should be taken not to heat diesel fuel above its flash point
as a leak could cause engine fire. Some engines (certain Mercedes
etc.) use engine oil to lubricate the injector pump which
provides heat to the pump.
Vegetable Oil Tank and Lines
Depending on what type of oil is used and at what ambient
temperature the veg fuel tank, lines and filter may need heating
to allow free flowing of fuel. At low temperatures the veg
oil will be thick or solid and hard or impossible to pump.
The filter is a definite bottle neck. Veg oil will flow more
freely through thicker fuel pipe.
Having a filter system for each of the fuel supplies will
reduce the amount of fuel that needs to be flushed. If a filter
becomes blocked due to waxing or impurities the vehicle can
still be run on the other fuel system.
Some proponents advocate using a more course filter in the
vegetable oil line to allow thick oils to flow at the desired
rate and helps to reduce waxing. This has to be balanced with
the possible increase of particles that may pass through the
filter and cause wear to the injector pump. Heating the vegetable
oil in or up stream of the filter will help the fuel flow
and reduce the possibility of waxing the filter.
Diesel Fuel Return
Having a valve which allows the diesel fuel to be returned
back down the vegetable oil feed through the filter will act
to clean the filter, pushing any particles back to the veg
oil tank. A drain plug at the bottom of the fuel tank allows
settled particles/water to be evacuated.
Pre Heating the Engine
Mains electric, diesel and petrol fired engine pre-heaters
are available that are switched on for approximately half
an hour before starting the engine. They heat the engine coolant
and pump it around the system providing heat for the engine
cabin heater and any heat exchanger fitted.
An engine thus heated would be more likely to start on a thicker
fuel due to the extra heat in the combustion chamber. Fuel
inside a heat exchanger would be up to temperature before
the engine was started.
These units also reduce emissions and engine wear connected
with engine cold running.
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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