Page 217 - Biofuels Refining and Performance

200 Chapter Seven

9. In many hot-climate countries, more precautions are often taken for
the use of more volatile spirit-based fuels, while alcohol is perfectly
safe in the hottest climate.
10. The major problem faced with ethanol is corrosion; special metals
should be used for the engine parts to avoid corrosion.
Alcohols are clean-burning, renewable alternative fuels that can come
to our rescue to meet the duel challenge of vehicular fuel oil scarcity and
fouling of the environment by exhaust emissions.
Alcohols inherently make very poor diesel engine fuels as their cetane
number is considerably lower. They can be used in dual-fuel engines or
with assisted ignition in diesel engine. In the dual-fuel mode, alcohol is
inducted along with air, compressed, and then ignited by a pilot spray
of diesel oil.

7.5 Use of Blends
Alcohol can be used as a blend with gasoline as this has the advantage
that the existing engines need not be modified and tetra-ethyl lead
(TEL) can be eliminated from gasoline, due to the octane-enhancing
quality of alcohol. If the engine is to be operated using only pure alco-
hol, then some major modifications are required in the engine and fuel
system, as listed below:

1. Both alcohols and blends with gasoline are corrosive to many of the
engine materials. These materials have to be changed.
2. Adjustment of the carburetor and fuel injection need to be made to
compensate for the leaning effect.
3. Change in the fuel pump and circulation system need to be made to
avoid vapor lock, as the methanol vaporization rate is very high.
4. Introduction of high energy ignition system with lean mixture.
5. Increase in compression ratio to make better antiknock properties of
the fuel.
6. Addition of detergent and volatile primers to reduce engine deposits
and assist in cold starting.
7. Use of cooler-running spark plugs to avoid preignition.
General properties of the blends are listed in Table 7.4. The volatil-
ity shown by the American Standard Testing Method (ASTM) distillation
characteristics of petrol is a compromise between opposing factors to
ensure good performance in petrol engines. This requires petrol to have
a sufficiently lighter reaction and a 10% distillation temperature in
order to start the engine as well as warm up, but the temperature should