Page 292 - Biosystems Engineering

Biodiesel and Ethanol in Engines 269

2. By direct hydration: Is formed per the following chemical
reaction:
C H + H O = C H OH
2 4 2 2 5
This type of conversion is not found very much, as the reaction
is exothermic. This method of production is not suitable for
mass production and contains 90 percent gasoline and 10 percent
ethanol.
3. Anhydrous alcohol from vegetable wastes:

The Philippines carries out an alcogas program to produce its
own anhydrous alcohol from local vegetable wastes for blending
with petrol. This program is currently based on sugarcane juice and
molasses, but it plans to diversify by using other raw materials. In the
basic process, cellulose conversion begins with pretreatment of raw
materials, which may include coffee hulls, rice straw, and grass-to-
sawmill wastes. Enzymes then take over by converting the feedstock
into a sugary liquid that is fermented and finally distilled into anhy-
drous alcohol. After distillation, waste residues can be evaporated
into syrup to feed animals, whereas unconverted cellulose is used as
the primary fuel for the plant. If the Philippines could engineer a
breakthrough in this area, it’s agricultural and forestry wastes could
supply the energy equivalent to 9.720 million liters of oil annually. In
the years to come, this new energy source could make a significant
economic impact on a country that depends on imports of crude oil
for 95 percent of its energy.
Ethanol has been more expensive than petroleum but can become
competitive when petroleum prices rise; for example, the Organiza-
tion of Petroleum Exporting Countries is able to control supplies to
raise crude oil prices.
Ethanol has a very high-octane rating, and it is a good spark–
ignition engine fuel. Ethanol is already in widespread use as an addi-
tive to gasoline for use in SI engines. Because cetane and octane
ratings vary inversely, however, ethanol necessarily has a low-cetane
rating and will not self-ignite reliably in most compression ignition
engines.
Ecklund et al. state that fumigation is a method by which alco-
29
hol is introduced into the engine by vaporizing the alcohol in the
intake airstream. This requires adding a carburetor along with a sepa-
rate fuel tank, lines, and controls. Alcohol delivery must be reduced
at low loads to prevent flame quenching and misfire and at high loads
to prevent preignition and engine knock. With these methods, fumi-
gation of ethanol offers several advantages, including the following:
1. Fumigation requires a minimum modification to the engine.
2. Fumigation can reduce NO emissions and smoke level.
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