Page 218 - Biofuels Refining and Performance

Ethanol and Methanol as Fuels in Internal Combustion Engines 201

TABLE 7.4 Evaluation of Ethanol and Gasohol against Petrol
Petrol and Ethyl Alcohol
(Gasohols)
BIS
specification Ethyl 95% 90% 85% 80%
Characteristics for petrol Petrol alcohol 5% 10% 15% 20%
ASTM distillation
Initial boiling
point, C . . . . 55 78 55 50 48 46
10% volume 70 (max) 64 . . . . 59 56 57 57
50% volume 125 (max) 92 . . . . 95 73 70 70
90% volume 180 (max) 128 . . . . 145 127 130 125
Final boiling, C 215 (max) 143 . . . . . . . . 147 156 156
Gum residue, 4 22 55 51 91 131 180
mg/100
Aniline point, C . . . . 44 30 40 35 32 30
Specific gravity . . . . 0.720 0.7966 0.7230 0.722 0.7289 0.733

not be so low that vapor-locking takes place and stops the engine due
to the nonsupply of fuel. As far as volatility is concerned, ethanol–petrol
blends are as good as petrol, if not better. Also gum resistance is greater
than that of petrol. Aniline points for blends are lower, which indicates
more aromatic content than petrol, due to the adding of ethanol to petrol,
which helps to improve the octane number marginally. If a small quan-
tity of water is introduced into a gasoline–alcohol blend, phase separation
takes place, with gasoline–content in the upper phase and alcohol in the
lower. This separation produces some undesirable effects. The alco-
hol–water mixture tends to pick up sediment and stall the engine on
reaching the carburetor [4]. To improve the water tolerance of the blend,
benzene and heptanes are added.
Since 1979, gasohol has been sold at 500 filling stations in the mid-
western United States, where the corn from which alcohol is commonly
made is abundant. This blend yields about the same mileage as unleaded
gasoline and even offers an ever renewable source of energy. Moreover,
if this blend were to replace gasoline, it could cut as much as 10% of the
nation’s oil imports, which totalled $40 billion in 1979. This fuel has a
good future in wealthy countries. The blends have some important
advantages over pure ethanol, as listed below:
1. The starting difficulty can be removed.
2. There is no abnormal corrosion compared with pure ethanol.
3. Lubrication in a petrol–alcohol blend is more or less the same.
4. Some benzene is added to prevent separation of the layers of petrol
and alcohol.