Environmental Engineering Reference
In-Depth Information
Table 8.5
Some properties of ethanol, gasoline and diesel fuel [51, 180]
Property
Gasoline (EN 590)
Diesel fuel (EN 590)
Ethanol
Specific gravity (at 15
◦
C)
0.73
0.82
0.79
Boiling point (
◦
C)
30-225
190-280
78.3
Specific heat (MJ/kg)
43.5
43.0
27.0
Heat of vaporization (kJ/kg)
400
600
900
Octane number
91-100
-
108
Cetane number
Below 15
40-60
Below 15
Flashpoint (
◦
C)
-40
64
13
Auto ignition temperature (
◦
C)
300
230
366
makes it safer for transportation and storage. Some properties of ethanol, compared
to diesel fuel and gasoline are showed in Table 8.5. However, bioethanol has several
drawbacks including a 66% lower energy density compared to gasoline, corrosive-
ness, low flame luminosity, lower vapor pressure (making cold starts difficult) and
its miscibility with water and relative toxicity to ecosystems [51, 179].
Due to its lower volatility and photochemical reactivity in the atmosphere com-
pared to gasoline, there is a reduced smog formation from evaporative emissions
in pure ethanol [181]. Bioethanol can also be conveniently blended with gasoline
to improve the octane number as well as to promote a more complete combustion.
The power output of the engine fueled with low ethanol/gasoline blends is higher
compared to gasoline-fueled engines. In general, 10% ethanol addition increases
the engine power output by 5%. However, even for low percentage ethanol/gasoline
blends (e.g. 10%), undesirable interactions between ethanol and gasoline may cause
the vapor pressure to increase. To compensate this effect, the vapor pressure of
the gasoline may be reduced. Bioethanol has a very low toxicity compared to
other petroleum-based fuels and is readily biodegradable in water and soils (>70%
biodegradable compared to diesel fuel), reducing the penetration of plumes of
smoke from leaks and environmental concerns as a consequence of spills.
8.3.2.1 Effect of Bioethanol on Diesel Engines Performance Properties
Alcohols can enhance the combustion in compression ignition engines. There are a
number of fuel properties that are essential for the optimum performance of a diesel
engine. The addition of ethanol to diesel fuel may affect key properties of the blend
with particular reference to blending stability, viscosity and lubricity, energy content
and cetane number. The properties of ethanol-diesel fuel blends have a significant
effect on safety, engine performance, durability, and emissions [177].
Homogeneous charge compression ignition (HCCI) engines tipically exhibit a
rapid combustion. However, the components in fuel mixtures do not ignite in uni-
son or burn equally. The combustion of fuel blends in HCCI engines may find a
preferential combustion of some the components of the blend [182].
The aromatic content of diesel fuel can also affect the solubility of ethanol in its
blend and therefore the effectiveness of emulsifiers and co-solvents [183]. The polar
nature of ethanol induces a dipole in the aromatic molecule allowing it to interact
