26
Alternative Fuels for Transportation
value of an oil increases with the decrease of its molecular weight. The C
and H percentages in oil increase with a decrease in molecular weight. The
decrease in saponification value results in the increase in heat content of
an oil. The increase in iodine value results in a decrease in heat content of
oil. The heat content of oil depends on iodine and saponification value. The
physiochemical properties of various vegetable oils are depicted in Table 2.4
(Deimbras 2003).
2.3 Methods to Use Vegetable Oils in Engines
2.3.1 Pyrolysis
Pyrolysis is a promising method for the production of environmentally
friendly liquid fuels. It is the chemical reaction caused by the application
of thermal energy in the absence of air. Vegetable oils and animal fats can
be pyrolyzed. Pyrolysis process takes place at higher temperatures of about
250–400ºC and at higher heating rates. Heating of vegetable oils breaks the
bigger molecules into smaller molecules and a wide range of HC are formed.
The pyrolyzed products can be divided into gaseous, liquid fractions consisting of paraffins, olefins and naphthenes, and solid residue. The pyrolyzed
vegetable oils contain acceptable amounts of sulfur, water, and sediment and
give acceptable copper corrosion values but unacceptable ash, carbon residue,
and pour point. Pyrolyzed vegetable oil contains compounds in the boiling
range of gasoline. The properties of bio-oil depends upon the nature of the
feedstock, temperature of pyrolysis process, thermal degradation degree and
catalytic cracking, the water content of the pyrolysis oil, the amount of light
ends that have collected, and the pyrolysis process used. The high oxygen
content of pyrolysis oil results in a very low energy density in comparison
to conventional fuel oils. The comparison of properties of pyrolyzed oil with
biodiesel and diesel is given in Table 2.5.
2.3.2 Microemulsification
The formation of microemulsions (cosolvency) is one of the potential solutions for solving the problem of vegetable oil viscosity. Microemulsions are
defined as transparent, thermodynamically stable colloidal dispersions. The
droplet diameters in microemulsions range from 100 to 1000 Å. The microemulsion can be made of vegetable oils with an ester and dispersant (cosolvent), or of vegetable oils, an alcohol and a surfactant and a cetane improver,
with or without diesel fuels. Water (from aqueous ethanol) may also be
present in order to use lower-proof ethanol, thus increasing water tolerance
of the microemulsions. Microemulsion can improve the spray characteristics
Alternative Fuels for Transportation
value of an oil increases with the decrease of its molecular weight. The C
and H percentages in oil increase with a decrease in molecular weight. The
decrease in saponification value results in the increase in heat content of
an oil. The increase in iodine value results in a decrease in heat content of
oil. The heat content of oil depends on iodine and saponification value. The
physiochemical properties of various vegetable oils are depicted in Table 2.4
(Deimbras 2003).
2.3 Methods to Use Vegetable Oils in Engines
2.3.1 Pyrolysis
Pyrolysis is a promising method for the production of environmentally
friendly liquid fuels. It is the chemical reaction caused by the application
of thermal energy in the absence of air. Vegetable oils and animal fats can
be pyrolyzed. Pyrolysis process takes place at higher temperatures of about
250–400ºC and at higher heating rates. Heating of vegetable oils breaks the
bigger molecules into smaller molecules and a wide range of HC are formed.
The pyrolyzed products can be divided into gaseous, liquid fractions consisting of paraffins, olefins and naphthenes, and solid residue. The pyrolyzed
vegetable oils contain acceptable amounts of sulfur, water, and sediment and
give acceptable copper corrosion values but unacceptable ash, carbon residue,
and pour point. Pyrolyzed vegetable oil contains compounds in the boiling
range of gasoline. The properties of bio-oil depends upon the nature of the
feedstock, temperature of pyrolysis process, thermal degradation degree and
catalytic cracking, the water content of the pyrolysis oil, the amount of light
ends that have collected, and the pyrolysis process used. The high oxygen
content of pyrolysis oil results in a very low energy density in comparison
to conventional fuel oils. The comparison of properties of pyrolyzed oil with
biodiesel and diesel is given in Table 2.5.
2.3.2 Microemulsification
The formation of microemulsions (cosolvency) is one of the potential solutions for solving the problem of vegetable oil viscosity. Microemulsions are
defined as transparent, thermodynamically stable colloidal dispersions. The
droplet diameters in microemulsions range from 100 to 1000 Å. The microemulsion can be made of vegetable oils with an ester and dispersant (cosolvent), or of vegetable oils, an alcohol and a surfactant and a cetane improver,
with or without diesel fuels. Water (from aqueous ethanol) may also be
present in order to use lower-proof ethanol, thus increasing water tolerance
of the microemulsions. Microemulsion can improve the spray characteristics