Ethanol
135
the combustion and reduces the partial combustion of fuel. Ethanol is the
preferred ingredient for the biodiesel transesterification process as it is produced from agricultural products and renewable in nature and it is less
objectionable to environment. The properties of ethanol in comparison with
gasoline and diesel are shown in Table 5.1.
Ethanol has higher research octane numbers (RON; > 100) than gasoline.
When ethanol is blended with gasoline, the RON is boosted but there is
minimal or no increase in motor octane number (MON). Ethanol–gasoline
blends of the same RON have given better performance during low-speed
and accelerating conditions, but were inferior in performance at higher speed
conditions in comparison with gasoline. The MON can be increased by adding suitable components in the refinery itself and hence the risk of engine
damage can be minimized.
High octane helps prevent engine knocking and is extremely important
in engines designed to operate at a high compression ratio to generate more
power. High compression ratios result in higher energy efficiency. Low-level
blends of ethanol, such as E10 (10% v ethanol, 90% v gasoline), generally have
a higher octane rating than unleaded gasoline. Low-octane gasoline can be
blended with 10% ethanol to attain the standard (M + R)/2 requirements of
87 for regular gasoline. (M + R)/2 is the numerical average of the MON and
RON. Abdel-Rahman and Osman (1997) tested 10%, 20%, 30%, and 40% volume blends of ethanol in gasoline for use in a variable compression ratio
engine. They found that increased ethanol content increased the octane
number, but decreased the heating value. They reported that E10 is an optimum blend for gasoline engine applications.
Ethanol is an effective solvent and can be considered a fuel detergent. Thus
ethanol use as a gasoline additive helps to remove gum and deposits from
fuel systems. Deposits in fuel tanks and carburetor bowls will eventually
cause problems in engines running on straight gasoline; however, ethanol
blends may accelerate the release of deposits. It has been reported that ethanol has some detergent properties that reduce buildup, which keeps engines
running smoothly and fuel injection systems clean for better performance
(EPA420-F-00-035 2002).
Blends of gasoline and ethanol form azeotropes that cause a disproportionate increase in vapor pressure and a reduction in front-end distillation temperature. This effect varies with the amount of ethanol content but
becomes significant at ethanol concentrations around 10% v . The increase in
vapor pressure could cause hot drivability problems in vehicles. Hence, random mixing of gasoline and ethanol should be avoided for hot drivability
problems. To tackle this problem, it is necessary to remove high volatility
components such as butane from the gasoline. Moreover, high ethanol concentrations in blends can cause cold drivability problems because ethanol
has a higher latent heat of vaporization than gasoline.
Though the Reid vapor pressure of pure ethanol is low in comparison with
gasoline, the RVP of gasoline-ethanol blends rises depending on the ethanol
135
the combustion and reduces the partial combustion of fuel. Ethanol is the
preferred ingredient for the biodiesel transesterification process as it is produced from agricultural products and renewable in nature and it is less
objectionable to environment. The properties of ethanol in comparison with
gasoline and diesel are shown in Table 5.1.
Ethanol has higher research octane numbers (RON; > 100) than gasoline.
When ethanol is blended with gasoline, the RON is boosted but there is
minimal or no increase in motor octane number (MON). Ethanol–gasoline
blends of the same RON have given better performance during low-speed
and accelerating conditions, but were inferior in performance at higher speed
conditions in comparison with gasoline. The MON can be increased by adding suitable components in the refinery itself and hence the risk of engine
damage can be minimized.
High octane helps prevent engine knocking and is extremely important
in engines designed to operate at a high compression ratio to generate more
power. High compression ratios result in higher energy efficiency. Low-level
blends of ethanol, such as E10 (10% v ethanol, 90% v gasoline), generally have
a higher octane rating than unleaded gasoline. Low-octane gasoline can be
blended with 10% ethanol to attain the standard (M + R)/2 requirements of
87 for regular gasoline. (M + R)/2 is the numerical average of the MON and
RON. Abdel-Rahman and Osman (1997) tested 10%, 20%, 30%, and 40% volume blends of ethanol in gasoline for use in a variable compression ratio
engine. They found that increased ethanol content increased the octane
number, but decreased the heating value. They reported that E10 is an optimum blend for gasoline engine applications.
Ethanol is an effective solvent and can be considered a fuel detergent. Thus
ethanol use as a gasoline additive helps to remove gum and deposits from
fuel systems. Deposits in fuel tanks and carburetor bowls will eventually
cause problems in engines running on straight gasoline; however, ethanol
blends may accelerate the release of deposits. It has been reported that ethanol has some detergent properties that reduce buildup, which keeps engines
running smoothly and fuel injection systems clean for better performance
(EPA420-F-00-035 2002).
Blends of gasoline and ethanol form azeotropes that cause a disproportionate increase in vapor pressure and a reduction in front-end distillation temperature. This effect varies with the amount of ethanol content but
becomes significant at ethanol concentrations around 10% v . The increase in
vapor pressure could cause hot drivability problems in vehicles. Hence, random mixing of gasoline and ethanol should be avoided for hot drivability
problems. To tackle this problem, it is necessary to remove high volatility
components such as butane from the gasoline. Moreover, high ethanol concentrations in blends can cause cold drivability problems because ethanol
has a higher latent heat of vaporization than gasoline.
Though the Reid vapor pressure of pure ethanol is low in comparison with
gasoline, the RVP of gasoline-ethanol blends rises depending on the ethanol