138
Alternative Fuels for Transportation
a proprietary additive of the Pure Energy Corporation. The oxy-diesel contained both ethanol and diesel fuel and thus, not surprisingly, fell between
the two in biodegradability.
5.4 Ethanol–Gasoline Engine Tests
Ethanol can be used either as a pure fuel or as a gasoline additive. Both
options can provide some advantages for engine performance, fuel economy, and exhaust emissions. Ethanol can be blended with gasoline at any
percentages in pure form and used in SI engines. Gasoline-ethanol blends
at low proportions can be used without any engine modification but pure
ethanol requires major modifications to the engine design and fuel system.
5.4.1 engine Dynamometer Tests
Palmer (1986) used various blend rates of ethanol-gasoline fuels in engine
tests. Results indicated that 10%v ethanol addition increases the engine
power output by 5%, and the octane number can be increased by 5% for each
10%v ethanol added. The reduction of CO emission is apparently caused by
the wide flammability and oxygenated characteristics of ethanol. Therefore,
the ethanol blends provided improvements in power output, efficiency, and
fuel economy. Al Hasan (2003) conducted tests using a four cylinder, four
stroke SI engine with a swept volume of 1452 c.c., a compression ratio of 9:1
and a maximum power of 52kW at 5600 rpm.
Brake thermal efficiency of the engine increased with increased ethanol concentration in the blends. The maximum brake thermal efficiency
was achieved with an E20 blend. Torque and power increased with ethanol content up to 20% v but decreased with higher ethanol concentrations
(Figure 5.3).
During the compression stroke, vaporization of fuel tends to decrease
the temperature of the fuel–air mixture and increase the quantity of vapor.
However, when a low-latent heat fuel such as gasoline is used, the effect
of cooling is not sufficient to overcome the effect of additional vapor.
Increasing the latent heat of the fuel blend used by increasing the ethanol
concentration increases the effect of cooling, which reduces the compression work. As the ethanol concentration increases in the fuel blend, the pressure and temperature decrease at the beginning of combustion. However,
increasing the ethanol concentration increases the AFR; that is, decreases
the heat transfer to the cylinder walls due to incomplete combustion, and
therefore, increases the value of maximum pressure. Hence, increasing the
ethanol concentration in the fuel blend increases the indicated efficiency
remarkably.
Alternative Fuels for Transportation
a proprietary additive of the Pure Energy Corporation. The oxy-diesel contained both ethanol and diesel fuel and thus, not surprisingly, fell between
the two in biodegradability.
5.4 Ethanol–Gasoline Engine Tests
Ethanol can be used either as a pure fuel or as a gasoline additive. Both
options can provide some advantages for engine performance, fuel economy, and exhaust emissions. Ethanol can be blended with gasoline at any
percentages in pure form and used in SI engines. Gasoline-ethanol blends
at low proportions can be used without any engine modification but pure
ethanol requires major modifications to the engine design and fuel system.
5.4.1 engine Dynamometer Tests
Palmer (1986) used various blend rates of ethanol-gasoline fuels in engine
tests. Results indicated that 10%v ethanol addition increases the engine
power output by 5%, and the octane number can be increased by 5% for each
10%v ethanol added. The reduction of CO emission is apparently caused by
the wide flammability and oxygenated characteristics of ethanol. Therefore,
the ethanol blends provided improvements in power output, efficiency, and
fuel economy. Al Hasan (2003) conducted tests using a four cylinder, four
stroke SI engine with a swept volume of 1452 c.c., a compression ratio of 9:1
and a maximum power of 52kW at 5600 rpm.
Brake thermal efficiency of the engine increased with increased ethanol concentration in the blends. The maximum brake thermal efficiency
was achieved with an E20 blend. Torque and power increased with ethanol content up to 20% v but decreased with higher ethanol concentrations
(Figure 5.3).
During the compression stroke, vaporization of fuel tends to decrease
the temperature of the fuel–air mixture and increase the quantity of vapor.
However, when a low-latent heat fuel such as gasoline is used, the effect
of cooling is not sufficient to overcome the effect of additional vapor.
Increasing the latent heat of the fuel blend used by increasing the ethanol
concentration increases the effect of cooling, which reduces the compression work. As the ethanol concentration increases in the fuel blend, the pressure and temperature decrease at the beginning of combustion. However,
increasing the ethanol concentration increases the AFR; that is, decreases
the heat transfer to the cylinder walls due to incomplete combustion, and
therefore, increases the value of maximum pressure. Hence, increasing the
ethanol concentration in the fuel blend increases the indicated efficiency
remarkably.