What are Advantages and Disadvantages of Gasohol?

Answer 1

Because the emissions produced by the burning of gasoline are a major source of air pollution, alternatives to gasoline are currently being developed. None of the alternatives (listed below) delivers as much energy content as gasoline. Therefore, it takes greater quantities of each of these fuels, than it does gasoline, to drive an equal number of miles. The most viable alternative to gasoline is called "flexible fuel," a combination of methanol and gasoline. The use of flexible fuel, however, would require an expensive fuel sensor and a longer fuel tank, adding at least $300 to the price of a car.

There are many disadvantages to using alcohols, particularly methyl and ethyl alcohol. Although these alcohols, when used near their stoichiometric air-fuel ratios, produce more power, a larger quantity of fuel is required to produce a specified power output. For example, in an automobile, more fuel is required for each mile driven. The relatively low boiling points and high vapor pressures of methyl and ethyl alcohol indicate that vapor lock could be a serious problem, particularly at high altitudes on warm summer days. Butyl alcohol, because of its low vapor pressure, is the least likely of the alcohols to cause vapor lock. The relatively high latent heats of methyl and ethyl alcohol cause problems in mixing these alcohols with air and transporting them through the intake manifold of the engine. Heating the intake manifold may be necessary in cold weather or before the engine reaches operating temperatures. Without external heat to more completely vaporize the fuel, the engine may be difficult to start and sluggish for a considerable time after starting. Butyl alcohol is the least likely to cause starting difficulties or problems during warm-up. Note that its latent heat is almost the same as the latent heat of octane. All of the alcohols are soluble in water, but butyl alcohol is relatively insoluble compared to methyl and ethyl alcohol. Less engine power is produced as the water content of an alcohol increases. Further, vapor lock, fuel mixing and starting problems increase with water. Table 1: Characteristics of chemically pure fuels.*

Chemical formulaChemical weight (lb/mole)Specific gravityBoiling point (C)Latent heat (Btu/lb)Combustion energy (Btu/lb)Vapor pressure @100F (psi)Solubility part in 100 parts H2OStoichio-metric air-fuel ratio Methyl alcohol CH3OH320.796550310,2604.6infinite6.5 Ethyl alcohol CH3CH2(OH)46.10.797839613,1602.2infinite9 Butyl alcohol C2H5CH2CH2(OH)74.10.8111718615,7700.3911.2 Octane C8H181140.7021015520,7501.72insoluble15.2 Hexa-decane C16H342400.79287--20,3203.46insoluble15 *To convert to metrics, use the following conversion factors: 1 pound = 45 kilogram; 1 degree F = degrees C - 32 x 5/9. ======