What does alcohol do in gasoline?

Answer 1

• The level of interest in using alcohol as a motor fuel has followed cycles of fuel shortages and/or low feed-grain prices.
• Alcohols burn more completely, thus increasing combustion efficiency.
• There are many disadvantages to using alcohols, particularly methyl and ethyl alcohol.
• Advantages of mixing alcohol with gasoline are that alcohol tends to increase the octane rating and reduce carbon monoxide emissions.
• Alcohols may corrode certain materials used in engines.

Alcohol has been used as a fuel for internal combustion engines since their invention. Reports on the use of alcohol as a motor fuel were published in 1907 and detailed research was conducted in the 1920s and 1930s. Historically, the level of interest in using alcohol as a motor fuel has followed cycles of fuel shortages and/or low feed-grain prices.

The properties of methyl, ethyl and butyl alcohol are compared with octane (high quality gasoline) and hexadecane (high quality diesel fuel) in Table 1. Note that octane and hexadecane (petroleum fuels) have higher boiling points, lower latent heats and are insoluble in water. The alcohols become more like petroleum fuels as their chemical weights increase.

Methyl alcohol has the lowest combustion energy of all the fuels listed. However, it also has the lowest stoichiometric or chemically correct air-fuel ratio. Therefore, an engine burning methyl alcohol would produce the most power. It also is possible to take advantage of the higher octane ratings of methyl (and ethyl) alcohol and increase the engine compression ratio. This would increase the efficiency of converting the potential combustion energy to power. Finally, alcohols burn more completely, thus increasing combustion efficiency.

Answer 2

Alcohol, such as ethanol, can be used as a fuel additive in gasoline to increase its oxygen content and raise the octane rating. This can lead to improved engine performance and reduce engine knock. Additionally, alcohol can also act as a cleaner, helping to reduce carbon buildup in the engine.