Ethanol – also known as ethyl alcohol, pure alcohol, grain alcohol, alcohol, spirit, and hydroxyethane – is a flammable and colorless liquid with a boiling point of 78.4°C, melting point of −114.3°C, and density of 0.79 g/cm3. Ethanol is used in alcoholic beverages, solvents, scents, flavorings, coloring, medicines, chemical synthesis, and thermometers. With its molecular formula of C2H5OH, ethanol contains 52 wt% carbon, 13 wt% hydrogen, and 35 wt% oxygen. Due to its heating value, ethanol has a long history of use as a fuel for heating and lighting; recently, it has been used as a fuel for internal combustion engines. The fermentation of sugar into ethanol is one of the earliest organic reactions employed by humanity. In modern times, ethanol intended for industrial use is also produced by hydration of ethylene byproduct in the petroleum industry.
When compared with gasoline, ethanol has a higher octane number, broader flammability limits, higher flame speeds, and higher heats of vaporization. These properties allow for a higher compression ratio, shorter burn time, and leaner burn engine, resulting in a higher efficiency. Ethanol is an oxygenated fuel that contains 35% oxygen, which reduces particulate and nitrogen oxides emissions from combustion. Disadvantages of ethanol include a lower energy density than gasoline, corrosiveness, difficult cold start due to low vapor pressure, low flame luminosity, miscibility with water, and some toxicity to the ecosystems.