Handbook of Cellulosic Ethanol

Fuel Characteristics of Ethanol

As discussed in the earlier section, ethanol was first introduced on a larger scale in the 1970s as a blend in fuel to serve as a replacement for methyl tertiary butyl ether (MTBE). Ethanol has a octane number of 108.6, comparable to 110 of MTBE [7]. Mixing about 10% of ethanol to gasoline can boost the octane number of the fuel [8]. The octane number is a measure of the gasoline quality for prevention of early ignition, which leads to cylinder knocking. Fuels with higher octane numbers are preferred in spark-ignition internal combustion engines (ICEs). An oxygenate fuel such as bioethanol provides a reasonable antiknock value [8]. In addition to a higher octane number, ethanol has broader flammability limits, higher flame speeds and higher heats of vaporization. These properties allow for a higher compres­sion ratio and shorter burn time, which lead to theoretical efficiency advantages over gasoline in an internal combustion engine. A com­parison of important physical properties and fuel characteristics of ethanol, methanol and gasoline is shown in Table 2.1.