Would you expect a substance like toluene see left to enhanc

Would you expect a substance like toluene (see left) to enhance the octane rating of gasoline? Why or why not? Would you expect a substance like ethanol to enhance the octane rating of gasoline? Why or why not?

Solution

16. Octane number is a measure of the performance of an engine. The higher the octane number, the engine can compress the fuel more and provide better performance.

In a typical air-fuel mixture, the compression of the fuel leads to heating of the mixture and is burnt by the spark plug. Too much compression of the fuel can lead to excessive heating which in turn leads to generation of excessive pressures. Engine components are usually not built to withstand such high pressures; therefore, the compression and heating can lead to “knocking” sound of the engine. Octane is used as an “anti-knock” agent. A fuel with higher octane number offers increased resistance to self-ignition by the spark plug and hence excessive heating. Toluene can be used as an additive to enhance “anti-knock” properties of fuels. Toluene is known to enhance octane number by offering better resistance to self-ignition. Toluene is denser than other gasoline fuels and liberates more energy and thus more power. However, 100% toluene is bad as it is explosive and can damage standard rubber fuels. Hence, a proper concentration of toluene with other performance boosters can be used for better results.