Describe two ways in which the octane number of a gasoline consisting of alkanes can be increased.

: One way to increase the octane number of gasoline is to increase the proportion of branched alkanes in the fuel mixture. Branched alkanes have a higher octane number than their straight-chain isomers because their structure makes it more difficult for them to ignite during combustion. The branches on the alkane interfere with the ability of the molecules to pack closely together, which lowers the overall volatility and reduces the likelihood of ignition. To increase the gasoline's octane number using this method, one should focus on incorporating more branched alkanes in the fuel mixture while replacing some straight-chain alkanes.

: Another way to increase the octane number of gasoline is by adding aromatics and additives that increase the fuel's resistance to knocking and pinging. Aromatics are hydrocarbons with one or more benzene rings (such as toluene or xylene), and they have higher octane numbers than alkanes because of their stability and higher energy content. Incorporating aromatics into gasoline can improve its overall octane rating. In addition to aromatics, several additives can help increase gasoline's octane number. One popular additive is tetraethyl lead (no longer widely used due to environmental concerns), which increases the fuel's resistance to autoignition. Another option is the use of ethanol or other oxygenates, which tend to promote cleaner burning and increases the octane number as well. To achieve higher octane number using this method, additives and/or aromatics should be blended with the gasoline to improve the overall performance and resistance to knocking.