Question

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

Short answer

The two ways to increase the octane number of a gasoline consisting of alkanes are: 1. Increase the branching of alkanes (e.g., incorporate more branched alkanes in the gasoline) as branched alkanes have higher octane numbers and better knock resistance. 2. Add oxygenates, such as ethers (MTBE) or alcohols (ethanol), to the gasoline mixture to improve the knock resistance, increase the overall octane number, and reduce harmful exhaust emissions.

Step-by-step solution

Way 1: Increase the branching of alkanes

One method to increase the octane number of gasoline consisting of alkanes is by increasing the branching of the alkanes. In simpler terms, the more the alkane molecules have branches, the higher their octane numbers. Branched alkanes have a more stable structure and burn more smoothly, thus providing better knock resistance. So, by incorporating more branched alkanes in the gasoline, the overall octane number can be improved.

Way 2: Add oxygenates to the gasoline

Another method to increase the octane number of gasoline is by adding oxygenates to the gasoline mixture. Oxygenates, such as ethers (e.g., MTBE - methyl tertiary-butyl ether) and alcohols (e.g., ethanol), have higher octane numbers and can improve the knock resistance of the gasoline. Blending these oxygenates with gasoline can increase the overall octane number, allowing for smoother combustion and less knocking in the engine. This method not only improves the gasoline's octane number but also helps in the reduction of harmful exhaust emissions.