Final answer:
The fuel octane rating indicates a fuel's ability to resist engine knocking or pinging, with a higher rating signifying better quality and performance. It's determined by comparing the fuel's performance to a standard mix of n-heptane and isooctane. Additives known as octane enhancers are used to increase this rating, although some, like tetraethyllead, have been phased out due to health concerns.
Step-by-step explanation:
The term fuel octane rating refers to a measure of a fuel's ability to resist knocking or pinging—a sign of premature combustion—in a combustion engine. Essentially, it expresses the quality of fuel with a higher octane rating indicating a greater resistance to knocking. This is important as knocking can lead to reduced power output and potential engine damage. The octane rating is based on a comparison to the performance of a standard mixture of n-heptane (which easily knocks and is given a rating of 0) and isooctane (which burns smoothly and is rated at 100). For example, a fuel with the same performance as a blend of 89% isooctane to 11% n-heptane would be given an octane rating of 89.
Over the years, compounds such as tetraethyllead were used as octane enhancers to improve the rating, but these have been phased out due to toxicity, with alternatives like ethanol becoming more common.