What test is used to determine the octane rating of gasoline?

The knock test is used to determine the octane rating of gasoline because it evaluates how resistant the fuel is to knocking during combustion. Knocking occurs when fuel combusts prematurely in the engine cylinder, which can lead to engine damage and inefficiency. The octane rating essentially measures this resistance; higher octane fuels are able to withstand higher pressures and temperatures before knocking occurs.

In the knock test, a standardized engine setup is used, and the fuel sample is subjected to conditions that simulate real-world combustion. The results show the performance of the fuel in terms of knocking, giving a numerical rating that indicates its octane level. This process is crucial for ensuring that fuels are suitable for use in various types of engines and for helping manufacturers formulate engines that maximize efficiency and performance based on the required octane levels.

Other tests such as the flash point, viscosity, and density tests measure different properties of the fuel but do not directly relate to its ability to perform without knocking in an engine, which is why they are not used for determining the octane rating.