The Difference Between Cetane and Octane

When you pull up to the gas pump, you will have three or even more choices of fuel, each with a number that indicates the octane level. Few of us really understand what that means. Ray Bohacz is Successful Farming’s engine man. He says the octane number represents the fuel’s ability to resist combustion through pressure and heat. 

"It has nothing to do with the power of gasoline, it has to do with its ability to resist combustion and wait for the arcing of the spark plug," says Bohacz. "So a higher octane fuel will resist more pressure and more heat before it auto-ignites or self-combusts.  When the fuel self-combusts, the engine will talk to us, and that is commonly known as ‘ping’ or ‘knock’."

If you hear the ping or knock, try using a higher-number octane fuel in your tank.

Cetane is the exact opposite of octane. Bohacz says it’s number represents the fuel’s eagerness to ignite through the pressure and heat created by the piston compressing the air in a diesel engine.

"The higher the cetane number, the better the engine will run, and also the quieter and more efficient it will be," he says. "There are commonly-available products to boost octane and cetane. Gasoline you really don’t need an octane booster because you can make that selection at the pump. But, with cetane on the farm, it’s always a good idea to add a cetane booster to that fuel to improve the performance of your engines."

Always make sure you refuel your vehicles and machinery with the recommended type of fuel for their engines.

Ray Bohacz talks more about cetane and octane ratings

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