Mechanics Corner: Octane is the King of the Castle

Octane is the King of the Castle. Or at least the gatekeeper. Without it, you are not going far.

When it comes to internal combustion spark-ignition engines that run on gasoline or a blend of ethanol and gas there are some rules. Poor quality fuel could not be thrown into any engine and be expected to work perfectly. If we did not have octane to aide in the combustion process the car as we know it today would certainly not exist. The high-output, supercharged engines that have come on the market over the past decade are a result, in part, due to the fuel we have available to us. Fuel that also results in cleaner tailpipe emissions. 

Let’s take a quick look at octane. For many of us it is a familiar term that is used in many ad campaigns and at the pump but what is it and what does it really do?

The Octane rating is the measure fuel stability, the more the better to a point. Octane controls the pressure at which a fuel will spontaneously combust in an engine, meaning ignite itself. To come up with the octane number they average the two different octane rating methods: motor octane number, or MON, and research octane number, or RON. The higher an octane the more stable the fuel. 

So, why should we care about how stable a fuel is once it is in our engine? It is just going to burn anyway right? So here is the deal. If a fuel is not very stable it will explode (auto-ignite without a spark). If that happens the engine will beat itself to death because the piston is not at the top of its travel when the fuel ignites and that makes the engine fight itself. You know this is happening because you can hear it while driving and it sounds like a rattle. That sound is damaging your engine. 
The higher performance cars today have higher compression and therefore need the higher octane, or they would have a huge problem with detonation. 

What would happen if the manufacturers had a higher octane mandated across the board at the fuel pump? Well, fuel mileage and horsepower could increase and if the octane comes from ethanol, harmful tailpipe emissions could be reduced. If manufacturers had the octane, they could increase compression. However, as it stands that will not work because the number at the pump is just too low unless you pay the high cost for premium. 

So why don’t we just raise the octane at the pump across the board? Well, octane is expensive to produce and if you were to raise the numbers across the board the price would increase quite a bit. There is a proven alternative though: ethanol. It is a natural way to greatly increase octane in gasoline when blended because pure ethanol is 113 octane without having to add anything to it. It is also much cheaper and cleaner than producing octane from oil, so low octane gasoline blended with high-octane ethanol is affordable for drivers, cleaner to the environment and proven to be a safe option for automotive engines. That would be an affordable way to keep drivers happy and give manufacturers what they need to continue to produce internal combustion engines.

The Under The Hood radio show is America’s Favorite Car-talk show heard on over 230 stations and podcast. The Motor Medics, Russ Chris and Shannon are three great friends having fun and offering a wide range of automotive advice without the aid of in-studio computers or reference guides.




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