Understanding Octane Rating

By: Nick Stanley / September 4, 2018


Each time you pull into a gas station you’ve certainly noticed several types of fuel to choose from, but how do you know which type is best for your vehicle?  On most gasoline pumps, there are bold numbers displayed on a yellow background from 87-94, these are referred to as the octane rating. In America, the octane rating is computed from the average of research octane (RON) and motor octane (MON) known as the Anti-Knock Index (AKI).  This is also displayed on the pumps generally right above the double digit numbers as (R+M)/2 Method.  In Europe however, the octane rating on the pump is simply the RON figure. While most gasoline vehicles are designed to run on 87 octane, let’s take a look at why other vehicles are designed to use higher octane fuel.

The U.S. Department of Energy describes the difference in octane levels as such; “Higher octane fuels are often required or recommended for engines that use a higher compression ratio and/or use supercharging or turbocharging to force more air into the engine. Increasing pressure in the cylinder allows an engine to extract more mechanical energy from a given air/fuel mixture but requires higher octane fuel to keep the mixture from pre-detonating.”  

Knowing which fuel your vehicle is designed to run on is something every car owner should consider.  For example, using a lower octane fuel than your engine requires could result in “engine knock”. Engine knock occurs when the fuel/air mixture ignites before the spark plug can do its job, creating a knocking or pinging sound.  Although many newer vehicles can adjust spark time to reduce the knock, eventually it can damage the engine.  For the reverse, using a higher octane fuel in your vehicle may increase performance/gas mileage.  But under normal driving conditions, the cost increase typically outweighs the fuel savings.   The easiest way to know which octane rating is recommended for your vehicle is to check your owner’s manual. A big effort has been made recently to increase miles per gallon and decrease emissions which many believe has opened the door to higher octane fuels.  According to the EPA they are in the process with the National Highway Traffic Safety Administration to develop rules that will set “more appropriate GHG emissions standards and Corporate Average Fuel Economy (CAFE) standards.”  What does this mean looking forward?  With the push now on to increase octane levels we could see more ethanol blended fuel.  Brian Jennings the CEO of the American Coalition for Ethanol (ACE) states “ethanol-enriched, high octane fuel enables automakers to simultaneously reduce GHG emissions and improve fuel economy.”     






Categories: gas, Fuel, driving, gasoline, vehicles

Nick Stanley

Written by

Nick Stanley

By listening to each of my customers unique fueling needs, I am able to pair them with the best solution. Through effective communication, I provide the highest level of personal customer service which creates long lasting professional relationships.

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