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WITH SUNOCO RACE FUELS
Words by Zachary Santner - Technical Specialist , Sunoco Race Fuels
OCTANE STABILITY :
High Octane Fuels vs Low Octane Fuels
Octane is the most talked about property when it comes to gasoline . It ’ s no surprise because selecting octane of gasoline is the only choice the consumer has , except what station to buy it from . In this article , Sunoco Race Fuels focuses on octane stability of regular and premium octane pump fuels versus racing fuels and what you can do to prevent octane loss in your fuel .
It is necessary to briefly review what octane is in order to dive deeper into stability issues . At fuelling stations in Australia , octane is typically displayed as the Research Octane Number , RON .
The RON is determined by a test method developed by American Society for Testing and Materials in the mid-1900s . This number provides a scale to measure how much heat and pressure can be put on the fuel before it spontaneously combusts . Spontaneous combustion is a source of engine knock which can quickly damage an engine . Octane ratings are important because different engines expose fuel to different amounts of pressure and heat – engines must use the proper octane fuel to avoid knock and provide reliable operation .
A key aspect of gasoline stability is vapor pressure . This is determined by how much pressure builds up inside a sealed fuel container when the fuel is heated to 38 ° C .
Pump fuels with high ( 12 pounds / square inch , psi ) vapor pressures are used in cold weather to prevent engine starting issues due to low temperatures . In warmer climates low vapor pressure fuels are used to prevent fuel boiling in fuel lines , also called vapor lock .
If stored in a vapor tight container , the vapor pressure can be maintained for long periods of time . Fuel exposed to the atmosphere can lose light components within a couple of days . Over time as vapor pressure decreases the fuel can become stale . Stale fuel doesn ’ t evaporate as easily and can cause rough engine idle and hard starting .
91 RON fuels tend to be less refined and contain more unstable hydrocarbons . As the months pass during storage these unstable components react to form gums , varnishes and lower octane hydrocarbons . As a result , the octane can decrease within months for 91 RON pump fuels , especially when stored under less than ideal conditions .
98 RON fuels are more refined and contain more stable hydrocarbons . These stable hydrocarbons can last two to three times longer than 91 RON fuel . Even in proper storage , 91 RON gas can start to degrade in three months , while 98 RON fuel should last closer to nine months before degradation is noticeable .
Octane stability in racing fuels is much different because fuel quality is valued more than production cost , unlike the pump gas industry where cost drives the majority of refining decisions .
A large part of any quality race fuel is consistency . Race fuels are designed to be high in octane to allow for increased compression ratios and boost levels .
In order to achieve high octane and consistent composition , pure chemical components are mixed with highly refined gasoline . The components used in Sunoco Race Fuels are very stable and can retain octane in excess of two years when properly stored . We have test results confirming octane stability in our unleaded , leaded , ethanol-free and ethanol fuels .
Some high octane unleaded fuels , 260 GT Plus , and octane