The secretive blend of stabilizers, detergents and friction modifiers in your gas

When you fill your tank with gasoline, what are you getting, exactly? It’s refined petroleum, of course, but there are also several additives and detergents in the mix.

“Gasoline is made up of molecules, and when you refine it, you take the different streams (of refined fuel) and blend them,” says Michael Howe, senior fuel scientist for Shell Global Solutions. “It has to meet a specification set by American Standard Testing and Materials, so when you buy something, you know what you’re getting.”

Additives primarily stabilize the gasoline, Howe says, so its components don’t react with one another and form deposits or gums that can possibly foul the engine. Other additives can include friction modifiers, which make it easier for the pistons to slide in their cylinders.

Additive blends also include detergents, which are similar to soap. When engines burn gasoline vapour, it creates carbon, which sticks to the valves. Known as engine gunk, these deposits can reduce the engine’s efficiency if they build up too much.

“The detergents are like a soap molecule, with a long tail and a small, reactive, polar head,” Howe says. “The long tail keeps it soluble, but when it comes across the deposits, the polar head gets stuck on the deposit and the interaction pulls off chunks of it. Then they’re carried into the combustion chamber where they’re burned.

“This continues until the deposits are gone off the valve. It’s essentially doing the same thing as soap when it interacts with greasy soil, but it’s not water-soluble, it’s gasoline-soluble.”

As the name implies, additives are put into the gasoline, blended together into what’s called an additive package. After the fuel is refined, the refinery pumps it into a pipeline, where it goes to a distribution centre and is stored in tanks. When it’s time to deliver it to gas stations, the fuel is pumped out of the tank and into a truck, and, at this point, the additive package is added to the fuel.

Although all companies use additives, the components in each package are proprietary, and their ingredients are a closely guarded secret.

“Refining fuel is a standard, specific action, but it’s never exactly the same,” Howe says. “You have to put in additives to correct it, or keep instabilities from happening.”

Gas facts

Gasoline contains octane, which controls how easily it will combust, but it isn’t an additive. Instead, the level of octane is set during the refining process.

Diesel fuel also contains additives. Sometimes diesel is also dyed red, indicating that it’s for farm machinery, and that its price doesn’t include road taxes. However, it’s illegal to use dyed diesel in regular vehicles, and the colour lets authorities know if it’s being used improperly.

Since additives do vary, try another brand of gasoline if you’re not seeing the engine

performance or mileage you think you should be getting.

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