Why are there so many options for vehicular gasoline at the pumps and what’s even the difference between them?
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Generally you have 2-4 options at a pump. 1 option is usually diesel, and of course thats for diesel cars.
Otherwise you generally have 3 gasoline options max, each with a different octane, primarily 87, 89, and 91 octane are the most common fuels (you will also see 92 or 93 in place of 91 in certain locations. In high altitude locations you may see 85 or 86 octane and they will often not carry 91 or higher, long story but altitude matters)
Different car motors are built differently. Certain motors, often those with more powerful engines, need more stable fuel so that it doesn’t explode prematurely and you get ‘engine knocks’ and poorer performance. These models usually use higher octane gas which thats what it is. A higher octane gas is less prone to lighting and exploding when its not supposed to. Many luxury and performance cars use 89 or 91 octane. Most economy cars use 87 octane.
A higher octane gas is not better. An engine is made in a highly specific way for a specific octane of gas for optimal use. Don’t consider these a scale of good better best, instead think of it as “we have options for all types of cars”. You should only use the fuel made specifically for your car. Your car manual will tell you which octane is the right fuel for your car
There’s also E85, which is a fuel that is a combination of gas + ethanol and can be used in place of pure gasoline in certain cars that are specifically designed for it, its adoption up and down
Edit: since this seems to be coming up a lot. This is for the US. There are different ways to measure octane so if you are in say Europe and used to 95 or 98 octane that’s the same as US 91 and 93.
Not all motors are equal. Just like how people are different so are motors. Those motors have different preferences, just like you and I.
The different fuels are to satisfy those different preferences.
Similar to how some might like spicy food, some motors prefer 93 octane over 87 octane.
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Car engines generate power by spraying gas into a cylinder that has a piston at the top. The piston then moves down squeezing the gas/air mixture before the spark plug fires igniting the mixture which pushes the piston back up very strongly.
Gas is rated by octane which is a measure of how hard that mixture can be squeezed before it will explode without a spark. Engines in high performance cars squeeze the gas/air mixture hard enough that standard (87) gas would explode too early so they require more stable fuels (higher octane ratings).
Lower octane fuels ignite easier, up to being ignitable just by squeezing them hard. Higher octane fuels need a spark to get them going. Different cars are designed for different octane ratings.
If let’s say my car / bike / truck etc hasn’t moved in a while… Let’s say it sat for a year or two.. would higher octane gas prove to be “better” then ?
In order to extract the most amount of energy from gasoline, it’s first squeezed and then ignited. Under some conditions, gasoline might ignite itself. Ignitions must be in sync, so self-ignition is unwanted. Higher gas number means the fuel is harder to self-ignite.
Some engines are built to take squeezing to an extreme, so high number fuel is necessary.
I’m going to start off by assuming you’re not asking about diesel or high ethanol fuels.
The octane number refers to the percentage of gasoline that is N-octane, which is a molecule composed of 8 carbon atoms in a straight line and saturated with hydrogens. The rest of the gasoline mixture is composed of other hydrocarbons that are similar in weight (such as other Octanes, septanes, nonanes, etc.) and thus difficult to separate during the refining process. These days a small amount of ethanol is often added as well, which accounts for much of the non N-Octane portion of the fuel.
N-Octane ignites at the appropriate time in the engine cycle (typically when a spark is introduced) however, some of the other molecules that are mixed in may ignite prematurely. If this happens it essentially causes the ignition of the fuel to occur before it would push the piston, and instead it either works against the rest of the engine or is simply wasted. This is called engine knocking, it reduces your fuel efficiency and can cause engine damage.
Gasoline mixtures with higher percentages of N-Octane are less likely to ignite prematurely because they have lower percentages of the other molecules. Thus they are less likely to cause engine knocking. Aside from this issue there’s little difference between the percentages because the other hydrocarbons that aren’t N-Octane will deliver roughly the same amount of energy per mass from a thermodynamics standpoint, so fuel efficiency isn’t really affected unless knocking is occurring.
Engine knocking, however, is far less common in newer vehicles due to better engine design, thus the higher octane fuels are typically less necessary these days and often don’t accomplish anything that the lower octane fuels wouldn’t.
I just fill it with water. But the car doesn’t work anyway. I’m not sure why, I bought it only a month ago.
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