Have you ever wondered why there are 2 to 3 types of unleaded fuels at gasoline stations? If you look at the fuel pumps, you'd typically see regular grade, premium, or high octane. Then you'll see 'minimum octane rating' with a number that ranges usually from 91-100. So what's the fuss all about?
Generally, it is said that the higher the octane rating, the better the fuel. In return, that makes your car perform better. But what exactly is an octane rating? Let us explain.
The scientific explanation behind octane is the measure of how much compression fuel can withstand before pre-ignition. Lost us for a second there? Simply put, the higher the octane rating, the less likely the fuel will burn before it's actually supposed to, which could damage your engine.
The longer answer is a bit more complicated. To understand it better, let's take a look at how engines work in the first place. We'll do our best not to bore you about it.
Majority of the engines being put into the vehicles we buy have what's called a four-stroke cycle. To simplify, just remember these four words: Suck, squeeze, bang, blow.
First, the engine sucks in air and fuel into the cylinder. It then squeezes the two via pistons, compressing the air and fuel, increasing the temperature and pressure in the cylinder. As a result, it goes bang thanks to the spark plug, which creates the energy that gives the engine power, moving all the oily bits (crankshaft, valves, etc) that propels the car into motion. This is followed by Step 4: blow. That's when the piston pushes what’s left of the combusted air and fuel, known as exhausts, out to your tailpipe. Then the cycle starts all over again.
How does this relate to octane? Why can't we just dump any kind of fuel in our cars? Every engine issued to a vehicle has a standard minimum octane rating that should be followed, as indicated in your vehicle's owner manual. The higher the octane rating, the more efficiently the fuel can burn, at the right time and not 'bang' in advance, which disrupts the natural cycle of the engine.
So let's say your vehicle is rated to run at minimum 95 octane and you accidentally load it with 91 octane fuel. What happens? This will result in what is know as “Engine Knocking”. It's a distinct sound and you'll have the sensation of your engine sort of quivering. Because the octane rating did not meet the minimum of the engine, the fuel combusts earlier than it should. That combustion pushes down against the piston while it is still moving upward during the 'squeeze' bit of the engine cycle.
Just imagine running uphill when, suddenly, somebody pushes you back down again. It causes a lot of strain on you, doesn't it? Now imagine that being done to you repeatedly and something will eventually break. In this case, your ankles. For engines, it's the connecting rod, responsible for connecting your pistons to the crankshaft, which takes the brunt of the knock. Keep loading up on lower than recommended octane and you'll either bend or snap the said rod.
So why then do some cars need high octane and others, not? The answer lies in compression. Some engines have high compression, some have low compression. It's a different (read: complicated) matter but here's the gist of it: high compression engines need the fuel to ignite at a very specific point, with little margin for error. And while low compression engines aren't as fussy, feeding it fuel with too high an octane rating may result in incomplete combustion, unburnt fuel, and less power. Since these engines don't often achieve the pressure required to combust the high octane fuel, the premium you pay for it is simply wasted.
Performance cars typically have higher compression engines, which, in turn, need the 'bang' to happen more consistently to run smoothly. That is something high octane (premium) fuels can deliver and low ones can't. Consequently, higher octane fuels burn leaner, allowing for cleaner emissions. As a general rule then, it's recommended to run on high octane fuel when you have a high-performance engine. It's the opposite when you put in low octane in a powerful engine.
So there you go, that’s octane in a nutshell. As long as you don’t fill up your car with a lower octane rated fuel than the manufacturer indicated nothing should go wrong. Now, if you’re feeling a little bit generous you could fill up with higher octane rated fuel that will give you better performance and lessen the strain on mother earth as well.