What, exactly, is octane and what IS the difference between 87, 89 and 92?

Question

So, what is octane? Which is really better for your car - 87, 89 or 92? And what is the difference between these levels? If you have a lower octane in your tank, then add a higher level (or vice versa), is that harmful to your engine?

Answer 1

The best octane fuel for your vehicle is the one that is recommended by your manufacturer. Most vehicles do not require high octane fuel. There are no additional benefits in using higher octane fuel in an engine that does not require it, and due to higher octane fuels resistance to ignition, it can actually cause fouling of an engine not designed to run on it.

Here is more info from howstuffworks.com:



What does octane mean?

by Marshall Brain





If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)



The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.



The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.



The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.



It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.



During WWI, it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:



Lead clogs a catalytic converter and renders it inoperable within minutes.

The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).

When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline (known as AvGas), and octane ratings of 100 or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, 100 is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane.

Currently engineers are trying to develop airplane engines that can use unleaded gasoline. Jet engines burn kerosene,

by the way.



I would also like to add, that if your vehicle is suffering from preignition (engine knock) it is best to determine the actual cause of the problem (such as engine running too hot, excessive carbon deposits in the cylinders, faulty egr system, etc) and repairing them before switching to a higher octane fuel as a remedy.

Answer 2

This Site Might Help You.



RE:

What, exactly, is octane and what IS the difference between 87, 89 and 92?

So, what is octane? Which is really better for your car - 87, 89 or 92? And what is the difference between these levels? If you have a lower octane in your tank, then add a higher level (or vice versa), is that harmful to your engine?

Answer 3

The octane ratings indicate the burn rate of fuel during combustion; the higher the number, the slower the burn rate. Long ago, the advice was to go higher octane as mileage got higher because with carburetors being used, carbon deposits formed in the cylinders and hot spots formed causing ping conditions (ignition of fuel mixture from hot spots and ignition of spark plug caused the pinging noise when the explosives met). In the last 10 years, the port fuel injection systems have been more precise; pinging conditions are rare. It is not a good idea to mix octane levels in the same tank; it could cause drive-ability conditions. Also in the owners manual, use what it states, for example, if the owners manual states use 87 octane, use it. Some vehicles designed to run on 87 octane could have drive-ability problems if you use a higher octane and using high octane on some vehicle could lead to expensive repairs.

Answer 4

Octane rating is the resistance of the gas to pre-ignition. When a gas is pressurized, it heats up. This occcurs in the cylinder as the piston moves up, compressing the air/fuel mixture. If the temp is high enough to ignite the mixture, the premature ignition is really bad for your engine. That's why higher performance cars, which have higher compression ratios, need the higher octane rating. Back in the days of leaded gasoline, the octane rating was actually a ratio of octane to septane (two hydrocarbons) but I think (not 100% sure) that this has changed, and now it's a number that tells the anti-knock quality, but not an actual ratio. In days gone by, there were laws that said you needed more detergents in the higher grades, and they got the reputation of being cleaner and better for your engine. Today, though, there is plenty of detergent in all grades, so unless you have a high performance car, don't bother with the higher grades.

Answer 5

The difference between the three is the octane (burn temperature) and additives in the fuel. The difference between the three isn't anything harmful if you accidentially put it in your vehicle once or twice. But the issue comes on two parts: 1) longer usage of a higher octane than recommended can cause damage to emmission components and sensors. 2) If there is damage to your vehicle related to putting in a higher octane than recommended, the service centre will charge you because it's voids the manufacturers warranty. This is because you weren't using the recommended fuel.

Answer 6

Octane used to be an actual ingredient in the formula for gasoline. It has since been replaced.



Octane ratings reflect the relative combustability of gasoline. Too little, and your car pings (detonation, or firing early). Too much, and you're wasting money. The more octane the further your timing can be advanced, increasing performance.



There are other factors as well. Higher octane fuel tends to have more cleaning additives to keep your system from clogging. But IMHO, it isn't worth the money for the added protection. And if your car isn't tuned for it, the performance advantage isn't there, either.



My advice: use the cheapest gas that your car runs well on.

Answer 7

I want known about octane RON 92.I want to known about change colour of octane .How many should be ethanol percent in octane 92 ?

Answer 8

I read the first answer and much of it is correct, however you will find that using the better grade available will do two things. #1 The better grade will give better fuel mileage to most cars. As much as 10% higher miles.

And a benifit will be found in lower maintainance costs over the years.

The higher grade fuel burns hotter and more complete, leaving behind fewer unburned deposits.

While the cheaper fuels tend to explode rather than burn and that is more destructive.

Answer 9

The difference is the price you pay at the pump!