What’s the Difference Between High-octane and Regular Fuel?

High-octane = high grade fuel?

High-octane fuel is a luxury product with a higher octane rating than regular fuel. Does it seems like it's going to burn and power up extremely. It's too expensive!

High-octane fuel does not burn more powerfully than regular fuel. So why do we bother being designated to fill up with high-priced fuel? Not many people can explain this area correctly, can they? What is high-octane fuel, after all?

About high-octane name

Let's start with the basics. The name "high-octane" is short for "high" + "octane".
In Japanese, it is called "high-octane".

So what's the "octane number"?

What is Octane Number?

There are two octane numbers, Motor Octane Number (MON) and Research Octane Number (RON), and we don't really care what they are. In short, all you need to know is that it's a 'number that represents the difficulty of knocking'.

In the case of Japan, the standard is 89 or higher for regular fuel and 96 or higher for high-octane fuel.

What's that number? That being said, the level of difficulty suddenly increases, but again, you don't need to know it. Just think of it as a 'fuel performance index' where the highest value is 100 and the lowest is 0!

The higher the number, the more difficult it is to knock, which means that the fuel is harder to knock. High-octane has a higher number, so it means that high-octane is more difficult to knock.

Also, it's normal for regular fuel to have an octane rating of 95 in Europe. The reason why many imported cars are designated as high-octane is that the performance of Japanese regular (89 octane) is not sufficient to meet the European standard. European regular = Japanese high-octane.

What happens when the octane level is high?

Now, I mentioned that the octane number is a performance index, but what does it mean for fuel to perform better? You don't need to know the hard theory on this either, just remember that the following happens when the octane level is high.

It's less likely to burn. It makes it harder to knock.

If it's a good idea to make it harder to knock, because it increases the number that represents the difficulty of knocking, then it's a good idea to make it harder to knock.

What makes it less flammable? Doesn't that mean it's not performing well?

What does it mean to be flame-resistant?

You're paying a lot of money and you're selling flammable stuff! I'd like to say that this is really what it is. A little more accurate term would be "hard to ignite".

That part alone makes high-octane fuel sound like it has lower performance, but of course it doesn't.

Difficult to ignite and hard to burn, both of which are bad words, but that's only if you compare them to fuel alone. You have to include the engine to understand the benefits of high-octane fuel.

Fuel Engine Characteristics (Part 1)

That's why I'm talking about the engine. In a fuel engine, a mixture of air and fuel (i.e., air mixture) is inhaled, the mixture is compressed and then ignited by the ignition plug to burn, and the pressure of the combustion gas generated by the mixture pushes down the piston to produce power.

By the way, when you compress a substance, it has heat according to the laws of physics. Of course, the same is true for the mixture, and the more you compress it, the hotter it gets. When that heat exceeds the ignition point of the mixture, you don't have to use a spark plug to blow the sparks away. The mere heat of compression is enough to cause it to spontaneously combust.

This is not the ignition timing for which the engine was designed, so abnormal combustion. Since it ignites and starts to expand on its own during compression, it prevents the engine from running smoothly and reduces power significantly.
You don't have to go that far to get crunchy! It is very uncomfortable to listen to the vibration and the noise like "I'm not going to do this". It's burning abnormally and in the worst case scenario, the engine could blow.

These abnormal combustion and the sounds and vibrations that accompany it are collectively called 'knocking'.

Fuel Engine Characteristics (Part 2)

If the abnormal combustion is caused by compression of the mixture, then it's a good thing we don't have compression, right? This is true, as long as you don't compress the mixture, the mixture won't spontaneously ignite because it won't become a point of ignition.

Unfortunately, however, the engine is not. The more you compress the mixture, the more power you get.

If you ignite an uncompressed mixture of air, it just burns with a whiff of fire, but if you compress the mixture and then ignite it, boom! and explosive combustion. The more you compress it, the more this "wham! is larger.

Originally, an engine uses the gas produced by explosive combustion to lower the pistons to produce power. So, a big bang! The more you have, the better. This means "The more the mixture is compressed, the better".

That would have led to a major discrepancy.

If you compress it too hard, it will spontaneously ignite, but if you lower the compression ratio, you won't be able to generate power. I need more power -> I want to increase the compression ratio -> Spontaneous ignition -> Hmmm, I'm in trouble!

I'm here to help you with that!

High-octane fuel, which is "flammable" and "hard to ignite", can help with this "trouble". Harder to burn = less likely to ignite naturally = less likely to knock = higher octane value.

Chickens first or eggs first? Or something like that. It takes a big bang to power up. You need high compression for a big bang. But, high compression causes spontaneous ignition (abnormal combustion). In order to avoid spontaneous ignition. You need fuel that is less likely to burn (less likely to ignite naturally).
the fuel that is difficult to ignite naturally = fuel that is difficult to knock = high-octane fuel= high-octane fuel. This is how it works.

Although it is said to be less flammable, it only means that it is harder to ignite even with high compression, and fuel is still very flammable (easily ignited). Please note that high-octane fuel does not reduce the need for caution when handling fire or anything like that.

Why a high-performance engine is designated as high octane?

I'm sure you've figured it out by now. To review again.

A big bang (explosive power) is necessary for high output. High compression is essential to get a big bang. But if you use high compression, spontaneous ignition (abnormal combustion) is more likely to occur, causing knocking. To prevent this, you need high-octane fuel that is difficult to knock.

For this reason, a high-octane engine is a sign of high performance. But there is a high fuel price of high performance.

What happens when you put regular in a high octane designated car?

Modern four-wheelers use sensors to read the quality of the fuel they contain, and they are controlled so that if you accidentally refuel with regular fuel, it won't break. If you have refueled your car with regular fuel, you can prevent the engine from blowing by drastically changing the ignition timing.

However, the fact that the octane rating of regular fuel is still highly compressed, so knocking ease is inevitable. Also, since the ignition timing is off from the best timing it should be, the power will be reduced by that amount.

It's okay if you refuel by mistake, just in case, but I'm not sure if you should always fill up with regular fuel to save money on fuel (good thing it doesn't break). Because it's definitely not good for the engine.

So what about motorcycles? In the case of motorcycles, the sensors don't seem to read up to the fuel type. There's a fair chance of breaking it if you put in regulars. Especially when the engine is turned up to high RPM, it is a critical point and the possibility of the engine blowing up due to abnormal combustion increases dramatically.

Even if you accidentally put a regular, it's not going to break as soon as the engine is started. But if you keep driving at full throttle, you're out. Ride gently until the tank is empty. It's best to just pull it out.

Intensely tuned engines are even more of a pinch and anything can happen, especially if the compression ratio is increased. It's not the same as the manufacturer's original, and that's exactly what could happen if it suddenly breaks down in a snap.

What happens when you put high-octane in a regular designated car?

It is an engine that is not prone to knocking, that is to say, it is not pursued to the limit of power, so even if you put a high-octane engine with high knocking resistance into it, you will still be able to drive it. Excessive fuel performance has no adverse effects.

Strictly speaking, the output will be reduced by the amount of additives that are not in regular fuel, but you will never be able to feel it, so don't worry about it. In addition, many of the additives included in high-octane engine oil contain cleaning agents to keep the inside of the engine clean as well as to improve knocking resistance.

It's a backdoor trick, but an air-cooled engine in the middle of summer is thermally demanding, so adding high-octane at such times will make it harder to knock. It's because it won't burn abnormally even when the engine is extremely hot.

Also, after many years of riding, there may be a buildup of burnt residue (carbon) in the combustion chamber.

When this happens, the combustion chamber capacity is reduced by the volume of the carbon deposits, which may result in unintentional high compression. At times like this, adding high-octane may improve the condition of the car as it is less likely to burn abnormally due to high compression.

Is there a price differential effect?

You hear a lot of stories about the cost-effectiveness of adding high octane, right? High-octane is about 0.09 USD per liter more expensive than regular, so I can understand why you want to keep it cheap.

But, as I'm sure you've figured out by now. It's not a matter of "it works/not works" in the first place.

The engine was designed to use high-octane fuel when it was designed. It has to be a fuel with a specified octane rating to begin with. Whether it's a regular or high-octane designation, it's designed to burn correctly and produce the correct power when you use that fuel. If it's a high-octane designation, put the high-octane in, even if you don't like it.

But (for the second time), if an engine designed for high-octane use is producing high power at high compression, you're wondering if it's powerful enough to make up the fuel price difference compared to a low compression engine designed for regular use? This is don't know. That's all I can say.

To begin with, this story is about 'What if we had a regular fuel version of the same engine, but with the same engine?' However, it is not as simple as just lowering the compression ratio to match the regular octane rating to complete a regular spec engine. The initial premise of 'keeping the same engine' is not feasible because the engine strength will be completely reviewed to match the lowered compression ratio.

If I could say one thing. Life is more affordable when you enjoy the fullness of your life in the vehicle you love rather than worrying about a small price difference.

That's what motorcycles are for.

High-octane fuel blending problem

On a different note, at the end of June 2020, a scoop from the Mainichi Shimbun revealed that high-octane fuel from gas station companies doesn't actually make any difference (each company's high-octane fuel is in the same tank and is mixed together).

Originally Kignas, which doesn't have its own refinery, was perceived to be a mixture of high-octane from various companies, but I didn't realize that other than Kignas, it wasn't its own high-octane either!

But it seems to be true because only Idemitsu Showa Shell answered that they do not mix with other companies' products, and all the other companies admitted that they do.

Depending on the company's response, all brands are the same except for the high-octane of the Idemitsu Showa Shells. Many of you may have been disappointed by the confirmation of the shocking details.

I personally don't agree at all with the companies' responses that "even if they were mixed, they would still meet the criteria for high-octane" and "there is no significant difference in the high-octane of each company. It's true that you can't really feel the difference in performance between the two companies, but I was disappointed because I thought they were competing with each other with their own additives for high performance.

In addition, regular fuel is the same for all companies, so there is no difference between brands.