Apie kura
Posted: 09 Oct 2008, 14:11
Octane
What it really means to you and your engines
By Arshag (Shog) Odabachian
Before we begin, I just want to let you know that I hate TV episodes that say at the end, “To be continued”. In this case, I am going to break this article up into 2 parts so that I don’t lose too many of you to reading induced, mid-day naps. This part is going to explain where the term “Octane” came from – what it means today – and last but not least – why you should care. In the next installment, we’ll get more technical for the gear-heads and give out some insider secrets from the petroleum industry. I’m going to stay pretty mild in the techno-babble department for this first segment.
First off, let’s get something straight: Gasoline is not a single product derived from crude oil. It is a mix of many types of hydrocarbons, chemicals and additives. It’s like saying, “Food”. We all know what food is, we all know we need it, but what we’re actually eating and what we get out of it is up to the “Mix” of components that make up our diet. From here on out, we are going to properly refer to the “Food” we put in out tanks as “Fuel” and not gasoline.
Now let’s get something else out of the way. Octane (or in our case – Octane ratings) is not in any way, shape or form, related to the power output of the fuel. Over time, this term has evolved to rate a fuels ability to resist detonation (spark knock, ping, etc.). I’ll explain it more later, but understand that if your engine does not require or detonate on regular fuel of a given Octane rating – increasing octane by either using premium or using octane boosters will do nothing for you except thin the wallet - and more times than not – may actually reduce the power output of the engine.
I think for a good basis of understanding of fuels and octane ratings; we need to know why it’s important and what “Detonation” really is. Detonation is the uncontrolled – spontaneous explosion of gases in the combustion chamber. We will get into this demon more in the next segment, but let’s be clear on this: This is a condition WE DO NOT EVER WANT in a spark plug triggered engine of any kind. What is supposed to happen when the spark plug fires - is a nice, fast controlled burn called a “flame front combustion”. Starting from the plug’s tip and evenly progressing outward to the ends of the chamber (like the waves a drop of water makes when falling into a calm pool-but much faster). During the flame front’s progress, heat from the burning of the fuel increases the pressure in the combustion chamber and forces the piston down – that turns the crankshaft – that gives us the rotational energy that we all have come to love and use.
OK class, before we can understand this evolution of terms used today, we have to have a little history lesson. So sit up straight, talk another swig of caffeine and pay attention.
Let’s go back to World War I. During this time of bi-planes, the need for speed and power was crucial to life and death in the skies. As engine builders found out that increasing compression ratios would boost power output - Aircraft engines here and there would self destruct through detonation. The problem was that some engines would live while others would not - even though they were running the supposed same fuel from the same refinery.
The petroleum companies of the time were doing whatever analysis they could to figure out why this was happening, but figuring out why certain batches of were more prone to detonation than others eluded them. A much needed form of real world testing was required to maintain quality control. This was not a good time to be a chemical engineer at a petrol plant. Pissed-off pilots that did manage to safely land their blown-up engine planes would sometimes have very physical discussions with the plant manager at the fuel companies. Now comes the birth of some of those rating systems you see on the pumps. You know, the RON (research octane number) and MON (Motor octane numbers) – or the US system of averaging the two into what we all see as (R+M)/2 on the pump.
Still during the WW-I era, a “Research” test engine was developed that had a special adjustable combustion chamber that the technician could raise or lower the compression ratio in very precise increments. Note: This was the beginning of the RON rating system. This engine - and its design and use specs - was given to every refinery that supplied fuel for the war effort. It was a single cylinder unit that would be warmed up to a standard testing temp, run at a very specific RPM and load. During the running of this engine, the fuel would be tested by increasing the compression ratio until the engine started producing measurable detonation (knock). The fuels anti-knock quality would then be rated as its HUCR (highest usable compression ratio). Ah, but all was not good in petrol land just yet. It was discovered that even the same fuel, tested differently in different location using the same test engine.
They needed an unvarying standard to rate the test fuels against. They decided on using two base reference fuels. The first that detonated quite easily was normal Heptane (n-heptane) and the second is the infamous Octane (iso-octane) that resisted detonation quite well (due to long chain of 8 carbon atoms that was harder to break apart under heat and pressure). See how this works – Octane – meaning like Octagon – like 8 sided or 8 carbon molecules in this case.
So, what they did was to run the test engine, find the HUCR of the fuel being tested as before, then they would switch over to use a mix of the Heptane and Octane – constantly changing the mix ratio of those two reference fuels until it exactly matched the knock properties of the test fuel. If the mix was 75% Octane and 25% Heptane, the fuel under test was given an octane rating of 75 (regardless of the actual amount of iso-octane in the test fuel – if any).
You can see that this method could only get you to a 100 octane rating. You can also see that this rating has nothing to do with the heat output (or energy) of a rated fuel. It has no meaningful data on specific gravity, oxygen content or air/fuel ratios. In short, it is a rating of a given fuel’s anti-knock (or anti-detonation) properties – nothing else.
Since then, a number of test procedures were thrown about that could get us ratings beyond the 100 octane limit. It was deemed necessary to come up with a test engine that was more in line with the severe environments of modern engines using superchargers, turbochargers, high output and high compression naturally aspirated (NA) engines as well. So, another single cylinder engine test engine was developed that was specified to run at higher engine speeds, higher air inlet temperatures and a more severe load. This new test of fuels is more real world to racing engines and is called the MON (motor octane rating). Since it is a more severe test, the same fuel will usually test 7 to 15 octane points below the RON test.
So you can see that depending on additives, two fuels of close rating, but from different suppliers can act differently in your race or performance bike. For example: Sunramaco 93 Octane might have a RON of 99 and MON of 87 to get an average of 94 octane, but BurPee 92 Octane might have a RON of 95 and a MON of 89. In high heat and load the only thing that matters is the MON number - so in this hypothetical case - BurPee wins out as the real performance fuel (from an anti-knock standpoint only).
So why would someone need a higher octane fuel than recommended by the engine maker? Unless you modified the engine so that the anti-detonation requirements of the fuel went up – you don’t. Be aware that some fuel makers put more cleaning agents in their premium fuels to lure you into using them. Although these additives do indeed help clean injectors and such, they do nothing to help raise the power output of the fuel.
What it really means to you and your engines
By Arshag (Shog) Odabachian
Before we begin, I just want to let you know that I hate TV episodes that say at the end, “To be continued”. In this case, I am going to break this article up into 2 parts so that I don’t lose too many of you to reading induced, mid-day naps. This part is going to explain where the term “Octane” came from – what it means today – and last but not least – why you should care. In the next installment, we’ll get more technical for the gear-heads and give out some insider secrets from the petroleum industry. I’m going to stay pretty mild in the techno-babble department for this first segment.
First off, let’s get something straight: Gasoline is not a single product derived from crude oil. It is a mix of many types of hydrocarbons, chemicals and additives. It’s like saying, “Food”. We all know what food is, we all know we need it, but what we’re actually eating and what we get out of it is up to the “Mix” of components that make up our diet. From here on out, we are going to properly refer to the “Food” we put in out tanks as “Fuel” and not gasoline.
Now let’s get something else out of the way. Octane (or in our case – Octane ratings) is not in any way, shape or form, related to the power output of the fuel. Over time, this term has evolved to rate a fuels ability to resist detonation (spark knock, ping, etc.). I’ll explain it more later, but understand that if your engine does not require or detonate on regular fuel of a given Octane rating – increasing octane by either using premium or using octane boosters will do nothing for you except thin the wallet - and more times than not – may actually reduce the power output of the engine.
I think for a good basis of understanding of fuels and octane ratings; we need to know why it’s important and what “Detonation” really is. Detonation is the uncontrolled – spontaneous explosion of gases in the combustion chamber. We will get into this demon more in the next segment, but let’s be clear on this: This is a condition WE DO NOT EVER WANT in a spark plug triggered engine of any kind. What is supposed to happen when the spark plug fires - is a nice, fast controlled burn called a “flame front combustion”. Starting from the plug’s tip and evenly progressing outward to the ends of the chamber (like the waves a drop of water makes when falling into a calm pool-but much faster). During the flame front’s progress, heat from the burning of the fuel increases the pressure in the combustion chamber and forces the piston down – that turns the crankshaft – that gives us the rotational energy that we all have come to love and use.
OK class, before we can understand this evolution of terms used today, we have to have a little history lesson. So sit up straight, talk another swig of caffeine and pay attention.
Let’s go back to World War I. During this time of bi-planes, the need for speed and power was crucial to life and death in the skies. As engine builders found out that increasing compression ratios would boost power output - Aircraft engines here and there would self destruct through detonation. The problem was that some engines would live while others would not - even though they were running the supposed same fuel from the same refinery.
The petroleum companies of the time were doing whatever analysis they could to figure out why this was happening, but figuring out why certain batches of were more prone to detonation than others eluded them. A much needed form of real world testing was required to maintain quality control. This was not a good time to be a chemical engineer at a petrol plant. Pissed-off pilots that did manage to safely land their blown-up engine planes would sometimes have very physical discussions with the plant manager at the fuel companies. Now comes the birth of some of those rating systems you see on the pumps. You know, the RON (research octane number) and MON (Motor octane numbers) – or the US system of averaging the two into what we all see as (R+M)/2 on the pump.
Still during the WW-I era, a “Research” test engine was developed that had a special adjustable combustion chamber that the technician could raise or lower the compression ratio in very precise increments. Note: This was the beginning of the RON rating system. This engine - and its design and use specs - was given to every refinery that supplied fuel for the war effort. It was a single cylinder unit that would be warmed up to a standard testing temp, run at a very specific RPM and load. During the running of this engine, the fuel would be tested by increasing the compression ratio until the engine started producing measurable detonation (knock). The fuels anti-knock quality would then be rated as its HUCR (highest usable compression ratio). Ah, but all was not good in petrol land just yet. It was discovered that even the same fuel, tested differently in different location using the same test engine.
They needed an unvarying standard to rate the test fuels against. They decided on using two base reference fuels. The first that detonated quite easily was normal Heptane (n-heptane) and the second is the infamous Octane (iso-octane) that resisted detonation quite well (due to long chain of 8 carbon atoms that was harder to break apart under heat and pressure). See how this works – Octane – meaning like Octagon – like 8 sided or 8 carbon molecules in this case.
So, what they did was to run the test engine, find the HUCR of the fuel being tested as before, then they would switch over to use a mix of the Heptane and Octane – constantly changing the mix ratio of those two reference fuels until it exactly matched the knock properties of the test fuel. If the mix was 75% Octane and 25% Heptane, the fuel under test was given an octane rating of 75 (regardless of the actual amount of iso-octane in the test fuel – if any).
You can see that this method could only get you to a 100 octane rating. You can also see that this rating has nothing to do with the heat output (or energy) of a rated fuel. It has no meaningful data on specific gravity, oxygen content or air/fuel ratios. In short, it is a rating of a given fuel’s anti-knock (or anti-detonation) properties – nothing else.
Since then, a number of test procedures were thrown about that could get us ratings beyond the 100 octane limit. It was deemed necessary to come up with a test engine that was more in line with the severe environments of modern engines using superchargers, turbochargers, high output and high compression naturally aspirated (NA) engines as well. So, another single cylinder engine test engine was developed that was specified to run at higher engine speeds, higher air inlet temperatures and a more severe load. This new test of fuels is more real world to racing engines and is called the MON (motor octane rating). Since it is a more severe test, the same fuel will usually test 7 to 15 octane points below the RON test.
So you can see that depending on additives, two fuels of close rating, but from different suppliers can act differently in your race or performance bike. For example: Sunramaco 93 Octane might have a RON of 99 and MON of 87 to get an average of 94 octane, but BurPee 92 Octane might have a RON of 95 and a MON of 89. In high heat and load the only thing that matters is the MON number - so in this hypothetical case - BurPee wins out as the real performance fuel (from an anti-knock standpoint only).
So why would someone need a higher octane fuel than recommended by the engine maker? Unless you modified the engine so that the anti-detonation requirements of the fuel went up – you don’t. Be aware that some fuel makers put more cleaning agents in their premium fuels to lure you into using them. Although these additives do indeed help clean injectors and such, they do nothing to help raise the power output of the fuel.
Siaip nieko naujo kaip ir minejau, bet idomi info apie tai is kur tas oktanas atsirado, kas jis toks, su kuo maisomas ir kas gaunama galutiniame rezultate ir ka naudoti geriausia 