Motofrakcija

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.

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Octane Part II


Detonation and the backyard chemist


By Arshag (Shog) Odabachian


In the first part we went over the origins of the term “Octane” and figured out it had become a rating system to gage a fuels ability to resist detonation (Spark knock, Pinging, etc). We also learned that the octane number has nothing to do with the power (or heat) output of the fuel. Depending on the additives used in a given fuel, one can even speed up, or slow down the combustion process (to a limited degree).

If you’re going to race or track-day your basically stock bike, don’t go nuts and spend a fortune on exotic racing fuels. Run the octane recommended by the manufacturer. If you feel you will be putting the engine under more heat and load stress than intended by the manufacturer, you may want to bump your octane a couple of points just to make sure detonation is kept at bay. Just don’t fooled to think the bike is going to make more power with 93 octane instead of 90.

Now we’re going to unravel some of the mystery and explain why detonation is such a bad thing. A spark fired gasoline engine likes a controlled and very rapid burn. When the piston comes up on the compression stroke, it is compressing a mixture of air and fuel as delivered by the carburetor (or fuel injectors) and throttle air valves controlled by your right wrist. If everything is going well, the mixture is swirling faster and faster and mixing completely as the piston rises. The sparkplug is fired BEFORE the piston reaches TDC (top dead center). Depending on the RPM and the engine design intent, it may be 30 degrees, or 5 degrees before TDC. If the fuel exploded (instead of burned), this would send the crankshaft backwards. The engines want a fuel that burns quickly and completely – in a controlled manner – not an explosion. The goal is to have the piston well past TDC when the pressure from combustion is at its peak. This way, the piston is forced down with great, but controlled force. Without detonation, this controlled burn is started by the sparkplug, which in turn starts a flame front that continues in all directions until the trapped mixture is completely burned. As this flame front progresses, the piston is moving past TDC and getting better leverage on the crankshaft to make mechanical power. Although the heat and pressure in the chamber is rising very quickly, it drops off rapidly as the piston gets about halfway down on the power stroke. Most all of the power transmitted by the burning of the fuel was sent to the crankshaft between 15 and 90 degrees after TDC.

Normally, the plug fires and starts the burn process. A little known “Sonic” wave-front moves outward faster than the flame front. If the fuel has a high enough octane rating, the sonic front is of no consequence and the flame front continues all the way to the trapped “end-gasses” at the outer portions of the combustion chamber and burns them as well. But if the heat and pressure in the chamber is at the critical limit of the fuel, this sonic front crashes into the already volatile end-gasses and spontaneously explodes them, way before the flame front gets there. This in turn sends a huge shock wave back towards the flame front and explodes (rather than burns) whatever is left. Pressure in the cylinder skyrockets before the piston gets a chance to pass TDC and all the parts get hammered by stresses they were never designed to have (unless it’s a Diesel).

The boundary layer: Ever seen drops of water dancing around the surface of a hot skillet? It’s amazing that a drop of water can last that long in such heat. If you were to reduce the temperature of the skillet enough, the whole droplet would absorb the heat and vaporize quickly. How about Island Fire-Walkers that walk across super hot coals in their bare feet in a religious ritual? These two things as well as your pistons have something in common protecting them. That drop of water has a boundary layer of steam acting as an insulator between the hot pan and its liquid surface. The firewalker better have damp feet and hot coals so a boundary layer can be formed and protect the skin.

During normal combustion, there is a thin boundary layer of gas on the surface of the piston, cylinder and head. This also helps insulate those parts from the intense heat and make life easier on parts as well as your cooling system. When we go into detonation, the extreme blast from the sonic and explosive pressure fronts “rips” that protective boundary layer off the parts. In fact, when you hear that “Pinging” sound, just visualize a hammer smacking all those parts in the combustion chamber, because that’s what is happening. With the boundary layer gone, all those parts have lost insulation and are absorbing heat like crazy, which makes them hotter for the next cycle, to help detonation occur again. Keep it up and you’ll break parts and melt pistons.

Note: When an engine detonates (even lightly) the exhaust gas temperature drops and the water temp goes up. This can be a very important sign and should not go unnoticed. Since the boundary layer is gone, the internal parts and cooling system take more of the heat and less is left over to go out the pipe.

Detonation is also a time dependent phenomenon. The longer the engine spends time compressing the mixture, the more time the mixture has a chance to pick up heat and the higher the chance of detonation occurring. So, low rpm engines have a better chance of detonation than high rpm ones (all else being equal). It also takes time for a flame-front to get to the end-gasses, the less distance to those outer portions of the combustion chamber from the spark plug the better. A 1000cc four cylinder would be less prone to detonation than a 1000cc twin (given the same compression ratio – all else being equal as well). Super high RPM multi cylinder engines require less octane than lower RPM ones for these reasons. Liquid cooled engines are also less prone to detonation than their air-cooled counterparts and can run higher compression ratios and consequently make more power (air-cooled engines cannot control combustion chamber temperatures anywhere near as well as LC engines). How many remember twin spark plug heads? This was not for complete burn or emissions, it was to have two flame fronts so the burn process could be done quicker and get the end gasses burned off before detonation could take hold (relative to a single plug head given the same fuel).

If you need to raise Octane because you have modified the engine to make more power/cc, there are many alternatives for you. You can go to any of many retailers that sell racing fuel, or you can mix your own as well. I’m not going to go into the blending extremes and specific gravity issues here in this segment. I will state just a few tricks to get octane and controlled power of your fuel up a bit.

I also will not go into oxygenated racing fuels (big power boosts – also known as liquid superchargers) as this is a great way to destroy engines if the fuel maps or jetting is not spot on.

I do not like using any pump fuel that contains alcohol. Although alcohol is a good octane booster (and racing fuel if the mixture is radically richened), unless you turn up the fuel mixture to compensate, power will be down. Alcohol is also very abrasive and acts like a scouring agent in many fuel systems. I like using a good base fuel like BP/Amoco.



If the fuel is to be used for off-road use, Tetraethyl lead is hard to beat as an octane boosting additive in unleaded fuels. One source is: http://www.kemcooil.com/product_info.php?pId=61
Go to the kemcooil.com site and do some research. Here is a chart to give you an idea of the capabilities of this additive. Its brand name is Octane Supreme 130.

0.6- Ounces OS-130 to 1 gallon / fuel……2.0 point octane increase
1.2- Ounces OS-130 to 1 gallon / fuel……3.5 point octane increase
1.8- Ounces OS-130 to 1 gallon / fuel……5.0 point octane increase
2.4- Ounces OS-130 to 1 gallon / fuel……6.5 point octane increase
3.0- Ounces OS-130 to 1 gallon / fuel……8.0 point octane increase
6.0- Ounces OS-130 to 1 gallon / fuel……11.0 point octane increase
18- Ounces OS-130 to 1 gallon / fuel……16.0 point octane increase


Another additive I use is Toluene (methyl Benzene) a.k.a. Toluol. This is getting harder to find at the Home depot and I have resorted to commercial automotive paint suppliers as a source. I can’t state what you will get with all base fuels, but with summer blended BP/Amoco Premium, we were able to get a 4 point octane boost running 10% Toluene. Some might remember the “Rocket fuel” used by Formula 1 turbo cars decades ago. It was 75% Toluene. Here is some interesting data on pure Toluene: (remember your Motor and Research octane numbers)

Specific Gravity = 0.87 RON=124 MON=114 Heat energy (Btu/lb) = 18,716

We have tested a blend 12 oz/gal of the Tetraethyl lead additive mentioned here along with 10% Toluene in a base pump 93 octane BP fuel and were able to run detonation free in a turbocharged snowmobile that used to detonate on 110 octane racing fuel! Don’t get lazy around these or any chemicals! Use solvent proof gloves and be in a well ventilated area. There are many links on the internet to help you further with your research. I’ll give you another one here that has helped many on these topics: http://www.faqs.org/faqs/autos/gasoline-faq/part1/

I hope this section explained detonation and its causes. Every one of the small points made here can be expanded into volumes. This is not the intent here. This is just to give you a better understanding and help keep some money in your wallet by not buying more than you need. For everyone’s information, I do not use anything but pump 93 in my personal “Premium fuel only” performance bike. There is no need. My highly modified snowmobiles on the other hand……

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esme pora sakiniu?

jo, nes neaišku, jie į savo kibirą įpilsiu 98, tai jau turėsiu lenktyninę maqšiną ar dar ne?

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Don’t buy a house. Don’t go to weddings. Don’t subscribe to magazines. Put everything you have into gas and oil and riding around.

labai daug skaityti, gal kas apibendrins?

bet tai pala, jei viskas susiveda i antidetonacines savybes, tai kodel daznai varzybose pvz neleidzia naudoti aukstesnio oktaninio skaiciaus kuro? ypac, jei pagal technini reglamenta variklio modifikacijos nera leidziamos ir lyg ir nebutu jokiu privalumu vaziuoti "sportiniu" benzu?

todel, kad ne visai jau taip viskas susiveda tik i antidetonacines savybes.
skiriasi degimo trukme (zemesnio oktaninio skaiciaus ilgiau dega, ilgiau slegia i stumokli, lyg ir daugiau jegos sukuria), o bet i auksto oktaninio skaiciaus kura (premium) gamintojai daznai maiso priedus gerinancius degimo savybes (ne visai NO2, bet skaiciau, kad deguonies kazkiek ishskiria. tai teigiamai atsiliepia variklio kuriamai galiai

cia beje risasi su kazkada diskutuota benz tema

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cross cojones PC

sita, kas perskaitet trumpai atsakykit, ar galiu i bandita pilt dizeli kad pigiau vazinet.

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+2/-14

Siulau vistiktai paskaityti, tikrai nera daug. Is esmes visi klausimai siame tekste ir yra atsakomi. Geriau neparasysiu ;) Siaip zinomos tiesos tik dar kazkiek papildytos.


Trumpai - oktanas nesusijes su arkliais. Aneikiek. Jeigu kyla del to papildomu klausimu ar noras smulkesnes info apie tai - zhr. i teksta auksciau

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tai čia ir arkliui aišku. Nes būtent keliant arklius reikia aukštesnio oktano, o ne atvirkščiai. O taip pat, naudojant aukštesnį oktaną, nei numatyta motoro konstrukcijoje, tų arklių kaip tik ir mažėja...

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Don’t buy a house. Don’t go to weddings. Don’t subscribe to magazines. Put everything you have into gas and oil and riding around.

Jeigu tavo kibirui numatyta gamintojo 95-tas tai ipyles 98-to netgi gal siek tiek mazesne trauka turesi. Arba tokia pacia. Bet ne didesne

Taip pat pamineta kad inline 4 high rpm varikliai yra labiau atsparesni detonacijai negu 1500CC V2 low rpm. Gal del to siuolaikiniai ZX6RK6 600cc inline 4 turedami suspaudimo laipsni 13.1:1 vis dar sekmingai naudoja 95ta benza..?

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Tai kurie cia dabar pas mus ne arkliai (asilai?) 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

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o as rishchiausi prie tos infos, kad benzas skiriasi ne tik oktaniniu skaiciumi. aukstesnio oktaninio skaiciaus benzas turi priedu, kurie galgi ne tik plauna purskalus, bet ir vis tik duoda daugiau arkliu.
neesu tikras del degalinese parduodamo benzo, bet "sportinis" benzas tikrai ne tik oktanas pakeltas.

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cross cojones PC

Yra kuras (vadinkim ji taip, nes tai mishinys ivairiu naftos produktu ir priedu) kuris duoda daugiau Ag del to kad jame yra visokiu papildomu priedu, power boosteriu ar kokio nors alkoholio ar dar kazko. Bet tai nesusije su oktanu.

Galetu buti ir 95tas benzas su atitinkamais priedais kurie ag pakelia.

Kad gamintojai "deda" kazka i brangesni kura, gali buti kazkiek tiesos. Klausimas ka deda ir kiek deda, ir kas deda ir ar tikrai deda...cia jau tik spejimai praktikoje.

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tai gal tada ir atskirk b nuo piršto. degalinėse paruodamas benzas yra absoliučiai vienodas, skiriasi priedų, didinančių oktaną, kiekis. Nekalbu apie ten visokius spešl benzinus, kur, kai kurios degalinės bruka pjariniais pavadinimasi, kaip antai "nitro3000" ar panašiai. Realiai, jie negali pridėti nieko tokio, kad išskirtų deguonį, kaip rašei kažkuriam poste, nes tada mašinos kompas imtų pjauti grybą, o jokia degalinė nenori ir nenorės turėti reikalų, dėl skundų.

Sportiniai KURO MIŠINIAI yra atskira tema, nedaug bendro turinti su degalinių benzinu.

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Don’t buy a house. Don’t go to weddings. Don’t subscribe to magazines. Put everything you have into gas and oil and riding around.

visi mes remiames internete skaityta infa ir kazkieno pasakojimais. abejoju ar kas is musu yra dares kokius kuro tyrimus ir dynouzvaziavimus su skirtingu kuru.
as savo infa ishdesciau: skaiciau inete apie priedus su deguonimi, ishsiskirianciu pakilus misinio temperaturai; dar kazka pasakojo kolega, kazkada vadovaves vienam lt benzo prekybos tinklui
kaip yra is tiesu, jei kazkokia viena tiesa aplamai galima ishvesti, bbz.
taip sportiniai benzai yra visiskai kita istorija.

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cross cojones PC

Beje visai nesenai (nu taip pries kokius 3-4 metus) buvau imetes kazkur dyno grafikeliu su 98 ir su 95 benzu. Inline 4 litraS, brytva.

su 98 gavosi -2rwhp pries 95.

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