Home
Basic Dirt Bike How-To's - Video
Dirt Bike How-To's - Video
Living The Moto Life - Video
Bike Tests | Shoot-Outs - Video
Forums
What's new
Latest activity
Log-In
Join
What's new
Menu
Log-In
Join
Navigation
Install the app
Install
More options
Close Menu
Forums
Dirt Bike Discussions By Brand
Canadian Daves JustKDX
93 octane.....pros vs cons?
Reply to thread
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Message
[QUOTE="Rich Rohrich, post: 1338744, member: 16241"] With all due respect, the octane rating of a fuel will give you no indication of the combustion speed . It’s common practice for writers in popular press to summon the gods of combustion speed to try and explain the magic powers of octane rating. They prattle on about race gas, toluene, acetone, any number of octane boosters and Home Depot speed secrets and the "burn speed" on a receptive but otherwise unknowing audience. They’ll tell you that these compounds raise the octane of the fuel and as a result slow down combustion and fend off detonation as a result. It’s just more pseudo-science BS from people who would have done well to pay more attention in Chemistry 101 in high school. [b]Real combustion events follow the real laws of chemistry[/b], and while it’s a pretty complex set of interactions there are a few things that are easy to explain and understand. Due to lots of magazine guys spreading incorrect info over the years it's a commonly held misconception that higher Octane fuel slows down the flame speed, which keeps the engine from knocking. Sorry, but that's a load of crap. [b]A fuel's laminar Flame speed (basically fuel burning without the influence of combustion swirl or tumble) is a function of fuel chemistry (specifically Hydrogen/Carbon ratio), not the Octane rating. The Hydrogen/Carbon make up of the fuel will determine it’s flame speed and the energy release whether it's a high-octane fuel or not. You can have fast and slow burning high octane fuels, but in most cases the differences are so slight as to not be an issue.[/b] The heat of combustion at a simple level is basically a function of combustion efficiency and the calorific (energy) value of a fuel. There isn't a lot of energy difference between most conventional fuels, but combustion efficiency can sometimes be improved with race fuels so a bit more heat release is possible. Overall it's pretty much a wash in most cases though. [b]In other words, you aren't going to change the energy release or the speed of combustion in any significant way by switching from 87 to 110 octane gasoline, or anything in between . If you lose or gain power by switching fuels there are other things at work.[/b] The influence of the distillation curve we discussed earlier being a major influence. The way octane influences knock has to do with the way fuel is burned (well it’s really chemically REACTED) in the combustion chamber. The components in higher-octane fuels are less likely to have weak molecular bonds that can break easily and form active radicals. Higher-octane fuel is just made up of components that are (for lack of a better term) stouter under high temperatures and high cylinder pressures. Things like our long lost friend lead and metallic additives like MMT (common in octane boosters) tend to work as an anti-catalyst and block the formation of the active radicals that lead to auto-ignition of the fuel and ultimately detonation. The longer it takes to react all the fuel the greater the chances are that heat will accelerate the reactions beyond what the fuel components can bear. The idea that purposely SLOWING things down in the chamber is somehow beneficial in light of the reactions taking place is pretty funny really Heat , pressure, and time tend to be the driving force in all of this. The more heat and pressure you subject the fuel to and the longer you keep the temps elevated the better and more stable the fuel you need . That's part of the reason why engines that run at high rpm and have small bores can run very low octane fuels even with high compression ratios and not suffer knock while lower rpm engines with bigger bores need comparatively higher octane ratings for the same compression ratio. It's just simple chemistry really. If you look at the chemistry of explosives you can see a lot of similar reactions taking place, and it can give you some real insights into what's happening inside the combustion chamber when things go wrong. It's a fine line between engine tuner and explosives engineer. [/QUOTE]
Verification
Which ocean is California closest to?
Post reply
Forums
Dirt Bike Discussions By Brand
Canadian Daves JustKDX
93 octane.....pros vs cons?
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
Accept
Learn more…
Top
Bottom