Tree Hugger gets a BINGO.
What Gives gasoline it's Kick?
- Thread starter DLazok
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I am not sure if Octane has any thing to do with flame speed which is primerely a function of hydrocarbone content in the fuel.
"Octane Number: The octane number of a gasoline has little to do with how fast it burns or how much
power the engine will make. Octane number is the resistance to detonation. If the octane number is high
enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make
any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality
are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame
speeds and some with slow flame speeds. It depends on how they are put together. At Rockett Brand
TM, we like
fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline
than one that has a slower flame speed.
Power: The ultimate goal in the racing gasoline business is to convert chemical energy from the gasoline
hydrocarbons into mechanical energy or horsepower. The most efficient way to convert the gasoline into horsepower
is to have the correct air-fuel ratio and the correct spark timing. A mixture that is too rich or too lean will
not make maximum horsepower. The same is true of spark timing: too much or too little will compromise
engine output.
Summary: As indicated above, flame speed and octane number both impact the amount of power that an
engine will develope, but they are independent of each other. To get maximum power from an engine, one must
have a gasoline with adequate flame speed (faster is always better), and adequate octane quality to support the
combustion process. Tied in with the optimized air-fuel ratio and the spark timing, we have a winner."
web page
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So high Octane gas ignites LATER.
Well, If we are going to start throwing up quotes from websites in here to support our arguments:
http://www.gti-vr6.net/library/misc/Pop_Hot_Rod_octane_article.html
"The burn rate of a fuel is a measurement of the time required
for complete combustion of the air/fuel mixture. The notion that octane
ratings affect the burn rate of fuel is about 180-degrees from reality;
bum rate is a function of several variables, and the two are completely
independent, although there is generally a correlation between octane
ratings and bum rates."
(I left that last sentence fragment in there so you know I am not trying to cover up info)
Sure, there can be a correlation. C12, C14 are going to burn slower than 87 octane gasoline, but not because of the octane but because of the distillates used to formulate the gasoline. Gasoline is a hodgepodge of different distillates all with independant burnrates, octane ratings and volatilities. One day you will get slower burning Regular grade, the next day you get quicker burning Regular grade depending upon what had to be dumped in the mix at the refinery. To come out with a blanket statement that "higher octane gases burn slower than low octane fuels" is wrong.
While I am on a mini rant, I don't know when Bohacz wrote that article but his information as to what detonation actually is (the colliding flamefront stuff) is a bit outdated. If it were true all multiplug cylinder engines would destroy themselves. All modern cars ping to some extent. You will never hear it, and your pistons will tolerate it. Engineers know it is going to happen and design pistons accordingly. Slight, imperceptable detonation means that the engine is running at the limit of timing and mixture to afford highest economy. Severe detonation will show itself around the edge of the piston (as diagrammed in the Bohacz article) nearest the intake valve, and this will result in the upper ring land getting soft, or result in it being pounded down and siezing the top ring. Preignition on the other hand is the engine killer. See a hole burned in the crown-preignition.
Don't mean to be a jerk about it, bit there is bad info all over the internet, some taken as gospel truth.
Well, I gotta go pick up junior from school now to see what PC #@$%! the teachers implanted in his fragile mind today.
read this
http://www.idavette.net/hib/fuel/index.htm
the extra kick in gasoline, today, is ethanol. but i wouldn't call it a kick. it is also used to help increase the octane rating of fuel, really a perk of blending it in, because it has an octane rating around 110 I think. But it has a lower energy content so I would never call it giving gasoline it's kick; it's also the reason why you get lower mpg using gasoline with 10% ethanol vs. gas with no ethanol.
some real octane boosters are xylene and toluene, which are already blended in gasoline to give the desired qualities of octane # and burn characteristics. try googling xylene toluene octane boost home homemade, a lot of people have done this. I thought xylene/toluene is something around 10% in gas, and you can safely add something like 15% more by volume to your fuel tank with no worries. But don't quote me on those %'s. Too much of them and you start to affect A/F ratio and combustion properties which defeats the purpose. Two other overlooked facts are air/fuel ratio and energy content. What most people don't realize is a lot of alternative fuels, ie ethanol, have lower AF ratios and energy content so they require more fuel per combustion cycle to burn, and if you want equivalent power of gasoline (with higher energy content) you have to force extra air (boost) into the cylinder... along with more fuel to have the correct AF ratio. Most of the octane boosters are snake oils. MMT is a real one, but it's cost and after effects make it not worth it in the long run, the best way is find a gas station selling 100 unleaded and blend it in with 91/93 octane fuel.
who is zhome? This is a good example why you shouldn't believe every web page on the web. I would consider wikipedia a more reliable source of info in this case.
octane: Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber.
http://en.wikipedia.org/wiki/Octane_rating
in plain english, all that octane rating means is: a fuel with a higher octane number can be compressed more (than a fuel with a lower octane number) before it will self igniting, or self detonate, without a spark.
http://www.idavette.net/hib/fuel/index.htm
the extra kick in gasoline, today, is ethanol. but i wouldn't call it a kick. it is also used to help increase the octane rating of fuel, really a perk of blending it in, because it has an octane rating around 110 I think. But it has a lower energy content so I would never call it giving gasoline it's kick; it's also the reason why you get lower mpg using gasoline with 10% ethanol vs. gas with no ethanol.
some real octane boosters are xylene and toluene, which are already blended in gasoline to give the desired qualities of octane # and burn characteristics. try googling xylene toluene octane boost home homemade, a lot of people have done this. I thought xylene/toluene is something around 10% in gas, and you can safely add something like 15% more by volume to your fuel tank with no worries. But don't quote me on those %'s. Too much of them and you start to affect A/F ratio and combustion properties which defeats the purpose. Two other overlooked facts are air/fuel ratio and energy content. What most people don't realize is a lot of alternative fuels, ie ethanol, have lower AF ratios and energy content so they require more fuel per combustion cycle to burn, and if you want equivalent power of gasoline (with higher energy content) you have to force extra air (boost) into the cylinder... along with more fuel to have the correct AF ratio. Most of the octane boosters are snake oils. MMT is a real one, but it's cost and after effects make it not worth it in the long run, the best way is find a gas station selling 100 unleaded and blend it in with 91/93 octane fuel.
who is zhome? This is a good example why you shouldn't believe every web page on the web. I would consider wikipedia a more reliable source of info in this case.
octane: Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber.
http://en.wikipedia.org/wiki/Octane_rating
in plain english, all that octane rating means is: a fuel with a higher octane number can be compressed more (than a fuel with a lower octane number) before it will self igniting, or self detonate, without a spark.
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Speaking of making use of auto-ignition, whatever happened to homogeneous charge compression ignition (HCCI) technology, which was touted as the cat's meow maybe ten years ago?
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The spark occurs LATER (once compression is high enough to cause auto-ignition) with high Octane fuel compared to lower Octane fuel.
Not sure what'sa in my 100 octane but it smells like rocket fuel.
There's a point ATDC where the piston has the best mechanical leverage on the rod and crankshaft for downward push. Ideally you want the peak of the combustion pressure to occur at that point. When you light the mix off BTDC is all about trying to make this ATDC pressure peak occur at the right time. A (lower octane) fuel that cannot tolerate detonation may require less ignition lead time or advance and result in a less than perfect pressure peak time. Higher octane fuel may tolerate enough ignition advance to hit the mark and make more power. NOT because it has higher octane or more advanced timing but because the pressure peak occurs at the correct time for the motor design. Advanced timing does not always make more power, rapidly expanding burning mixure BTDC creates pumping losses. Things like increased compression ratio and squish velocity s in the combustion chamber can speed the pressure rise and allow for timing retard (instead of advance) to make the ATDC pressure peak occur ideally with less ignition advance (less pumping losses). Kind of getting off topic here but when working with software to design combustion chambers and predict pressure peaks and maximum squish velocity, flame speed is pretty much the same for pump fuels, be it 87 oct or 93. Saying prem burns slower than reg is just an oversimplified (incorrect) way of trying to understand the effect of ignition advance of combustion peak pressure timing. Logic might say I can use premium and advance the igniton timing, thus it burns slower, but that's not the way it works.
14 degreea ATDC.
give or take, depends on the stroke, rod length to stroke ratio, piston pin location etc.
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I`ve always been curious. What exactly happens in an engine that requires premium unleaded if you use regular unleaded?
Pinking (pinging). Not good
Many modern engines with knock sensors will hear the "ping" and retard the timing to eliminate it. The result is possibly less power and combustion efficiency but no harm to the engine. Since gas IC engines are variable compression (indirectly set by throttle position), and compression is related to detonation, a driver that has a light foot might not "fill" the combustion chamber to a point that raises the trapped compression and causes ping with low octane. In this case a prem only motor can run fine on reg octane fuel and not ping the knock sensor.
Well,
I'd like to thank the forum for all the informative input. I have a lot more info now, than before, and know why my "spirited" 3.3L likes Mid-High grade gas but tollerates low grade fuel. It all makes sense. Thanks again, Dave
I'd like to thank the forum for all the informative input. I have a lot more info now, than before, and know why my "spirited" 3.3L likes Mid-High grade gas but tollerates low grade fuel. It all makes sense. Thanks again, Dave
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