Hang on boys...let's get on the same page.

What I'm reading here is:

1. Octane rating directly effects the BTU rating of a fuel type
Goat_Cheese
Miami993c297

2. Octane rating directly effects the combustion rate of a fuel type
Armageddon

3. Those opposed to both claims
Engineermike
Adrenaline_Z
Maggie
J-Rod

Can everyone please read this article and let's debate it.

http://en.wikipedia.org/wiki/Octane_rating

If there's one thing I don't know much about it's fuel chemistry. From the
articles I've read, it seems that:

a. Octane does not dictate BTU, but rather the fuel type (IE: Gasoline, Ethonol, Methonal).

b. Octane does not dictate the combustion rate of a fuel. The combustion
rate is determined by the fuel type, and mixture.

Pump gasoline that is mass produced for the consumer market that sits in
underground tanks and has unknown additives, tank sediments (water), and
likely a poor quality of chemicals per batch is NOT the same as a refined racing
fuel with a similar octane rating.

 

Under this abnormal restriction, based on the dyno test from the magazine, the higher octane fuel did make more power, even at the same timing level. Now, going outside the test, VP sells oxygenated fuels that produce up to 5% more hp than regular. Again, the hp gain has to do with the oxygen in the fuel, not the octane or even the btu/lbm.

Mike

 

You gotta let us know

what CR are you running.

and you have no boost since you have a NA engine... so what CR is your engine? Give more details.

Things to remember:

octane is an engines resistance to knock.

buy gasoline from a busy gas station so that it will not be stale gasoline

volatility is how fast something can evaporate( it has nothing to do with octane rating)

dont use jet fuel!!!


"I use a higher octane race fuel as insurance to fight off detonation during hot weather conditions or where I might be force to hot lap the car and low ET isn't the primary goal such as brackets or an index race that I am a little quick for."

Hot weather conditions shouldnt have to do much with detonation. instead volatility may be an issue..

 

I'm running 11.6:1 SCR. The camshaft is a 248/252 112+4. I did fight a little detonation early on when the PE enable was set at stock settings. I can run 30* at anything over 4900 rpm on 93 octane. I have not attempted more as the dyno showed little gain at 29* on 93 octane pump gas. I currently run a max timing of 27* and it's happy, but I want a tad bit more if fuel will allow more HP safely.

It's a daily driver that is at 10.1s now and I want to prove 9.9xs are realistically capable. I can do it with perfect air, but is there a fuel that can push me to my goal without "perfect" conditions? That's my hidden agenda that stimulated the original question. I feel that we have sacrificed nothing at this point. We just want to squeek through once so we can prove it's an achievable goal.

Great data guys!!

 

for consideration...
Definitions:

Octane: the eighth hydrocarbon from the cracking process of crude oil. It is the most resistant of the eight basic cracked hydrocarbons to spontaneous combustion when compressed..

Fact: Octane cannot exceed 100 %

heptane: the seventh hydrocarbon from the cracking process of crude oil. It will combust spontaneously with minimal compression.

Octane Rating: a fuels resistance to spontaneous combustion based on the model fuel (gasoline) of octane & heptane. Example: 93 octane gasoline would = 93% octane + 7% heptane. Note: An octane rating of over 100% would require additives to push spontaneous combustion value above normal octane.

How ‘power’ in fuel is measured: Volume of detonation (reaction) gases, Heat of explosion (order of burn usually measured in kcal/kg ), Specific energy (mt/kg, kj/ kg) and Duration of Bubble ( the measure of time it takes for a volume of expanding gas produced from a reaction to return to normal state).
Example: a fuel that produces a volume of gas = to 1000 l/kg will make more ‘power’ in a combustion engine than a fuel that produces a volume of gas = to 900 l/kg (regardless of it’s resistance to detonation).

 

ditto this, if your car is stock it was designed to use the recommended minimum octane fuel to keep the engine safe (prob 92). if you were to say increase compression of the engine and thus increase heat it would be detonation prone and you would need higher octane (less volatile). Could go on forever about this.

 

Absolutely not, octane rating has nil to do with the BTU content of gasoline.

 

sorry gues i missed the comment about changing the btu rating which is not changed. it is the flash point that is changed.

 

Ok, I think we've covered this before in several threads. There is also a good FAQ to read
http://www.faqs.org/faqs/autos/gasoline-faq/part1/
http://www.faqs.org/faqs/autos/gasoline-faq/part2/
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
keep going...
(Parts 6 and 7 talk about octane ratings)

But here goes. In very simple terms.

Octane is a measurement of resistance to heat based combustion. Gasoline is not just one part. Its a blend of a whole bunch of crude oil distalates mixed together. There are components in gasoline which will ignite much sooner than other parts. The idea is to control this ignition. Heat and pressure are factors which can affect the ignition of the fuel itself. As you increase each either from an increase in mechanical compression, or because of the latent heat in the combustion chamber. Something has to prevent that fuel charge from lighting off early. Hence, we use distalates to retard ignition like ISO-Octane, or aromatics like Toluene.

But, again to be clear, octane rating is not resistance to combustion. It is resistance to heat based combustion, and there's a huge difference there. The common example of lower octane gasoline having a net increase in total power efficiency assumes that we are using heat based ignition, which we aren't.

This is an Otto cycle engine we are speaking of with spark based ignition, and one of the basic tenants in such an engine design states that an increase in static compression, assuming there is no onset of auto-ignition, will ALWAYS increase the thermal efficiency of said engine. The positive effects of increased static compression on engine power output, low RPM throttle response and cylinder filling are well documented in the annals of engine performance.

The trick to heat based ignition is end gas decomposition (where one fuel is more resistant to heat based ignition than another).


We've all seen the RocketFuel FAQ on blending your own octane boost.

http://www.gnttype.org/techarea/misc...explained.html

Most folks use pure Tolune or Xylene at a 20% ration with pump gas to get around 96 octane. If you want to kick it up a notch, and if you want to mix your own octane boost you can mix Iso Octane blended with 20% toluene. This will yield a fuel supposedly around 110-octane. For anyone interested my understanding is Sigma Aldrich sells iso octane in 4 liter bottles.


Anyhow, there is plenty of reading on octane and what it is or isn't...

Here is a pretty good thread with a good explantion on how Octane is figured:

https://ls1tech.com/forums/showpost....9&postcount=11

Now, as has been said in here. Octane in and of itself is not indicative of power. Its a measurement of resistance to detonation. The key indicator of what makes power is BTUs/gal. Along with that you need to know what the stoich value of the fuel is to know how much fuel you need to extract x ammount of fuel.

If you want an example in the extreme, look at Nitromethane. If you felt Octane was the measure of power, then Octane for Nitromethane should be eleventybillon . In fact, the Octane rating on 100% pure nitromethane is something like 50. But, the BTUs per gallon, and a stoich value of 1.7 make it a powerful fuel

Here is another good article

https://home.pacbell.net/sfnelson/fu...ion__etc_.html

Anyhow, the bottom line is you want a fuel that will burn quickly. You want it to burn hot, and you want it to release a ton of energy. For anyone who hasn't read it in here, an increase of 1 point in mechanical compression normally increases power output by ~4% on motors like ours (all things being equal). As you increase increase mechanical compression you need higher octane fuel to prevent pre-igniton. So, here is where the tradeoff between octane and power rears its head.

Folks always seem to think if 8 is good, then 10 must be better. Its no different in any of the other topics I post in. Whether it be flow numbers on cylinder heads, camshaft duration, or ignition timing folks always wrongly assume that the more you throw at it, the more power you will make.

WRONG!!!

If you motor only needs 87 octane to make peak power at peak efficency, then thats all you need to run.

If you combo only needs X duration, hanging the valve open excessive long only slows down airspeed and cylinder fill.

If your motor only needs 22 degrees of timing, giving it 28 only makes negative work for the motor.


Now, the question becomes how can you leverage what you know to go make more power. You can find a smart chemist who understands what will mix with gasoline (safely or not) to increase combustion efficency and BTUs gal. For example, the nitro based compound (nitropropane) that I alluded to earlier carries a lot of oxygen. So when you add it to your fuel, you need to jet up, as the car will lean out otherwise (remember the stoich value I was talking about earlier?).

Maggie seems to have a VERY firm grip on what I'm talking about here.

Anyhow, most of the power adders to fuel that have been banned are oxygenates that simply allow your motor to be "bigger" since some of the "air" in the motor is carried by the fuel itself. When you have this, you can keep adding fuel so long as you can keep enough air in the cylinder to keep your A/F correct.

Playing with fuel has been around since the early days of of the engine. Some of the exotic blends between early T/F and F1 are crazy. Look at the fuel the Germans used in its race cars in the 30's. There were blends that resemble rocket fuel more than they do motor fuel. Mixing things like Nitromethane and Hydrazine for example.

It'd be interesting to see if someone could figure out a nice way to mix Hydrogen Peroxide (H2O2) and gasoline, as the breakdown of it in the combustion chamber could really help in the release of power.... Most people who understand chemistry cringe when I bring that up though...

 

simple expanation is the higher the octane the higher the flash point