Interesting video on leaded avgas, and alternatives coming along

[OM617YOTA]

Might be other options than leaded avgas, $25/gal premix, or finding racing gas soon.



Scott Manley normally does space industry content, worth a subscription if that's your thing.

 

[bwalker]

The problem with AVGAS is getting it certified for backwards compatibility.

 

[bwalker]

He isn't technically correct on the slower burning thing, which is a common old wives tale. Also his description of what detonation leaves alotnto be desired. Otherwise it's a good video.

 

[HavinFun]

Great video, thanks for posting. BWalker, trying to test my knowledge. What do you find wrong with the slower burning thing he mentioned about high octane gas? As I understand it, the higher octane allows the timing to be advanced because of the slower burning properties. This then allows a longer burn time for the fuel which translates into more complete combustion as it has had more time to burn. Thanks.

 

[bwalker]

Great video, thanks for posting. BWalker, trying to test my knowledge. What do you find wrong with the slower burning thing he mentioned about high octane gas? As I understand it, the higher octane allows the timing to be advanced because of the slower burning properties. This then allows a longer burn time for the fuel which translates into more complete combustion as it has had more time to burn. Thanks.

In a general sense burn speeds correlation with octane number is such that the highest octane fuels burn the fastest.
Keep in mind that octane is a measure of flame stability and that detonation takes exposure to high heat over time to occure. Given this it's pretty easy to see that burning slower would increases the risk of deto and not lower it.
You mention timing. Increasing the timing increases the amount of time the combustion event takes. Given this it increases the octane requirement for the very reason I mentioned in the previous paragraph. In a two stroke that's poorly scavenged timing increases can help, but they also increases your risk of detonation.

 

[HavinFun]

Thanks for your explanation. I’m talking mostly about 4-stroke engines, not as knowledgeable about 2-strokes but should apply too. Where you say because an increase in timing gives a longer burn time and that it is exposing the fuel to higher pressure and heat and that leads to detonation as the piston approaches TDC, I thought that is where high octane makes its money as it won’t detonate prematurely under those conditions. And if that is the case then the burn is more complete in the rotation and is firing at where a low octane fuel would fire anyways. I can see the theory of what you said, but having trouble processing it. Best regards.

 

[bwalker]

Thanks for your explanation. I’m talking mostly about 4-stroke engines, not as knowledgeable about 2-strokes but should apply too. Where you say because an increase in timing gives a longer burn time and that it is exposing the fuel to higher pressure and heat and that leads to detonation as the piston approaches TDC, I thought that is where high octane makes its money as it won’t detonate prematurely under those conditions. And if that is the case then the burn is more complete in the rotation and is firing at where a low octane fuel would fire anyways. I can see the theory of what you said, but having trouble processing it. Best regards.

I am speaking of the relative likelihood of detonation happening. Another way to look at it is as stress. Increased combustion time increases the likelihood hood of detonation because it increases the stress on the combusting charge.
High octane does decrease the likelihood of detonation, but it does so by being a more stable combustion event. Not by slowing the event down and exposing the combusting charge to more heat.
What I have said is not theory. It's scientific fact.
This particular subject has tons of misinformation, but if your interested Google Kevin Cameron, Detonation.

 

[sean donato]

Higher octane, in a nut shell, can be described at the fuels resistance to self or pre ignition. Doesn't really have much of anything to do with burn rate or flame propagation once it's lit.

 

[bwalker]

Higher octane, in a nut shell, can be described at the fuels resistance to self or pre ignition. Doesn't really have much of anything to do with burn rate or flame propagation once it's lit.

It's a fuels resistance to detonation, which happens well after the sprak plug has fired. Detonation happens mostly at the tail end of the combustion event, because it takes heat and time to happen. That's why the damage from it is often on the exhaust side of the piston still the outside edge.
High octane won't help pre ignition, because it's just something other than the spark igniting the charge.

 

[HavinFun]

It does have everything to do with burn rate- it burns slower which is why higher performance engines use more timing and have more complete burn of the fuel charge and make more power. If it burned as fast as lower octane fuel you would get detonation with the advanced timing rate, and that would damage the piston/engine. There is a difference in low octane and high octane fuel.

 

[HavinFun]

Double post

 

[bwalker]

It does have everything to do with burn rate- it burns slower which is why higher performance engines use more timing and have more complete burn of the fuel charge and make more power. If it burned as fast as lower octane fuel you would get detonation with the advanced timing rate, and that would damage the piston/engine. There is a difference in low octane and high octane fuel.

None of that is accurate..

 

[HavinFun]

All good. You with your theory, and me with mine.

 

[bwalker]

All good. You with your theory, and me with mine.

You have a misguided theory. I have the science. Open your mind and you might learn something. Or not, for all I care.
BTW I do refine gasoline for a living, so you are barking up the wrong tree.
https://www.cycleworld.com/story/blogs/ask-kevin/fuelish-myths/

 

[HavinFun]

In just a few seconds I found plenty or articles talking about how higher octane gasoline burns more slowly, or maybe as you are saying it, controlled, than lower octane. So, tangentially what you are saying could be mostly correct, but plenty of differences of opinion on the subject. Best regards.

 

[bwalker]

In just a few seconds I found plenty or articles talking about how higher octane gasoline burns more slowly, or maybe as you are saying it, controlled, than lower octane. So, tangentially what you are saying could be mostly correct, but plenty of differences of opinion on the subject. Best regards.

Plenty of BS articles on the web because plenty of people recycle the same old wives tales over and over. Rest assured, I am correct and opinions have nothing to do with it.
The article i attached above was written by a Harvard physics graduate and noted two cycle tuner. Read it.

 

[HavinFun]

Again, we all have opinions. Best regards.