Better gas mileage and performance.

[Pinger]

Parking this (something I just read) here as I think it was this thread that flame propagation was discussed.
We think of combustion as a ball of flame in the combustion chamber - or that at least is how it is presented in video animations. In truth what goes on in there is the flame progressing spherically from the spark plug with the products of combustion behind it and the as yet unburned mixture ahead of it. Two distinct zones (like a balloon within a balloon) separated by the flame front. So far so obvious. What blew me away though is the thickness of the flame. 0.2mm, 0.008''. It's barely there! What a delicate thing it is that creates so much power.

 

[GrimsterGMC]

Parking this (something I just read) here as I think it was this thread that flame propagation was discussed.
We think of combustion as a ball of flame in the combustion chamber - or that at least is how it is presented in video animations. In truth what goes on in there is the flame progressing spherically from the spark plug with the products of combustion behind it and the as yet unburned mixture ahead of it. Two distinct zones (like a balloon within a balloon) separated by the flame front. So far so obvious. What blew me away though is the thickness of the flame. 0.2mm, 0.008''. It's barely there! What a delicate thing it is that creates so much power.

So, less of a flame and more of a point of transition line between unburnt and burnt fuel.

 

[Scooterwrench]

Used to be rule of thumb was higher compression,better fuel economy.
More bang for the buck,literally.

Heavier flywheel helps by sustaining crankshaft inertia.

Running high octane fuel in a low compression motor is just wasting your money. High octane doesn't mean hotter burning fuel. Octane additives control frontal flame burn rate.

 

[Pinger]

So, less of a flame and more of a point of transition line between unburnt and burnt fuel.

Yep, and that less then wafer thin layer of flame separating the two (but moving at 20-25m/s (45-55mph)). Blew my mind that it is so thin.

When driving at 45-55mph, the part of the flame front that is behind the spark plug (relative to the vehicle) is actually stationary. I'll stop now before ending up in playing-bowls-on-a-moving-train territory.

 

[GrimsterGMC]

Yep, and that less then wafer thin layer of flame separating the two (but moving at 20-25m/s (45-55mph)). Blew my mind that it is so thin.

When driving at 45-55mph, the part of the flame front that is behind the spark plug (relative to the vehicle) is actually stationary. I'll stop now before ending up in playing-bowls-on-a-moving-train territory.

You got me curious and started watching videos of small engines with glass cylinder heads being videoed at high speed so they could slow down the replay. Gave a good veiw of how the fuel enters the cylinder and ignites. Wasn't to the detail you spoke of but certainly a good perspective.

 

[Pinger]

You got me curious and started watching videos of small engines with glass cylinder heads being videoed at high speed so they could slow down the replay. Gave a good veiw of how the fuel enters the cylinder and ignites. Wasn't to the detail you spoke of but certainly a good perspective.

I've seen some where a cylinder head is made of perspex for a side valve engine and guessing that's what you watched. Lab research has used test engines with glass/quartz access panels for some time now and it has moved on with complex laser, infra-red, etc, etc measurement of in-cylinder air motion and combustion - then there's the computer modelling. At that level, it is massively complex.

You got me curious and

Careful there - it can become an obsession. Ask me how I know!

 

[HotWheelsBurban]

We filled up Rawhide yesterday...gas has gone down a little bit here, so I thought, I'll use mid grade 89 octane again. Checked the mileage after filling up and guess what? This truck went from 10.5 to 13.85! So I think that's worth 40¢ a gallon....

 

[L31MaxExpress]

We filled up Rawhide yesterday...gas has gone down a little bit here, so I thought, I'll use mid grade 89 octane again. Checked the mileage after filling up and guess what? This truck went from 10.5 to 13.85! So I think that's worth 40¢ a gallon....

My van also hated 87 when it was stock.

 

[HotWheelsBurban]

My van also hated 87 when it was stock.

My two (and IIRC the other 99 Burb too, all L31s) run well on 87, but the crew runs great on 89. I was really surprised by the mileage though.

 

[GrimsterGMC]

I've seen some where a cylinder head is made of perspex for a side valve engine and guessing that's what you watched. Lab research has used test engines with glass/quartz access panels for some time now and it has moved on with complex laser, infra-red, etc, etc measurement of in-cylinder air motion and combustion - then there's the computer modelling. At that level, it is massively complex.

Careful there - it can become an obsession. Ask me how I know!

Yes, that's what I watched. I am 56 years young and still get excited by learning new things. I just installed a EBL FlashII in my truck and am learning about tuning so seeing how the fuel burns in a cylinder helps to understand ignition timing etc. My wife will let me know when it has become too much of an obsession I'm sure.