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Originally Posted by nelsmar
2 things.
1) isnt the double hump showing the first hump being the compression stroke, and hte second being combustion? So you arent actually "gaining" pressure, that pressure would exist regardless of spark or not. So this isnt actually showing that positive atmosphere would increase power by using retarded timing correct?
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That first hump is from the compression. If the spark is advanced enough, you have one big hump, instead of a small hump and a second bigger one to the right. As you advance the spark from the retarded position, the second hump moves left, closer to the first one, and eventually you get one big hump. If you advance past MBT, the hump "leans" to the left. Go
back to my first post in this thread and look at the picture.
At a fixed rpm on a dyno, it is conceivable that you could be running a lot higher load (say more boost) with retarded combustion and still have lower peak pressure than running lower load at MBT. Peak pressure in terms of magnitude (say having 90 bar vs 70 bar max) can be highly sensitive to combustion phasing. So that means burn rates and spark advance.
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2) Lets go more hypothetical, i am just talking about a fuel burn rate regardless of combustion engine. Say we take a 1 liter canister. Fill it full of stoich mixed E85 and atmosphere. Ignite at the top and calculate the burn duration & time until shock hits the bottom of canister. Now lets take the same canister but fill with the same mixture but in a pressure of 2bar (so twice the density, twice the mass). Will the burn rate & shock rate change?
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that's sort of a textbook problem... I suppose you could say it goes faster at higher pressure, but that's kind of a useless answer. It's like in school physics talking about dropping a rock from a plane and only talking about gravity, neglecting the air it would be falling through. That's your simple "free fall" problem. But then try taking that simple discussion and using it to understand how a real bomb falls out of a plane. There's a whole lot more going on.
In a real piston engine, the instantaneous pressure and volume is always changing as the piston is going up and down. What you are asking and trying to understand is really what 3D modeling is for, and to a lesser extent optical single cylinder engines with high speed photography. When you look at modeling software output it will give you heat release, pressures, etc on a degree-by-degree basis to answer those kinds of questions.
Now that we've gone down that tangent... I too would like to see pics of a messed up bearing.