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? on combustion
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Date: 2009/06/20 05:37
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By: Dutchdivco
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Status:
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Karma: 0
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O.k., got to lay out the premise for my ?...We all know gas is composed of many fractions, and they vaporise at different temp./pressures.Pressure comes into it if we equate vaporising with boiling; water boils at a certain temp. at sea level, but at a lower temp at higher elevations, because of lower aptnospheric pressure. So, reducing pressure, like a vacuum, reduces the temp necessary to boil, (or vaporise) a given fraction. Increasing the pressure, as in compression, increases the temp. required.
Now, as atomised fuel droplets enter the intake airstream, the lightest fractions vaporise immediately on contact with the air.These are the fractions we can see vaporising off a bowl of gas, sitting in the sun on a spring day.If they vaporise at those temps and pressures, it stands to reason they would vaporise in the vacuum of the intake, and the temp in the engine bay.This vapor mixes with the air, and is the first to ignite from the ignition spark. The flame kernal begins to spread down the cylinder, expanding as it goes, and keeping the pressure up, even tho the piston is moving down the cylinder. As the flame kernal spreads, it is encountering droplets of liquid fuel. Each drop is composed of a mixture of medium and heavy fractions, including some of the "uber-heavy" fractions, that only boil off at around 900 degrees F., at aptnospheric pressure.
At this point, I can see 1 of 2 scenarios, and I don't know which is accurate.
1) As the flame kernal comes into contact with a droplet, the lightest fractions in the droplet boil off, or vaporise, and then ignite.This raises the temp in the immediate area of the droplet, which vaporises heavier fractions, they ignite, etc. and finally the heaviest "Uber-Heavy fractions of this drop, ignite.
2)As the flame kernal comes into contact with the droplet, its heat vaporises the lightest fractions in this droplet, and they ignite. The heavier fractions in this droplet do not vaporise, cause the temp is not yet high enough, so the droplet is just pushed ahead of the kernal, down the cylinder. When the overall temp in the cylinder rises enough, the heavier fractions vaporise and burn, etc. and the Uber-heavy fractions all end up at on top of the piston, as it nears the bottom of the stroke, when the temp finally rises high enough to vaporise them so they can ignite.
Anyone have any ifomation or opinions on which scenario is more accurate? Jim
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