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Old 07-04-2016, 05:25 PM
rotrex rotrex is offline
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Default "Knock Limits in Spark Ignited Direct InjectedEngines Using Gasoline/Ethanol Blends"


"Knock Limits in Spark Ignited Direct InjectedEngines Using Gasoline/Ethanol Blends"

This is very interesting as it compares the influence of chemical and evaporative effects on forced induction engines by examining the knock threshold via a change in intake air temperature using the engine either with port injection or with direct injection. This way you can observe what happens to fuel evaporating before the intake valve closes, port injection, or after the intake valve has closed, direct injection.

It also contains diagrams stating droplet lifetimes of isooctane vs temperature and crank degree. At about 400K or about 130C, a 100 Ál fuel droplet has a lifetime of 100 Milliseconds! At 530C, we still talk some 30 ms.
So much for water spray with its 100 Ám droplets significantly evaporating in the inlet tract.

A signifikant fraction of the fuel actually evaporates on the walls, intake, valve, cylinder and piston unless you pay a lot of attention to fuel spray dynamics for a direct fuel injection system. With the walls receiving cooling, you lose the charge cooling effect.
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