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Old 02-09-2011, 04:22 PM   #83 (permalink)
NachtRitter
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Helga - '00 Volkswagen Jetta TDI
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You have it right here...

Quote:
Originally Posted by FourBinLabs View Post
If once diesel fuel ignites, it is an uncontrolled explosion, that sounds like detonation. If when gasoline ignites, it's a controlled explosion, then does this mean that gasoline burns slower than diesel?
Once diesel ignites, it burns significantly faster, and in a more uncontrolled fashion, than gasoline. As well, there are additional points of secondary ignition when the diesel burns. The higher the octane, the slower it burns, and the lower the chance of secondary ignition points.

Quote:
Originally Posted by FourBinLabs View Post
It boils down to this. It takes ~600°F to auto ignite diesel. It takes 495°F to auto ignite gas. If a gas engine has enough compression to make diesel fuel auto ignite, then the cylinder temp must reach ~600°F during compression. If the cylinder reaches ~600°F, then it must invariably reach 495°F on it's way there. If it reaches 495° The gasoline wile auto ignite long before the diesel will.
Read the Gasoline FAQ link I posted previously... no, really, read it. You're still equating the octane rating (RON, MON, AKI) with initial auto-ignition under temperature and pressure. It is not the same, as I said in my previous post.

Octane rating conveys what happens once the fuel has been ignited, not how difficult it is to ignite the fuel initially, according to the FAQ.
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