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Old 01-27-2009, 01:35 AM   #30 (permalink)
ConnClark
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Join Date: Jun 2008
Location: Richland,WA
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Das Schlepper Frog - '85 Mercedes Benz 300SD
90 day: 23.23 mpg (US)

Gentoo320 - '04 Mercedes C320 4Matic
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Quote:
Originally Posted by Christ View Post
I actually said that you could compensate for the density by adding fuel... this doesn't work on fuel injection systems though (including diesels, without human intervention)... they don't take fuel density into account. Most injection systems are designed to "assume" a specific density, and inject a pre-set amount of fuel based on "duration" and "pressure".

So - this is a case where you'd have to alter more than just one single parameter of your vehicle to keep things in sync. You can't just heat your fuel and expect to change nothing else, which makes it a moot point.
My dumb mechanical injection system has no idea what volume it is injecting. Also my cruise control (if it were working) would just add more fuel until the desired speed was reached. It is sensitive to the timing change due to the change in compressibility though.

A common rail injection system wouldn't suffer from the change in compressibility however and could compensate by just extending the duration of the injection pulse. This is what is done to deal with the change in btu content in winter diesel.

Note: the drop in lubricity of the fuel due to the temp increase and viscosity drop might accelerate wear of your injection system. but this is unrelated to the outcome in regards to fuel efficiency though.
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