[Vwdiesel] New to list

Lee Hillsgrove hillsgrove at adelphia.net
Sun Mar 7 20:11:06 EST 2004

> Lower cetane is lower energy content and thus lower economy.

  I'm not sure I agree with that statement. The cetane number in diesel is a
measure of the willingness to ignite, much as the octane number in gasoline
is a measurement of the resistance to auto-ignition. Large, low-speed
stationary engines burn stuff with cetane ratings so low our engines
wouldn't even run on it, yet they deliver phenomenal economy. A fuel with
low cetane tends to run poorly, smoke more, not start so well in the cold,
and return less economy in a high-speed diesel more as a function of
essentially altered injection timing due to the fuel not being so willing to
ignite. It effectively retards the injection timing. Look at the low-speed
tractor-trailer sized stuff, they run generally OK on low-quality fuel
because it has plenty of time to ignite and burn completely. The high-speed
diesels such as we have in our VWs, on the other hand, require fuel with a
higher cetane rating due to the comparatively short window of time available
for the fuel to be injected and burned completely. The TDIs, for example,
were designed for and really want to see a minimum of 50 cetane fuel such as
they have almost everywhere else in the world. Because the USA's diesel
market consists of predominantly low-speed, heavy-duty engines that run on
low-grade fuel, that's what we get. The trucking industry has absolutely no
incentive to pay extra for fuel that is over and above what their rigs
require to run, as that would negatively impact profits.

...or maybe I'm way off-base. Could be.  :-p


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