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In Bert writes:

In news:1321147426.4755.14.camel@Thinkpad Bill Horne
wrote:

Diesel is (so I've heard) less expensive than gas,

Not around here, it's not.

At the moment, regular unleaded gas is going for about $3.25/gal, while
diesel is about $4.00/gal.

The few times I've actually looked at the price of diesel, it's always
been more expensive than gasoline.

--
Bert Hyman W0RSB St. Paul, MN

True, but what's important to look at is the overall cost relative to
the energy produced.

Diesel fuel has more energy per gallon than gasoline (145,000 BTU's
vs. 125,000):

http://auto.howstuffworks.com/diesel3.htm

Diesel engines, which use the Carnot cycle, are more efficient,
recovering about 45% of the energy from diesel fuel, versus 30% of the
energy for a gasoline engine:

http://en.wikipedia.org/wiki/Diesel_engine

So the increased energy content and the the increased energy efficiency
means that diesel engines will have an energy advantage over a gasoline
engine of about 1.75 to 1 per gallon of fuel. This more than
compensates for the greater cost ratio of about 1.25 to 1. Diesel
engines may have other drawbacks that were pointed out in this thread
(maintenance, heating, noise, pollution), but energy efficiency and cost
of fuel isn't one of them. That's why it's used in transportation that
requires a lot of energy and fuel (railroads, long-haul trucking,
container ships, etc.).

Conversely, E85 (85% ethanol, 15% gasoline) has less energy content:

http://en.wikipedia.org/wiki/E85

and engines that are designed to burn both gasoline and E85 are not
optimally efficient to burn E85 (requires higher compression).
Therefore, though E85 is much cheaper per gallon, it is only worthwhile
to use when the "price spread" is at least 15% or more. Seems that
there's a web site that surveys prices by region, and identifies when
and where this price spread makes it cost-advantaged to use E85
vs. gasoline:

http://www.e85prices.com/

Locally, this usually happens when the price of gasoline goes much over
$4/gallon.

- --
73, Paul W. Schleck, K3FU

http://www.novia.net/~pschleck/
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