[ST] Californian fuel consumption

["Anderson, Neil G (CPR)" <andersng@xxxxxx>]

One of the listers in Californian recently mentioned that fuel consumption
is much worse on CA fuel than in other states.  I was interested to know
what causes the difference, as I would have expected the same octane rating
of fuel to give the same miles per gallon.
Since I work for one of the oil majors I thought I'd see if I could get some
inside information.  A colleague who previously worked at a CA refinery
pointed me to the WSPA website http://www.wspa.org/factcleanerburning.htm
Western States Petroleum Association (WSPA) is "a non-profit trade
association that represents approximately 36 companies that account for the
bulk of petroleum exploration, production, refining, transportation and
marketing in the six western states of Arizona, California, Hawaii, Nevada,
Oregon and Washington. Founded in 1907, WSPA is the oldest trade association
in the United States."
In other words, this website will give you the oil industry party line.
The site says "Independent reviews by the Lawrence Livermore National
Laboratory and Consumer Reports and real world research by the Automobile
Club of Southern California found that the gasoline's impact on fuel economy
is modest and well within the estimates of the Air Resources Board. Lawrence
Livermore scientists also found that other factors such as how fast you
drive, traffic congestion and using an air conditioner effect mileage far
more than cleaner-burning gasoline"
So according to the WSPA, the impact of clean gasoline on fuel economy is
small.  But here's a more detailed response from one of the process people
at the refinery in CA:

"The simple answer to your question is that the energy content of a fuel can
vary considerably, with oxygenates blending, winter to summer density
changes, compositional differences, etc., while still meeting the octane
specification. And it is the energy content rather than the octane rating
that can determine vehicle mileage.   As you probably know, octane is a
measure of a fuel's ability to resist engine knock (ping).  Here's textbook
description of knock---"In an engine of a given compression ratio, each
grade of gasoline has a limit to how much it can be compressed and still
burn evenly, supplying a smooth even thrust to the piston.  But when octane
quality of a gasoline is insufficient for the engine's compression ratio, it
burns unevenly and causes the engine to knock.  The spark-ignited flame
progresses rapidly across the combustion chamber and heat and pressure build
up on the unburned fuel in front of the flame front.  Instead of continuing
to burn smoothly and evenly, the unburned portion of the air/fuel mixture
explodes violently from spontaneous combustion, causing the pinging or
knocking sound."  Two fuels with the same ability to resist knock can give
greatly different vehicle mileage.  As an example, ethanol has an octane
rating of about 113 vs. say an 87 octane for regular gasoline.  However, the
energy content of ethanol is about 76,000 BTU/gallon vs. an energy content
of maybe 115,000 Btu/gallon for conventional 87 octane regular.  Ethanol's
octane is much higher but you'll get a lot fewer miles per gallon from it
because of its lower energy content per gallon."

So if CA blend gasoline includes a lot of ethanol to meet clean fuels
regulations, your mileage will definitely vary.

Neil

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