Alternative Fuels: Diesel
By Carey Russ (c) 2003
Ten or twenty years in the future, cars and trucks are likely to be
powered by hydrogen fuel cells. Until then, expect internal
combustion (IC) to continue to provide power, but it will not be
business as usual. While gasoline will continue to be used, it will
continue to evolve as it is reformulated to lower pollutants. Natural
gas is already in limited use for commercial fleets, and specially-
modified gasoline engines have successfully run on hydrogen, at
least experimentally. But, although both natural gas and hydrogen
burn very cleanly, with minimal exhaust pollutants, they have a
much lower energy density than gasoline. Simply put, it takes more
of either fuel to provide as much energy as an equivalent amount
of gasoline. And, since both are gases at normal temperatures, they
need to be compressed. Hybrid vehicles, with a natural gas,
hydrogen, or gasoline-electric drivetrain, are one way to lessen the
disadvantages of range. Gasoline-electric hybrids are already
available, but there is another fuel that, when used in cars, can
produce fuel economy equal to that of today's hybrids.
That fuel is diesel.
Pick yourself up off the floor and stop laughing. It's not the 1970s
any more. Today's diesels are not what they once were, especially
modern European diesels. If you associate the word ``diesel'' with
``smelly,'' ``dirty,'' and ``sooty,'' think again. Because of their
inherently efficient design, diesels produce lower levels of
unburned hydrocarbons, carbon monoxide, and carbon dioxide
than gasoline engines. Diesel problem areas are in particulates and
nitrogen oxides, but those problems are being solved. According to
the Diesel Technology Forum, today's diesel trucks and busses
produce only one-eighth the emissions of their counterparts of the
late 1980s. By 2007, diesel emissions will be virtually eliminated.
Emissions from construction equipment and even railroad
locomotives are also decreasing.
Technology that has cleaned up gasoline engines can also be
applied to diesels. This includes improved design and materials,
precise electronic controls, and exhaust catalysts and particulate
filtration. Also, as with gasoline, diesel fuel will evolve to lower
emissions.
Unlike other internal combustion engines, in which an electric
spark ignites the fuel/air mixture to produce power, diesels work
by compression ignition. The fuel/air mixture is compressed to a
much higher degree than in a gasoline (or alcohol, natural gas, or
hydrogen) engine, to the point where it ignites due to the heat of
compression. The more a fuel/air mixture is compressed, the more
power can be produced. A 10-to-1 compression ratio is common
for gasoline engines. Alcohol and hydrogen are around 14:1.
Diesels have compression ratios from 18:1 to 21:1.
Because of their high compression, diesels produce more torque at
lower engine speeds than other IC engine designs. Low-rpm torque
is what provides acceleration at everyday speeds, and it also
contributes to the towing abilities of diesel trucks. The high
compression and high operating temperature of a diesel contribute
to its fuel efficiency, typically 20 to 40 percent better than a
comparable gasoline engine. When properly constructed, diesel
engines last longer than other types. Yes, they're heavier because
of the torque and temperatures that need to be handled, but modern
materials are making current diesels lighter than their counterparts
from the past. Today's automotive-sized diesels are not huge,
heavy pieces of machinery.
Although diesel cars are few and far between in this country, diesel
pickups are popular, particularly at the larger end of the size and
duty spectrum. And diesel cars are coming here. The Volkswagen
Golf and Jetta TDI models will soon be joined by a Passat TDI,
and the Mercedes-Benz diesel is rumored to be coming back to
America. If these cars succeed in the American marketplace,
expect American and Japanese manufacturers to follow.
In Europe, emissions requirements are different and fuel is much
more expensive, so more diesel cars are sold. One-third of
European cars are diesels, with 61 percent in Austria and over 50
percent in Belgium and France. And these are not just small
economy cars. Forty-four percent of European luxury cars are
diesel powered.
Diesel luxury car? Believe it. At the recent Challenge Bibendum
alternative fuels event, I had the opportunity to take short drives in
an Audi A8 TDI, BMW 5-Series diesel, Volkswagen Passat TDI,
and Fiat Stilo diesel. The Audi and BMW were true luxury cars,
and as smooth and quiet as their gasoline counterparts. The only
clue to diesel power was a different exhaust note - but in both it
was very subdued and quiet, not the raucous rattle associated with
old diesels. Although the VW and Fiat were a little lower in the
socioeconomic spectrum, they were no less refined. Power was not
a problem, even up the steep hills at Sears Point. If fuel economy is
a concern for you, check out a diesel next time you're in the market
for a new car or truck. You're likely to be pleasantly surprised.