Is There A Diesel In Your Future?
By Carey Russ
When someone mentions ``diesel'', what comes to mind? If you
are a typical American driver, it probably won't be pretty.
``Diesel'' is that smelly, smoky bus you got stuck behind the other
day, or the noisy semi next to you in traffic. Although diesel is the
norm for heavy trucks, and not unheard of in full-sized pickups,
diesel automobiles are an eccentric rarity on American highways.
In Europe, it's a different story. In some parts of Europe, over
40 percent of new vehicles sold are diesel-powered, and there is
such at thing as a diesel sport wagon. Ford of Europe is
investigating use of a diesel in its World Rally Championship cars.
(Competitive use of diesels is not exactly new – the Cummins
Diesel Special got pole position at the 1952 Indianapolis 500.)
Diesels are popular in Europe because of high fuel prices.
Gasoline, and diesel fuel, are much less expensive in the U.S., but
you will see more diesels here in the future.
Why? The diesel is the most efficient internal combustion
engine, for a variety of reasons. Rudolf Diesel's main reason for
development of the engine bearing his name was a preoccupation
with efficiency. A student of chemistry, mathematics, and physics,
Diesel developed the engine bearing his name more by
mathematical modeling and theory than by trial and error. Instead
of the flames or hot tubes used by other primitive internal
combustion engines of the 1890s, Diesel's used the heat generated
by compression of the air in the cylinder to ignite a charge
precisely injected into the cylinder. Diesel development has lagged
behind that of the spark-ignition gasoline engine, but those two
characteristics have characterized it over the past century. Modern
technologies developed for gasoline engines to reduce emissions
are being applied to diesels.
Compression ignition and high-energy fuel are the diesel's
advantages for efficiency. Diesel fuel has a high flash point, and
does not burn as easily as gasoline, a definite safety factor.
Because of its chemical composition, it contains about 11 percent
more energy than an equivalent amount of gasoline. Air heats as it
is compressed, and air in a diesel engine is considerably more
compressed than in a gasoline engine. Gasoline engine
compression ratios are between 8:1 and 12:1; diesels are between
14:1 and 25:1. When the piston reaches the proper point, fuel is
injected directly into the cylinder, and ignition takes place without
need for a spark plug.
Compression ignition is also the source of the diesel's technical
difficulties. But those problems can be overcome. The higher
compression that results in greater efficiency also places more
stress on engine parts. It means that the engine block and heads
must be stronger than that of a gasoline engine, although modern
casting techniques and alloys of iron or aluminum can help reduce
weight compared to past designs. More torque is produced because
of the high compression, so the engine's connecting rods and
crankshaft need to be stronger than for a gasoline engine. So
diesels are heavier than equivalently-powerful gasoline engines,
although the difference is less now than in the past, and less for the
smaller diesels likely to be used in cars and light trucks.
Fuel injection is the other technology that makes diesels more
expensive, at least initially. In fuel-injected gasoline engines, fuel
is injected into the intake manifold, either at a throttle body or
(more rarely, and expensively) near each intake valve. In a diesel,
fuel is injected directly into the cylinder. Timing is critically
precise. The mechanical systems that were used in older diesels
were complex and expensive; modern electronics has simplified
the matter, as it has with gasoline injection, and made fuel
injection less expensive and more precise. It's that imprecision,
especially under changing conditions like acceleration, that results
in an improper mixture and a cloud of foul smoke. New
electronically-controlled fuel injection systems are being
developed to allow diesels to meet upcoming emissions
regulations, and they'll run cleaner than ever. (And direct injection
also works for gasoline engines, expect to see that very soon.)
Research in diesel combustion and combustion chamber design is
also improving efficiency and lowering emissions.
So, with modern combustion chamber design, lighter-weight
alloy construction, electronic control of the injection and
combustion process, cleaner-burning low-sulfur fuel, and
particulate traps and catalytic converters to remove unburned
material and noxious gases from the exhaust, diesels will be
cleaner and quieter than ever. The compression-ignition process
inherently produces lower levels of carbon monoxide and dioxide,
and unburned hydrocarbons. Future emissions regulations require
virtually eliminating diesel pollutants.
This will happen, and at that time you may not only be pleased
that the truck or bus next to you is odor-free, you may be driving a
diesel-powered vehicle yourself. Car and light-truck diesels can
use 30 percent less fuel than gasoline-powered equivalents. Less
fuel equals less pollution, even without anti-pollution technologies.
The diesel's excellent torque characteristics make it a good choice
for real-world driving. Engine block and vehicle body design can
further decrease engine noise. Also, a small diesel is an excellent
engine to use in an internal combustion-electric hybrid vehicle, as
it can further decrease fuel consumption and increase efficiency.
And, if worst-case scenarios in fact do become true and petroleum
becomes scarce, biodiesel fuel can be made from renewable