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 

resources.