Environmental Engineering Reference
In-Depth Information
mass-produced during WW I had 1.34 g/W; and the
Wright Cyclone R-3350 air-cooled 28-cylinder engine
powering B 29 bombers during WW II had 0.67 g/W,
which was only slightly surpassed in the 1960s by an-
other Wright (R-1820-82A) with 0.59 g/W.
These excellent achievements did little to boost the
relatively low efficiency of gasoline engines. Although
the ideal efficiency of Otto cycle engines is 60%, actual
peak performance is no higher than about 25%, inferior
to engines patented by Rudolf Diesel in 1892 and com-
mercialized after 1900. These are distinguished by high
compression ratios (15-24) designed to produce sponta-
neous ignition of the injected fuel and hence no need for
a carburetor or a sparking device. Their weight/power
ratio was 40-60 g/W, maxima up to 120 g/W, and
their speed only about 300 rpm. The disadvantages of a
heavier, low-speed engine were offset by superior thermal
efficiency and the possibility of using a cheaper, more
energy-dense, less volatile, less flammable liquid fuel. In
his classic tests Clerk (1911) calculated the following effi-
ciencies for a 445-kW diesel engine: mechanical efficiency
77%, indicated thermal efficiency 41%, brake thermal effi-
ciency 31.7%. In contrast, typical efficiencies of Otto
engines were 14%-17%. Engines with low volatility and
flammability are particularly suitable for vessels as well as
for the use in tropics to minimize evaporation from truck
and bus fuel tanks.
The first niche conquered by the engine was in marine
propulsion, where its weight was of little consequence.
Submarine engines were followed by increasingly larger
ship plants. By the year 2000 some 90% of the world's
largest cargo ships, including supertankers, were powered
by diesel engines. MAN, W¨rtsil¨, Mitsui, and Hyundai
are their leading makers. The maximum sizes of these
machines are still increasing; in 1996 the world's largest
marine diesel engine rated about 56 MW, a decade later
the largest W¨rtsil¨ engines had capacities in excess of 80
MW. On land the replacement of steam and gasoline
engines by diesels began after WW I, the first diesel
trucks in 1924 and the first heavy passenger cars in
1936. By the late 1930s most new European trucks and
buses had diesel engines, and this dominance was
extended after WW II to the rest of the world. Bus
engines with up to 350 kW, weighing 3-9 g/W, can
log up to 600,000 km without overhaul. Similarly, die-
sels dominate all nonelectrified railway traction with
engines up to 3.5 MW weighing 5-10 g/W.
The weight/power ratios of automotive diesels
eventually declined to 2-5 g/W, and today's lightest
passenger car diesels are only slightly heavier than
gasoline-fueled engines. Rare in North America, diesels
had about 45% of the new car market in Western Europe
by 2005. Very large stationary diesels (up to@50 MW)
have been used for electricity generation in remote loca-
tions as well as for standby capacity. Ratings of the largest
diesel-powered stations reached 200 MW by the late
1990s. Efficiencies have surpassed 42%, and performance
above 35% should be attainable with most well-
maintained engines. Diesels also dominate in heavy con-
struction machinery, tractors, self-propelled harvesters,
and locomotives on nonelectrified railways.
The third type of internal combustion engine that has
revolutionized many industries appeared during the late
1930s, when Frank Whittle in England and Pabst von
Ohain in Germany began testing their independently
invented prototypes of gas turbines to power military jet
aircraft (Constant 1981; Smil 2006). The post-WW II
perfection and diffusion of this powerful prime mover
