Environmental Engineering Reference
In-Depth Information
In a way, the steam engine became a victim of its own
success. As its performance grew, more was demanded of
it than it could deliver. Its improvements and adaptations
during the nineteenth century were admirable. Its maxi-
mum ratings went up from about 100 kW to 3 MW,
largely owing to a 100-fold increase of operating pres-
sures (from 14 kPa to 1.4 MPa) and resulting in the
best efficiencies climbing from just 2.5% to 25% (fig.
8.8). But the engines had their inherent weaknesses.
They were massive and hence impractical for very large
stationary applications and for light mobile use, and they
were relatively inefficient. They could not fill two impor-
tant emerging needs: to supply unprecedented capacities
for efficient and convenient generation of electricity; and
to provide a convenient energizer for mechanized road
and airborne transport, which required lightweight, com-
pact power plants. Steam turbines, internal combustion
engines, and gas turbines filled these needs; only in rail-
way transport did steam engines retain their global indis-
pensability until after WW II.
The superiority of steam turbines for delivery of rotary
power is clear. Steam engine rotations rarely surpassed
100 rpm, whereas modern turbines have up to 3600
rpm and work under pressures of 14-34 MPa and tem-
peratures up to 600
C. They can be built in capacities
ranging from 10
4
W to over 1 GW; their mass to power
ratio (1-3 g/W) is only a fraction of that of steam
engines (250-500 g/W); and their top efficiencies are
40%-42%. In sum, steam turbines are an excellent source
of power for electric generators, compressors, centrifugal
pumps, and ship propellers. Charles Parsons followed his
first patented 1884 reaction turbine design with a 75-kW
public power station in Newcastle in 1888, the first con-
densing turbine of 100 kW in 1891, and the first 1-MW
unit for the Elberfeld station in 1900. It took less than
two decades to demonstrate the superiority of the steam
turbine over the steam engine (fig. 8.9). The exponential
rise of turbine ratings was interrupted only during the
late 1920s, resumed in the mid-1950s, and reached a pla-
teau in the early 1970s.
Many unsuccessful attempts preceded the first com-
mercially successful design of an internal combustion
engine, a horizontal double-acting machine with slide
valves to admit a mixture of illuminating gas and air and
to release the burned and expanded gas. This was
patented in 1860 by Jean Joseph
ยด
tienne Lenoir and
subsequently sold as a 2-kW machine for workshops.
This slow (200 rpm) engine ran on an uncompressed ex-
plosive mixture of gas and air ignited with an electric
spark, and its efficiency was a mere 4% (Smil 2005a). In
1862, Alphonse Eug`ne Beau (or Beau de Rochas) out-
lined the operation of a four-stroke cycle but did nothing
to translate the concept into a working machine. That
pioneering step was taken by Nicolaus August Otto
who, after years of building improved Lenoir engines,
patented a horizontal four-stroke design powered by coal
gas in 1877. This was a very successful machine. Some
50,000 units, in sizes from 375 W to 12 kW, were even-
tually sold, but because it was slow (160 rpm) and heavy
(250 g/W), it was suitable only for stationary uses.
Decisive breakthroughs into the transportation market
came only with the introduction of gasoline engines
mounted on road vehicles, steps taken independently
during the mid-1880s by Gottlieb Daimler and Wilhelm
Maybach in a suburb of Stuttgart and by Karl Benz in
Mannheim. With about 33 MJ/L gasoline has about
1,600 times the energy density of the illuminating gas
(usable in transportation only if highly compressed), and
its low flash point (
40
C) makes it ideal for easy start-
ing. At the same time, this low flash point makes it haz-
