Today, a new breed of Diesel engines fights an old
metaphor. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
The thermal efficiency of a
power plant is a measure that reaches right into
your pocketbook. When a power plant burns, say,
coal or oil, thermal efficiency is the fraction of
chemical energy in the fuel that reaches the
electric generator.
A big coal-fired steam power plant does well to
reach forty percent efficiency. A lot more capital
expense will buy fancy combined cycles with
efficiencies as high as fifty percent. For years
that's been as good as we get, and then only in
huge plants producing hundreds of megawatts. Your
automobile can reach only 20 or 25 percent
efficiency, and then only under optimal conditions.
Now that 50 percent barrier is finally being broken
by an unexpected contender: Today, huge 68-MW
Diesel engines are reaching efficiencies over fifty
percent. You can buy a single engine big enough to
serve 40,000 households. Yet Diesels came into
being as early variants on the lightweight internal
combustion engine.
We should've seen great size coming long ago. As
early as twenty years after Rudolf Diesel's patent in 1892,
3000 to 4000-horsepower Diesels were appearing in
small ships. But steam kept providing the high
power needed for fast-moving warships and liners.
So we overlooked how well suited Diesel engines
were to playing the large, slow-moving,
high-efficiency role of the stationary power plant.
We used both gasoline and Diesel engines to change
transportation. Diesel engines began by displacing
steam on smaller steamships. Then they replaced the
old steam locomotives. The automobile industry has
also used Diesel engines now and then. Maybe you're
one of the few who drive a Diesel-powered car
today.
Diesel himself built his first engines at Germany's
Maschinenfabrik Augsburg-Nürnberg (or
MAN). Today the same company (now MAN B&W)
makes the biggest of these new engines. One of
their twelve-cylinder plants is 80 feet long, and
it stands 46 feet tall. It weighs over two thousand
tons, and its great crankshaft turns at 100 rpm.
Your car engine, turning at 3000 rpm, is like a
wasp beside that elephant.
When internal combustion appeared over a century
ago, it shaped a new metaphor of lightness and
speed. It revolutionized transportation. It made
powered flight feasible and gave birth to
automobiles and motorcycles. I once built model
airplanes powered by both gas and Diesel engines
that weighed scant ounces.
Internal combustion parted ways with the big steam
power plants that began electrifying cities in the
1880s. That's why these huge new Diesel power
plants are a surprise. They're not radical, but
they violate the metaphor of lightness which
internal combustion claimed at the outset. Once any
metaphor takes root, it's almost impossible to
escape. But these new monsters are escaping it.
They're tiptoeing back across a metaphorical line
that's separated them from major power production
for a century.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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