Page 55 - Piston Engine-Based Power Plants

CHAPTER 5 5

Diesel Engines

The diesel engine, sometimes called the compression ignition engine,
was developed by Rudolph Diesel who built his first engine in 1892
and patented it in 1893. When Diesel developed his engine, current
steam and gasoline reciprocating engines achieved around 10% effi-
ciency. He believed that it should be possible to convert more of the
energy released from fuel into power by exploiting thermodynamic
heat engine principles developed by Carnot. His first engine was
around 25% efficient. Modern diesel engines can achieve twice this
efficiency.

The diesel engine is a reciprocating engine, just like a spark ignition
engine, and it shares many of the same parts. Where it differs is in the
manner of ignition of the fuel. This takes place spontaneously as a
result of the high temperature reached by the air in the cylinder of the
engine during compression. In consequence, no ignition system is
required.

To achieve the high temperature necessary, the engine must com-
press the air in the cylinder very significantly. Diesel’s original engine
used coal dust as the fuel and had a compression ratio of roughly 100.
This, combined with the absence of any cooling system, meant that
this prototype engine was potentially extremely dangerous and it
exploded, almost killing its inventor. He soon adapted it, reducing the
compression ratio to 37, adding a cooling jacket and using a liquid
fuel. This version proved a success.

In order to cope with the higher pressures inside the engine, a diesel
engine is more robust, and hence heavier than a gasoline engine. This
makes it more expensive, but this is offset by the higher efficiency.
Another advantage is that the engine can burn heavier fuel than a gas-
oline engine and this heavier fraction, obtained from fractional distilla-
tion of petroleum after gasoline, has traditionally been much cheaper
than the lighter gasoline. The price differential is much smaller in the
21st century.
Piston Engine-Based Power Plants. DOI: https://doi.org/10.1016/B978-0-12-812904-3.00005-7
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