Diesel Engine Fundamentals
Figure 1 Example of a Large Skid-Mounted, Diesel-Driven Generator
The modern diesel engine came about as the result of the internal combustion principles first
proposed by Sadi Carnot in the early 19th century. Dr. Rudolf Diesel applied Sadi Carnot's
principles into a patented cycle or method of combustion that has become known as the "diesel"
cycle. His patented engine operated when the heat generated during the compression of the air
fuel charge caused ignition of the mixture, which then expanded at a constant pressure during
the full power stroke of the engine.
Dr. Diesel's first engine ran on coal dust and used a compression pressure of 1500 psi to
increase its theoretical efficiency. Also, his first engine did not have provisions for any type of
cooling system. Consequently, between the extreme pressure and the lack of cooling, the engine
exploded and almost killed its inventor. After recovering from his injuries, Diesel tried again
using oil as the fuel, adding a cooling water jacket around the cylinder, and lowering the
compression pressure to approximately 550 psi. This combination eventually proved successful.
Production rights to the engine were sold to Adolphus Bush, who built the first diesel engines
for commercial use, installing them in his St. Louis brewery to drive various pumps.
A diesel engine is similar to the gasoline engine used in most cars. Both engines are internal
combustion engines, meaning they burn the fuel-air mixture within the cylinders. Both are
reciprocating engines, being driven by pistons moving laterally in two directions. The majority
of their parts are similar. Although a diesel engine and gasoline engine operate with similar
components, a diesel engine, when compared to a gasoline engine of equal horsepower, is
heavier due to stronger, heavier materials used to withstand the greater dynamic forces from the
higher combustion pressures present in the diesel engine.