DIESEL ENGINES
When Rudolph Diesel applied for the patent on his revolutionary new engine, he
was granted Patent No. 67207 for a “Working Method and Design for
Combustion Engines, . . . a new efficient, thermal engine.” The diesel engine
achieves combustion by injecting diesel fuel into a combustion chamber filled
with highly compressed, super-heated air. That’s why the patent office described
Diesel’s engine as a “thermal engine.”
The diesel engine uses a four-stroke cycle just like a gasoline engine;
however, there is no electrical ignition system used to achieve combustion, and
the compression ratio is much higher than in a gasoline engine.
Intake Stroke
The intake valve opens, letting in air. The piston travels down, drawing the air
into the cylinder. At BDC the valves close, sealing the combustion chamber in
preparation for the compression stroke.
Compression Stroke
The piston travels back up to TDC, tightly compressing the air in the cylinder.
Power Stroke
As the piston reaches the top of its travel (TDC), fuel is injected at the height of
the compression. When air is super compressed, it gets hot because there is an
increase in molecular collisions and friction. It’s so hot that it ignites the fuel.
The expanding explosion of the fuel-air mix forces the piston downward,
creating the power stroke.
Exhaust Stroke
The exhaust valve opens, the piston moves back to the top (pushing out the
exhaust gases created by combustion of fuel), and the cycle repeats itself.
Key Differences Between Gasoline and Diesel Engines
- Gasoline engines take in a mixture of gas and air, compress it, and then ignite
the mixture with a timed electrical spark. A diesel engine takes in only air and
compresses it to a compression ratio that produces high combustion chamber
temperatures. The fuel is injected into the chamber at the height of
compression and the heat from the compressed air ignites the fuel