Compression stroke: When the corresponding piston moves upwards, the sucked-in air is compressed. This would be nothing special if the air was not compressed to a very high degree, as is the case with a gasoline engine. In the case of diesel «Volkswagen» the sucked-in air is compressed by almost 1/23 of its volume, i.e., by almost 23 times. Through this abnormal compression, the air naturally becomes very hot (similar effect to you. for example, you can watch in a bicycle pump when tires are inflated).
Combustion stroke (working stroke): Diesel fuel is now injected into the hot air, and the fuel droplets ignite spontaneously; hence another name "self-ignition engine" for diesel engine. It does not need spark plugs to ignite the air-fuel mixture. The point in time when ignition occurs in the combustion chamber of our engine is determined by the high pressure fuel pump (injection pump), which at the right time injects the right proportion of diesel into the hot air.
As with a gasoline engine, the pressure of the burnt mixture pushes the piston down and it does work on that cycle.
Exhaust stroke: The crankshaft moves more and the piston rises again, with the exhaust gases being squeezed out of the cylinder. The piston and cylinder are again ready for the next cycles.
Since, in a diesel engine, the fuel particles that are injected into the combustion chamber, in contrast to a gasoline engine, burn almost instantly, this leads to extremely harsh operating noises; the motor bearings are also heavily loaded. The so-called divided workspace allows you to achieve the desired «soft» combustion.
In this case, combustion begins in a separate chamber in the cylinder head. emerging "flame front" goes through the so-called «Shuss channel» (from «Schuss-shot») with a slight delay in the space above the piston (see fig.). With this delay, more than «soft» and quiet engine operation.
1 - camshaft
2 - hydraulic pusher
3 - valve
4 - piston
5 - connecting rod
6 - crankshaft
7 - intermediate shaft
8 - oil pump
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