1. Intake Stroke: The piston moves downward in the cylinder, creating a low-pressure area. This draws air into the cylinder through the intake valve.
2. Compression Stroke: The piston moves back up the cylinder, compressing the air to a high pressure (typically between 15:1 to 25:1 compression ratio). This increases the air temperature significantly.
3. Injection: As the piston reaches the top of the compression stroke, a fuel injector sprays a fine mist of diesel fuel directly into the highly compressed and heated air in the combustion chamber.
4. Auto-ignition: The high pressure and temperature cause the diesel fuel to self-ignite. This is known as auto-ignition or compression ignition. The fuel rapidly ignites and burns, creating a rapid expansion of gases.
5. Power Stroke: The expansion of gases pushes the piston down the cylinder, generating mechanical power. This power is transmitted to the crankshaft, which converts the reciprocating motion into rotational motion.
6. Exhaust Stroke: The piston moves back up the cylinder, pushing the exhaust gases out through the exhaust valve. This completes the combustion cycle, and the process starts again with the intake stroke.
In summary, in a diesel engine, the fuel is ignited solely by the heat and pressure created by the compression of air in the combustion chamber. This process allows diesel engines to operate at higher compression ratios and achieve better fuel efficiency compared to spark-ignition engines.
