1. Compression Ignition (Compression Ratio): Diesel engines operate with a higher compression ratio compared to gasoline engines. As the piston moves upward during compression stroke, it compresses the air trapped in the cylinder to a very high pressure and temperature. This high compression causes the air to heat up significantly.
2. Fuel Injection: Diesel fuel is injected directly into the compressed hot air in the combustion chamber at a precisely timed moment before the piston reaches the top of the compression stroke. This is achieved using a high-pressure fuel injector.
3. Autoignition Temperature: Diesel fuel has a higher autoignition temperature compared to gasoline. This means it requires a higher temperature to self-ignite. When the temperature and pressure in the combustion chamber reach the diesel fuel's autoignition point (typically around 850-950°C), it spontaneously ignites, initiating combustion.
4. Fuel Spray and Mixing: The diesel injector sprays the fuel in a finely atomized form into the hot compressed air. This creates a high surface area for the fuel droplets to mix with oxygen, enhancing rapid combustion.
5. Knock in Diesel Engines: Unlike gasoline engines, diesel engines are prone to knocking, which is an undesirable condition characterized by an audible pinging or rattling sound. Knocking occurs when fuel auto-ignition occurs too rapidly, leading to uncontrolled and uneven combustion.
In summary, ignition in a diesel engine is achieved through the combination of high compression, precisely controlled fuel injection, and the autoignition properties of diesel fuel. This self-ignition initiates combustion, which drives the piston downward, generating power in the diesel engine.
