How does a diesel engine work?

A Diesel Engine works through a series of precise steps that convert the chemical energy stored in diesel fuel into mechanical energy. Here's a detailed breakdown of how a diesel engine works:

1. Intake Stroke
Process: The piston starts at the top of the cylinder (top dead center, TDC) and moves downward as the crankshaft rotates. This creates a vacuum inside the cylinder, allowing air to be drawn in through the intake valve.
Key Point: Only air is during this stroke, unlike gasoline engines that mix air with fuel.

2. Compression Stroke
Process: As the piston moves back up towards TDC, it compresses the air trapped inside the cylinder. This compression raises the air's temperature and pressure significantly.
Key Figures: Diesel engines typically have a high compression ratio, ranging from 16:1 to 22:1. This results in air pressures reaching 3.5-4.5 MPa and temperatures up to 750-1000K.
Importance: The high temperature and pressure created during compression are crucial for igniting the diesel fuel later in the cycle.

3. Power Stroke
Fuel Injection: As the piston nears TDC, diesel fuel is injected into the highly compressed air through the fuel injector. The fuel is pressurized to over 10 MPa before injection.
Ignition: The diesel fuel, with its low ignition temperature, spontaneously ignites when mixed with the hot compressed air. This ignition occurs without the need for a spark plug, which is a key difference from gasoline engines.
Combustion: The rapid combustion of the diesel fuel creates a sudden increase in pressure and temperature inside the cylinder. This forces the piston downward, converting the expanding gas's energy into mechanical work.
Key Figures: During combustion, cylinder pressures can reach 6-9 MPa, and temperatures can soar to 2000-2500K.

4. Exhaust Stroke
Process: After the power stroke, the piston moves back up towards TDC, pushing the burned exhaust gases out of the cylinder through the exhaust valve.
Result: This completes one full cycle of the diesel engine, and the process repeats continuously as long as the engine is running.

Summary
In summary, a diesel engine works by compressing air to a very high temperature and pressure, injecting diesel fuel into this compressed air, allowing the fuel to ignite spontaneously, and then harnessing the resulting combustion to drive the piston and generate mechanical energy. This process differs from gasoline engines primarily in the way fuel is mixed with air and ignited. Diesel engines rely on the high compression ratio to ignite the fuel, whereas gasoline engines use a spark plug.