Compression Ignition Engine Combustion Explained

Compression ignition engines operate by igniting fuel through the high temperature generated by compressing air within the cylinder, without the need for a spark plug. Diesel engines are a primary example.

During the combustion cycle, fuel is injected into the cylinder containing hot, compressed air. The fuel spray atomizes, and the mixing process with the air occurs simultaneously with the burning.

This means that at any point during combustion, the fuel-air mixture is not uniform throughout the combustion chamber. There are areas rich in fuel, areas rich in air, and areas where mixing is still incomplete.

Heterogeneous Combustion Process

This characteristic, where fuel and air are mixed in an uneven manner during combustion, defines the process as heterogeneous combustion.

This is distinct from homogeneous combustion, typically seen in spark ignition engines, where fuel and air are thoroughly mixed before ignition occurs.

Thus, the combustion process in compression ignition engines is inherently heterogeneous.