SDI (engine)

SDI, often standing for "Single Direct Injection," refers to a type of internal combustion engine, typically a diesel engine, characterized by a single injection point directly into the combustion chamber. This direct injection contrasts with indirect injection systems where fuel is injected into a pre-chamber or swirl chamber.

The defining feature of an SDI engine is the placement of a single fuel injector per cylinder. Fuel is injected directly into the cylinder's combustion chamber, mixing with air already present within the cylinder. This direct injection allows for precise control of fuel delivery and timing.

While the term "SDI" is most frequently associated with early generations of direct injection diesel engines, modern diesel engines have largely moved towards Common Rail Direct Injection (CRDI) systems featuring multiple injection events per combustion cycle. Consequently, the term "SDI" is less frequently used in contemporary engine descriptions. The term primarily describes engines developed before the widespread adoption of common rail technology.

Compared to indirect injection, SDI engines generally offer improved fuel efficiency and reduced emissions. However, older SDI designs often suffered from higher levels of combustion noise (diesel knock) due to the rapid combustion of the fuel-air mixture. More advanced engine management systems and improvements in injector technology have mitigated this issue in subsequent engine generations.

The benefits of SDI, in comparison to indirect injection, include more efficient combustion and greater power output for a given engine size. However, early SDI engines may require more robust engine components to withstand the higher combustion pressures compared to indirect injection designs.