How does fuel injection timing affect diesel engine performance?

Precise control of fuel injection timing is critical to the performance of a diesel engine because the entire combustion process is governed by when the fuel is introduced into the cylinder.1

To achieve optimal performance, fuel injection must begin at the correct piston position, measured by the crank angle, as the piston approaches top dead centre. The timing of this process dictates how the fuel burns:1

• Constant-volume process: Initially, fuel is burned while the piston is near top dead centre, which occurs as a nearly constant-volume process.1
• Constant-pressure process: As the piston moves away from top dead centre, fuel injection continues, and the combustion process transitions into a nearly constant-pressure process.1

Because the combustion in a diesel engine is heterogeneous—meaning fuel and air are not premixed—the timing must be synchronized with the engine's cycle to ensure thorough burning. Proper timing, combined with effective mixing techniques like air swirl and squish, is essential for efficient fuel utilization and power generation.12