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Injection consistency is a critical performance indicator for modern diesel injectors, especially under high-pressure and multi-injection operating conditions. While much attention has been given to spray formation and needle dynamics, the influence of residual fuel and internal backflow behavior between injection events remains less explored. These internal phenomena can significantly affect injection quantity repeatability and long-term stability.

During high-pressure injection, not all fuel is discharged through the nozzle orifices. A portion of the fuel remains trapped within internal cavities such as the control chamber, needle seat region, and sac volume. After the injection event ends, pressure relaxation causes this residual fuel to redistribute through internal leakage paths and backflow channels. The resulting pressure fluctuation alters the initial conditions of the subsequent injection cycle.

Internal backflow is mainly governed by the clearances between precision-matched components, including the needle–seat interface and control valve assemblies. Variations in clearance size, surface roughness, and fuel viscosity directly influence backflow rate. Excessive backflow can delay needle reopening, while insufficient backflow may lead to pressure accumulation, both of which reduce injection repeatability.

Experimental observations show that at high injection frequencies, residual fuel effects become more pronounced. The time available for pressure equalization shortens, causing cycle-to-cycle variations in injected fuel mass. This issue is particularly critical for pilot and post injections, where small quantities are highly sensitive to initial pressure conditions.

To investigate this behavior, combined pressure sensing and high-speed injection rate measurement techniques are commonly used. By correlating internal pressure decay characteristics with injection quantity fluctuation, the impact of residual fuel dynamics can be quantitatively evaluated. Simulation models incorporating internal volumes and leakage paths further help predict backflow behavior under different operating conditions.

Design optimization strategies focus on minimizing uncontrolled residual fuel effects while maintaining adequate lubrication and cooling. These include optimizing sac volume geometry, refining internal flow channels, and improving surface finishing of sealing interfaces. Additionally, adaptive control strategies can compensate for residual pressure effects by adjusting energizing timing and duration.

In conclusion, residual fuel and internal backflow play an important role in determining injection consistency, especially in high-speed and multi-injection regimes. A deeper understanding of these internal processes provides valuable guidance for injector design optimization and precision control improvement.