Impact of injector variability on transient spray characteristics in Diesel injectors

Journal article, 2025

In dual-fuel engines, injectors are typically used to deliver a small quantity of pilot fuel. Although these injectors were originally designed for continuous, steady-state operation, they are often employed in transient or pilot injection modes in DF engine applications. Variations in spray characteristics are frequently observed in injectors under transient mode, even when they share nearly identical specifications and are designed for the same use case. This study systematically measured the spray characteristics across different injectors and reported the observed variability. The spray characteristics of four multi-hole diesel injectors with nearly identical specifications were systematically investigated and compared. Testing was conducted in an optical spray combustion chamber under non-evaporative and non-reactive conditions, with varying fuel injection and back pressures. Spray visualization was performed using diffused back-illumination to capture individual spray plumes and Mie-scattering to image multi-plume sprays. A root-mean-square error metric was applied to quantitatively evaluate the injectors’ behavior. This metric identifies plume-to-plume variations and characterizes both symmetric and asymmetric spray patterns. Additionally, a “thimble” method was utilized to isolate and investigate individual spray plumes without altering the nozzle geometry, ensuring precise spray measurements. The results showed both symmetric and asymmetric plume behaviors under identical test conditions, emphasizing the influence of injector variability
and actual start of injection on transient spray characteristics. Furthermore, the findings demonstrate that the thimble method is an effective approach for isolating and studying individual spray plumes.