Influences of High-Pressure Pump and Injector Nozzle Geometry on Hydraulics Characteristics of a Mechanical Diesel Direct-Injection System

The geometry of high-pressure pump and injector nozzles crucially influences hydraulic behaviors (e.g., the start of injection, the pressure profiles developed in the high-pressure line, needle lift, and injection rates) in diesel engines. These factors, in turn, significantly impact fuel atomization, fuel-air mixing, combustion quality, and the formation of emissions. The main geometry parameters such as plunger diameter and the number and diameter of nozzles lead to the system complexity, requiring careful analysis, design, and calibration. In this study, a high-speed shadowgraph system and a high-resolution pressure recording system were developed to capture the start of injection, spray structure, and pressure profiles in the high-pressure line. Additionally, a model was developed using GT-Fuel package built within the GT-Suite of simulation tools to explore different plunger diameters and numbers and diameters of injector nozzles. These models were validated using the pressure profiles, fuel quantity, and start of injection timing obtained from the experiments. This approach can either individually analyze the influence of each parameter or assess their overall impact. The results indicate that an increase in plunger diameter advances the start of injection (SOI). Furthermore, an increase in the number and/or diameter of nozzles results in a higher amount of fuel delivered per cycle. Overall, replacing an injection system with 10 mm plungers and injectors with 7 × 250 μm nozzles with one featuring 12 mm plungers and injectors having 8 × 300 μm nozzles can increase the fuel delivery by 1.85 fold. This approach could be useful for practical applications, including turbocharging engines and/or designing more efficient fuel systems. Future investigations into the high-speed shadowgraph images captured in this study could offer additional insights into the Rayleigh-Taylor and Kelvin-Helmholtz models concerning the primary and secondary atomization processes. © 2024 SAE International.