Generation and stability of bulk nanobubbles in liquid fuel and their influence on spray characteristics

Abstract

Nanobubbles have attracted increasing attention due to their unique physicochemical properties; however, their application in fuel and combustion research remains limited. This study investigates the generation of air nanobubbles (ANBs) in gasoline and their influence on spray characteristics in gasoline direct injection (GDI) systems. ANBs were produced using a custom-designed hydrodynamic cavitation generator incorporating a zero-clearance pump. Dynamic light scattering and nanoparticle tracking analysis demonstrated the formation of a highly concentrated nanobubble population (5.12 × 10¹¹ particles/mL), with diameters ranging from 40 to 200 nm and a negative zeta potential between −20 and −25 mV, indicating good stability in gasoline. Spray behavior of ANB-enriched gasoline was evaluated in a constant-volume chamber using a single-hole GDI injector at injection pressures of 50, 100, and 150 bar. Diffused back illumination technique was employed to analyze macroscopic spray characteristics, while phase Doppler anemometry was used to measure droplet size and axial velocity distributions. Compared to baseline gasoline, ANB fuel exhibited consistently shorter penetration lengths, smoother spray boundaries, and lower spray density factors, suggesting improved atomization and air–fuel mixing. PDA measurements further revealed reduced axial droplet velocities, attributed to enhanced secondary breakup associated with nanobubble dynamics. These findings demonstrate that air nanobubbles can significantly influence spray development in GDI systems, offering a promising approach for improving fuel atomization and supporting the development of advanced, high-efficiency combustion technologies.