Effects of fuel viscosity on the primary breakup dynamics of a high-speed liquid jet with comparison to X-ray radiography

One of the major concerns in combustion engines is the sensitivity of engine performance to fuel properties. Recent works have shown that even slight differences in fuel properties can cause significant changes in performance and emission of an engine. In order to design the combustion engines with multi-fuel flexibilities, the precise assessment of fuel sensitivity on liquid jet atomization process is a prerequisite since the resulting fuel/air mixture is critical to the subsequent combustion process. The present study is focusing on the effect of physical fuel properties, mostly viscosity difference, on the breakup process of the liquid jet injected into still air. Two different jet fuels, CAT-A2 and CAT-C3, are considered here as surrogates for a fossil-based fuel and a bio-derived high-viscosity alternative fuel. The simulations are performed using the volume-of-fluid (VoF) interface tracking method coupled to Lagrangian particle method in order to capture the breakup instabilities of jets and the resulting droplets. The investigations take the actual geometry of the injector into account to resolve the unsteady flow phenomena inside the nozzle that impact the turbulence transition and atomization. The simulation results are compared to the experimental measurement using X-ray radiography. Both simulation and X-ray measurements consistently describe the effects of different fuels on the fundamental properties of atomization including the breakup length, transverse liquid volume fraction and the droplet sauter-mean-diameter. The application of a Detailed Numerical Simulation approach complemented by unique X-ray diagnostics is novel and providing new understanding and research directions in engine spray dynamics.