Numerical Investigation of Liquid Jet Breakup and Droplet Statistics with Comparison to X-ray Radiography

Abstract

In direct injection engines, the jet primary and secondary breakup processes have a significant influence on the fuel/air mixture formation and drop-size distribution directly affecting the fuel conversion efficiency and combustion characteristics. In this work the disintegration process of turbulent liquid jets from a realistic diesel injector issuing into a still environment is investigated numerically using a coupled liquid/gas interface capturing technique and a high-fidelity DNS/LES approach. This study is aimed at assessing the influence of NJFCP aviation jet fuel mixtures on the disintegration and droplet-size spray characteristics at simulated diesel operating conditions. For this purpose, an unstructured unsplit Volume-of-Fluid method is employed in conjunction with a realistic diesel injector geometry to simulate the pulsed jet disintegration and breakup process. Flow and droplet PDF statistics are extracted to demonstrate the impact of physical properties (A2, C3 fuel) on the mixing behavior and droplet distribution. The simulations are compared against X-ray radiography volume fraction measurements from Argonne National Laboratory and also serve as numerical benchmarks for calibration of lower fidelity models. NomenclatureAccronyms VOF = Volume of Fluids LES = Large Eddy Simulation DNS = Direct Numerical Simulation PDF = Probability Density Function ROI = Rate of Injection Re = Reynolds number We = Weber number Oh = Ohnesorge number NJFCP = National Jet Fuel Combustion Program _________________________________ 1 Research Engineer, Vehicle Technoloy Directorate, APG, MD, AIAA Member.

The turbulent bubble break-up cascade. Part 2. Numerical simulations of breaking waves

“…Surface tension gradients are assumed to be negligible. The solver has been used to simulate a number of liquid jet break-up problems involving primary atomization, including laminar, transitional and turbulent jets in quiescent gas (Bravo et al 2015(Bravo et al , 2016(Bravo et al , 2018b(Bravo et al , 2019, jets in cross-flows (Bravo et al 2018a) as well as jets from swirling injectors (Kim et al 2014;Ham et al 2014).…”

Analytical modelling of laminar drag and freestream turbulence eddies on droplet breakup criterion for internal combustion engines

“…Moreover, there has been no consensus in droplet breakup criterion from CFD simulations of spray flows, especially in a turbulent flow field, see References. 19–22 for complete review.…”

Computational Modeling of the Atomizing of a Gas Stream from a Pneumatic Nozzle

“…Atomizing of liquid is widely used in modern technology [1][2]. Atomizing occupies an extremely important place in power engineering, when burning liquid fuels.…”

“…Large eddy simulation (LES) directly resolves large scales and models small scales [2,12]. Modelling only small scales and solving the large scales, allows the use of a much coarser mesh and larger time steps in LES compared with Direct Numerical Simulation (DNS).…”