Eulerian-Lagrangian Modeling of Flash-boiling Injection Processes in Internal Combustion Engines

Reducing greenhouse gas emissions from the transportation sector, especially carbon dioxide, is one of the main global challenges to achieve a more sustainable future. Developing internal combustion engines with advanced injection and combustion concepts that improve efficiency and decrease pollutant emissions are essential steps towards reducing their environmental impact. Over the past decades, flash-boiling injection has become a promising alternative to generate a much finer spray compared to high-pressure injection. The rapid phase-change phenomenon during flash-boiling injection occurs due to the superheating of the liquid fuel upon entering the combustion chamber, resulting in tiny droplets due to the abrupt disintegration of the liquid jet, which in turn enhances the mixture homogeneity between air and fuel by increasing the vaporization rate, widening the spray plume due to the increased radial expansion via bubble growth, and reducing the droplet velocities, thus leading to shorter penetrations. A detailed understanding of the underlying mechanisms of the flash-boiling process, such as nucleation of vapor bubbles, bubble growth, and finally jet burst, at a microscopic droplet level is necessary to accurately quantify its effect on the macroscopic spray structure. In this talk, I will first discuss the modeling of single-droplet flash-boiling behavior using a Lagrangian particle tracking (LPT) technique. Following this, a novel reduced-order Lagrangian model will be introduced to accurately capture the vapor bubble growth in superheated microdroplets, accounting for interaction among multiple bubbles. Next, a simplified nondimensional semi-analytical solution for bubble growth, based on dimensional analysis of the modified Rayleigh-Plesset equation, will be presented. This solution offers accurate predictions of bubble growth considering bubble interactions using larger time step sizes, making it effective for simulating large-scale superheated sprays with numerous droplets under varied conditions. Finally, a three-dimensional two-way coupled large-eddy simulation of superheated spray case will be discussed, incorporating the newly developed bubble growth model within the LPT framework.

Speaker : Dr. Avijit Saha

Biography:

Dr.-Ing. Avijit Saha is a postdoctoral researcher at the Center for Aeromechanics Research, Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, USA. His current research primarily focuses on terahertz time-domain spectroscopy (THz-TDS) for the characterization of plasma properties, including electron density and collision frequency. In addition to his experimental work, he is developing a novel Bayesian framework for quantifying uncertainties in measurement data, with the goal of enhancing the reliability and interpretability of spectroscopic diagnostics. He obtained his Ph.D. in Mechanical Engineering from RWTH Aachen University in September 2023, making him the youngest individual to receive the doctorate degree from ITV. His dissertation focused on the physics based reduced-order modeling of flash-boiling injection processes in internal combustion engines. Prior to this, he completed his B.Tech. (Hons.) and M.Tech. in Aerospace Engineering from IIT Kharagpur. He was the first recipient of the distinguished ASME IGTI Student Scholarship in the Aerospace department. His research interests span experimental fluid dynamics, optical diagnostics, multiphase flow modeling (DNS, LES, reduced-order models), combustion instabilities, high-performance computing, and their applications in aerospace propulsion systems. He has authored numerous publications in leading international journals and conferences, earning recognition through several prestigious awards. Among his accolades are the Jang Young Sil Post-doctoral Research Fellowship from Korea Advanced Institute of Science & Technology (KAIST) in 2024, Post-doctoral fellowship from MIT in 2025, and his role as Principal Investigator for a high-impact compute-time research project under National High-Performance Computing Center for Computational Engineering Science (NHR4CES), Germany. Dr. Saha also serves as a reviewer for several notable journals like Nuclear Technology, Physics of Fluids, Proceedings of Combustion Institute, Atomization and Sprays, and SAE International Journals.