Dimensional Analysis of Vapor Bubble Growth Considering Bubble-bubble Interactions in Flash Boiling Microdroplets of Highly Volatile Liquid Electrofuels

• Main Authors: Saha, Avijit, Deshmukh, Abhishek Y, Grenga, Temistocle, Pitsch, Heinz
• Format: Journal Article
• Language: English
• Published: 13-03-2023
• Subjects: Physics - Fluid Dynamics
• DOI: 10.48550/arxiv.2303.07124

Electrofuels (e-fuels) produced from renewable electricity and carbon sources
have gained significant attention in recent years as promising alternatives to
fossil fuels for the transportation sector. However, the highly volatile
e-fuels, such as short-chain oxymethylene ethers are prone to flash
vaporization phenomena, which is associated with the formation and growth of
vapor bubbles, followed by explosive bursting of the liquid jet. The simulation
of a flash boiling spray of such highly volatile liquid fuels in the context of
automotive or cryogenic engines is numerically challenging due to several
reasons, including (1) the complexity of the bubble growth process in the
presence of multiple vapor bubbles and (2) the need to use an extremely small
time step size to accurately capture the underlying physics associated with the
flash boiling process. In this paper, we first present a bubble growth model in
flash boiling microdroplets considering bubble interactions along with the
finite droplet size effects. Based on the dimensional analysis of the newly
derived Rayleigh Plesset equation, a simplified semi-analytical solution for
bubble growth, which also includes the bubble interactions, is then derived to
estimate the bubble growth behavior with reasonable accuracy using the larger
time step sizes for a wide range of operating conditions. The derived
semi-analytical solution is shown to be a good approximation for describing the
bubble growth rate over the whole lifetime of the bubble. The bubble
interactions are found to delay the onset of droplet bursting due to the slower
growth of the vapor bubble compared to the bubble growth without bubble
interactions. Furthermore, in a comparison with DNS results, the proposed
bubble growth model is shown to reasonably capture the impact of bubble
interactions leading to smaller volumetric droplet expansion.