Temperature effects on droplet oscillation decay with application to fuel property measurement

Document Type

Article

Publication Date

1-1-2021

Abstract

Observation of oscillation decay in droplets has been shown to be an effective approach in determining physical properties, e.g., as viscosity and surface tension for emerging biofuels using μl quantities. This Approach was applied to higher temperatures relevant to fuel injection conditions for internal combustion engines. Experiments were performed using high-resolution strobed imaging of moving, heated, μm-sized, fuel droplets to capture shape oscillation decay through image processing and analysis. Two fuels were studied, iso-butanol and a primary reference fuel (PRF 84), which is a mixture of iso-octane and n-heptane. A piezoelectric droplet generator was used to generate a continuous train of single droplets, which are given an initial perturbation and subsequently undergo damped oscillations, captured using strobed imaging. Surface tension and viscosity calculated at four different temperatures ranging from 30°C–55°C using the frequency and decay time associated with the fundamental mode were found to be within approximately 10% of reference values obtained from previous data. Complementary numerical simulations were performed that utilize a volume-of-fluid approach to track transient droplet oscillation phenomena along with heat and mass transfer in a two-dimensional axisymmetric domain. Simulations, where droplet size and temperature could be independently varied, capture an expected decrease in oscillation frequency and increase in decay time, with increase in fuel temperature. The simulations were further used to investigate the relative contribution to deviations in surface tension and viscosity predictions due to heat and mass transfer from the droplet, as well as viscous effects violating the inviscid flow assumption in the droplet oscillation theory. Mass loss effects were negligible. Temperature change due to heat transfer had the next highest sensitivity, particularly for the more volatile PRF 84, which had a lower viscosity and associated Ohnesorge number. For isobutanol, which has a higher viscosity and Ohnesorge number, viscous effects contributed the most to deviation in fuel property predictions.

Publication Source (Journal or Book title)

Atomization and Sprays

First Page

1

Last Page

23

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