Fourier-Transform Infrared Absorption Spectroscopy in Binary Hydrocarbon-Alcohol Single Droplet Evaporation
Shane Daly, Nicholas Olson and Christopher Hagen, 2016

Abstract: Broadband absorption spectroscopy, by way of FTIR, was used to investigate the vapor cloud of a single millimeter sized liquid droplet suspended by a syringe as it evaporates at standard conditions. Single beam data were collected every 8 seconds resulting in a time-resolved record. Species concentrations were tracked using their resonant absorption peaks and correlated with a multidimensional numerical model. The numerical model combined a Gaussian beam transmission through a temporally changing spherical vapor cloud with radial concentration gradients, informed by the  D-squared law and interpreted using the Abel transform. There was fair agreement with temporal evaporation trends for single component runs. Multicomponent experiments of ethanol and isooctane showed synergistic blending effects and preferential evaporation of ethanol. Droplets were also suspended by a thermocouple to track the droplet temperature over time as they were subject to evaporative cooling. This work is the foundation of a basic technique for collecting useful data to inform a complex transport problem.


Quantified Measurement of Droplet Evaporation Rates
of a Two Component Mixture

Nicholas Olson and Christopher Hagen, 2014

Abstract: In this work we are using an FTIR to measure the evaporation rate of a suspended binary mixture droplet. The intent here is to devise a method that may be useful to calibrate fuel evaporation models. It is hoped that this information will be used to learn more about distillate fuels injected into small internal combustion engines. 
The procedure involves taking a background spectrum using the FTIR (considered the incident light, Io). Next, a droplet is suspended in the instrument beam path beam path and another spectrum is captured (considered as transmitted light, I). The Beer-Lambert law will be applied to determine the path averaged concentration of the evaporated components.  Of course beam steering and droplet absorption will be considered.  This measurement will be repeated at the scan rate of the instrument to provide a time resolved record of droplet shrinkage.
The components of the droplet will be selected such that their volatilities and absorption spectra are sufficiently different in order to definitely separate the components temporally and optically.