Ignition Delay of Fatty Acid Methyl Ester Fuel Droplets: Microgravity Experiments and Detailed Numerical Modeling
Anthony J. Marchese, Timothy L. Vaughn, Kenneth Kroenlein, Frederick L. Dryer
Recent optical engine studies have linked increases in NOx emissions from fatty acid methyl ester combustion to differences in the premixed autoignition zone of the diesel fuel jet. In this study, injection (and subsequent ignition) of single, isolated liquid droplets into quiescent, high temperature air was considered as an analog to the transient, partially premixed autoignition zone of a fatty acid methyl ester fuel jet. Normal gravity and microgravity (10-5g) droplet ignition delay experiments were conducted using a variety of neat methyl esters and commercial soy methyl ester. Droplet ignition experiments were chosen as an analog because spherically symmetric droplet combustion represents the simplest two-phase, time-dependent chemically reacting flow system permitting a numerical solution with complex physical submodels. To create spherically symmetric conditions for direct comparison with a detailed numerical model, experiments were conducted in microgravity using a 1.1 second drop tower. In the experiments, droplets were grown and deployed onto 14 mm silicon carbide fibers and injected into a tube furnace containing atmospheric air at temperatures up to 1000 °C. The ignition event was characterized by measurement of UV emission from hydroxyl radical (OH*) chemiluminescence. The experimental results were compared against predictions from a time-dependent, spherically symmetric droplet combustion simulation with detailed gas phase chemical kinetics, spectrally-resolved radiative heat transfer and multi-component transport. Using a reduced chemical kinetic mechanism (125 species, 713 reactions), the computed ignition delay for methyl decanoate (C11H22O2) compared favorably with experimental results.
, Vaughn, T.
, Kroenlein, K.
and Dryer, F.
Ignition Delay of Fatty Acid Methyl Ester Fuel Droplets: Microgravity Experiments and Detailed Numerical Modeling, Proceedings of The Combustion Institute, Beijing, CN, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=904769
(Accessed May 28, 2023)