Date of Award
5-2023
Document Type
Thesis
Degree Name
Master of Science
Degree Discipline
Mechanical Engineering
Abstract
The present research investigates the autoignition of fiber-supported n-decane droplets rapidly inserted into a high-temperature oven using elevated pressure in normal and microgravity. The first and total induction times are measured during these experiments to show the dependence of the ignition process on ambient oxygen concentrations for a fixed ambient temperature and pressure. Normal alkanes can ignite in two stages when introduced into a hot environment under certain ambient conditions. There is first a cool-flame ignition (defined by the first induction time), followed by a hot-flame ignition (defined by the total ignition time). The normal and microgravity experimental results are compared to evaluate the role of buoyancy in the autoignition process. All experiments are conducted at ground-based research facilities at NASA Glenn Research Center (Cleveland, OH), including the Zero Gravity Facility (ZGF) for the microgravity testing. Droplet diameters are approximately 1.1 mm, with the oven temperature and pressure respectively 700 K and 3 atm for all experiments, and the oxygen mole fractions varied from 0.10 to 0.30. Recordings and observation produce the induction times by using high-speed shadowgraph images.
The results show the independence of the oxygen mole fraction on the first induction time. They are consistent with the notion that the first induction time is primarily controlled by evaporation and mixing as the droplet enters the chamber. The characteristic times for these physical processes are much longer than the characteristic low-temperature chemical reaction time. The second induction time has a significant dependence on oxygen mole fraction. The second induction time strongly depends on the characteristic chemical kinetic time due to the low-temperature oxygen-addition reactions. The results show that
at ambient oxygen mole fractions below 0.15 in normal gravity and 0.10 in microgravity, no hot flame ignition is observed for the initial droplet diameter. The induction times are slightly lower in microgravity when compared to normal gravity results. Additionally, the cool and hot flame starts closer to the droplet in microgravity. These results provide unique insights into the autoignition dynamics of a single, isolated fuel droplet and help to better the understanding of complex combustion processes in practical combustion systems.
Keywords: Autoignition, Droplet Combustion, Microgravity, Oxygen Concentrations
Committee Chair/Advisor
Yuhao Xu
Committee Member
Daniel Dietrich
Committee Member
Ziaul Huque
Committee Member
Paul Biney
Publisher
Prairie View A&M University
Rights
© 2021 Prairie View A & M University
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Date of Digitization
6/25/2024
Contributing Institution
John B Coleman Library
City of Publication
Prairie View
MIME Type
Application/PDF
Recommended Citation
Johnson, M. J. (2023). Autoignition Of N-Decane Droplets In Varying Oxygen Concentrations Under Normal And Microgravity. Retrieved from https://digitalcommons.pvamu.edu/pvamu-theses/1536