Ph.D. Thesis Proposal

by

Aimee Williams

(Advisor: Prof. Jerry Seitzman)

 “The Role of Droplets in the Autoignition of a Polydisperse Jet-A Spray in Vitiated Co-flow”

9 a.m., Tuesday, June 5
Montgomery-Knight 317

Abstract:

Autoignition of droplets is a fundamental parameter of any fuel-air mixture.  It can occur any place where fuel is introduced to oxidizer at an elevated temperature.  For safety concerns and the need to understand the effect of autoignition on flame properties and stabilization, it is important to study the behavior of autoignition in real combustion systems, such as liquid Jet-A sprays. A polydisperse spray of a multicomponent fuel involves interactive and simultaneous processes of spray formation, droplet evaporation, fuel-air mixing, and chemical reaction.  Autoignition of homogeneous mixtures has been thoroughly studied, mostly for the validation of chemical mechanisms or surrogate fuels.  Autoignition of single droplets provides insight into large droplet sizes, but these are often much larger than what occurs in a real system and can evaporate and dilute before autoignition can occur.  Droplet stream studies have shown the importance of studying the effects of droplet interaction on autoignition.  In droplet streams, there exists an inter-droplet spacing that leads to minimum ignition delay time. In droplet clouds, heat transfer plays an important role in autoignition; as the droplets evaporate, they cool the mixture and produce non-homogeneous temperature profiles.  The majority of liquid fueled autoignition studies parameterize autoignition with properties in the modified Arrhenius rate equation.  Limited work has been done on the study of local autoignition phenomena in non-homogeneous situations.  Non-homogeneous gaseous fueled studies have shown that autoignition is formed in kernels, preferentially in mixing areas and vertically dominated regions, such as the wage of a jet-in-cross flow or mixing layer of a jet in co-flow. Limited droplet studies found kernels formed and grew on the outer edge of droplet clouds.  Another study found autoignition in kernels, but due to their dilute sprays did not find an interaction with the spray. There is potential for study of autoignition of a realistic fuel spray on a local droplet scale using modern diagnostics.  This study seeks to investigate the formation of growth of autoignition kernels in a uniform co-flow with symmetric fuel spray and determine the interaction of local autoignition events with fuel droplets.

Preliminary results have validate the test facility, characterized the fuel spray, shown the behavior of autoignition kernels at a range of test conditions, and show the validity of using UV PLIF and Mie scattering to simultaneously view autoignition kernels and fuel spray.  Future investigation will measure the formation locations and growth of autoignition kernels and their behavior in the vicinity of droplets.

Committee:

• Professor Jerry Seitzman, School of Aerospace Engineering, Georgia Tech
• Professor Jechiel Jagoda, School of Aerospace Engineering, Georgia Tech
• Professor Joseph Oefelein, School of Aerospace Engineering, Georgia Tech