You are invited to hear

Dr. Timothy Ombrello

Senior Research Aerospace Engineer
Aerospace Systems Directorate
Air Force Research Laboratory

“Shifting the Paradigm of How Ignition is Approached in a Flowing Environment”

October 24 @ 11:00 a.m.
Montgomery Knight Room 317

Abstract:
Ignition success in real world combustion systems hinges upon multiple local and global parameters. From a global perspective, success is driven by the probability of ignition, as well as how “on demand” the system can respond. More succinctly, how to guarantee that ignition will always occur, and within the shortest time possible. These global parameters are of course governed by local factors, such as the fuel concentration, gas temperature, and velocity and turbulence levels, as well as the quantity of energy deposited, and the volume in which the energy is deposited. Because of all these parameters, energy deposition devices for ignition can be tailored to couple into and enhance the kinetic or fluid dynamic phenomena. The majority of this work has been focused on discrete ignition events where single pulses can be tailored for different levels of excitation or duration. While systems have been developed to pulse repetitively in a burst to increase the probability of ignition, each pulse remained discrete with no coupling between pulses.

Recently, the switching technology in pulsed power systems has allowed for high voltage, high current, high-frequency repetitive pulsed systems to become a reality. The systems are capable of producing short duration pulses (~10 ns) with voltages in excess of 10 kV, at pulse repetition frequencies greater than 100 kHz. The time scale between pulses allows for a synergy between pulses on both fluid dynamic and kinetic time scales that changes the conventional understanding of how ignition is approached.

In this talk, the application of nanosecond-pulsed high-frequency discharges to a range of reactive systems will be discussed; starting with ignition in a quiescent environment to provide a baseline understanding, and building up to ignition in a scramjet cavity-based flame holder. The primary metric for comparison is the total energy, but varying the rate of deposition (i.e. power). Global effects of ignition probability and kernel growth rates will be presented, as well as detailed measurements of temperature and intermediate species.
 

Timothy Ombrello earned his Bachelor of Engineering in Mechanical Engineering from The Cooper Union for the Advancement of Science and Art in 2003, and his Ph.D. in Mechanical and Aerospace Engineering from Princeton University in 2009. Upon completing his graduate degree, he went on to work at the Air Force Research Laboratory, initially as a National Research Council Research Associate for one year before becoming a civilian employee. Currently he is a Senior Research Aerospace Engineer in the Aerospace Systems Directorate, predominately performing research related to high-speed air-breathing propulsions systems, specifically supersonic combustion ramjets. His research covers a wide range of fluid dynamic and combustion challenges, with strong collaborations across academia and industry. His interests lie in performing research and crafting techniques to enhance reactivity for more rapid ignition and more robust flame propagation and stabilization, from fundamental bench-top to supersonic wind tunnel experiments. His contributions thus far have allowed him to be a recipient of the Air Force Research Laboratory’s Early Career Award and Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House.

He serves as a guest editor for IEEE Transactions on Plasma Science and he is an Associate Fellow of the American Institute of Aeronautics and Astronautics.