Accession Number : AD1004855


Title :   Schlieren Imaging and Pulsed Detonation Engine Testing of Ignition by a Nanosecond Repetitively Pulsed Discharge


Descriptive Note : Journal Article


Corporate Author : Aerospace Systems Directorate Wright-Patterson AFB United States


Personal Author(s) : Lefkowitz,Joseph K ; Guo,Peng ; Ombrello,Timothy ; Won,Sang H ; Stevens,Christopher A ; Hoke,John L ; Schauer,Frederick ; Ju,Yiguang


Full Text : http://www.dtic.mil/dtic/tr/fulltext/u2/1004855.pdf


Report Date : 16 May 2016


Pagination or Media Count : 12


Abstract : A nanosecond repetitively pulsed (NRP) discharge in the spark regime has been investigated as to its effectiveness in reducing ignition time, both in a flow tube and a pulsed detonation engine (PDE). The flame-development time for methaneair mixtures in the flow tube is found to be a function of the total ignition energy and the pulse repetition frequency. Schlieren imaging revealed that at low pulse-repetition frequency (05 kHz), ignition kernels formed by the discharge are each transported away from the discharge gap before the following pulse arrives. At higher pulse-repetition frequencies (P10 kHz),multiple pulses are all coupled into a single ignition kernel, thus the resulting ignition kernel size and the total energy deposition into the kernel are increased, resulting in a faster transition into a self-propagating flame. Imaging of the NRP discharge in air revealed that at high pulse frequencies(10 kHz) and peak pulse amplitude (9 kV), the plasma emission is not quenched in-between pulses, resulting in a building up of heat and radicals in the center of the ignition kernel. Optical emission spectra revealed the presence of electronically excited N2, O, and N, as well as O+ and N+, during and between the discharge pulses. Numerical modeling of the plasma indicated that reactions of excited species mainly lead to the production of O atoms and the increase of gas temperature, which shortens induction chemistry timescales, and thus reduces the flame-development time through both kinetic and thermal mechanisms. Ignition of aviation gasolineair mixtures by NRP discharge in a PDE also demonstrated a noticeable reduction in ignition time as compared to an automotive aftermarket multiple capacitive-discharge ignition system.


Descriptors :   Flame propagation , combustion , ignition , Space propulsion , Schlieren photography


Distribution Statement : APPROVED FOR PUBLIC RELEASE