MS Thesis Presentation by
David M. Chapin
Tuesday, November 1, 2005
(Dr. Timothy Lieuwen, Chair)
" A Study of Deflagration to Detonation Transition In a Pulsed Detonation Engine "
A Pulse Detonation Engine (PDE) is a propulsion device that takes advantage of the pressure rise inherent to the efficient burning of fuel-air mixtures via detonations. Detonation initiation is a critical process that occurs in the cycle of a PDE. A practical method of detonation initiation is Deflagration-to-Detonation Transition (DDT), which describes the acceleration of a subsonic deflagration created using low initiation energies to a supersonic detonation. Although not well understood, DDT is known to be influenced by many factors. Introducing turbulence into the tube PDE via spaced obstacles has been shown to significantly decrease the tube length needed to transition to detonation. For obstacle induced DDT, factors including obstacle spacing, blockage ratio (BR), and length of the DDT section have been shown to affect the behavior of DDT.
This thesis will present the effects of obstacle spacing, blockage ratio, DDT section length, and airflow on DDT in hydrogen-air and ethylene-air mixtures for a repeating PDE. The test rig designed was a 2” diameter, 40” long, continuous airflow, repeating PDE located at the General Electric Global Research Center in Niskayuna , New York . Data was captured using time of flight measurements between dynamic pressure transducers and also through use of a high-speed video camera and a clear combustion chamber to capture chemiluminescence and track flame front progression.
It is seen that airflow, obstacle spacing, and obstacle section length have the most significant effects on DDT. In fact, obstacles in quantities more than what is minimally required for detonation transition are found to inhibit detonation formation. For the obstacle geometry tested in this research, the minimum length required for detonation in hydrogen-air mixtures is 8 L/D from the spark location, while for ethylene it is 16 L/D. It is also observed that increasing the airflow rate through the tube from 0.1 to 0.3 lbs/sec decreases the time required for DDT by 26%, from 3.9 ms to 2.9 ms. Effects of obstacle blockage ratio on pressure drop, effects of PDE diameter on DDT, and Comparisons between experiments and simulations are also reported.