PhD Research
| Detonation
waves |
- Structure of the detonation
wave
A detonation wave is defined as a supersonic combustion driven shock wave and it can reach speeds of kilometers per second. The GE Global Research Blog posted a revealing video showing the initiation of a detonation wave and its subsequent motion. A few equally spaced frames appear in the figure above showing the approximately planar front and its nearly constant velocity.
In the above figure, the basic theoretical schematic for the planar detonation is shown. In this case, a shock wave propagates at some speed D in to a quiescent (i.e. still) combustible gas mixture. This typically involves oxigen and hydrogren or athylene, ethylene etc... The jump across the shock wave produces a large jump in temperature. As an example, this could reflect a increase to 2000 degrees Kelvin from say a room temperature quiescent gas.
This temperature jump triggers the heat release of the reacting gas mixture through due to the increase the intermolecular collision energy. This is described in the figure below. Therefore, the immeadiate area after the shock wave jump is called the reaction zone.
Per our figure, the reaction begins behind the shock wave where the gas is in its reactant phase. As mentioned the jump in temperature will cause the energy of the intermolecular collisions to increase markedly. This will continue steadily until we reach a critical threshold activation energy which will be a property of the reaction. At the point the gas will rapidly transition to the products phase. This brings us to the end of the reaction and the beginning of the burnt gas or following flow region.
The structure of this region will depend on the boundary conditions in the rear of the detonation wave. This could be a driving piston or a rigid confining wall. This introduces the crucial property of overdrive. For detonation, based on analysis of the relevant conservation relations one can establish there will be a minimum detonation velocity that can satisfy the conservation of mass, momentum and energy across the shock wave front.
Last edited on May 18, 2008.
- Linear stability of
the ZND theory
A
section explaining the linear stability analysis will follow here.
Some
cool links
- Video of experiment in detonation waves - GE Global Research Blog
- Computer simulation of detonation initiation - U. of Colorado Multi-scale Modeling and Simulation Laboratory (scroll to Detonation Initiation).
