Premixed Flame Stability And Its Application To Pulse Detonation Engine

Pulse detonation engine (PDE) is a new concept of propulsion system which uses pulse detonation waves to product thrust. Due to its obvious advantages PDE has become the research hotspot. Efficient ignition is one of the key techniques. Since the energy required to initiate detonation directly is so large that it is extremely difficult to generate the conditions where direct initiation can result from a typical energy source. Low energy source for detonation initiation to provide fast and reliable detonation has become the current focus.In the paper the phenomena of detonation onset induced implosion combustion were studied experimentally and numerically. Since the phenomenon is related with two elementary physics phenomenas of shock-flame interaction and flame jet impinging, the two phenomenas were firstly studied.The experimental visualization measurements by using a high-speed shadow photograph technique were performed to study the shock-flame interactions within the combustion chambers with planar reflected wall and parabolic reflected wall, respectively. The numerical simulations were based on the two-dimensional, axisymmetric reactive Navier-Stokes equations with detailed elementary chemical reactions and finite volume method modified by traverse wave. The results show that for both planar and parabolic reflected walls, flame bubble can be penetrated through by incident shock wave in the vicinity of axis and form a cylindrical flame. Unreacted gas is filled inside and outside the cylindrical flame. The interaction of reflected shock with flame alters vorticity direction in local region and forms a vortex ring in the flame head that rolls fresh unreacted gas into the flame. Correspondingly, burning rate and propagating speed of flame increase and a mushroom-like flame forms. Inside the flame bubble there is the region with high temperature and low density. When the shock wave interacts with the flame, it can bifurcate on the flame surface and form aλwave. After interaction of the reflected wave with the flame front, the wave reflects on the flame front again, and then converges towards axis and collides again on axis, and so on. The repetitive reflection process leads to a complicated shock train inside the cylindrical flame. Compared with the case of planar reflected shock wave, at the early stage of interaction between the focusing shock wave and flame, a traverse wave produced by reflection can compress flame towards axis. This leads to a larger mushroom-like flame than that of planar reflection case.The phenomena of opposed-jet flames were studied experimentally and numerically. When two flame jets entere the combustor, flames become mushroom cloud with vortex because of Helmholtz instability. Subsequently, convection is the leading factor in flame propagation. After impinging at the axis, flame grows through all directions and formes disc shape. In the influence of background flow the thickness of the flame disc diminishes gradually while the diameter of the flame pole does not change obviously.The mechanism of detonation onset induced implosion flame were studied numerically in combustors with two open ends, one closed and another open end, various types of closed end gradually. The results show that shcok waves induced implosion flame reflect on axis, wall and reflecting end again, which leads to detonation onset. Finally, a facility of detonation onset was designed which achieves DDT in the conditions of low energy source,no barrier and short distance.