  Dynamics of ethylene autoignition and Deflagration-to-Detonation Transition
(DDT) in a one-dimensional shock tube are numerically investigated using a
skeletal chemistry including 10 species and 10 reactions. Different combustion
modes are investigated through considering various premixed gas equivalence
ratios (0.2 to 2.0) and incident shock wave Mach numbers (1.8 to 3.2). Four
ignition and DDT modes are observed from the studied cases, i.e., no ignition,
deflagration combustion, detonation after reflected shock and deflagration
behind the incident shock. For detonation development behind the reflected
shock, three autoignition hot spots are formed. The first one occurs at the
wall surface after the re-compression of the reflected shock and contact
surface, which further develops to a reaction shock because of the explosion in
the explosion regime. The other two are off the wall, respectively caused by
the reflected shock rarefaction wave interaction and reaction induction in the
compressed mixture. The last hot spot develops to a reaction wave and couples
with the reflected shock after a DDT process, which eventually leads to
detonation combustion. For deflagration development behind the reflected shock,
the wave interactions, wall surface autoignition hot spot as well as its
induction of reaction shock are qualitatively similar to the mode of detonation
after incident shock reflection, before the reflected shock rarefaction wave
collision point. However, only one hot spot is induced after the collision,
which also develops to a reaction wave but cannot catch up with the reflected
shock. For deflagration behind the incident shock, deflagration combustion is
induced by the incident shock compression whereas detonation occurs after the
shock reflection.
