Numerical modeling of plasma assisted deflagration to detonation transition of a H₂/O₂ mixture in a microscale channel

The plasma assisted deflagration to detonation transition (DDT) of a H₂/O₂ mixture in a microscale channel is studied numerically with detailed chemistry and transport. The effects of a repetitively-pulsed nanosecond discharge on fuel oxidation and DDT dynamics are investigated. The results show that low temperature plasma discharge leads to fast radical production and fuel oxidation at low temperature and that the DDT onset time is non- monotonically dependent on the total pre-detonation discharge pulse number. It is shown that with plasma discharge, DDT is initiated more rapidly at a small plasma pulse number. This is because the chemically active species generated by plasma will accelerate radical production at low temperatures by inducing new pathways such as e + H₂ → e + H + H, e + O₂ → e + O + O(¹D) and O(¹D) + H₂ → H + OH and enhance the auto-ignition and shock-ignition coupling. It is also revealed that with the increase of pulse number, the fuel oxidation leads to the higher radical concentration, pre-detonation temperature, and fuel concentration reduction, which lead to an increase of the DDT onset time. At a very large plasma discharge number, it is shown that the DDT onset time can be even longer than that without plasma discharge although plasma produces much higher radial concentrations and raises higher temperature. Two different DDT regimes are observed. With a small number of plasma discharge, DDT occurs after the acoustic choking of the burned gas. However, at a large number of plasma discharge with a significant rise of the initial temperature, a direct auto-ignition to DDT is observed without the acoustic chocking of the burned gas in the micro-channel. This work provides good explanation to the experimental observation of nonlinear DDT onset time dependence on plasma discharge and guidance to control DDT in advanced detonation engines and control of fire safety of hydrogen fueled catalytic reactors by non-equilibrium plasma discharge.