Numerical study of nonequilibrium plasma assisted detonation initiation in detonation tube

Abstract

Nonequilibrium plasma has shown great merits in ignition and combustion nowadays, which should be especially useful for hypersonic propulsion. A coaxial electrodes configuration was established to investigate the effect of alternating current (AC) dielectric barrier discharge nonequilibrium plasma on the detonation initiation process in a hydrogen-oxygen mixture. A discharge simulation-combustion simulation loosely coupled method was used to simulate plasma assisted detonation initiation. First, the dielectric barrier discharge in the hydrogen-oxygen mixture driven by an AC voltage was simulated, which takes 17 kinds of particles (including positively charged particles, negatively charged particles, and neutral particles) and 47 reactions into account. The temporal and spatial characteristics of the discharge products were obtained. Then, the discharge products were incorporated into the combustion model of a detonation combustor as the initial conditions for the later detonation initiation simulation. Results showed that the number density distributions of plasma species are different in space and time, and develop highly nonuniformly from high voltage electrode to grounded electrode at certain times. All the active species reach their highest concentration at approximately 0.6T (T denotes a discharge cycle). Compared with the no plasma case, the differences of flowfield shape mainly appear in the early stage of the deflagration to detonation transition process. None of the sub-processes (including the very slow combustion, deflagration, over-driven detonation, detonation decay, and propagation of a self-sustained stable detonation wave) have been removed by the plasma. After the formation of a C-J detonation wave, the whole flowfield remains unchanged. With the help of plasma, the deflagration to detonation transition (DDT) time and distance are reduced by about 11.6% and 12.9%, respectively, which should be attributed to the active particles effect of nonequilibrium plasma and the local turbulent enhancing effect by the spatial characteristics of discharge. In addition, as the duration of forming a shock wave in the combustor is shortened by approximately 8.1%, it can be inferred that the plasma accelerates the DDT process more significantly before the flow becomes supersonic.

Effect of actuating voltage and discharge gap on plasma assisted detonation initiation process

“…A total of 47 discharge elemental reactions [33] are used while taking the positively charged particles + H , A high frequency sinusoidal AC power supply is used for the DBD. When considering the variation of actuating voltage amplitude, the peak-to-peak voltages of 7, 10 and 14 kV are chosen for comparison, while the size of the discharge gap is fixed as 5 mm; when considering the variation of the discharge gap size, the discharge gaps of 5 and 10 mm are chosen for comparison, while the actuating voltage is fixed as 14 kV.…”

“…The loose coupling approach is used to deal with the simulation of PADI here [33,37]. According to the operation sequence, the heat ignition is performed firstly, then the discharge starts.…”

Effect of actuating frequency on plasma assisted detonation initiation

“…A total of 47 discharge elemental reactions [25] are used where the positively charged particles O Boundary conditions are expressed as n k = 0 (for negative charged particles) and ∂ n k /∂ y = 0 (for positive charged particles) at the high voltage electrode, φ = 0 V at the grounded electrode, and ∂ n k /∂ y = 0 at the surface of the dielectric layer. The particle velocity at the electrode surface is limited in practice, yet the boundary conditions used here lead to an infinite velocity value of particle, so the distributions of species concentration are given by fitting functions, which are determined based on the overall distributions excluding the several values near the electrode boundary.…”

“…Details concerning the equations, reaction mechanisms, boundary and initial conditions, together with the numerical solving schemes can be found in Ref. [25].…”

The Influence of Electric Field Inhomogeneity on Repetitive Performance of a Corona-Stabilized Switch

“…The gas-discharge plasma generated by high-voltage pulses with high repetition frequency offers a number of desirable attributes such as high electron temperature, strong chemical reaction activity, and excellent instantaneous power [1], [2]. Typical industrial applications requiring high pulserepetition frequencies (PRFs) include plasma assisted combustion [3], pulsed extreme ultraviolet light source [4], non-thermal plasma processing [5]- [7], plasma medical [8] and so on. The development of repetition rate applications has resulted in an increasing demand for the reliable switches in pulsed power systems capable of operating at a high PRF.…”