Hydrogen and methane plasma assisted ignition by NS discharge behind reflected shock wave

Summary form only given. The kinetics of ignition in lean H₂:O₂:Ar and CH₄:O₂:Ar mixtures has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected shock wave was measured with and without the discharge when detecting OH* radiation. It was shown that the initiation of the discharge with a specific deposited energy of 10 - 30 mJ/cm³ leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time - resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. Good agreement was obtained between the calculated ignition delay times and the experimental data. It was shown that ignition delay time is difficult to measure in too lean mixtures. Possible approaches to solve this problem were discussed.To make the interpretation of experimental data easier, we separated in time the discharge processes occurring in our case on a nanosecond scale and ignition processes important at times longer than tens microseconds. A high - voltage nanosecond discharge was used to produce active particles, which could favor the ignition of hydrocarbon-containing mixtures at elevated gas temperatures. The gas mixtures were heated in advance with shock wave technique, an ordinary approach to study autoignition delay in combustible mixtures. To demonstrate the effect of non - equilibrium discharge plasma, the ignition delay time was measured under the action of the discharge and in its absence. The Plasma Shock Tube facility at Princeton University was used for these experiments. The high pressure channel (HPC) length is 2.5 m, and sho- k tube (ShT) is 6 m in length and 100 mm in diameter. Shock arrival to the discharge test section is monitored by deflection of a He-Ne laser beam directed across the test section. The facility is instrumented with an array of pressure gauges and a Schlieren system to determine the incident and reflected shock wave velocities, and static pressure variation. After preheating of a premixed fuel-air mixture by the incident shock, a uniform, nonequilibrium plasma is established in the 80 cm long discharge test section by means of the Fast Ionization Wave (FIW) approach using a high-current pulsed nanosecond discharge. The shock tube itself can operate over a very wide range of incident (i.e. behind the shock) temperatures (T=500-2500 K) and pressures (P=0.0110 bar), and has a run time of up to 2 msec. For combustion measurements, incident conditions for undiluted fuel-air mixtures will be in the range of P=0.01-3 bar and T=8001800 K. The pulsed discharge energy at peak voltage of U=200 kV is approximately 0.4 J/pulse, with pulse duration of ~60 ns. Thus, we have made an experimental and numerical study of the ignition of lean C2H6 - containing mixtures under the action of a high - voltage nanosecond discharge and showed that its initiation leads to a noticeable decrease in gas temperatures at which the mixtures are ignited and to an order of magnitude decrease in ignition delay time. The measurements agree well with the calculated results for ignition delay times. It follows from the analysis of the calculated results that, under the conditions considered, the main mechanism of the effect of gas discharge on the ignition of hydrocarbons is the electron impact dissociation of O2 molecules in the discharge phase; this leads to an essential increase in the density of O atoms at the beginning of ignition. Ignition delay time turns out to be difficult to measure in too lean mixtures using CH emission. There is need to develop new methods to measure ignition delay in this ca