Electric probe measurements of chemical ionization behind reflected shock waves

Abstract

Chemical ionization is the process of formation of charged particles as a result of energy release during the formation of chemical bonds in chemical reactions between neutral components. Chemical ionization is most often observed in the processes of hydrocarbon combustion. Measurements of ionization current in internal combustion engines are of great practical interest. Most experiments on chemical ionization were carried out in flames with obvious limitations: the composition of the mixture cannot be changed in an arbitrarily wide range of concentrations of fuel and oxidant, to investigate the pyrolysis processes, to arbitrarily change the temperature and pressure, it is impossible to dispose of the transfer processes and gradients of temperature and reactive components. Experiments in shock tubes in the reflected shock waves are free of all of the above disadvantages. In the present work, electric currents to the electrically insulated and uninsulated cylindrical probes were recorded, to which a negative (−9V) or positive (+9V) potentials were applied. In these experiments, the displacement and the total currents were recorded respectively. In the same experiments, the signals of chemiluminescent emission of electronically excited OH* radicals (λ = 308 nm) were simultaneously recorded. The main goal of the present work was to measure experimentally (1) the displacement currents on positive and negative probes, (2) the total and displacement currents on a negative cylindrical probe during acetylene pyrolysis and oxidation, and (3) to confirm correlation of the displacement currents and the signals of chemiluminescent emission of electronically excited OH* radicals.