Emission Spectroscopy Study of the Microwave Discharge Igniter

Requirements for reducing consumption of hydrocarbon fuels, as well as reducing emissions force the scientific community to develop new ignition systems. One of possible solutions is an extension of the lean ignition limit of stable combustion. With the decrease of the stoichiometry of combustible mixture the minimal size of the ignition kernel (necessary for development of combustion) increases. Therefore, it is necessary to use some special techniques to extend the ignition kernel region. Pulsed microwave discharge allows the formation of the ignition kernels of larger diameters. Although the microwave discharge igniter (MDI) was already tested for initiation of combustion and demonstrated quite promising results, the parameters of plasma was not yet studied before. Present work demonstrates the results of the dynamics of spatial structure of the MDI plasma with nanosecond time resolution. It was shown that the size of the plasma region increases from 2-4 to 10-15 mm³ during the discharge development. Gas temperature and vibrational temperature were measured with optical emission spectroscopy. The electric field in the discharge was measured from the analysis of emission intensities of the first negative (N⁺₂(B²?⁺_u) → N⁺₂(X² Σ ⁺_u)) and the second positive (N₂(C³π_u) → N₂(B³π_g)) systems of molecular nitrogen. The electron density was estimated from the atomic line broadening.