Experimental study of pulsed microwave discharges at pressures ranging over five orders of magnitude

Abstract

Microwave discharge igniter (MDI) is a discharge system developed to initiate combustion at the conditions of automotive engines. The MDI uses a sequence of N = 700 microwave (2.45 GHz) pulses 100 ns in duration separated by 1 µs. The initial breakdown is provided by the first microwave pulse, 5 µs in duration. The aim of pulsing the microwave signal is to keep an optimal combination of parameters when, even at elevated pressures, (i) the discharge is spread over a maximum possible volume; (ii) the plasma in non-equilibrium. Properties of plasma produced by MDI igniter in non combustible gas mixtures at ambient gas temperature and gas pressure between 0.2 mbar and 8 bar were studied experimentally. Discharge spatial structure was analyzed with the help of time-resolved ICCD imaging. Optical emission spectra in near UV taken in different pulses provided the information about rotational and vibrational temperatures. The electric field was estimated on the basis of ratio of emission of the second positive and the first negative systems of molecular nitrogen.

Development of 2.45 GHz Semiconductor Microwave System for Combustion Ignition Enhancement and Failure Analysis

“… Oscillation pattern of microwave input of microwave discharge igniter (MDI) initiates plasma breakdown and sustains ignition for a long period [ 30 ]. …”