Laser Induced Fluorescence and High Speed Imaging of Nanosecond-Pulsed Discharges for Application in Plasma Assisted Combustion in a Microchannel

This study examines low temperature chemistry (LTC) enhancement by nanosecond (ns) dielectric barrier discharge (ns-DBD) plasma on a dimethyl ether (DME) and oxygen (O2) premixture for plasma assisted enhancement of deflagration to detonation (DDT). Non-equilibrium plasma generates electronic and vibration excitations as well as ions and radicals to enable kinetic acceleration of combustion. However, it can also reduce the fuel concentration via plasma enhanced low temperature oxidation and thus delays DDT. The experimental installation has been assembled to examine the influence of the ns discharge on the low temperature chemistry of dimethyl ether (DME) using formaldehyde (CH2O) laser induced fluorescence (LIF). Firstly, the competition between the plasma enhanced kinetic effect on ignition and the reduced heat release rate of combustion wave front due to the plasma assisted partial fuel oxidation is studied. Then, by combining with high-speed imaging, the LIF is used to trace the presence of low temperature chemistry throughout the flame front propagation and transition of deflagration to detonation. The results show that with an appropriate number of discharge pulses, plasma enhances the low temperature chemistry of DME and increases CH2O formation, leading to accelerated DDT. Therefore, plasma enhanced low temperature chemistry plays an important role in DDT. Moreover, it is found that with a large number of discharge pulses, CH2O concentration decreases, indicating that excess number of discharge pulses may inhibit DDT. The present experimental data helps to explain our previous observation of nonlinear enhancement of DDT in a micro channel by non-equilibrium plasma.