Principal Investigator Manuel Martinez-Sanchez
Project Website http://web.mit.edu/aeroastro/labs/spl/research_carmen.htm
In non-equilibrium or non-thermal plasmas, electrons are typically much more energetic than heavy species (ions and neutrals) and their energy distribution function may not follow a Maxwell-Boltzmann function. These electrons multiply through cascade ionization and can create large pools of radicals (atoms or molecules with unpaired electrons and a high affinity to react) through electron impact dissociation or electronic excitation followed by dissociative quenching. The share of the energy deposited in the gas between the different electron impact reactions is a strong function of the reduced electric field in the discharge gap and by modifying this parameter different electron impact processes can be favored.
Many situations can benefit from this ‘selective’ creation of reactive species, amongst them challenges arising from combustion applications. Non-thermal plasmas can be used as an artificial injection of radicals to accelerate the chain branching reactions of the combustion process in order to stabilize flames, extend lean flammability limits or reduce ignition delay times.
At the Space Propulsion Laboratory at MIT we have been exploring high voltage (kV), pulsed nanosecond discharges at high repetition frequencies (kHz) as a means of creating non-thermal plasmas. Future work will try to extend the experiments performed to a practical combustion application.
High voltage nanosecond duration discharges can be used in a repetitive manner to create a sustained pool of short-lived excited species and ions and longer-lived radicals in a gas. Experiments with nanosecond discharges have been performed in different gases at pressures ranging from 0.1-1atm and temperatures up to 1000K. The electrical pulses used had voltages up to 10kV, pulse width of 10ns and maximum repetition frequencies of 30kHz and were triggered in 5-10mm long discharge gaps. The study tried to evaluate the energy share between thermal (gas heating and shock waves generated by the rapid energy deposition) and non-thermal (chemical species produced) processes taking place in the plasma. Measurements taken included: electrical, optical emission spectroscopy and Schlieren photography.
Scaling of the different discharge regimes observed at atmospheric pressure to sub-atmospheric conditions was achieved.