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6078499 
Journal Article 
Numerical modeling of ignition enhancement of CH4/O-2/He mixtures using a hybrid repetitive nanosecond and DC discharge 
Mao, X; Rousso, A; Chen, Qi; Ju, Y 
2019 
1 
Proceedings of the Combustion Institute
ISSN: 1540-7489
EISSN: 1873-2704 
Elsevier 
37 
4 
5545-5552 
WOS:000457095600138 
Ignition enhancement using a hybrid repetitive nanosecond and DC discharge is studied in CH4/O2/He mixtures at atmospheric pressure by using a hybrid ZDPlasKin-CHEMKIN method. Special attention is placed on the control of vibrational and electronic excitations of methane and oxygen using different electric field strengths. A plasma-ignition kinetic mechanism incorporating the reactions involving both vibrational and electronic excitations of CH4 and O2 as well as the low temperature methane oxidation pathways of O2(a1Δg) is developed and validated. The results show that the hybrid non-equilibrium plasma excitation is much more effective in ignition enhancement than thermal heating and the nanosecond discharge alone. O2(a1Δg) is generated more efficiently in the hybrid discharge and shortens the ignition delay time more effectively than O(1D) and O produced in the nanosecond discharge. Vibrationally excited species CH4(ν) and O2(ν) are also produced but mainly contribute to ignition enhancement via energy relaxation and gas heating. The results also show that e + O2 → e + O2(a1Δg) and e + O2 → e + O + O(1D) reactions compete with each other for oxygen consumption and play opposite roles in ignition enhancement in a hybrid NSD/DC discharge with a given plasma energy. For a given repetitive nanosecond discharge, there is an optimum DC electric field strength which has the minimum ignition delay time due to the selective production of excited species and the difference in electron density. This work provides fundamental understanding for the design of a hybrid discharge to optimize low temperature ignition enhancement and fuel reforming. 
Non-equilibrium plasma; Ignition enhancement; Vibrational excitation; Hybrid nanosecond and DC discharge