This study investigates the plasma properties and chemical kinetics of plasma-assisted methane reforming in a He diluted nanosecond-pulsed plane-to-plane dielectric barrier discharge (ns-DBD) through the combination of time-resolved in situ laser diagnostics and a 1-D numerical model. Plasma-assisted fuel reforming kinetic mechanisms have predominantly been evaluated on the basis of matching reactant conversion and syngas production to steady-state measurements, which cannot describe the full range of chemistry and physics necessary to validate the model. It was found that adding 1% CH4 to a pure He ns-DBD led to a faster breakdown along the rising edge of the applied voltage pulse, thereby lowering the reduced electric field (E/N), electron number density, and electron temperature. Further addition of CH4 did not continue to alter the E/N in the model. Laser absorption spectroscopy was used to measure gas temperature, C2H2, H2O, and CH2O in a CH4/CO2/He discharge to serve as validation targets for the predicted reaction pathways. CH2O was predicted within 25% of the measured value, while H2O and C2H2 were under-predicted by a factor of two and three, respectively. From path flux analysis, the major pathway for CH2O formation was through the reaction between CH3 and O, while C2H2 formation had multi-step pathways that relied on ions like CH+3 and C2H+5. The path flux analysis also shows that CH2 is a significant intermediate for production of both CH2O and C2H2, and increased CH2 concentration could improve model predictions. The results show that the use of reaction rate constants with lower uncertainties and inclusion of He+2 are needed to improve the predictions. Finally, varying the "equivalence ratio", defined by the CH4 dry reforming reaction to H2 and CO, from 0.5 to 2 was shown to have a weak effect on measured product species and experimental trends were explained based on pathways extracted from the model.
Bibliographical noteFunding Information:
This work was supported by ExxonMobil through its membership in the Princeton E-filliates Partnership of the Andlinger Center for Energy and the Environment. T.Y. Chen is partially supported through the Program in Plasma Science and Technology at Princeton University Fellowship. S. Yang gratefully acknowledges the faculty start-up funding from the University of Minnesota. All simulations were conducted in the Minnesota Supercomputing Institute (MSI). Y. Ju would like to acknowledge the grant support from NSF CBET 1903362 , NSF-EFRI grant for distributed chemical manufacturing, DOE DE-SC0020233 of Plasma Science Center, and DOE -NETL DE-FE0026825 .
© 2020 The Combustion Institute.
- Chemical kinetics
- Methane dry reforming
- Non-equilibrium plasma
- Plasma assisted fuel reforming