AUTHOR=Ban Yangyang , Zhang Fan , Zhong Shenghui , Zhu Jiajian 

TITLE=The numerical simulation of nanosecond-pulsed discharge-assisted ignition in lean-burn natural gas HCCI engines

JOURNAL=Frontiers in Mechanical Engineering

VOLUME=8

YEAR=2022

URL=https://www.frontiersin.org/journals/mechanical-engineering/articles/10.3389/fmech.2022.930109

DOI=10.3389/fmech.2022.930109

ISSN=2297-3079

ABSTRACT=<p>A plasma-assisted internal combustion engine model is established based on detailed plasma kinetics, combustion kinetics, and physical compression/expansion processes. The effects of nanosecond repetitively pulsed discharge (NRPD) on plasma-assisted ignition characteristics of mixtures under different fuel concentrations are studied under HCCI engine-relevant conditions. The coupled plasma and chemical kinetic model are validated with experiments. The comparison between NRPD and thermal ignition with a certain amount of input energy is carried out, and the results show that the former can ignite a mixture owing to the kinetic effect of nonequilibrium plasma, but the latter cannot ensure ignition. Path flux analysis shows that excited states and electrons react with fuel, providing O and H directly, increasing the possibility of ignition at a low temperature. The effect of NRPD on combustion performance under various equivalence ratios (<italic>φ</italic>) is investigated. It was found that in ICEs with NRPD, the ignition delay time under the lean-burn condition (<italic>φ</italic> = 0.5) is the shortest among three demonstrative cases. Even though the leaner mixture case with <italic>φ</italic> = 0.2 is more favorable for the production of O and OH during the discharge, after discharge, the heat release in case 2 with <italic>φ</italic> = 0.5 dramatically increases, resulting in the temperature exceeding that in the ultra-lean case. As the piston moves up, the higher amounts of CH<sub>3</sub>, HO<sub>2</sub>, and H<sub>2</sub>O<sub>2</sub> as well as higher temperature for the lean-burn (<italic>φ</italic> = 0.5) case lead to the rapid increase of OH and O, which accelerates the consumption of methane and finally the earliest hot ignition near TDC. Finally, a series of parameter studies are performed to show the effects of <italic>E/N</italic>, current density, <italic>φ</italic>, and discharge timing on the ignition process. The results suggest that discharge parameters <italic>E/N</italic> and current density together with discharge timings and equivalence ratios can improve ignitability in internal combustion engines.</p>