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

• Published in: Frontiers in mechanical engineering 2022-07, Vol.8
• Main Authors: Ban, Yangyang, Zhang, Fan, Zhong, Shenghui, Zhu, Jiajian
• Format: Article
• Language: English
• Subjects: HCCI engine; methane–air plasma kinetics; nanosecond-pulsed discharge; nonequilibrium plasma; plasma-assisted ignition/combustion modeling
• ISSN: 2297-3079; 2297-3079
• DOI: 10.3389/fmech.2022.930109

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 ( φ ) is investigated. It was found that in ICEs with NRPD, the ignition delay time under the lean-burn condition ( φ = 0.5) is the shortest among three demonstrative cases. Even though the leaner mixture case with φ = 0.2 is more favorable for the production of O and OH during the discharge, after discharge, the heat release in case 2 with φ = 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 3 , HO 2 , and H 2 O 2 as well as higher temperature for the lean-burn ( φ = 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 E/N , current density, φ , and discharge timing on the ignition process. The results suggest that discharge parameters E/N and current density together with discharge timings and equivalence ratios can improve ignitability in internal combustion engines.