Accurate understanding of hydrogen-NOx/N2O interaction chemistry is crucial for optimizing exhaust gas recirculation (EGR) systems, minimizing NOx formation in hydrogen-fired internal combustion engines (ICEs), and improving post-treatment strategies for NOx emissions. In this study, we conducted a comprehensive investigation using advanced spectroscopic analysis, multi-species laser diagnostics, and ignition delay time (IDT) measurements under elevated pressure conditions.
Our research focused on identifying interference-free absorption lines for precise species measurements under variable pressure conditions and establishing a robust laser diagnostics platform within a shock tube setup, enabling simultaneous measurements of OH, H2O, NO, NO2, N2O using multiple aligned lasers, as shown in Fig. 1. Furthermore, we performed time-resolved speciation measurements of various gas mixtures to gain deeper insight into H2/NOx interaction chemistry. In addition, we reevaluated the unimolecular decomposition rates of NO2 and N2O and assessed the third-body effects. To further understand ignition kinetics, we conducted IDT measurements of lean H2 mixtures under realistic EGR conditions, exploring the ignition behavior at elevated pressures.
To enhance predictive capabilities, we updated and refined a comprehensive hydrogen-NOx/N2O-O2 kinetic model from our recent work. Our key findings indicate a considerable enhancement in ignition at ~20 bar by varying N2O concentrations, whereas negligible effects were observed at ~1.8 bar. Higher NO2 concentrations in the H2/O2/Ar system significantly inhibited ignition at ~1.8 bar; however, this inhibitory effect shifted to a promotional role at ~20 bar.
This study provides valuable insights into the fundamental kinetics of hydrogen-NOx/N2O-O2 systems, offering a refined understanding of reaction mechanisms and paving the way for improved predictive models, as shown in Fig. 2. These findings contribute to the advancement of hydrogen combustion strategies and emissions control, supporting the development of cleaner and more efficient energy conversion technologies.