Role of Transient-Plasma Generated Free Radicals in Hydrogen Combustion: Spectroscopic and Theoretical Insights
Year: 2026
Type: article
Abstract: Transient plasma ignition is known to improve the combustion of various fuels. Here, we compare the combustion mechanisms of carbon-free fuels containing mixtures of H2 and O2 via transient plasma ignition and conventional spark ignition. The transient plasma ignition is produced by five 20 ns pulses at a frequency of 1 kHz with an amplitude of 20 kV. Compared to conventional spark ignition (CSI), TPI ignited four times faster at a lean equivalence ratio (ϕ = 0.4). Optical diagnostics confirmed the presence of Hα emission during TPI, providing direct evidence of atomic hydrogen radicals generated by nanosecond plasma discharges. These radicals, coupled with electrostatic flow effects, reduced ignition delay and accelerated flame propagation beyond enhancements attributable to flame wrinkling alone. Complementary kinetic modeling with Cantera and one-dimensional Lagrangian simulations revealed that plasma-generated H· radicals bypass high-temperature initiation pathways. This shortens induction times and promotes earlier OH· formation, thereby accelerating H2 oxidation and water production under both adiabatic and non-adiabatic conditions. Together, these findings demonstrate that TPI enhances hydrogen combustion by coupling radical-driven kinetics with fluid-dynamic effects, offering a promising strategy to improve ignition reliability and efficiency in carbon-free propulsion systems.
Source: Fuel
Institution: University of Southern California
Language: English
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,330
Awards: G1385827936, G1536541855, G6605635983
OpenAlex ID: W7128915179