Chemical-kinetic investigation of hydrogen autoignition under HPDI relevant thermodynamic conditions

Future sustainable heavy power and propulsion sectors will likely employ hydrogen as an energy vector. High pressure direct injection (HPDI) mitigates some limiting aspects of hydrogen use in combustion applications, whilst coupling with hydrocarbon pilot fuel in compression ignition (CI) mode ensures reliable ignition under low-temperature, high-pressure conditions. However, this approach introduces carbon emissions and dual-fuel logistics. Therefore, this study adopts a chemistry-focused numerical approach using Ansys Chemkin-Pro to investigate hydrogen autoignition behaviour under thermodynamic conditions representative of in-cylinder states near top dead centre (TDC). Three core contributions are presented. First, a H 2 /O 2 /N 2 kinetic mechanism was compiled for high-pressure, low-temperature conditions relevant to late-cycle HPDI combustion environments. Second, sensitivity and reaction pathway analysis suggests that nitrogen-containing pathways, notably via NNH chemistry, may contribute to HO 2 formation during early radical buildup under the considered conditions. Third, a subsystem-level mechanistic feasibility study assessed whether an imposed hydrogen-derived H/OH radical seed could accelerate main-charge ignition. For the radical-seeded, non-adiabatic homogeneous-reactor case at 810 K and 175 bar, an ignition delay of approximately 4.8 ms was predicted. This value applies specifically to the imposed radical-seeded case and is not the unseeded hydrogen autoignition delay. The result is therefore interpreted as a mechanistic feasibility bound rather than an experimentally validated engine-scale prediction. These results suggest that radical-enhanced hydrogen autoignition pathways may be achievable under HPDI relevant thermodynamic conditions. More broadly, the study demonstrates how simplified homogeneous reactor frameworks can be used to isolate and evaluate ignition-sensitive chemical pathways prior to higher-fidelity multidimensional engine investigations. These findings support continued investigation of hydrogen-derived ignition support strategies for low-carbon HPDI combustion systems.