The European Union is preparing to enforce stricter CO₂ emissions regulations targeting heavy-duty vehicle (HDV) manufacturers. Manufacturers that do not meet these standards may face substantial financial penalties. To meet these regulation targets, HDV manufacturers must introduce zero-emission vehicles powered by either electric powertrains or Hydrogen Internal Combustion Engines (H2 ICE). When H2 ICE are adapted from diesel counterparts with minimal design changes, the combustion analysis tools play a major role in evaluating the risks of abnormal combustion and high metal temperatures. One of the key challenges in H2 ICE modeling is selecting a matching reaction mechanism. The literature offers a wide range of H2 detailed chemistry kinetic models, each with distinct ignition delay times and laminar flame speeds, typically validated under controlled conditions such as shock tube experiments. However, translating these mechanisms to real-engine scenarios remains difficult due to the complex and transient nature of hydrogen combustion. This study evaluates several H₂ reaction mechanisms through combustion simulations of a production-ready low-pressure direct injection (LPDI) heavy-duty hydrogen engine.