<div class="section abstract"><div class="htmlview paragraph">The modern solution of two-stage combustion, namely the Turbulent Jet Ignition, enables the combustion of ultra-lean mixtures. Thanks to this solution, it became possible to reduce fuel consumption and, at the same time, to increase the combustion process indicators (including the overall combustion system efficiency). The article presents the results of numerical tests of a heavy-duty engine equipped with the TJI system running on hydrogen fuel. The operating conditions of the Heavy-Duty engine at n = 1500 rpm and IMEP = 10 bar with a prechamber with 7 holes were analyzed. The research was conducted with the use of lean mixtures (global lambda ca. 2 or more). The AVL FIRE software was used to perform the analysis of different fuel doses delivered to the main chamber, with a constant global excess air coefficient value. Increasing the proportion of hydrogen in the pre-chamber resulted in its reduction in the main chamber. The research used a Coherent Flame Model as the combustion model - and the Extended Zeldovicz (NO) as the exhaust emission model. The variations of the excess air coefficient in the prechamber were determined along with the changes of the fuel dose. The maximum combustion pressure values in both chambers were investigated. The analysis of inter-chamber mass flow and temperature change during combustion were performed for both of the chambers. The differences in the excess air coefficient value in the main chamber and prechamber were investigated in relation to the indicators of the combustion process. Changes in the amount of heat released and its release rate were determined. Combustion efficiency was then determined using the measured operating parameters. Nitrogen oxides formation analysis along with the obtained combustion efficiency value made it possible to select the optimal prechamber fuel dose during hydrogen combustion in the modern Turbulent Jet Ignition combustion system.</div></div>