Zero emission transport solutions are key on net zero objectives. On commercial vehicles three main propulsion systems were defined as zero emission: battery-electric, fuel cell and hydrogen internal combustion engine (H2-ICE). Due to high efficiency, especially on high load operations, application suitable durability, lower sensitivity on hydrogen purification and reduced costs, H2-ICE is receiving high attention. The first generation of hydrogen engines for commercial vehicles follow spark ignited engine combustion processes, which are operated lean with intake manifold or low-pressure direct injection. The achievable efficiencies and power densities are limited due to the combustion system characteristics. Due to Total Cost of Ownership (TCO) and range requirements, an alternative combustion process is required, to bring H2-ICE efficiency closer to diesel engine combustion. It involves hydrogen to be injected under high pressure near top dead center. During the presentation, the ways to derive such a highly efficient hydrogen engine from a diesel engine will be shown. The available or necessary approaches to initiate the diffusion combustion of the hydrogen are also discussed to show maximum efficiency in the hydrogen combustion engine, targeting 50% or higher brake thermal efficiency (BTE). Evaluations on the effective benefit of different compression ratios and different air boosting levels were assessed in transient dyno tests and will be presented and commented in the paper.