Liebherr H966 is a highly compact 13.5 liters 6-cylinder hydrogen engine. Still in development, this engine presents promising and encouraging results in terms of CO2 and nitrogen oxides (NOx) emissions. This 6-cylinder engine comes with port-fuel technology (PFI). PFI takes place at pressures below 20 bar directly into the intake system. The power density is 20 - 30% lower to that of a diesel engine due to air displacement effects. Port fuel injectors work in less demanding operating conditions which results in an easier design.