Ammonia is emerging as a carbon-free fuel but its corrosive effect on metal engine components, particularly those made of copper and copper alloys, is a major concern to be addressed. Herein, typical corrosion inhibitors are investigated in the presence of NH3. They have been ranked experimentally based on their corrosion initiation time while the NH3 diffusion barrier through inhibitor films has been evaluated using molecular dynamics simulations using a classical force field that was tuned to improve the Cu/inhibitor interactions. The excellent agreement with experiments indicates that this simulation approach could allow for the screening of new corrosion inhibitors.