Ammonia can be used as a carbon-free alternative green fuel for Internal Combustion Engines (ICE). It has an excellent potential to replace fossil fuels. In this study, gaseous ammonia is injected into the intake port and then a pilot dose of diesel is injected into the cylinder to initiate the combustion of premixed ammonia air. Hence, the effects of various ammonia/diesel ratios on combustion, emissions, and engine performance are analyzed experimentally and numerically and compared with pure diesel. Results reveal a significant reduction of CO2, CO, and HC emissions by increasing the ammonia ratio. However, it increases NOx emissions due to nitrogen content in ammonia (NH3). Results of the developed 1D model show that the Start Of Combustion (SOC) is delayed by increasing the ammonia mass flow, however, the Combustion Duration (CD) is decreased compared to pure diesel operation. Furthermore, the efficiency of ammonia/diesel operation is slightly lower compared to only diesel in the same operating point.