This study focuses NH3 as an alternative fuel for internal combustion engines, because NH3 is known as a H2 carrier and its combustion does not produce CO2 causing global warming. On the other hand, some reports show that unburned NH3 and N2O appear in exhaust gas, when NH3 is used as fuel for compression ignition or spark ignition engines. NH3 is toxic and N2O is one of the greenhouse gases. These emissions should not be emitted. These reports point out that exhaust gas after treatments and/or injection strategies can be effective to reduce these emissions. From our previous investigations, it was confirmed that NH3 and N2O were contained in the exhaust gas of a conventional diesel engine with NH3 gas mixed into the engine intake. In this study, NH3 combustion processes in the diesel engine were investigated from the experimental results. Based on the investigations, a pilot or postinjection was conducted to reduce emissions of NH3 and N2O. In this paper, first the experimental results of the combustion and exhaust emission characteristics on the conventional diesel engine with NH3 gas mixed into the engine intake are shown. NH3 and N2O emissions are then verified by analyzing the exhaust gas. Next, NH3 combustion processes in the diesel engine are considered from the experimental results to report on the effects of a pilot and postdiesel fuel injection on NH3 and N2O production processes. The experimental results suggest that the multiple diesel fuel injections would be one of the effective measures to reduce N2O and NH3 emissions on NH3 and diesel dual-fueled engine.