In this study, diesel fuel and diesel fuel + hydrogen mixtures were used as fuel in a diesel engine, which was single cylinder, four strokes, and with air cooled. Hydrogen was admitted to the engine's intake manifold at determined rates of 5, 10, 15, and 20%. The experiment was conducted at full load conditions and the results were compared for both operations. In the results of the experiments, it was seen that adding the hydrogen to a diesel engine made the engine volumetric production bad. For this reason, it is not suitable to use hydrogen in diesel engines as a fuel addition.