In this study, a diesel engine was operated both in dual fuel mode and with nanoparticle additives. The aim is to experimentally investigate the effect of both carbon nanotube additives and the addition of hydrogen/natural gas mixture to the combustion air in a compression ignition engine. 100%NG, 10%H2 + 90%NG, and 20%H2 + 80%NG gas mixtures were added to the diesel with and without CNT additives at a mass flow rate of 250 g/h using combustion air. 50 ppm nanoparticles were added to one liter of liquid fuel and mixed with an ultrasonic mixer to form a diesel fuel-CNT mixture. Engine tests were carried out at constant speed and four different engine loads and no-load conditions. Under all load conditions, in-cylinder pressure, brake specific fuel consumption, brake thermal efficiency, and exhaust emissions were investigated. Based on the experimental results, the combustion of CNT-added diesel fuel with gaseous fuels has made significant contributions to the basic engine performance parameters. The diesel with CNT additive reached a cylinder pressure of approximately 64 bar, while the D@50ppm + NG@90%+H2@10% mixture provided a 2% increase in in-cylinder pressure compared to diesel fuel. The D@50ppm + NG@90%+H2@10% also offered the highest value among all fuel alternatives with a brake thermal efficiency of 39% at full load, resulting in 9% more efficient than diesel fuel. Gas mixtures with CNT additives effectively reduced CO and HC emissions compared to other mixtures except for diesel and D@50ppm.