In the present study, water electrolysis was employed for Hydroxy gas (HHO) production as a gaseous additive. The engine test was performed using the Diesel, B5, and B20 as pilot fuels. HHO was imported into the engine's combustion chamber at three volumetric flow rates of 3, 4, and 5 cc/s through the inlet manifold as the low-level HHO rate.The engine test setup was a single-cylinder dual-fueled diesel engine at a constant speed (1500 rpm) and full load condition. According to the results, HHO by 3 and 4 cc/s did not have a significant effect on BP, BTE, and BSFC. Using HHO gas by 5 cc/s significantly increased BP by about 2.5, 3.1, and 0.5% compared with Diesel, B5 and B20, respectively, and decreased BSFC by about 11, 7.8, and 13.5% compared with Diesel, B5, and B20, respectively.HHO gas by 5 cc/s significantly decreased CO2 by about 7, 6.3, and 10.6% compared with Diesel, B5, and B20, respectively, and decreased CO emissions by about 6, 14.3, and 21.2% compared with Diesel, B5 and B20, respectively. However, the use of HHO gas and biodiesel increased NOx emission by about 16, 13.7, and 10.5% compared with Diesel, B5, and B20, respectively.