In this study, performance and combustion characteristics of biogas and biogas+hydrogen mixtures were experimentally analysed and compared with baseline diesel fuel in a common-rail diesel engine with and without thermal barrier coated piston. Tests were conducted at three different loads (50 Nm, 75 Nm, and 100 Nm) and a constant speed of 1750 min-1. Engine pistons were coated with Yttria Stabilized Zirconia by atmospheric plasma spray method. Results showed that by replacing the standard pistons with the coated pistons, an increase for diesel, biogas, and hydrogen enriched biogas was respectively defined by 8.1%, 6%, and 23% in cylinder pressure, and 19.8%, 12.6%, and 25% in HRR at medium load. Similarly, there was an increase in range of 1.05-12.8% in gas temperature and 20.5-117.2% in knock intensity by the piston coating. CA10-90 was prolonged between 1-15 oCA with gaseous fuel modes and increased with the engine load. Volumetric efficiency was reduced by 0.1-4% with the gaseous fuel operations, while it was increased by using the coated piston for all fuels. Exhaust gas temperature increased with the gaseous fuels whereas showed discrepancies with the coated piston engine. Dual-fuel mode and coated pis-ton application caused brake specific energy consumption to increase significantly.