In this paper, the combustion, performance and emission characteristics of a single cylinder diesel engine was investigated using two combustion chamber geometries such as toroidal combustion chamber and standard piston combustion chamber in a 5.2 kW single cylinder diesel engine. The experiments were carried out at an ambient temperature of 30 ± 2 °C. The performance was observed at no load 20, 40, 60, and 80%, and full load operating conditions. The results showed that the GOME 25 operated with toroidal combustion chamber has improved combustion, performance, and emission characteristics when compared to standard piston combustion chamber. The GOME 25 has improved brake thermal efficiency by about 23, 13.6, 10.6, 9.9, and 10.9% when compared to standard piston combustion chamber operated with diesel at no load, 20, 40, 60, 80, and 100% loading conditions, respectively. The smoke density and CO were reduced by about 14.8% and 38%, respectively. The NOx emission operated with GOME 25 using toroidal combustion chamber was increased by about 36% when compared to standard piston combustion chamber with diesel. The heat release rate of GOME 25 with toroidal combustion chamber was observed to be better when compared to diesel with standard piston combustion chamber. The results con-firmed that toroidal combustion chamber piston is a good option for the use of GOME 25 blend.