The purpose of this work is to investigate syngas composition (of constituents H2, CO, and CO2) and compression ratio (CR) effects on the combustion and emissions characteristics of a syngas-fueled homogenous charge compression ignition (HCCI) engine, which operates in very lean air–fuel mixture conditions for power plant usage. Investigations were conducted using ansys forte cfd package at low (3 bar indicated mean effective pressure (IMEP)) and medium (5 bar IMEP) loads, and the calculated results were compared with the Aceves et al.’s multi-zone HCCI model, using the same chemical kinetics set (Gas Research Institute (GRI)-Mech3.0). All calculations were carried out at maximum brake torque (MBT) conditions by sweeping the air–fuel mixture temperature at intake valve closing (IVC) (TIVC).This study found out that the H2 consumption rate is slightly high in a low-temperature range in the early period of combustion while the CO consumption rate is high in a high-temperature range in the later period of combustion. The results reveal that the change of H2 /CO ratio and inert gas volume fraction according to fuel composition affects combustion, but the TIVC is the dominant factor affecting combustion phasing at MBT conditions. For each fuel and load condition, the TIVC was significantly reduced with the increase of CR (17.1–22.3) to get MBT conditions, which causes to retard combustion phasing and lowers in-cylinder peak temperature. The oxides of nitrogen (NOx) emissions reduced with increasing the CR due to the lowering of the in-cylinder peak temperature.