PERFORMANCE EVALUATION OF A GAS ENGINE OPERATING ON HIGH-CO₂ NATURAL GAS AT LATE INJECTION TIMING

The increasing energy demand in the transportation sector and the depletion of conventional fossil fuel reserves necessitate the exploration of alternative fuel sources. Malaysia holds significant untapped natural gas reserves with high carbon dioxide (CO₂) content, which has historically been considered unsuitable for commercial use due to economic and technical challenges associated with CO₂ removal. This study investigates the feasibility of utilizing highCO₂ natural gas directly in internal combustion (IC) engines and its effects on engine performance. A single-cylinder, four-stroke, direct-injection compressed natural gas (DI-CNG) engine was used to evaluate the impact of CO₂ addition on key performance parameters, including brake torque, brake power, brake specific fuel consumption (BSFC), and brake thermal efficiency (BTE). Experiments were conducted at a late injection timing of 120° crank angle before top dead center (BTDC) and an engine speed of 2100 rpm, with CO₂ proportions ranging from 0% to 40% by volume. The results demonstrated that moderate CO₂ additions (up to 20%) improved BTE and reduced BSFC due to enhanced combustion control and lean-burn stability. However, higher CO₂ proportions (>20%) led to significant reductions in brake torque and brake power, attributed to dilution effects and reduced calorific value. The findings suggest that controlled CO₂ inclusion in CNG can optimize combustion and emissions, offering a potential pathway for utilizing Malaysia’s undeveloped natural gas reserves.