Homogeneous Charge Compression Ignition (HCCI) Engine Fueled With Natural Gas for Stationary Power Generation Applications

In this study, a single-cylinder HCCI engine was used to study the technical feasibility of HCCI engines for stationary power generation applications. The compression ratio (CR) of the engine was set at 13.8:1 considering a hybrid system with diesel micro-pilot injection. The engine was operated under various loads at a rated speed of 1800 rpm. Intake manifold temperature of the air/fuel mixture was used to control the start of combustion (SOC) of the HCCI engine. Oil and coolant temperatures were set at 100°C. Location of peak in-cylinder pressure (PPL) was maintained within 6∼9°ATDC in order to obtain maximum thermal efficiency by initiating the SOC between 2∼4°BTDC. Intake boost was increased up to 2.5 bar absolute to increase engine power output. Results of the HCCI combustion were also compared with those of diesel and diesel micro-pilot natural gas combustion. The results showed that the required intake temperature ranged from 149°C to 261°C depending on engine loads. The highest net mean effective pressure (NMEP) was about 10.6 bar. Higher intake boost pressure would increase NMEP even higher. Maximum indicated thermal efficiency (ITE) was about 49% at the excess air ratio (λ) of 3.2 and maximum combustion efficiency was about 94% at λ = 2.6. Oxides of nitrogen (NOx) emissions were below 10 ppm when λ was above 3. At these excess air ratios, in the good HCCI operating regimes, carbon monoxide (CO), total hydrocarbons (THC), and methane (CH₄) were equivalent to those of conventional natural gas engines.