An experimental and numerical study of the effects of reformer gas (H2 and CO) enrichment on the natural gas homogeneous charge compression ignition (HCCI) engine

Different approaches have been proposed to improve the combustion process and decrease pollutants in internal combustion engines. Among them, more attention has been paid to the use of the homogeneous charge compression ignition (HCCI) concept. The benefits of this combustion concept are the simultaneous reduction of fuel consumption, nitrogen oxides (NOx) and soot emission together with thermal efficiency improvement. However, there are still tough challenges in the successful operating of HCCI engines, such as controlling the combustion phasing, extending the operating rang, and high unburned hydrocarbon and CO emissions. In this study, experimental work were performed on a single cylinder engine and the simulation results were compared to the experimental data. The comparison showed the numerical data had a good agreement with experimental data. By increasing the ratio of reformer gas, the maximum pressure and maximum pressure rise rate are significantly increased. Keeping the air-fuel ratio constant and increasing the ratio of the reformer gas reduce the IMEP and heat efficiency, also increasing reformer gas blend fraction decreased HC and increased CO emissions considerably. In addition, using reformer gas expands the operating range lean limit and increases the possibility of engine well operation in this region.