Investigating various effects of reformer gas enrichment on a natural gas-fueled HCCI combustion engine

• Chemical, thermal and dilution effects of RG enrichment were investigated.
• The Multi-zone model well predicts the SOC for Natural-gas blending with RG.
• Dummy species method developed to separate the different effects of additives.
• Chemical effect has strongest impact on SOC in Natural-gas blending with RG.
• Combustion phasing was studied upon various RG compositions.

Homogenous charge compression ignition (HCCI) combustion has the potential to work with high thermal efficiency, low fuel consumption, and extremely low NOx-PM emissions. In this study, zero-dimensional single-zone and quasi-dimensional multi-zone detailed chemical kinetics models were developed to predict and control an HCCI combustion engine fueled with a natural gas and reformer gas (RG) blend. The model was validated through experiments performed with a modified single-cylinder CFR engine. Both models were able to acceptably predict combustion initiation. The result shows that the chemical and thermodynamic effects of RG blending advance the start of combustion (SOC), whereas dilution retards SOC. In addition, the chemical effect was stronger than the dilution effect, which was in turn stronger than the thermal effect. Furthermore, it was found that the strength of the chemical effect was mainly dependent on H2 content in RG. Moreover, the amount of RG and concentration of species (CO–H2) were varied across a wide range of values to investigate their effects on the combustion behavior in an HCCI engine. It was found that the H2 concentration in RG has a more significant effect on SOC at lower RG percentages in comparison with the CO concentration. However, in higher RG percentages, the CO mass concentration becomes more effective than H2 in altering SOC.