Application of dynamic φ-T map: Analysis on a natural gas/diesel fueled RCCI engine

In this study, dynamic φ-T map analysis was applied to an RCCI (reactivity controlled compression ignition) engine fueled with NG (natural gas) and diesel. The combustion process of the engine was simulated by coupled KIVA4-CHEMKIN with a DOS (diesel oil surrogate) chemical mechanism. The φ-T maps were constructed by the mole fractions of soot and NO obtained from SENKIN and φ-T conditions from engine simulations. Five parameters, namely NG fraction, 1st SOI (start of injection) timing, 2nd SOI timing, 2nd injection duration and EGR (exhaust gas recirculation) rate were varied in certain ranges individually, and the φ-T maps were compared and analyzed under various conditions. The results revealed how the five parameters would shift the φ-T conditions and influence the soot-NO contour. Among the factors, EGR rate could limit the highest temperature due to its dilute effect, hence maintaining RCCI combustion within LTC (low temperature combustion) region. The second significant parameter is the premixed NG fraction. It could set the lowest temperature; moreover, the tendency of soot formation can be mitigated due to the lessened fuel impingement and the absence of C-C bond. Finally, the region of RCCI combustion was added to the commonly known φ-T map diagram.