The influence of fuel chemical properties on combustion characteristics of a RCCI (reactivity controlled compression ignition) engine was investigated using multi-dimensional simulations. The operating ranges of combustion phasing (CA50) for gasoline/diesel and methanol/diesel RCCI combustion were determined with respect to limited boundaries of fuel efficiency, RI (ringing intensity), and NOx (nitrogen oxide) emissions. The results indicated that a more retarded CA50 was necessary for methanol/diesel RCCI to avoid excessive RI due to its fast combustion rate. Because of the shortened combustion duration, reduced incomplete combustion, and lower heat transfer losses, improved fuel efficiency was achieved by methanol/diesel RCCI than gasoline/diesel RCCI. The trade-off relationship between RI and EISFC (equivalent indicated specific fuel consumption) could be defeated by increasing premixed fuel ratio (methanol or gasoline). For methanol/diesel RCCI, the more retarded CA50 was the primary reason for the higher sensitivity of CA50 to the variation of in cylinder initial temperature (T-IVC), which consequently could lead to higher cyclic variations. In addition, the weakened low temperature heat release of methanol/diesel also deteriorated the stability of CA50 with the variation of T-IVC Overall, with optimized premixed fuel ratio, RCCI combustion demonstrated more advantages in EISFC, RI, controllability, and stable operation over HCCI (homogeneous charge compression ignition) combustion for a wide load range. (C) 2016 Elsevier Ltd. All rights reserved.