To reduce toxic engine emissions and meet the strict regulations, split injection has been adopted to optimize engine performance and fast-idle has been selected as the researching condition. Two sets of experiments have been conducted to investigate the effect of split injection on particulate number (PN) emissions at fast-idle. The first set is conducted in a constant volume vessel to get detailed spray characteristics, while the second is conducted in engine bench analyzing the effect of split injection on real engine PN emissions. Establishing direct connection from spray characteristics and real engine PN emissions is the main objective of this paper. Higher ambient temperature can reduce spray angle, while spray tip penetration is insensitive to experimental parameters. Long injection pulse width combined with short height of damper (HOD) will increase the possibility to impingement. Total PN concentration of four injection modes all decreases at first and then increases with increasing coolant temperature, and split injection can obviously reduce total PN to 50% from single injection. With increasing coolant temperature, accumulation mode particles all decrease while nucleation mode particles show different trends under four injection modes. In addition, the last injection within split injection has obvious influence on PN emissions. (C) 2018 Elsevier Ltd. All rights reserved.