The Reactivity Controlled Compression Ignition (RCCI) is a promising dual-fuel Low Temperature Combustion (LTC) strategy that provides a precise means for controlling the heat release rate and combustion phasing. Optimum RCCI engine operation depends cm optimum selection of fuel injection parameters. In this study, a detailed 3D/Computational Fluid Dynamics (CFD) combustion model in CONVERGE CFD code is developed and validated against experimental data at different engine operating conditions. Next, the effects of fuel injection parameters on the performance and emissions characteristics of an RCCI engine are analyzed. The fuel injection parameters include spray angle, injection pressure, Start of Injection (SOI) timing, and Premixed Ratio (PR). The baseline simulation results show that a proper selection of spray angle can cause significant reduction in HC and CO emissions, while improving combustion and gross indicated efficiencies. Furthermore, decreasing injection pressure and PR along with advancing SOI timing can improve the RCCI engine's HC and CO emissions productions. The developed CFD model is then used in an extensive computational study to determine optimum fuel injection parameters for the best RCCI engine performance. The optimization results show that spray angle 55, SOI = -53 degrees aTDC, 580 bar injection pressure, and PR = 0.76 provide the best combination of four major fuel injection parameters for the speed and load conditions studied. By choosing this set of parameters, HC and CO emissions decrease by 23% and 39% from the baseline condition while a notable improvement is observed in gross indicated and combustion efficiencies. (C) 2015 Elsevier Ltd. All rights reserved.