The main feature of RCCI is the significant reduction of nitrogen oxides and soot pollutants as efficiency and fuel consumption decrease. The aim of this study was to investigate the effects of the start of diesel fuel injection and injection pressure and two stage fuel injection strategies on RCCI combustion. The engine under investigation is a single cylinder engine with diesel fuel injection as high-reactivity fuel directly into the cylinder and natural gas fuel injection as low-reactivity fuel at the intake manifold. The start of injection, injection shape, and injection length in both injectors are controlled by the developed ECU. All tests were performed at an inlet air temperature of 37 ° C and the inlet pressure of 87kPa and 1800rpm. The results of this study show that by increasing diesel fuel injection pressure from 300 to 600 bar, at the 55 °BTDC start of injection, the ignition starts 2.5 degrees earlier and the in-cylinder maximum pressure and HRR increase by 0.66% and 2.68%, respectively. By delaying the start of diesel fuel injection by 6 degrees, we see a 12.37 % reduction in maximum in-cylinder pressure, and the start of ignition is delayed to 5 degrees. Increasing the spray pressure of diesel fuel increases NOx by 154 % and decreases UHC and CO by 32 and 57%, respectively. Increasing the diesel injection pressure increases NOx by 154 % and decreases UHC and CO by 32 and 57 %, respectively. On the other hand, the results of the two-stage injection of diesel fuel show that by postponing the first start of injection, the in-cylinder maximum pressure, HRR, IMEP, and NOx emission increase and UHC and CO decrease. Also, by postponing the second start of injection, the in-cylinder maximum pressure, HRR, IMEP and NOx emissions are reduce,d while UHC and CO increase.