A modified multi zone model (MMZM) is developed for RCCI engines simulation. The CFD model is used to predict the evaporated n-heptane stratification to introduce as input to the MMZM to predict the SOC (start of combustion) and CA50 with sufficient accuracy. In the next step, a physic-base model is developed for SOC prediction and parameterized with 70 multi-zone results and validated using the same results and extra 25 experimental data. The model prediction average error for 95 steady-state operating conditions is below 1.2 CAD. Also, a modified fuel burn rate model is developed for predicting 50% of fuel mass burn and burn duration. Predicted results are in good agreement with all multi-zone results and operating conditions in prediction of both CA50 and burn duration. The MMZM can predict CA50 and burn duration with acceptable accuracy as the average error are about 1 CAD and 1.2 CAD.