Using an ejector as an additional component in a vapor compression refrigeration system is a promising way to increase the system efficiency. The efficiency increase of the refrigeration system depends strongly on the ejector. Using CFD simulations, it is possible to obtain a better understanding of two-phase CO2 ejectors in order to design more efficient ejectors. In this work, a numerical model based on a homogeneous equilibrium approach, which is implemented in OpenFOAM, is used to simulate the CO2 ejector. The numerical investigation of an ejector operated with and without a suction mass flow is presented and the numerical results are compared to experimental data published in previous works to validate the simulations. If the ejector is operated without a suction flow, no mixing losses occur and the friction losses are one of the main losses affecting the flow. Thus, this operating condition is suitable to validate if the friction losses are determined correctly by the numerical model. Afterwards, an ejector which is operated with a suction flow is simulated in order to validate the accurate prediction of the mixing losses by the numerical model. In the presented data range, the numerical model predicts the driving mass flux within an error margin of 10%. The pressure recovery of the ejector operated without a suction flow is determined with an error of 10%. This error increases to 20% when the ejector is operated with a suction flow.