## 4 Conclusions  
This study successfully developed an accurate and predictive numerical 3D CFD model to simulate the combustion process and pollutant emissions of fuels with different ethanol contents in a turbocharged, direct-injection spark-ignition gasoline engine. The CFD simulations were conducted using the CONVERGE CFD commercial software (Version 3.1). The operating points investigated were defined based on RDE measurements. The four most common operating conditions were selected for numerical analysis, with each operating point having different engine speeds and loads. The simulations can be divided into three sets. The results of the first set are not presented here, as their sole purpose was to refine the oxygen content in the cylinder using 1D simulation data to determine the injection quantity as accurately as possible. The second set of simulations was validated using E10 fuel against test bench measurements, and assuming the predictive capability of the models, simulation models were then built for E20 fuel. The only differences between the E10 and E20 simulations were the fuel composition and the injected quantity, in order to maintain the same lambda value despite the different AFR. For combustion modeling, the SAGE detailed chemistry model was used, which included a reaction mechanism with 201 species and 1013 reactions; thanks to the four-component ETRF fuel surrogate, no tuning was necessary. For turbulence modeling, the RNG k-epsilon turbulence model was employed, which also required no tuning. After conducting a mesh sensitivity analysis, the E10 simulations were compared with the test bench measurements. When comparing cylinder pressures, the smallest deviation in the studied range was 0.35 RMSE, while the most significant deviation reached 1.43. From the perspective of the combustion process, the simulations closely matched the cylinder pressure measurements from the test bench across all operating points. This statement similarly applies to IMEP as well. In terms of pollutant emissions, the results were mixed. The simulations significantly underpredicted HC emissions at all operating points, likely due to the level of detail in the reaction mechanism. Conversely, CO emissions were overpredicted, which is logical given  
Figure 15: Comparison of simulated NOx emissions with E10 and E20 fuel. the close relationship between HC and CO. For CO\({}_{2}\) and NOx emissions, the simulations approximated the test bench values satisfactorily, with the magnitude of NOx deviation correlating with differences in cylinder pressure during combustion. Assuming the predictive nature of the model, the E20 simulations were analyzed by adjusting the fuel composition and injection quantity based on the validated E10 simulations. Overall, it was found that at lower speeds and loads, engine performance with E20 was slightly lower than with E10; however, as speed and load increased, this trend reversed. Regarding emissions, HC emissions increased slightly, while CO emissions increased more significantly. This can be explained by the lower AFR of E20, requiring a higher amount of fuel to maintain the same lambda, which was not offset by E20's higher combustion efficiency. NOx emissions slightly decreased due to the faster combustion process and lower combustion temperatures. CO\({}_{2}\) emissions also decreased in all operating points, similar to NOx, thanks to the lower carbon content of E20. Conceptualization, B.Z. ; methodology, B.Z. ; investigation, B.Z. ; writing--original draft preparation, B.Z. ; writing--review and editing, A.L.N. and M.Z. All authors have read and agreed to the published version of the manuscript. This article is published in the framework of the project \"Synthetic fuels production and validation in cooperation between industry and university\", project number \"EZFF/956/2022-26 ITM_SZREZ\". Not applicable. Data Availability Statement: Data for the study are available upon request from the corresponding author. The authors declare no conflicts of interest.