## 3 Results and Discussion
### Validation of the E10 Simulations  
The reaction mechanism and fuel surrogate used during the simulations were sufficiently detailed, so there was no need to apply the combustion model's reaction rate multiplier function or to modify the turbulence parameters. The regions were initialized using experimental and 1D simulation data, which allowed a single cycle to be simulated. This contributed to a reduction in computational time. One cycle simulation took approximately 20 h. To validate the model, simulations were also performed over multiple cycles to examine the variations between them. However, thanks to the use of a first-order non-conservative solver, no significant differences were observed between the cycles. Figure 2 compares the simulation results and the test bench measurements in terms of cylinder pressure. It can be observed that the accuracy of the simulation decreases with increasing engine speed and load, as reflected in the Root Mean Square Error (RMSE). The smallest deviation occurred in the first operating point. In this case, the compression, combustion, and expansion phases matched the measured values from the test bench. The largest deviation was during the compression phase, where the pressure difference reached 2.5 bar. Two major discrepancies were observed in the second operating point--during the compression phase and the combustion process. The simulation showed slightly higher pressure at the end of the compression stroke, suggesting that the amount of air in the cylinder at the intake valve closing moment differed slightly from the actual condition. After the top dead center (TDC), when combustion had already begun, the cylinder pressure was lower in the simulation, indicating that flame propagation was slower than the measurements. The maximum pressure difference in this case was also 2.5 bar, but in the opposite direction. There were some discrepancies during the combustion and expansion phases in the third operating point. Here, the simulation overpredicted the pressure during combustion, while during expansion, the simulated pressure remained consistently lower. This operating point showed the largest pressure deviation--up to 5 bar. The fourth operating point was the least accurate. The reaction mechanism used in the simulations likely becomes less accurate under high-pressure and high-temperature conditions. This point had the highest RMSE, although the maximum pressure deviation was similar to that of the first two operating points. No clear trend was observed in terms of peak cylinder pressure or combustion progress, as the results varied across the operating points. Overall, the simulation results were sufficiently accurate in all operating points compared to the test bench measurements. The models demonstrated predictive capabilities, making them suitable for further investigations. Figure 1: Comparison of simulated cylinder pressure curves with three levels of mesh refinement in the first operating points using experimental data as reference. Figure 3 illustrates the comparison of IMEP values. It is clearly visible that the simulation closely matches the measured data, with the maximum deviation being 4%, occurring at the third operating point. However, the cylinder pressure analysis above indicated that the largest discrepancy appeared at the fourth operating point. This difference arises because the RMSE was calculated only within the evaluation range, whereas the IMEP calculation considers the entire engine cycle. A clear trend can be observed: except for the first case, the simulation slightly underpredicts the values measured on the test bench across all operating points. The main focus of this study is the investigation of pollutant emissions. As mentioned above, the emission measurements on the test bench were carried out upstream of the catalyst. However, this is not feasible within the simulation model. In the simulation, the most suitable method for evaluating emissions is to analyze the composition of the in-cylinder gases at the moment of exhaust valve opening.