## 3 Results and Discussion
### Comparison of the E10 and E20 Simulations  
The E10 simulations showed good correlation with the test bench measurements, and no tuning of the physical models was necessary. This indicates that the model is likely predictive. In the E20 simulations, only the fuel composition and the injected fuel quantity were modified. Due to the differences in air-fuel ratio (AFR) requirements between the fuels, it was necessary to increase the injected amount to maintain the same value of lambda. The simulation strategy remained the same: boundary and initial conditions were provided by 1D simulation data, and a single cycle was analyzed. Figure 8 shows the comparison of cylinder pressures between the two fuels. It can be observed that no significant pressure differences developed between the fuels. There is no clear trend in the maximum cylinder pressure values; the changes vary in direction regardless of engine speed or load. In OP1 and OP4, the E20 fuel results in slightly higher maximum cylinder pressure, despite E20 having a smaller lower heating value (LHV). This can be attributed to ethanol's higher combustion efficiency and faster flame speed, which compensate for the lower energy content. The largest pressure difference occurs at OP3, reaching nearly 2 bar. Figure 9 illustrates the temperature field distribution in a side-view cross-section of the cylinder for both E10 and E20 fuels, at the time of ignition and at various crank angle degrees after ignition, across all four operating points. In OP1, it can be observed that at every examined time point, the flame front is smaller for E20 fuel. At 30\({}^{\circ}\) after ignition (AIGN 30), the flame sizes are similar, but the temperature is lower for E20. No significant differences can be seen in flame propagation within the observed crank angle range in the second operating point. However, it is clearly visible that 30\({}^{\circ}\) after ignition, the core flame temperature is lower for E20. In the third operating point, E20 shows slightly higher flame propagation speed and core flame temperature, but no substantial differences are observed at this point either. In the fourth operating point, the flame propagation speed is also slightly higher with E20. Figure 10 illustrates the IMEP values for E10 and E20 across the four investigated operating points. It can be seen that at lower engine speeds and loads, the difference between the fuels is negligible. However, as the load increases, IMEP rises in favor of E20, due to the improved combustion efficiency. The largest deviation occurs at OP4. Figure 7: Comparison of simulated NO\({}_{\text{X}}\) emissions against experimental data with E10 fuel. Figure 8: Comparison of simulated E10-fueled cylinder pressure against simulated E20-fueled cylinder pressure at operating point 1 (**a**), operating point 2 (**b**), operating point 3 (**c**), and operating point 4 (**d**); dashed line represents difference between experimental and numerical values. Figure 9: Comparison of flame propagation between E10-fueled and E20-fueled simulations. To further investigate the combustion process, examining the mass fraction burned (MFB) curve is useful--specifically, the duration between the 10% and 90% points. Figure 11 shows the MFB10-90 duration. A similar trend can be observed with IMEP. At lower speeds and loads, combustion takes longer with E20. However, due to the higher ethanol content, the combustion process becomes shorter at higher speeds and loads. Despite the fact that the simulation overpredicted CO emissions and underpredicted HC emissions, it is still worthwhile analyzing how the emission components change with different fuels. Figure 12 presents the HC emissions for both fuels across the examined operating points. Except for the low-load operating point, HC emissions are consistently higher when using E20. This contradicts several studies, but the lower AFR of the E20 fuel can explain it. To maintain the same lambda value, a larger fuel mass must be injected.