## 4 Results and Discussion
### Reliability Assessment of Heat Transfer Models  
As mentioned earlier, the effect of different heat transfer correlations is studied, including Anand, Hohenberg, Woschni, and the proposed heat transfer model developed for uniflow scavenged two-stroke engines. This study uses the information from the experimentally validated model at 2250 rpm with a Config-1 exhaust manifold. All the heat transfer correlations are validated for the same initial conditions at the exhaust port opening, as depicted in Figure 4.  
The information in Figure 4 shows that the fluid behavior for all heat transfer correlations, compared to CFD, is similar. These include the peaks and trends in the intake mass flow rate-Figure 4A, exhaust mass flow rate-Figure 4B, pressure in the cylinder-Figure 4C, and pressure in the exhaust manifold-Figure 4D during the scavenging process. At the same time, comparing results with the 1D model, Figure 4C not only shows the information of the 1D model to CFD comparison but also provides the information with experimental in-cylinder pressure traces. This validates the 1D model compared to experimental results and the CFD simulation predictability of experimental results. The study focuses on the effect due to heat transfer in predicting the in-cylinder temperature. For such studies, not only are the fluid parameters, such as pressure and mass flows in the intake and exhaust, needed for validation, but also the thermal parameter needs to be equal. For this reason, the temperature values at the exhaust port opening need to be identical to those observed in CFD simulations. This was achieved by calibrating the correction coefficient of each correlation. Maintaining identical initial conditions in in-cylinder pressure and temperature ensured that the trapped mass at the exhaust port opening would be constant. The information on similar thermal boundary conditions and trapped mass is provided in Figure 5.  
Figure 3: (**A**): Mass flow rate at intake and exhaust pipes, (**B**): Average mass flow rate, (**C**): Convective heat transfer for proposed and Woschni models, (**D**): Actual convective heat transfer of overall cycle. Figure 4: 1D model to CFD comparison for different heat transfer coefficients. **(A)**: Intake mass flow rate, **(B)**: Exhaust mass flow rate, **(C)**: In-cylinder pressure during scavenging process, **(D)**: Exhaust manifold pressure. Figure 5: 1D model vs. CFD comparison of **(A)**: Heat transfer coefficient (**B**): Temperature, **(C)**: In-cylinder trapped mass, **(D)**: Experimental vs. 1D simulation results comparison for logarithm pressure vs. Volume evolution. Figure 5A provides information on the heat transfer coefficient used in this study during the scavenging process. A solid black line depicting the instantaneous heat transfer coefficient from CFD simulation is depicted in Figure 5A. It can be seen from Figure 5A that the methodology followed in developing the proposed heat transfer provides similar peaks and follows trends as in CFD simulations during scavenging. On the other hand, the state-of-the-art heat transfer correlations fail to provide the necessary heat transfer coefficient during the same process. Figure 5B provides the information with temperature traces achieved due to the adjusted heat transfer coefficient. Figure 5C depicts the information on the trapped mass inside the cylinder during scavenging. Figure 5B,C show CFD results plotted with a solid black line, showing the temperature and trapped mass, respectively, which are the same as in the 1D model at the opening of the exhaust ports. Figure 5D provides information (in logarithmic scales) related to evolution inside the combustion chamber for the 1D model and experimental data. Figure 5D results justify that the combustion settings used in the modeling stage provide accurate results. Observing the trends and patterns from Figures 4 and 5, it can be justified that comparing different heat transfer models is viable as all models have similar behavior.