## 4 Results and Discussion
### Reliability Assessment of Heat Transfer Models
On observing the instantaneous temperature traces in the zoomed area 'a' in Figure 5B, it can be seen that the classical heat transfer correlations based on the Reynolds number calculated with the mean piston speed predict higher temperature during scavenging compared with CFD results. Due to the lack of temperature predictability during scavenging, the state-of-the-art correlations also fail to reproduce the trapped mass in the cylinder while comparing results with CFD, as shown in Figure 5C when the exhaust ports close (around 255 CAD). On the other hand, the proposed heat transfer model developed considering the pseudo-velocity inside the cylinder accurately captures the temperature and trapped mass calculated by CFD. To quantify the results for trapped mass and temperature, readings for the same are captured at specific moments and presented in Table 4. The four instances are: at the exhaust port opening (130 CAD), intermediate positions (170 and 210 CAD), and finally, at the exhaust port closing (255 CAD). Moreover, since [PERSON], [PERSON], and [PERSON]'s heat transfer coefficients provide similar outputs, only results from [PERSON] are used for further comparisons. Using Equations (18) and (19), differences in CFD and 1D modeling results are provided in Table 4 for in-cylinder trapped mass and temperature, respectively. \[Error(\%)=\left(\frac{CFD-Model}{CFD}\right)\times 100, \tag{18}\]  
\[Error(^{\text{o}}\text{C})=CFD-Model. \tag{19}\] \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Crank** \\ **Angle** [\({}^{\text{o}}\)] \\ \end{tabular} } & \multicolumn{2}{c}{**Trapped Mass**} & \multicolumn{3}{c}{**Temperature**} \\  & & **[g]** & & & [\({}^{\text{o}}\)C] & \\ \hline \multirow{3}{*}{130} & \multirow{3}{*}{**CFD**} & **Proposed** & **Woschni** & \multirow{3}{*}{**CFD**} & **Proposed** & **[PERSON]** \\  & & **(Error \%)** & **(Error \%)** & & **(Error \({}^{\text{o}}\)C)** & **(Error \({}^{\text{o}}\)C)** \\ \hline \multirow{3}{*}{130} & \multirow{3}{*}{0.39} & 0.39 & 0.39 & \multirow{3}{*}{\(1015\)} & \multirow{3}{*}{\(1024\)} & \multirow{3}{*}{\(1000\)} \\  & & (0) & (0) & & (\(-9\)) & (\(15\)) \\ \hline \multirow{3}{*}{170} & \multirow{3}{*}{0.37} & 0.38 & 0.36 & \multirow{3}{*}{\(519\)} & \multirow{3}{*}{\(511\)} & \multirow{3}{*}{\(564\)} \\  & & (\(-2.7\)) & (2.7) & & (\(7\)) & (\(-46\)) \\ \hline \multirow{3}{*}{210} & \multirow{3}{*}{0.65} & 0.65 & 0.60 & \multirow{3}{*}{\(246\)} & \multirow{3}{*}{\(255\)} & \multirow{3}{*}{\(319\)} \\  & & (0) & (7.69) & & (\(-9\)) & (\(-73\)) \\ \hline \multirow{3}{*}{255} & \multirow{3}{*}{0.48} & 0.47 & 0.42 & \multirow{3}{*}{\(12.5\)} & \multirow{3}{*}{\(201\)} & \multirow{3}{*}{\(226\)} & \multirow{3}{*}{\(285\)} \\  & & (2.08) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of CFD vs. 1D modeling results of different correlations at 130, 170, 210, and 255 CAD for in-cylinder mass and temperature. Since the initial conditions at the exhaust port opening for CFD and heat transfer models are very similar, no significant differences are found in either trapped mass or temperature. At 170 CAD, the proposed and Woschni heat transfer correlations show a trapped mass of 0.38 and 0.36 g, respectively. These results are almost the same, as CFD simulations depict a trapped mass of 0.37 g. Contrarily, the temperature predictions using the Woschni correlation show an absolute deviation of 46 \({}^{\circ}\)C. This deviation in temperature is due to the lower convective heat transfer coefficient, which according to the calculation, provides 230 \(\frac{W}{m^{2}K}\). On the other hand, the proposed heat transfer correlation calculation provides a convective coefficient of approximately 800 \(\frac{W}{m^{2}K}\).