## 3 Results  
The effect of WiGE on the engine performance was investigated through the in-cylinder pressure analysis. As aforementioned and further discussed in the following, with reference to the TIT results, the gasoline case at stoichiometric A/F mixture, and SA = \(-10\) CAD ATDC is missing because it is not feasible with the maximum TIT target. Figure 2 shows a comparison between the gasoline and WIGE in-cylinder pressure traces at the reference engine operating condition (\(\lambda\) = 0.9, SA = \(-10\) CAD ATDC). As aforementioned, this condition is representative of commercial ECU map and the spark timing under rich air/fuel mixture corresponds to the gasoline knock limit. When switching to WiGE, the injection duration and the plenum pressure were adjusted to keep the A/F ratio and IMEP load constant. The first effect of WiGE is the charge cooling, due to the evaporation of water droplets; moreover, the water in the combustion chamber acts as an inert during the combustion process; this causes a slowdown of the rate of energy release with a reduction in the pressure peak proportional to the water content. Figure 3 shows the relationship between water content and combustion duration and phasing, at different spark timings and relative A/F ratios and WiGEs, considering a representative engine cylinder (Cyl #2). For each spark timing sweep, a clear indication of knock-limit (KL) point is depicted in Figure 3a. This indication of KL points extends to the other figures proposed below. In agreement with the pressure traces shown in Figure 2, at SA = \(-10\) CAD ATDC and \(\lambda\) = 0.9, the use of WiGE prolongs the combustion duration (Figure 3a) and delays the combustion phasing (Figure 3b). On the other hand, proportionally to the water content, the cooling and dilution effects of WiGE on the in-cylinder charge mitigate the knock tendency and allow us to advance the spark timing up to \(-13\) and \(-16\) CAD ATDC (for WiGE 10 and WiGE 20, respectively); consequently, also the combustion center is advanced with respect to gasoline reference case. At stoichiometric condition, the knock-limited spark timing can be further advanced with the result of a better combustion phasing (MFB50 = 12.4 CAD ATDC @ SA = \(-19\) for WiGE20). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Fuel** & \(\lambda\) [\(\pm\)**0.01**] & **ST [cad atdc]** & **DOI [cad]** & \(\mathbf{P_{INT}}\) [bar]** \\ \hline
**WiGE 10** & \(1.00\) & \(-11\) & \(213\) & \(1.77\) \\ \hline
**WiGE 10** & \(1.00\) & \(-12\) & \(210\) & \(1.75\) \\ \hline
**WiGE 10** & \(1.00\) & \(-13\) & \(208\) & \(1.73\) \\ \hline
**WiGE 10** & \(1.00\) & \(-14\) & \(206\) & \(1.76\) \\ \hline
**WiGE 20** & \(0.90\) & \(-10\) & \(255\) & \(1.70\) \\ \hline
**WiGE 20** & \(0.90\) & \(-12\) & \(255\) & \(1.70\) \\ \hline
**WiGE 20** & \(0.90\) & \(-14\) & \(255\) & \(1.70\) \\ \hline
**WiGE 20** & \(0.90\) & \(-16\) & \(255\) & \(1.70\) \\ \hline
**WiGE 20** & \(1.00\) & \(-10\) & \(250\) & \(1.84\) \\ \hline
**WiGE 20** & \(1.00\) & \(-12\) & \(243\) & \(1.81\) \\ \hline
**WiGE 20** & \(1.00\) & \(-14\) & \(235\) & \(1.78\) \\ \hline
**WiGE 20** & \(1.00\) & \(-16\) & \(230\) & \(1.74\) \\ \hline
**WiGE20** & \(1.00\) & \(-19\) & \(225\) & \(1.72\) \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._Figure 4 shows the trend of TIT against spark timing and relative air-to-fuel ratio. As shown, at a reference spark timing of \(-10\) CAD ATDC, the turbine inlet temperature is almost the same for gasoline and WiGE in rich mixture condition. Of course, the rich A/F mixture at the reference point was selected in the manufacturer calibration to avoid, with a certain safety margin, the knock onset and the excessive thermal stress to the turbine. On the other hand, in the case of the engine mounted on the test bench, a lower heat transfer can be realized for the turbine compared to the case of an engine on the real vehicle.