## 3 Results
Based on this consideration, even if the allowable maximum TIT is 950 \({}^{\circ}\)C, a target of 819 \({}^{\circ}\)C, which is representative of the gasoline reference condition, was set for WiGE. In light of the above discussion, the criterion followed for the engine tests is the identification of knock-limited operations with WiGE and stoichiometric mixture realizing a TIT level equal or lower to the one achieved at the reference ECU condition and a lower ISFC. By increasing the spark advance, the earlier combustion phasing allowed by WiGE results in a significant reduction in the turbine inlet temperature, because the temperature of the in-cylinder gases is lower at the opening of the exhaust valves if the combustion takes place early in the engine cycle. The use of WiGE10 does not allow us to reach the TIT target at stoichiometric condition (TIT = 827 \({}^{\circ}\)C at knock limit; SA = \(-14\) CAD ATDC), while WiGE20 resulted in a lower TIT than gasoline reference case at the two most advanced spark timing: 818 \({}^{\circ}\)C at SA = \(-16\) CAD ATDC, and 804 \({}^{\circ}\)C at SA = \(-19\) CAD ATDC. The Indicated Specific Fuel Consumption (ISFC) for all the investigated WiGE fuels, spark timings and relative air-to-fuel ratio is shown in Figure 5. It is worth pointing out that fuel consumption is estimated by considering only the gasoline content of WiGEs, as the water is inert. As expected, introducing water in combustion chamber prolongs the combustion duration with a worsening in efficiency. Hence, at fixed spark timing (\(-10\) CAD ATDC) and at the same air/fuel ratio (\(\lambda\) = 0.9), fuel consumption associated to WiGE is higher than the one measured in the reference condition. When leaning WIGE/air mixture the fuel efficiency is improved. On the other hand, this improvement is not large enough to eliminate the gap with gasoline reference case. Therefore, at fixed spark timing (\(-10\) CAD ATDC), the WiGE fuel consumption at stoichiometric condition is still higher than the one measured for gasoline at rich condition (\(\lambda\) = 0.9). Figure 2: In-cylinder pressure trace and rate of heat release at SA = \(-10\) CAD ATDC, \(\lambda\) = 0.9. Thus, to achieve the same IMEP as the reference case, it is necessary to inject a higher amount of gasoline. Higher consumption is measured for WiGE20 compared to WiGE10. This behavior is probably ascribed to the water-induced lengthening of combustion process. A decreasing trend of ISFC with advancing the spark timing is observed for both air-to-fuel ratios and both emulsions. At \(\lambda\) = 0.9 and reference spark timing (SA = \(-\)10 CAD ATDC), WiGE employment induces a worsening in the ISFC values compared to gasoline reference condition, due to combustion duration extension induced by water. On the other hand, the improved knock resistance related to water presence allows us to optimize the combustion phasing. The discussed water effects are mutually conflicting for the engine efficiency, and ultimately the ISFC level of KL points (for WiGE 10 and 20) under the rich A/F mixture never reaches the one attained by the ECU-reference rich gasoline case. At engine operation under stoichiometric A/F mixture, the combined effect of WiGE knock mitigation and the leaner mixture allows for an ISFC reduction of about the 3.7% and 7.1% compared to ECU-reference gasoline point at rich mixture condition, for WiGE 10 and WiGE 20, respectively. Figure 4: Turbine inlet temperature against spark timing and relative air-to-fuel ratio. Figure 3: Combustion duration (2 xMFB10-50) (**a**) and combustion center (MFB50) (**b**) against spark timing and relative air-to-fuel ratio for WiGE 10 and WiGE 20. Figure 6 shows the correlation between the CO and CO\({}_{2}\) exhaust emissions and emulsion fueling. For the rich A/F mixture condition, coherently with fuel consumption results, an increase in CO\({}_{2}\) is measured for emulsions (both with WiGE 10 and 20) if compared with the ECU reference gasoline case, while the CO is almost similar.