## 3 WLTC-Based Analysis of Study Results
### Ecological Parameters
HC emissions are primarily caused by the uneven mixing of fuel and air and through flame front quenching in various regions of the combustion chamber. Bioethanol increases the oxygen content during combustion, enhancing the combustion process and reducing the emission of incomplete combustion products. The average concentration of unburned hydrocarbons during the WLTC, measured before the catalytic converter (test phase i), decreased by approximately 8% and 21% when E0 was replaced with E10 and E70, respectively (Figure 7a). Other studies have observed similar trends [36]. When the engine was running on pure gasoline (E0) before the catalytic converter, the HC emissions over the test cycle (\(E_{\text{HC\_X\_WITC}}\)) were calculated to be approximately 2.95 g (Figure 7a), with specific emissions \(E_{\text{HC\_WITC}}\) of around 0.127 g/km. When the engine was fueled with E10 and E70, the cumulative WLTC HC emissions were 2.44 g and 2.14 g, respectively, with specific emissions of 0.105 g/km and 0.092 g/km, representing reductions of approximately 17% and 27% compared to E0. Downstream of the catalytic converter (measurement step ii), the HC concentration was reduced by approximately 80 times (Figure 7b). The WLTC HC emission with E0 was approximately 0.037 g (Figure 7b), with a specific emission of 0.0016 g/km. Switching from E0 to E10 and E70 resulted in additional reductions of approximately 12% and 15% in the specific emissions of \(E_{\text{HC\_WITC}}\) downstream of the catalytic converter, to 0.0014 g/km and 0.00139 g/km, respectively. Figure 6: CO concentration and emission during the WLTC, using different fuels: (**a**) before the catalytic converter; (**b**) after the catalytic converter. The Euro 4 emission standard requires HC emissions below 0.1 g/km. E0 fuels have been found to produce HC emissions approximately 60 times lower than this limit when measured behind an efficient catalytic converter, and the addition of bioethanol further reduces these emissions. A more detailed analysis of the first stage of the test (i) shows peaks of increased HC concentrations when the engine is running on E70 fuel. These peaks are likely associated with the advanced ignition timing enabled by the higher knock resistance of bioethanol. Early combustion can lead to increased HC emissions because ignition occurs before the fuel/air mixture is fully homogenised. In the second test phase (ii), pollutants measured downstream of the catalytic converter in low-speed mode (I) show higher HC concentration peaks with E70 fuel. This correlates with increased CO concentrations in the same mode, likely due to reduced exhaust and catalytic converter temperatures. However, these peaks in HC and CO concentrations are transient. The role of bioethanol in improving the quality of fuel mixture preparation and combustion is confirmed by the overall reduction in total HC and CO emissions. NO\({}_{\text{x}}\) is formed as a by-product of the combustion process, and its emissions increase significantly when the engine is operated at higher loads and combustion temperatures. Bioethanol has a significantly higher latent vaporisation heat than pure gasoline, which can reduce the temperature of the intake air/fuel mixture. Increasing the bioethanol concentration results in a cooler fuel mixture during the compression stroke, lowering the combustion temperature. This reduction in the combustion temperature directly impacts the formation of NO\({}_{\text{x}}\) compounds. The average concentration of nitrogen oxides measured during the WLTC test before the catalytic converter (test phase i) decreased by approximately 13% when E0 fuel was replaced with E70 (Figure 8a). When the engine was running on pure gasoline (E0) before the catalytic converter, total NO\({}_{\text{x}}\) emissions over the test cycle (\(E_{\text{NO}_{\text{x}}\_\_WLTC}\)) were calculated to be approximately 41.8 g (Figure 8a), with specific emissions (\(E_{\text{NO}_{\text{x}}\_\_WLTC}\)) of about 1.80 g/km.