## 3 WLTC-Based Analysis of Study Results
### Ecological Parameters
When using E10 and E70, total NO\({}_{\text{x}}\) emissions during the WLTC cycle were 31.6 g and 29.0 g, respectively, with specific emissions of 1.36 g/km and 1.25 g/km, representing reductions of approximately 24% and 30% compared to E0. The catalytic converter reduced NO\({}_{\text{x}}\) emissions by approximately 74 times (Figure 8b). Total NO\({}_{\text{x}}\) emissions with E0 after the catalytic converter \(E_{\text{NO}_{\text{x}}\_\_\_WLTC}\) were approximately 0.57 g (Figure 8b), with specific emissions \(E_{\text{NO}_{\text{x}}\_\_WLTC}\) of about 0.024 g/km. Increasing the bioethanol concentration to 10% and 70% resulted in further reductions of approximately 16% and 21% in specific NO\({}_{\text{x}}\) emissions downstream of the catalytic converter, to 0.021 g/km and 0.019 g/km, respectively. Figure 7: HC concentration and emission during the WLTC, using different fuels: (**a**) before the catalytic converter; (**b**) after the catalytic converter. A more detailed analysis of the first test run measuring NO\({}_{\rm x}\) emissions upstream of the catalytic converter (i) indicates that the highest NO\({}_{\rm x}\) emissions were produced with E0 fuel, while E70 and E10 exhibited the lowest emissions in different driving modes; different studies have found that NO\({}_{\rm x}\) emissions increase, especially in hybrid vehicles, when regular gasoline is used [6]. In low-speed mode (I), NO\({}_{\rm x}\) emissions were lower with the E10 blend compared to E70. This can be attributed to the greater ignition timing advance with E70, which, at lower engine speeds, leads to a more significant increase in the combustion temperature due to slower combustion chamber expansion. As the vehicle speed and engine load increased in modes II, III, and IV, NO\({}_{\rm x}\) emissions were minimised with E70 fuel. In the second test step, NO\({}_{\rm x}\) emissions measured downstream of the catalytic converter (ii) were significantly reduced due to catalytic reduction processes \(E_{\rm NO_{x}\_BLUTC}\). The lowest NO\({}_{\rm x}\) emissions in driving modes I and II were observed with E0, while E10 and E70 exhibited higher emissions. In mode III, NO\({}_{\rm x}\) emissions with E10 were notably higher, whereas, in the very high-speed mode (IV), the lowest NO\({}_{\rm x}\) emissions were recorded with E70, while the highest was with E0. The higher NO\({}_{\rm x}\) emissions downstream of the catalytic converter in the initial WLTC modes with E70 are linked to increased emissions upstream of the catalytic converter and the lower catalytic converter temperature, caused by the reduced exhaust gas temperature. The lower NO\({}_{\rm x}\) peaks seen with E70 in modes III and IV, compared to E0 and E10, are attributed to bioethanol's ability to lower combustion chamber temperatures. The Euro 4 emission standard limits NO\({}_{\rm x}\) emissions to 0.08 g/km. The catalytic converter performance with E0 fuel resulted in emissions approximately 3.3 times lower than this limit, \(E_{\rm NO_{x}\_BLUTC}\), and the addition of 10% and 70% bioethanol further reduced emissions to 3.8 and 4.2 times lower, respectively. Reducing NO\({}_{\rm x}\) emissions has a significant impact not only on improving air quality but also on mitigating greenhouse gas emissions. CO\({}_{2}\) is a product of the complete combustion of carbon and depends primarily on fuel consumption [6], the fuel's carbon-to-hydrogen (C/H) ratio, and combustion quality. The average CO\({}_{2}\) concentration during the WLTC, measured before the catalytic converter (i), decreased by approximately 2.5% when E0 fuel was replaced with E70 (Figure 9a). Considering the CO\({}_{2}\) concentration, fuel consumption, air intake, and exhaust gas characteristics, it is estimated that the engine running on E0 fuel before the catalytic converter resulted in a cumulative carbon dioxide emission over the test cycle (\(E_{\rm CO_{x}\_BLUTC}\) of approximately 3367 g (Figure 9a) and a specific emission of around 145.2 g/km.