## 3 Results and Discussion
This improved HC combustion at lower combustion temperatures, differing from the trend observed in CO emission reductions with hydrogen. The specific HC emissions over the full WLTC were calculated at 0.395 g/km for G100 and 0.256 g/km for G95H5. The tested vehicle is certified to meet the Euro 4 emission standard, which allows a maximum HC emission level of 0.1 g/km. With the use of a catalytic converter, HC emissions would be significantly reduced and would meet the ecological requirements for both fuels. Numerical modelling using the AVL Cruise(tm) software shows that a 5% hydrogen additive in gasoline has a varying impact on NO\({}_{\rm x}\) emissions across different WLTC phases. At the end of the city driving cycle (Phase I), the total NO\({}_{\rm x}\) emissions were 2.0 g for G100 and 2.46 g (22.7% higher) for G95H5 (Figure 17), with specific emissions of 0.647 g/km and 0.794 g/km, respectively. In the medium-speed regime (Phase II), NO\({}_{\rm x}\) emissionsincreased due to higher engine loads, with hydrogen further increasing NO\({}_{x}\) emissions by 25.9%. Specific emissions rose to 0.787 g/km for G100 and 0.991 g/km for G95H5, resulting in total emissions of 5.6 g for G100 and 7.0 g for G95H5 after two phases. In the high-speed regime (Phase III), the impact of hydrogen on NO\({}_{x}\) emissions remained significant, increasing emissions by 23.5%. Specific emissions reached 0.897 g/km for G100 and 1.108 g/km for G95H5, with total NO\({}_{x}\) emissions after three phases amounting to 11.3 g for G100 and 14.0 g for G95H5. During the very high-speed regime (Phase IV), higher engine loads and elevated combustion temperatures in the cylinder resulted in substantially higher NO\({}_{x}\) emissions. Specific emissions in this phase reached 1.714 g/km for G100, while the hydrogen additive increased NO\({}_{x}\) emissions by 19.7%, raising specific emissions to 2.051 g/km for G95H5. At the end of the WLTC, the total NO\({}_{x}\) emissions were 22.7 g for G100 and 27.6 g for G95H5, representing a 21.4% increase due to hydrogen. An analysis of individual cycle phases indicates that the hydrogen additive had the greatest impact on NO\({}_{x}\) emissions during Phases II and III, which involved more accelerations and higher engine loads. Over the full WLTC, the specific NO\({}_{x}\) emissions were 0.978 g/km for G100 and 1.187 g/km for G95H5. The Euro 4 emission standard allows a maximum NO\({}_{x}\) emission of 0.08 g/km. It is expected that with the use of a catalytic converter, this standard will be met. The AVL Cruise(tm) software calculated CO\({}_{2}\) emissions over the WLTC by evaluating the elemental fuel composition and fuel consumption (Figure 18). The addition of 5% hydrogen by mass to gasoline reduced fuel consumption by approximately 10.4%, due to increased engine brake thermal efficiency and a 6.8% higher lower heating value of the fuel (Table 1). This hydrogen additive led to a 5% reduction in the elemental carbon content of the fuel (Table 1), which collectively contributed to a decrease in greenhouse gas CO\({}_{2}\) emissions. In the city driving mode (Phase I), total CO\({}_{2}\) emissions were 476 g for G100 and 399 g for G95H5 (16.1% less), with specific CO\({}_{2}\) emissions of 154 g/km for G100 and 129 g/km for G95H5, respectively. In the medium-speed mode (Phase II), specific CO\({}_{2}\) emissions decreased to 135 g/km for G100 and 115 g/km for G95H5 (15.3% less), and at the end of this phase, total CO\({}_{2}\) emissions were 1.119 kg for G100 and 0.994 kg for G95H5. In the high-speed mode (Phase III), fuel consumption per kilometre and specific CO\({}_{2}\) emissions were at their lowest--126 g/km for G100 and 107 g/km for G95H5 (14.9% less), with total CO\({}_{2}\) emissions at the end of this phase reaching 2.017 kg for G100 and 1.708 kg for G95H5. Figure 17: Instant and total NO\({}_{x}\) emissions during the WLTC test: I—Urban cycle; II—Medium-speed cycle; III—High-speed cycle; IV—Very high-speed cycle.