## 3 Results and Discussion
This reduction was attributed to the altered fuel composition and more efficient combustion process. The hydrogen additive decreased the C/H ratio in the fuel mixture by 27.9% and increased the combustion rate. In city driving conditions (Phase I), the total CO emissions reached 8.9 g for G100 and 6.9 g for G95H5, representing a 22.9% reduction in total emissions. As the vehicle transitioned to suburban conditions (medium  
Figure 16: Instant and total HC emissions during the WLTC test: I—Urban cycle; II—Medium-speed cycle; III—High-speed cycle; IV—Very high-speed cycle. Figure 15: Instant and total CO emissions during the WLTC test: I—Urban cycle; II—Medium-speed cycle; III—High-speed cycle; IV—Very high-speed cycle. speed regime) in Phase II, hydrogen reduced the total CO emissions by 23.6%. After the first two WLTC phases, the total CO emissions reached 20.3 g for G100 and 15.6 g for G95H5. During rural conditions (high-speed regime) in Phase III, numerical simulation determined that the hydrogen additive reduced CO emissions by 23.4%, with cumulative CO emissions after the first three phases reaching 34.9 g for G100 and 26.7 g for G95H5. In Phase IV, during highway conditions (very high-speed regime), aerodynamic drag increased fuel consumption, leading to the most intense growth in CO emissions. In this phase, a 23.9% reduction in CO emissions due to hydrogen was observed. The total CO emissions after all four WLTC driving phases amounted to 51.3 g for G100 and 39.2 g for G95H5, reflecting a 23.6% decrease. The greater effect of hydrogen in reducing CO emissions was achieved when the engine operated dynamically, under higher loads, and with a richer air-fuel mixture. The specific CO emissions for individual WLTC driving phases using G100 and G95H5 fuels were as follows: Phase I: 0.384 g/km (G100) vs. 0.296 g/km (G95H5), Phase II: 2.57 g/km (G100) vs. 1.97 g/km (G95H5), Phase III: 2.34 g/km (G100) vs. 1.79 g/km (G95H5), and Phase IV: 3.04 g/km (G100) vs. 2.32 g/km (G95H5). Considering the total WLTC driving distance of 23.27 km, the calculated specific CO emissions were 2.21 g/km for G100 and 1.69 g/km for G95H5. The tested vehicle must comply with the Euro 4 emission standard, which permits a maximum CO emission level of 1.0 g/km. This study evaluated emissions before the catalytic converter. With the use of a catalytic converter, CO emissions would be significantly reduced, and for both fuels, they would meet the standard requirements. The addition of 5% hydrogen to gasoline during the WLTC significantly reduced total HC emissions in all driving conditions. In city driving conditions (Phase I), the hydrogen additive reduced total HC emissions by 37.1%, from 2.65 g (G100) to 1.66 g (G95H5) (Figure 16). During suburban conditions (Phase II), the reduction in cumulative HC emissions with hydrogen was 36.5%, with total HC emissions after the first two phases reaching 4.54 g for G100 and 2.89 g for G95H5. In rural conditions (Phase III), hydrogen reduced HC emissions by 35.2%, with cumulative HC emissions after three phases totaling 6.75 g for G100 and 4.32 g for G95H5. During highway conditions (Phase IV), where increased aerodynamic drag raised fuel consumption, the hydrogen additive reduced HC emissions by 34.1%. After all four WLTC phases, the total HC emissions were 9.19 g for G100 and 5.95 g for G95H5, resulting in a 35.2% decrease in HC emissions across the full driving cycle. The specific HC emissions for individual WLTC phases using G100 and G95H5 fuels were as follows: Phase I: 0.853 g/km (G100) vs. 0.537 g/km (G95H5), Phase II: 0.617 g/km (G100) vs. 0.391 g/km (G95H5), Phase III: 0.405 g/km (G100) vs. 0.262 g/km (G95H5), and Phase IV: 0.455 g/km (G100) vs. 0.300 g/km (G95H5). This analysis shows that HC emissions were of similar intensity across all driving phases. The positive effect of the hydrogen additive was more pronounced in the initial WLTC driving phases, where engine loads were lower.