## 2 Materials and Methods
### The Methodology of the Experimental Study on the Engine Load Test Bench  
The first stage of the experiments involved testing the engine operation with G100 fuel. Fuel consumption and pollutant concentrations were measured across the full range of engine speeds and loads (Figure 2). The maximum brake torque achieved was 156 Nm. A fuel consumption map (\(B_{f\_{\rm C100}}\), kg/h) was created based on the measured data, illustrating fuel consumption across the operating conditions (Figure 3). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Specification** \\ \hline Engine Type & 4 cylinder, DOHC \\ Displacement & 1.6 L (1598 cm\({}^{3}\)) \\ Fuel System & Multi-point fuel injection (MPFI) \\  & Continuously Variable Valve Timing Control \\  & System (CVTCS) \\ Bore & 78.0 mm \\ Stroke & 83.6 mm \\ Compression Ratio & 10.7:1 \\ Block and Head Material & Aluminum alloy \\ Ignition System & Distributorless ignition system (DIS) \\ Maximum Power & 84 kW (6000 rpm) \\ Maximum Torque & 156 Nm (4400 rpm) \\ Emissions Compliance & Euro 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main parameters of the tested engine. Before conducting tests with the dual-fuel G95H5 mixture, the gasoline consumption map from the initial G100 testing (\(B_{f\_G100}\) map, Figure 3) was used to preliminarily calculate the required hydrogen mass flow (5% of G100 by mass). Based on these calculations, a hydrogen consumption map (\(B_{f\_H2}\), Figure 4) was created to guide the hydrogen supply during dual-fuel operation. During the dual-fuel experiments, the hydrogen flow specified in the \(B_{f\_H2}\) map was supplied to the intake manifold through additional gas injectors controlled by the electronically managed OSCAR-N gas injection system. This system received real-time data from the MoTeC M800 ECU, enabling precise synchronization with the gasoline injection system. Gasoline was simultaneously injected via the standard fuel system, with the injector opening duration managed by the MoTeC M800 system. To maintain a stoichiometric mixture (\(\lambda=1.0\)), the control system adjusted the gasoline injection volume based on signals from an oxygen sensor installed in the exhaust system. By supplementing the air-gasoline mixture with hydrogen gas (5% of the gasoline mass), while maintaining the same excess air ratio as in the G100 tests, the maximum engine brake torque decreased to 137 Nm, approximately a 12% reduction compared to G100. A dual-fuel consumption map (\(B_{f\_G95H5}\), kg/h) was developed (Figure 5). Fuel consumption with G95H5 decreased by approximately 18% compared to G100. This reduction resulted from several complex factors:  
1. The low density of hydrogen increases its volumetric displacement, reducing the air intake and thus volumetric efficiency, which decreases torque. 2. G95H5 requires 8.8% more air for combustion compared to G100. 3. The lower heating value (LHV) of the fuel blend increased by 6.8% (Table 1). Figure 3: Fuel consumption map for G100. Figure 2: Engine load map. The composition of engine exhaust gasses (pollutant concentration) was measured using a stationary gas analyser. Results are given after measuring the pollution before the catalytic converter.