# Experimental Activities on a Hydrogen-Fueled Spark-Ignition Engine for Light-Duty Applications
## 3 Methodology  
The methodology employed in this investigation aimed to assess hydrogen combustion under various operating conditions and injection systems in an SI research engine. For this research, a multitude of data points were collected to determine the most significant effects on the hydrogen combustion engine parameters.  
The experimental campaign encompassed three distinct load conditions, representing key areas within the operating map, all at an engine speed of 1500 rpm [30]. To determine the load for these operating points, the quantity of injected hydrogen was utilized. Two injector systems were utilized: PFI and DI. For PFI, a wide range of \(\lambda\) values was measured (from 1.4 to 4.0), whereas for DI, measurements were taken from 2.2 to 3.4. Additionally, for each data point, a sweep of the start of injection (SOI) was performed to analyse the impact of the injection timing. To mimic realistic boosting conditions, the exhaust back-pressure was carefully regulated, maintaining a 0.1 bar difference between the intake and exhaust pressures. Table 4 presents a summary of the tests conducted for this investigation.  
The experimental data were collected following a testing protocol similar to the one described in reference [27]. To minimize measurement uncertainties, each test was repeated three times. The results presented in the following sections represent the average values of the parameters under study.  
\begin{table}
\begin{tabular}{l l l} \hline
**Signal (High Frequency)** & **Sensor** & **Specification** \\ \hline In-cylinder pressure & Piezoelectric sensor & 0 to 250 bar \(\pm\) 0.3\% linearity \\ Intake pressure & Piezoresistive sensor & 0 to 10 \(\pm\) 0.001 bar \\ Exhaust pressure & Piezoresistive sensor & 0 to 10 \(\pm\) 0.001 bar \\ \hline
**Variable (Low Frequency)** & **Sensor** & **Specification** \\ \hline Engine speed & Optical angular encoder & 1 to 6000 \(\pm\) 1 rpm \\ Engine torque & Strain-gauges torque-meter & \(-\)200 to 200 \(\pm\) 1 N m \\ Intake pressure & Piezoresistive transducer & 0 to 10 bar \(\pm\) 1\% \\ Exhaust pressure & Piezoresistive transducer & 0 to 10 bar \(\pm\) 0.3\% \\ Intake temperature & Thermocouple type K & 0 to 1000 \(\pm\) 0.5 \({}^{\circ}\)C \\ Exhaust temperature & Thermocouple type K & 0 to 1000 \(\pm\) 0.5 \({}^{\circ}\)C \\ Fluid temperature & Pt100 thermoresistance & \(-\)200 to 850 \(\pm\) 0.3 \({}^{\circ}\)C \\ Air mass flow & Air flow meter & 0.6-100 m\({}^{3}\)/h \(\pm\) 1\% \\ Hydrogen mass flow & Thermal mass flow meter & N\({}_{2}\) 200–1600 L/min \(\pm\) 0.5 \% \\ \hline
**Pollutant/Analyzer** & **Range** & **Accuracy** \\ \hline HC/FID & min. 0 to 10 ppm C & \(\pm\)3\% \\  & max. 0 to 50 kppm C & \\ NO\({}_{\mathrm{x}}\)/CLD & min. 0 to 10 ppm & \(\pm\)3\% \\  & max. 0 to 10 kppm C & \\ CO/NDIR & min. 0 to 3 kppm C & \(\pm\)3\% \\  & max. 0 to 12 vol\% & \\ CO\({}_{2}\)/DIR & min. 0 to 5 kppm C & \(\pm\)3\% \\  & max. 0 to 20 vol\% & \\ O\({}_{2}\)/PMA & min. 0 to 5 vol\% & \(\pm\)3\% \\  & max. 0 to 25 vol\% & \\ \hline \end{tabular}
\end{table}
Table 2: Instrumentation accuracy.  
\begin{table}
\begin{tabular}{c c} \hline RON & \textgreater{}130 \\ AF\({}_{\mathrm{st}}\) & 34.3 \\ LHV & 119.9 MJ/kg \\ Molar mass & 2.01 g/mol \\ Purity & \(\geq\)99.9\% \\ \hline \end{tabular}
\end{table}
Table 3: H\({}_{2}\) properties.