## 4 Evaluation of Hydrogen Combustion with the Addition of Helium  
### Cylinder Pressure  
Research on helium addition in hydrogen fuel was carried out in the aspect of analyzing pressure changes in the cylinder. On its basis, most indicated and thermodynamic parameters were determined. The primary combustion process was carried out using pure hydrogen (Figure 5). The combustion pressure is shown as a red function. This refers to the use of the passive prechamber. It is described with the value of the excess air ratio (red color). The value of \(\lambda\) is the largest in this case (each successive supply of fuel to the PC resulted in a decrease in the global value of \(\lambda\)). The curves contained in Figure 5 are for pressure functions with increasing fuel delivery to the PC (\(\Delta\)t = 2 ms). As presented earlier, the effect of helium addition in the He/H\({}_{2}\) mixture and varying the hydrogen dose in the prechamber was analyzed at different values of \(\lambda\). Figure 5 shows the changes in the fuel dose to the prechamber, which result in small increases in combustion chamber pressure (an increase in the total fuel dose results in a parallel decrease in the \(\lambda\)). Increasing the fuel injection into the PC results in faster combustion, due to a change in the \(\lambda\). A lower value of this coefficient provides better ignition of such mixtures (despite the wide ignition limits of hydrogen). The highest acceleration of the combustion process occurs after switching from the passive to the active prechamber (increasing fuel injection to the PC above zero). The following extension of the fuel injection time to the PC does not bring such a large change in the start of the combustion. The increase in cylinder pressure caused by the change in the injection mode (from passive to active) is significant. The rise in maximum combustion pressure (Pmx) is quite notable, especially after \(\lambda\) is higher than 1.5. The passive combustion chamber system could not be realized at a high excess air ratio (around \(\lambda\) = 3.00), due to the lack of a combustion process. Similar conclusions regarding the lack of combustion of a mixture of hydrogen and methane (HCH\({}_{4}\)) and CH\({}_{4}\) at high values of \(\lambda\) were noted by [PERSON] and [PERSON] [19]. The combustion of HCH\({}_{4}\) was stopped at \(\lambda\) = 1.9, while with the active chamber, it was carried out to \(\lambda\) = 2.2 (it should be noted that pure hydrogen was not used). Similar conclusions during hydrogen combustion in a Constant Volume Chamber (CVC) were obtained by [PERSON] et al. [20]. Figure 5: Pressure: (**a**) in the main chamber; (**b**) in the prechamber; with a hydrogen supply (He/H\({}_{2}\) = 0/100) and with varying excess air ratio values; n = 1500 rpm; IMEP = 3.5–4.25 bar; red line—passive prechamber data; other—active combustion chamber with increased fuel dose in PC. On the basis of 100 engine work cycles, the variation in the indicated mean effective pressure was determined (IMEP). The change in IMEP was caused by increasing the throttle angle (TH) (which increased the excess air ratio \(\lambda\))--Figure 6a. At the same time, increasing the addition of helium in the fuel reduced \(\lambda\). More helium and less hydrogen results in less energy contained in the fuel dose (constant mass of the fuel but change in its composition of He/H\({}_{2}\)). IMEP is given by [21; 22] the following:  
\[\text{IMEP}=\frac{\Delta\alpha}{\text{V}_{\text{s}}}{\sum_{\alpha=1}^{720} \text{P}(\alpha)\frac{\text{dV}(\alpha)}{\text{d}\alpha}}, \tag{1}\]  
where Vs, p(\(\alpha\)), dV(\(\alpha\))/d\(\alpha\), and \(\Delta\alpha\) are the mean cylinder swept volume, cylinder pressure at crank angle position \(\alpha\), derivation of cylinder volume at crank angle position \(\alpha\), and indicated crank angle resolution, respectively. Increasing He addition at a low \(\lambda\) results in an IMEP decrease of approximately 10%.