## 1 Introduction
Numerous authors have published data on the energy in hydrogen. The heat of combustion of hydrogen is 143 MJ\(\cdot\)kg\({}^{-1}\), which means 39.72 kWh\(\cdot\)kg\({}^{-1}\)[12], whereas [PERSON] [13] demonstrates a calorific value of hydrogen of 33.3 kWh\(\cdot\)kg\({}^{-1}\). The undoubted disadvantage of hydrogen is its low energy density. Under atmospheric conditions, the heat of combustion of hydrogen per unit volume is 10.79 MJ/m\({}^{3}\) for hydrogen gas. When hydrogen is liquefied, its density improves, and the heat of combustion amounts to 1010 MJ\(\cdot\)kg\({}^{-1}\). Unfortunately, hydrogen liquefaction is a highly energy-intensive process and requires special apparatus. Hydrogen has the highest energy value per unit weight of fuel (120 MJ\(\cdot\)kg\({}^{-1}\)) In terms of its weight, hydrogen has almost three times the energy content of, for example, petrol (44.5 MJ\(\cdot\)kg\({}^{-1}\)) and methane (50.0 MJ\(\cdot\)kg\({}^{-1}\)). However, in volume terms, the situation is reversed. The heat of combustion of liquid hydrogen relative to volume is 8960 MJ\(\cdot\)m\({}^{-3}\), petrol 31,170 MJ\(\cdot\)m\({}^{-3}\) and methane 21,250 MJ\(\cdot\)m\({}^{-3}\). The low density of hydrogen, about 0.08 kg\(\cdot\)m\({}^{-3}\) results in storage problems, particularly in automotive applications [14; 15]. In research conducted by [PERSON] et al. [16], 5%, 10%, and 15% of hydrogen energy was added to biogas and tested in a spark ignition engine at a constant speed and at different equivalence ratios to analyze its impact on performance, emissions, and combustion. Hydrogen significantly increased the rate of combustion and raised the limit for the use of the biogas mixture. The thermal efficiency and braking power improved. However, the addition of over 15% of hydrogen, required an ignition delay to control knocking combustion and did not improve biogas properties at high equivalence ratios. A significant reduction in hydrocarbon levels in exhaust fumes was observed. Furthermore, nitrogen oxide emissions did not increase due to the delayed ignition and the presence of carbon dioxide. Peak pressures and heat release rates were observed to be lower when hydrogen was added as the ignition time was delayed to avoid knocking. The research concluded that the addition of 10% of hydrogen to biogas was the most favorable [16]. As for the use of hydrogen for transport, it can be stored at a pressure of 700 bar. Such high pressures are necessary due to the low energy density of hydrogen. Meanwhile, methane tanks presently used in CNG systems usually have a pressure of 200 bar. Other research on the hydrogen enrichment of biogas was conducted for a dual-fuel diesel engine. Parameters such as thermal efficiency, pollutant emissions, and combustion parameters were determined. Experiments were carried out on a stationary compression ignition (CI) engine coupled with a generator running in dual mode at a typical biogas composition of 60% CH\({}_{4}\) and 40% CO\({}_{2}\). The volume concentration of hydrogen varied from 5 to 20% of H\({}_{2}\). The results showed an increase in peak pressure in the combustion chamber to 10.7 bar and diesel substitution levels of up to 80% under conditions of stable combustion without knocking. Further, thermal efficiency increased to 16% and carbon monoxide emissions decreased to 13% at full load and with the addition of 20% hydrogen [17]. [PERSON] et al. [18] conducted research on the injection of hydrogen additive into the gas network and the impact of this additive on gas system components. As a result of the experiments, two levels of acceptable hydrogen content were determined: 10% and 8%. The first level resulted from the acceptable method of calculating the compressibility factor, whereas the second one pertained to the explosion safety of measuring equipment intended for use in explosive atmospheres.