Abstract
This study presents experimental investigations of a hydrogen power unit operating on hydrogen–oxygen gas mixtures produced by water electrolysis (HHO gas). The system was operated with additional molecular hydrogen enrichment in order to investigate the influence of hydrogen concentration on combustion characteristics and system performance. The flame temperature of the HHO + H2 mixture was measured as a function of hydrogen concentration. The results show that the flame temperature increases nonlinearly with hydrogen content, approaching ~2800 °C under the investigated conditions at about 30 vol.% hydrogen in the enriched mixture. Despite the increase in flame temperature, the effective calorific value of the HHO + H2 mixture remains significantly lower than that of pure hydrogen because the electrolysis-derived gas contains oxygen and excess water vapor. The presence of water vapor acts as a thermal diluent, influencing combustion behavior and suppressing autoignition under the investigated operating conditions. Optimal operating parameters for the hydrogen power unit were determined from experimental measurements. The results indicate that hydrogen-enriched HHO mixtures can be operated safely under controlled conditions and may represent a potential working medium for hydrogen-based energy conversion systems.