Synergetic effects of hydrogen energy share, Fe₂O₃ nano-additives, and oxygen enrichment on the combustion, performance, and emission characteristics of a gasoline engine

This study investigates the effects of hydrogen energy share, potential nano-additive of iron oxide (Fe₂O₃) nanoparticles, and oxygen enrichment on combustion, performance, and emissions of a gasoline engine. Different hydrogen energy shares of 0%, 25%, 50%, and 75% were investigated at a constant engine throttle of 75% and engine speed of 1500 rpm. To enhance combustion further, two doses of Fe₂O₃ nanoparticles of 50 ppm and 100 ppm were added to the baseline gasoline fuel at different hydrogen energy shares. Besides that, the effects of oxygen enrichment concentrations of 21%, 22%, 23%, 24%, and 25% were investigated at 50% hydrogen energy share (H50). The findings indicate that hydrogen enrichment accelerated combustion, reducing the rapid burning duration from 10.50 °CA (H0) to 7.66 °CA (H75), while the addition of Fe₂O₃ nanoparticles (100 ppm) further reduced it to 7.14 °CA, indicating improved flame propagation and reaction kinetics. However, high hydrogen substitution reduced brake output due to lower mixture energy density. The optimal performance was achieved at H25_Fe₂O₃ (100 ppm), where brake power and brake thermal efficiency increased to 6.03 kW and 28.11%, respectively, corresponding to improvements of 4.33% and 4.34%, while BSFC decreased to 0.223 kg/kW.hr. Oxygen enrichment further intensified combustion, advancing combustion phasing and increasing heat release. The flame initiation angle decreased from 14.15 °CA at 21% O₂ to 12.76 °CA at 25% O₂, while the rapid burning duration decreased from 8.88 °CA to 7.55 °CA, and peak heat release rate increased by 14.75%. These changes improved engine performance, with brake power increasing by 3.4%, BTE by 3.4%, and BSFC decreasing by 3.29%. An optimal condition was identified at 24% O₂. In terms of emissions, both Fe₂O₃ nanoparticles and oxygen enrichment significantly enhanced oxidation processes. CO emissions decreased from 0.49% at 21% O₂ to 0.04% at 25% O_2, and HC emissions from 93 ppm to 49 ppm. However, NOx emissions increased from 2623 ppm to 7495 ppm due to higher combustion temperatures and intensified radical-driven reactions.