The complementary utilization of oxyhydrogen and bio-isopropanol in carbon-neutral fuel engines can effectively enhance power output and combustion stability. However, oxyhydrogen blended combustion results in an increase in NOx emissions. To address this issue, this study explores the synergistic mechanisms of lean-burn coupled with exhaust gas recirculation (EGR) in an engine featuring oxyhydrogen negative pressure inhalation (ONPI), bio-isopropanol direct injection (BIDI), and gasoline port i