To address the challenge of reducing greenhouse gas emissions from the transport sector, innovative strategies are being investigated to enhance the efficiency of internal combustion engines (ICEs). Among these, hydrogen enrichment in spark-ignition (SI) engines has shown considerable potential for reducing CO2 emissions, both by lowering the fuel's carbon content and by improving combustion efficiency. Recent experimental studies have explored a dual-fuel engine concept combining port-fuel-injected (PFI) hydrogen with direct-injected (DI) liquid fuels, specifically gasoline (RON95E10) and methanol. These investigations demonstrated that hydrogen addition mitigates knock in gasoline-fueled engines, enabling more favorable combustion phasing. Moreover, hydrogen's high laminar flame speed across a wide range of air–fuel ratios significantly extends the lean-burn limit, resulting in substantial efficiency gains.