Karagöz, YasinPusat, ŞabanTeksan, A. EmreTunçer, ErdalTetik, Tuğba2026-09-122026-09-122026Karagöz, Y., Pusat, Ş., Teksan, A. E., Tunçer, E., & Tetik, T. (2026). Extreme lean hydrogen combustion in SI engines: NOx emissions and exergy destruction analysis. International Journal of Exergy, 50(4), pp. 278-289. https://doi.org/10.1504/IJEX.2026.1559221742-82971742-8300https://doi.org/10.1504/IJEX.2026.155922https://hdl.handle.net/20.500.13055/1636This study examines the effects of excess air coefficient (lambda) and late ignition timing on NOx emissions and exergy destruction in a hydrogen-fuelled internal combustion engine converted from a conventional diesel engine. Experiments are conducted at 1,500 rpm and 3.5 kW using two ignition timings [10 degrees and 0 degrees before top dead centre (BTDC)] and three excess air coefficients (lambda = 1.05, 2.15, and 3.75). Results indicate that late ignition (0 degrees BTDC) and ultra-lean operation (lambda = 3.75) significantly reduce NOx emissions. The impacts on brake thermal efficiency (BTE), brake specific energy consumption (BSEC), and exergy destruction are also evaluated.eninfo:eu-repo/semantics/closedAccessHydrogenExtreme Lean CombustionCold CombustionExergyArticle10.1504/IJEX.2026.155922504278289Q4WOS:001861682400004Q3