A comprehensive full-metal and optical engine study of hydrogen-diesel dual-fuel combustion

This study experimentally investigates hydrogen-diesel dual-fuel combustion using full-metal and optical single-cylinder research engines. Premixed hydrogen is ignited by a diesel pilot over a range of engine speeds, lambda ( λ ), combustion phasing, and hydrogen energy shares (HES), at constant total fuel energy input. The full-metal engine achieves stable operation up to 50% HES, with ∼ 50 % CO 2 reduction and gross indicated thermal efficiency of ∼ 44%–47%. At the highest-soot condition, 50% HES reduces soot by ∼ 80 % , while NO x and H 2 O increase by up to ∼ 66 % . Exhaust gas temperature decreases by ∼ 4%–5% with increasing HES. AHRR analysis shows increasing hydrogen influence on the mixing-controlled stage beyond ∼ 30 % HES. Optical measurements show delayed NFL and OH ∗ signal appearance and increasing IDT with HES, opposite to the full-metal trend. This difference may be attributed to the combined influence of in-cylinder thermal conditions and injector-dependent mixture formation.