Extreme lean hydrogen combustion in SI engines: NOx emissions and exergy destruction analysis

This 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.