Towards clean, efficient, and stable operation: experimental evaluation and multi-objective optimization of a turbocharged hydrogen engine

Hydrogen is a promising sustainable and zero-carbon fuel for internal combustion engines. This study investigates the clean efficient and stable hydrogen engine based on four important metrics of brake thermal efficiency (BTE), NO _x emissions, coefficient of variation of IMEP (CoV_IMEP), and ringing intensity (RI). Experiments are conducted in a 1.5 L variable geometry turbocharged direct-injection hydrogen engine under typical range-extender conditions (2500 rpm, 30 kW), with seven control parameters varied by a multi-factor design. Statistical analysis and correlation are used to extract relationships from nonlinear trends. A peak BTE of 40.62 % is obtained at excess air fuel ratio 1.89 with split injection, but NO _x exceeds 15 g/kW·h. An NH₃–SCR after-treatment system is applied. NO _x conversion exceeds 99 % across a wide range, reducing post-SCR NO _x to < 0.1 g/kW·h. This significantly shifts the multi-objective balance: entropy weight–TOPSIS analysis shows the influence of NO _x in the score calculation drops from 42.8 % to 28.4 %. The optimal configuration achieves BTE > 39 %, CoV_IMEP < 1.3 %, RI < 1.5 MW/m², and fully compliant NO _x emissions. These findings quantify metric and demonstrate a practical optimization framework that combines in-cylinder control with aftertreatment to support clean, efficient, and stable hydrogen engine operation.