Influence of Compression Ratio on Combustion and Emission Characteristics of Hydrogen Internal Combustion Engines Under Different Excess Air Coefficients

Hydrogen internal combustion engines (H 2 -ICEs) are a promising solution for decarbonizing heavy-duty transportation. This study investigates the effects of compression ratio (CR: 9, 11, 13) and excess air ratio (λ: 1–5) on the performance, emissions, and combustion characteristics of a turbocharged direct-injection H 2 -ICE under lean-burn conditions. A validated one-dimensional GT-POWER model, calibrated using experimental data (1500 rpm, 0.6 bar intake pressure), was employed to analyze volumetric efficiency (VE), indicated thermal efficiency (ITE), NOx emissions, and combustion stability. Results demonstrate that increasing λ reduces VE and indicated mean effective pressure (IMEP) but enhances ITE, peaking at 41.25% (CR = 13, λ = 2.5). NOx emissions exhibit a non-monotonic trend, reaching 1850 ppm at λ = 1.5 (CR = 13) before declining under leaner conditions. Higher CR extends the lean-burn limit (λ = 5.0 for CR = 13) and advances combustion phasing, though it elevates risks of abnormal combustion. Trade-offs between power, efficiency, and emissions highlight λ = 2.5 as optimal for balancing ITE and NOx control, while λ = 1 maximizes power output. This work provides critical insights into optimizing H 2 -ICE operation through CR and λ adjustments, supporting the transition toward sustainable heavy-duty transport systems.