Investigation on a combined system with methanol on-board hydrogen production and internal combustion engine

The progression of hydrogen fuel vehicles is hindered by persistent challenges in storage, transportation, and safety. However, onboard methanol reforming technology combining internal combustion engine emerges as a promising transitional solution to overcome these obstacles. This study utilizes Aspen Plus software to construct a combined system model capable of facilitating two utilization modes: direct methanol combustion and reforming prior to combustion. Comparative analyses were conducted to assess the power, economy, and emissions of both the combined system mode and methanol engine mode at engine loads of 25 %, 45 %, 65 %, and 85 %. The principle of Gibbs free energy minimization to thermodynamically was employed to optimize the steam-methanol reforming process. The results indicate that in the combined system mode, the conversion of initial methanol into hydrogen-rich synthesis gas fuel via fuel reforming technology is an effective approach. Compared to the methanol engine mode, the combined system mode yields higher output power for the same amount of methanol, with an increasing system thermal efficiency by 6.4%–7.9%. Across engine loads ranging from 25 % to 85 %, the fuel consumption rate is lower in the combined system mode, saving 17–22% of initial methanol compared to the methanol engine mode, demonstrating better economic feasibility. Additionally, a waste heat recovery rate of 18%–21% and a thermal conversion coefficient of 1.2518 were obtained in the combined system mode. Furthermore, the thermal conversion coefficient under two steam-to-methanol ratios were compared and behaves differently below and exceeds 200 °C. Finally, the combined system mode exhibits a significant advantage in reducing carbon emissions, with a decrease in CO₂ emissions by 19.1%–26.9% and CO emissions by 82.4%–88.9% compared to the methanol engine mode.