Numerical simulation of ammonia refueling process for ammonia-powered vehicles

ObjectiveAmmonia energy, a zero-carbon carrier, is emerging as a key solution for the green transformation of transportation, including vehicles and ships. Developing safe and efficient ammonia refueling technology is essential for large-scale adoption of ammonia-powered vehicles. MethodsAn Aspen HYSYS model was developed based on the ammonia refueling process with gas-phase reflux. After validating the model through experimental tests, pressure, temperature, and gas-phase fraction changes during refueling were analyzed in detail. The effects of gas-phase reflux, ambient temperature, pump head, and valve opening on the refueling performance were systematically examined through the single-factor analysis method. ResultsComparison of simulation and experimental results indicated that the relative errors for cumulative refueling mass and pipeline pressure were less than 5％, confirming the model’s reliability. At system startup, temperature and pressure in both liquid- and gas-phase pipelines fluctuated, with greater fluctuations observed in the gas-phase pipeline. During stable ammonia refueling, both pipelines exhibited a stepwise pressure drop. After passing through the liquid ammonia pump, both pressure and temperature increased. Compared to pure liquid refueling, ammonia refueling with gas-phase reflux reduced the back-pressure of the receiving bottle, increased refueling efficiency by 13％, and resulted in more stable system pressure. Higher ambient temperatures improved refueling efficiency by promoting gas-phase reflux and reducing the gas-phase fraction before the pump; as temperature increased from 15 °C to 35 °C, efficiency rose by 17.6％. However, higher temperatures also increased the risk of over-pressure leakage in the pipeline. Increasing pump head and valve opening shifted the pump operating point toward higher flow, further improving refueling efficiency. Nevertheless, the resulting increase in flow velocity enhanced valve throttling, raising refueling resistance and causing diminishing returns in efficiency improvement. ConclusionThe ammonia refueling process is characterized by a stepwise pressure drop and a temperature increase after the pump, with partial vaporization of liquid ammonia occurring in the pipeline before the pump. Enhancements such as gas-phase reflux, higher initial medium temperature, high-head pumps, and increased valve opening all improve the refueling rate. These findings provide guidance for process design and equipment selection, and offer theoretical support for predicting ammonia refueling efficiency and ensuring flow assurance, thereby advancing the green transformation of the transportation industry.