Objective Incorporating methanol transport into refined oil pipelines can address the declining throughput of these pipelines while providing a safer transportation route for liquid hydrogen energy. As the market demand for gasoline declines more rapidly than for diesel, the batch transportation of methanol and diesel has emerged as the most viable option for integrating methanol transport into refined oil pipelines. Therefore, studying the mixed oil characteristics of methanol-diesel batch transportation is of significant importance.

Methods Due to the poor miscibility of methanol and diesel, determining the mixed oil length using the traditional mixed oil length calculation method for refined oil is challenging. However, methanol’s strong water solubility makes its mixing with diesel in batch transportation resemble oil-water two-phase flow. Consequently, the one-dimensional multiphase flow transient modeling software OLGA was utilized to simulate the methanol-diesel mixing process during batch transportation, and a method for estimating the mixed oil length based on the simulation results was proposed. First, the impact of the velocity difference between methanol and diesel on mixed oil length at different flow velocities was examined. Second, the variation of mixed oil volume during methanol-diesel batch transportation was analyzed under different computational mesh sizes and inclination angles of the up-dip segment. Given that shutdown conditions significantly affect the mixing and stratification of methanol and diesel, the analysis focused on the migration and stratification behaviors of methanol and diesel post-shutdown across different inclination angles and computational mesh sizes.

Results The methanol-diesel mixed oil length was found to be linearly related to the velocity difference between the two phases, indicating that this velocity difference was the primary factor affecting mixed oil length. While OLGA could simulate the oil mixing process due to the density difference between methanol and diesel, it did not account for molecular and turbulent diffusion from a mechanism perspective. Consequently, the calculation results were highly dependent on the configuration of the computational mesh.

Conclusion It is not advisable to use OLGA for calculating the mixed oil length in methanol-diesel batch transportation under normal operating conditions of refined oil pipelines. If its use is necessary, it must be demonstrated that the calculation results are independent of the mesh configuration. For shutdown conditions, while OLGA’s results align with physical laws, they are influenced by numerical diffusion and should only be used for qualitative analysis until further experimental verification is conducted.