Purpose: This paper aims to improve the previous fuel scrubbing model and find out the relationship between bubble diameter and scrubbing efficiency (ƞ). Design/methodology/approach: A fuel tank scrubbing test bench was established to verify the accuracy of this model. Ullage and dissolved oxygen concentration were measured, and images of bubble size and distribution were collected and analyzed using image analysis software. Findings: The bubble diameter has a great influence on ullage and dissolved oxygen concentration during the fuel scrubbing process. The scrubbing efficiency (ƞ) has an exponential relationship with bubble diameter and decreases rapidly as the bubble diameter increases. Practical implications: The variation of the ullage and dissolved oxygen concentration predicted by this model is more accurate than that of the previous model. In addition, the study of bubble size can provide a guidance for the design of fuel scrubber. Originality/value: This study not only improves the previous fuel scrubbing model but also develops a method to calculate scrubbing efficiency (ƞ) based on bubble diameter. In addition, a series of tests and analyses were conducted, including numerical calculation, experiment and image analysis.