Colorimetric Assessment as a Complementary Approach to Visual Copper Corrosion Evaluation in Automotive Fuels

The standardized copper strip corrosion test is commonly used to assess the corrosive effects of automotive gasoline and diesel fuels on metallic materials. This test relies on visual evaluation of copper strip discoloration, which may introduce subjectivity and limit quantitative interpretation. The aim of this study was to compare the conventional visual evaluation with a colorimetric approach as a quantitative alternative. Copper strip corrosion tests were performed according to EN ISO 2160 using gasoline and diesel fuel samples. While all samples were visually classified within corrosion Class 1, colorimetric analysis revealed measurable differences in surface discoloration, with ΔE*ab values ranging from 0.4 to 11.1, and highest values observed for aged fuels. These results demonstrate that colorimetric evaluation provides additional quantitative information beyond conventional visual classification and enables differentiation between fuels within the same acceptance category.