Corrosion assessment of cast aluminum parts in ethanol fuel blends

บทคัดย่อ

Nowadays, the use of ethanol fuel blends in automobiles has become more and more worldwide since the ethanol mixture would enhance the performance of the engine and fuel economy ($/mile), while reducing the hazardous exhaust released to the environment. However, the use of ethanol fuel blends may induce some material compatibility issues on some automotive parts that were not designed to be used in contact with ethanol. In other words, the humidity in the ethanol would cause corrosion problem on these parts. The goal of this study is to assess the corrosion value of two cast aluminum parts in a motorcycle, which are cylinder head and carburetor. Sample specimens were prepared from the two aluminum parts, then immersed in three different ethanol fuel blends, containing ethanol at 20 (E20), 85 (E85), and 100 (E100) vol.%, testing at two different temperature levels (room and 50°C). Based on the immersion test results, corrosion was observed on the surface of the specimens, and determined to be a pitting corrosion type. The weight loss and depth of pit were measured after 1, 2, and 4 weeks. From the measurement results, higher weight loss and deeper pit depth values were found in the case of fuel blends with a higher ethanol content (E100 > E85 > E20) and at a higher temperature level (50°C > 25°C). As time progressed, the corrosion also continued on (i.e., higher weight loss and deep pit depth), but at a slower rate (i.e., lower weight loss and pit depth occurred during a later week). This slower rate may have been caused by the formation of oxide film at the surface of the specimens, which acts as a protective film and prevent further corrosion into the material. Nonetheless, the weight loss and pit depth values on both aluminum parts under the selected testing conditions used in this study were still within an acceptable range for the utilization of these parts with ethanol fuel blends in a motorcycle.