Bioethanol is gaining popularity as a renewable energy source, and understanding the wear characteristics of materials used in its engine components is crucial for improving engine durability. Wear tests of stainless steel (SUS304) were conducted using an autoclave friction testing machine in a high-temperature, high-pressure ethanol-water environment to investigate the wear mechanism of SUS304 in a bioethanol engine environment. The tests were performed under two types of bubbling gases, oxygen and nitrogen, and sodium sulfate concentrations ranging from 0 to 4.00 ppm. The results showed that under nitrogen bubbling conditions, the wear of SUS304 increased with rising sodium sulfate concentration, from 3.49 × 10-5 mm3/Nm at 0 ppm to 12.78 × 10-5 mm3/Nm at 4.00 ppm. In contrast, under oxygen bubbling conditions, the wear decreased from 9.93 × 10-5 mm3/Nm at 0 ppm to 4.58 × 10-5 mm3/Nm at 4.00 ppm as the sodium sulfate concentration increased. Additionally, Atomic Force Microscopy (AFM) scratch tests and X-ray Photoelectron Spectroscopy (XPS) analysis on the wear scar revealed that under oxygen bubbling conditions with 4.00 ppm sodium sulfate concentration, the scratch depth was the smallest, and a significant amount of Cr2O3 was detected on the topmost surface. These results suggest that under oxygen bubbling conditions, the formation of a hard chromium oxide film on the surface helps suppress wear.
KAWAI et al. (Wed,) studied this question.