# Effect of Marine Coolant Additives on Cavitation Erosion-Corrosion of Diesel Engine Cylinder Liner
## 2 Experimental Method
### Cavitation Erosion Test  
Cavitation erosion tests were performed using equipment designed to meet ASTM G32 [37] specifications. The experimental equipment utilized a vibration generation device based on the piezoelectric effect. The device, powered by 60 Hz, 220 V electricity through an electronic circuit, generates a rated vibration output of 20 kHz, which is supplied to the vibrator. The amplitude was automatically controlled and maintained at a constant value of 50 \(\upmu\)m. Vibration generation by the piezoelectric element is achieved by applying an alternating electrical current to a conical horn, which induces axial vibrations and creates a cavity.  
During cavitation erosion tests, the temperature of the solution was maintained at \(25\pm 1\)\({}^{\circ}\)C using a chiller to minimize temperature-induced variations in cavitation behavior. A chiller system consisting of a circulating constant-temperature water bath equipped with both a heater and a cooling unit was used to maintain the set temperature (CORETECH, HQ-DRCW21 (CORETECH, Anyang, Republic of Korea)). The operating temperature range of the unit was \(-10\)\({}^{\circ}\)C to 95 \({}^{\circ}\)C and the built-in digital PID controller automatically maintained the target temperature with a precision of 0.1 \({}^{\circ}\)C. The horn immersion depth was consistently maintained at 12 mm. The test specimen was fixed to a fixture in such a way that it faced the vibrator's horn, allowing the cavity generated by the horn to affect  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Condition** \\ \hline Appearance & Light yellow liquid \\ Specific gravity @25 \({}^{\circ}\)C & 1.23 \\ pH & 12.3–12.9 \\ Freeze point & \(-12.2\)\({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table}
Table 4: Physical properties of coolant additive.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Solution Type** & **Solution Condition** \\ \hline Distilled water + Additive (DW + A) & 13,000 ppm additive in distilled water \\ Distilled water + Chloride (DW + C) & 100 ppm chloride in distilled water \\ Distilled water + Additive + Chloride & 13,000 ppm additive and 100 ppm chloride \\ (DW + A + C) & in distilled water \\ \hline \hline \end{tabular}
\end{table}
Table 3: Types and conditions of experimental solutions.  
the specimen. This setup is referred to as the \"stationary specimen method\". The distance between the vibrator and the specimen was kept constant at 0.5 mm. After cavitation erosion tests, weight loss measurements were conducted. Specimens were ultrasonically cleaned in distilled water, dried in an oven at 60 \({}^{\circ}\)C for 24 h, cooled in a desiccator for 30 min, and weighed at room temperature with a precision of 10\({}^{-4}\) g. The cavitation erosion experiment was repeated three times for each experimental condition to ensure reproducibility, and then the average weight loss was calculated. Surface morphology before and after cavitation erosion tests was examined using a scanning electron microscope (SEM, SNE-4500M Plus (SEC, Daejeon, Republic of Korea)). In addition, a confocal 3D laser microscope (Olympus, OLS5000-SAF (Jiangsu Caidao Precision Instruments Co., Ltd., Suzhou, China)) was used to measure surface roughness and maximum surface damage depth, providing a detailed analysis of cavitation-induced damage.