# Effect of Marine Coolant Additives on Cavitation Erosion-Corrosion of Diesel Engine Cylinder Liner
## 1 Introduction  
Internal combustion engines convert the energy generated from the combustion of fuel and air within the cylinder liner into mechanical output. Cylinder liners are subjected to rapid fluctuations in load, temperature, and speed, and thus must be fabricated from materials capable of withstanding such harsh conditions [1]. Cast iron is commonly used for marine diesel engine cylinder liners due to its low cost and excellent machinability [2]. During solidification, carbon in cast iron forms graphite structures, either flake or spheroidal, which enhance wear resistance [3]. Effective coolant management is critical for maintaining optimal engine performance [4]. To prevent engine damage from excessive thermal loads during combustion, coolant must be adequately supplied to the outer surfaces of cylinder liners [5]. As the coolant directly contacts the liner surface, its condition is closely linked to corrosion and cavitation erosion [6]. Therefore, distilled water free of impurities should be used. However, distilled water produced by onboard freshwater generators is often highly corrosive, necessitating the addition of corrosion inhibitors to maintain coolant performance. Additionally, seawater, due to its high salinity, has the potential to induce corrosion damage in the cooling water system, necessitating careful consideration [7]. Seawater primarily entersthe system due to damage to the seals of seawater-based cooling systems, which are used to cool high-temperature coolant, during the heat exchange process [8]. Cast iron has poor corrosion resistance even under atmospheric conditions, and it is known to be easily corroded by small amounts of corrosive substances such as chlorides, nitrates, sulfates, and carbonates [9]. To mitigate this, engine coolants typically incorporate corrosion inhibitors that enhance both corrosion resistance and thermal conductivity [10; 11]. Cooling water can contain a variety of additives. Coolants based on ethylene glycol, carboxylates, and traditional nitrites have been extensively used over a long period to mitigate corrosion of cylinder liners [12; 13]. In particular, nitrite has attracted considerable attention from researchers due to its low cost and relatively excellent corrosion inhibition performance [14; 15]. In the context of iron corrosion, nitrite has been studied under various corrosive conditions such as solution temperature [14; 16; 17], nitrite concentration [17; 18], the concentration of aggressive ions [19], and the pH of the solution [20; 21]. In this context, primary attention has been focused on investigating the optimal characteristics of corrosion inhibitors and appropriately controlling the concentration of nitrite to reduce the risk of corrosion [22]. Nevertheless, if the nitrite concentration falls below the level required for effective corrosion prevention, pitting corrosion may occur. [23; 24]. Nitrite-based coolants require periodic replenishment due to the continuous depletion of nitrite ions. If proper coolant management is not carried out, corrosion may occur, causing leakage in various sealing areas, which may reduce the life and safety of engine parts. Cavitation erosion is another major cause of cylinder liner damage during engine operation [25; 26; 27]. Vibrations generated during the operation of internal combustion engines induce the formation and collapse of cavitation bubbles, causing erosion on the outer surface of the cylinder liner. This phenomenon is caused by the piston slap motion in which the piston moves up and down within the cylinder liner, impacting the inner wall of the cylinder liner [28]. The excessive vibrations generated on the outer surface of the cylinder liner induce rapid formation and collapse of micro vapor bubbles within the coolant, resulting in cavitation erosion damage to the cylinder liner surface. The most significant adverse effect of such cavitation erosion damage is the formation of holes in the cylinder liner surface, leading to the mixing of engine coolant with the lubrication oil system.