Regulators have imposed more stringent regulations on the emissions of marine engines (Tier II NOx regulations). These regulations together with the pressure to reduce operating costs have resulted in more fuel efficient engine designs that operate at a temperature that is below the dew point of water.
In previous engine design sulfur was only present in the form of SOx gas. Now, because of the lower temperature, sulfur can react with water, that condenses on the liner of the cylinder walls, to form sulfuric acid, resulting in corrosion on the liner surface. This process is called cold corrosion.
Cold corrosion not only impacts the latest engine designs but also earlier engine designs that have been modified for part-load or low-load operation (known as ‘slow steaming’). Many ship operators have switched to slow steaming to save costs.
The key parameters that influence cold corrosion are the cylinder temperature, the base number of the cylinder oil, the load factor, the lubricator feed rate and the sulfur content of the fuel. These parameters are interdependent making it a challenge to find the optimum working point of the engine. The IR SPhinx spectrometer range is a very useful tool optimize the engine operation. By analyzing the infrared absorption spectrum of the cylinder oil many relevant oil parameters such as Total Acid Number (TAN) and Total Base Number (TBN) can be extracted. This information can then be used to adjust feed rate and the sulfur content of the fuel to optimize the engine.