Numerical Investigation of the Effect of Conjugate Heat Transfer on Sulfuric Acid Condensation in a Large Two-Stroke Marine Diesel Engine

Sulfuric acid condensation on liner walls in large two-stroke marine diesel engines may lead to cold corrosion and hence excessive liner wear rates. Understanding of the phenomenon and factors influencing it is therefore important. In this study we present results from a numerical investigation of sulfuric acid and water vapor condensation in a large two-stroke marine diesel engine using computational fluid dynamics (CFD) incorporating conjugate heat transfer modeling between the cylinder gas and liner wall.

The combustion phase of the engine cycle is simulated using a reduced n-heptane chemical kinetic mechanism including a sulfur chemistry subset for modeling the formation of sulfur oxides and subsequently sulfuric acid vapor. Condensation of sulfuric acid and water vapor on the cylinder liner is evaluated by determining if the local liner temperature is below the local dew point of sulfuric acid and water, respectively.

A layer of 25 solid cells is added on the cylinder liner to represent the liner material for the implementation of conjugate heat transfer calculations between the cylinder gas and liner. The thickness of the cell layer is 5 mm, and we use a temperature boundary condition on the backside of the cell layer based on experimental measurements.

We compare the obtained results with results where conjugate heat transfer calculations are not considered, and the influence on the results is evaluated to determine the importance of incorporating the interrelated thermal dynamics of the combustion gas-solid wall system.