Condensation-Fouling Interaction in Low-Temperature EGR-Coolers

Abstract

EGR cooling is a worthwhile technology capable of reducing NOx-emissions and increasing the efficiency of CI engines. Challenges arise when low-temperature cooling is applied with high fuel sulfur contents. The resulting sulfuric acid condenses in conjunction with the water of the exhaust gas and gives rise to corrosion of coolers and engine components. Additionally, fouling of the EGR cooler is exacerbated by the condensation of acidic components compromising EGR performance. In order to gain a better understanding of the underlying processes a combined experimental and model-based approach is presented. Tests of two different EGR-cooler concepts under various conditions showed a strong influence of the fuel sulfur content on fouling and condensation. The one-dimensional cooler model developed alongside these experiments consists of an activity coefficient model (NRTL) of the binary system water -sulfuric acid and a condensation model that allows for simulating the coupled condensation of both vapor components. Comparison of experimental fouling and simulated condensation results show good agreement in interpreting critical fouling phenomena that occur at temperatures in between the acid-water dew point and the dew point of pure water.

An experimental study of the effect of condensing water vapour on the cold corrosion wear of marine engine cylinder liners

“…The analogy has been frequently used to model condensation of sulfuric acid onto various shaped surfaces. 4,[28][29][30] The subscript "i" refers to either H 2 SO 4 or H 2 O. For both species, the difference between its partial pressure within the bulk cylinder gas (x i,B Á p) and its partial pressure in the gas-liquid interphase at the liner surface (x i,S Á p) acts as a "driving force" for the condensation.…”

“…The continuous improvements of the thermal efficiency and emission reductions of large two-stroke marine diesel engines have led to higher operating pressures, especially under low-and part load operation (slow steaming). It is generally accepted, that liner corrosion is coupled to the fuel bound sulfur, [1][2][3][4][5] and the higher cylinder gas pressures in combination with the use of heavy fuel oil (HFO) with up to $5% (by mass) sulfur can negatively affect the liner wear rates.…”

Modeling the condensation of sulfuric acid and water on the cylinder liner of a large two-stroke marine diesel engine

“…Teetz [18] formulated a corrosive threat factor (without modeling condensation) based on the partial pressures of H2O and H2SO4 in the cylinder gas and argued that the thread is high in the top of the liner. For gas coolers with various geometries sulfuric acid condensation has been modeled using the Chilton-Colburn-analogy [19][20][21]. The analogy couples convective heat and mass transfer.…”