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.
Highlights
Wang [13] reported that the reduction in heat transfer due to inert gases is more significant at low pressures and low Reynolds numbers
Another fog building mechanism was reported by Land [5]: If the exhaust temperature near the interface falls below the dew point, droplet condensation in the boundary layer takes place causing fog formation
The interacting condensation model assumes that the equilibrium at the interface of condensate and exhaust gas forms in the same way as it would without inert gases; that means by a local change in binary composition
Summary
Goldbrunner [14] assumed that at high Reynolds numbers gaseous flow entrains droplets of the interface resulting in fog Another fog building mechanism was reported by Land [5]: If the exhaust temperature near the interface falls below the dew point, droplet condensation in the boundary layer takes place causing fog formation. In order to calculate the dew point of water and sulfuric acid this modelling approach, uses empirical formulas of Abel [19] These correlations base upon sparse date regarding the gas phase and show discrepancies with recent measurement data. A more recent model developed by Jeong [20] assumes pure film condensation and estimates the rates of mass transfer for condensation of sulfuric acid and water individually. In addition to experimental work with two cooler concepts, a one-dimensional condensation model taking the VLE of the binary system sulfuric acid - water into account is applied to achieve this
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