Influence of water vapor condensation on exhaust gas recirculation cooler fouling

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger known as an EGR cooler. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. The focus of this study was to investigate whether surface condensation of water vapor could be used to remove the accumulated deposit mass from various types of deposit layers typically encountered in EGR coolers. Both visual and quantitative evidence of water vapor condensation and deposit removal were collected. A multi-cylinder diesel engine was used to produce three different deposit layers in a custom built single rectangular channel EGR cooler. The deposit layers were then exposed to water vapor condensation over a range of coolant temperatures, flow rates and exposure times by adjusting the engine operating conditions. Significant flaking and removal of deposit layers made up of mostly soot particles was observed when exposed to condensation of water vapor even with an exposure duration as low as 5 min. However, very little removal of deposit mass with exposure to water vapor condensation was observed when the deposit layer consisted of condensed exhaust hydrocarbon species in addition to soot. In addition to engine experiments a visualization test rig was setup to visualize condensation of water vapor from clean humid air and its effect on different deposit layers. Surface condensation of water vapor can lead to significant removal of certain deposit layers from the cooler walls and, thus, mitigate fouling of the EGR cooler. It could potentially be used as regeneration strategy for periodic on-board regeneration of fouled EGR coolers.