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Exhaust Gas Recirculation (EGR) is a consolidated in-cylinder technique in the automotive industry to decrease the Nitrogen Oxide (NOx) emissions of both diesel and gasoline engines. In order to comply with more stringent NOx limits the recirculating technology has evolved to enable higher EGR flow rates and accommodate more advanced control strategies. The increase in the cooling load demands the utilization of compact coolers with high thermal efficiency and the minimum pressure drop in both gas and coolant sides. In addition to the performance requirements, the design of the EGR cooler has a severe packaging constraint, is affected by the pulsating flow and fouling in the gas side and has to withstand high thermal stresses due to the large temperature gradients between the hot exhaust gases and the coolant.

Future NOx emissions limits are very difficult to meet with conventional high pressure EGR loop. This limitation causes diesel engine manufacturers to give much more attention to low pressure EGR systems. This configuration enables higher EGR flow rates and therefore lower NOx emissions at the same engine operation conditions. The implementation of low pressure loop ensures sufficient driving pressure for the EGR flow rate however conventional compressors are not specifically designed to endure the fouling of Diesel exhausts. An improved version known as clean low pressure loop takes the EGR source downstream of the diesel particulate filter keeping the compressor free of soot. The performance of the compressor improves substantially but it is necessary to protect it from eventual ceramic particles that can be discarded from the DPF.