Doctor Diesel

Negative feedback?

IconI have been meaning to ask you, Doctor, about exhaust gas recirculation (EGR), and its associated problems. We’re always reading about EGR systems getting gummed up with short run driving, and use of inferior fuels and oils, but is this really surprising, if the EGR works the way that I understand it does? Surely if the exhaust gas is taken direct from the exhaust manifold, and pushed back, or sucked back, into the inlet air, then this gas must be contaminated with the particulates that get taken out of the exhaust gas further along the exhaust system in the particulate filter? So the particulates in the recycled gases are sent around the block again, as you might say, without anything being filtered out. Is this not an obvious negative feature, and a possible reason why EGR systems and their valves regularly get clogged up?
Bill Newsome

This is indeed the case Bill, and it’s the reason why manufacturers are moving towards what they call long route low pressure EGR, where the recirculated gases are taken from a point in the exhaust system after the diesel particulate filter (DPF), after they have been cleaned up in the DPF, and where they are also considerably cooler. That improves turbocharger life, a greater proportion of clean and cold exhaust gas recirculation is possible, the gases being much cooler too, reducing combustion temperatures and helping to reduce NOx generation. It’s an appropriate point to also observe that anyone having their DPF removed on a car equipped with this type of EGR is going to probably significantly reduce the life of their turbocharger, apart from running the risk of an MOT failure.

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