Which is right there and does a fairly miraculous job chilling things out, in relative terms. The actual EGR valve itself - which controls how much exhaust gets recirculated - is just there: #05.īut the bit we’re interested in is the EGR cooling system: #06. The EGR system taps into the highly energetic exhaust flow, just before the turbo. Even though that’s completely the wrong word for the mechanism of heat loss that’s doing the work. That’s bad, in inlet air, so intercoolers are air-to-air convective coolers. Air gets hot when the turbo compresses it. The zig-zaggy tube on the left (I know - it’s a big, scary technical word: ‘zig-zaggy’) - that is the intercooler: #02. It’s a way of doing something useful with heat energy which would otherwise be wasted. The orange side is the turbine driven by energetic exhaust gas flow. The blue side is the inlet compressor - which pumps air into the engine. Right up the top we’ve got a turbocharger: #01. That heat is ultimately rejected in the vehicle’s radiator, which is designed to stop some sort of mini, automotive Chernobyl. Therefore, water from the engine’s cooling system is pumped through the EGR unit, in a mini heat exchanger, whence it captures some of this heat before it gets to the EGR valve. Short version: The EGR system is water cooled - it’s capturing hot, highly energetic exhaust gas from between the manifold, and sending it back to the inlet side of the engine, and that heat is a gross disadvantage to engine operation. Certainly it’s counter-intuitive, but in fact doing this actually improves fuel economy and also reduces toxic emissions, because: physics. And I know you’re thinking: pumping exhaust back into a perfectly serviceable engine sounds bad. EGR stands for the ‘exhaust gas recirculation’, a system that pumps exhaust back into the inlet of your engine, at times, in measured doses.ĭiesels do this more enthusiastically than petrols, but they both do it.
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