MAX NOX is a direct function of peak combustion temperatures. Exhaust Gas Recirculation was the first solution back in the late 60s.
By adding exhaust gas to the intake mix the peak temperatures were lowered abbout 300 degrees. When people tried to disconnect them the engines knocked themselves to death unless they retarded the timing which caused power losses and unburned hydrocarbons.
Modern engines have, some cases eliminated EGR by changing valve timing of the exhaust valves to keep more exhaust gas in the combustion chamber without the necessity for an egr valve.
I always hated EGR beacuse when it combines with PCV vapors it forms a tar like residue in the intake manifold, and when the EGR passageways become plugged, the CPU retards the ignition to prevent knocking and your power and mileage suffer significantly, because the system was designed to work properly with EGR.
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This debate is suffering badly from lack of data, and lack of new arguments. Everyone seems to be going back and forth with the same stuff. So, I googled it up, and found lots of information on another hypermiling forum. I'll post it in chunks to make it easier to review and respond.
My '00 Civic (with knock sensor) is showing ~10% mileage improvement with a WAI pulling hot air from right next to the exhaust manifold. Aside from driving style, it has been the best single thing I've done for FE.
I recently got the idea to block the door from the exhaust manifold to the breather in the open position all the time to act as a WAI. Since doing this I've been seeing considerablely better mileage. MPG since doing this have been 46.478, 41.976, 44.198, 44.2 and 42.853. Some of these mileages are in line with what I usually get during summer months when the weather is warm and have summer blend gas.
Within the framework of research and development (R&D) activities on four-cylinder internal combustion (IC) engine in a low load state, a research for influence of mixture temperature on engine parameters has been performed. Content of this article will be describe of changes of low load engine parameters by increasing of mixture temperature. On the base of measured data, the increasing of mixture temperature causes increasing of mixture combustion rate and it has a positive effect on the low load engine parameters, especially on fuel consumption. Achieved results in this topic give impulse for continue of this research.