Why does NOx increase with EGR at 8% engine loading?

[Ali Durrani]

Hello
i have done tests on Exhaust gas re circulation on my engine test bench and these are the results, i don't know what's wrong? but at 8% loading conditions i am getting some weird results
the trendlines in the graph shows an increase in NOx with EGR
is there any explanation for this ? thanks

 

[Ketch22]

Do you have access to the fuel map for the engine you are using? NOx production is indirectly related to the Stoichiometric ratio. At different volumetric efficiencies the AFR tends to migrate. This is often due to the Map used in the Engine Control Unit. Some of them use a grid as small as 16x16 to cover all load and RPM conditions. This can lead to wandering results which are occasionally cyclic.
I would suggest running tests with a wide band O₂ sensor to evaluate mixture and again with an Exhaust Gas Temperature sensor to look for variations and effects that may be contributing.