lets clarify somethings first

EGR- exhaust gas recirculation

Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates(from wikipedia)

sa loob ng combustion chamber mainit at mataas ang pressure... pag pasok ng hangin(air with oxygen and nitrogen components) together with fuel(either petrol or diesel) plus spark, magkakaroon ng combustion(pagsabog sa loob ng cylinder) one by product is NOx(nitrous oxide) which is harmful to most life forms(kasama mga tao), the greater the temperature(inside the cylinder) the higher the NOx that will be produce. unfortunately dahil modern times tau, we are using electronic controlled fuel and air delivery system( varied and air and fuel ratio according sa need ng vehicle) it will result again into higher NOx..

kaya naimbenta ang EGR, yung exhaust gases coming from the combustion process na papunta na sana sa labas ng tambutso gets recycled( a portion of the gases). it will be sucked and brought to the combustion chamber again to reduce the temperature. pag stable and temperature, ang NOx emission is reduced.

nitrogen +oxygen+high temp combustion=high NOx
nitrogen +oxygen+high temp combustion+ EGR= tolerable NOx

sa mga bagong vehicles, the valve that controls the amount of gases recirculated back is controlled and monitored by the ECU according to the demands of the vehicle.. in short mahirap paki-alamanan!

kapag CRUISING KA (around 60-80kph) the EGR is working at its best... why? because constant ang engine load so predictable ang amount of exhaust gas to be recirculated(LEAN BURN).. so the vehicle does not need so much oxygen or air that is.. therefore pag idle ka the EGR valve is fully closed.

kapag umaarankada ka o paahon o humahataw ka ng takbo the ECU will close the EGR valve to allow more oxygen to be burned.. when the engine needs more power , it needs more volume of air containing oxygen so the EGR will be closed off to provide a rich oxygen environment.. kaya pag mabilis takbo you are polluting the environment more..

IDLE= EGR closed.
CRUISING SPEEDS= EGR open
ACCELERATION/LOAD= EGR closed

in other countries it is illegeal to close EGR. kung luma sasakyan mo its forgivable, kase it will benefit the vehicle..

in the long run, EGR is a primary cause of Gunk and dirt inside the engine.