TimothyPilgrim wrote:
But what is the intended outcome? What's the benefit?
An EGR routes exhaust (soot and all) back into the air intake in low
engine power situations. This reduces combustion temperatures and
reduces the formation of oxides of nitrogen. It also reduces combustion
efficiency, increases fuel consumption and increases particulate/soot
production. Most older ('80s or older) Mercedes turbodiesels with a
working EGR feel a little sluggish at low speeds and (especially if
largely city driven) develop considerable soot accumulation in the
intake air path. When soot accumulation becomes sufficient, the pressure
path from the intake manifold to the ALDA is eventually blocked so that
fuel enrichment is inhibited or prevented and engine power can be
limited to about 70% of rating (a 120 hp turbo engine is limited to
about 80 hp).
Because there is no enrichment circuit on non-turbo engines, EGR
operation is much less detrimental (but the air intake path will
eventually become choked and that can cause a detectable power loss).
By disabling the EGR, soot from the exhaust is no longer redirected thru
the air intake path so there's no soot to accumulate, combustion
efficiency is preserved, particulate content of the exhaust is reduced
dramatically, BUT NOx output increases a bit.
The decrease in NOx that the EGR provides for Mercedes diesels is rather
modest. Last time I researched it, it was claimed that most Mercedes
diesel engines even without a working EGR produce less NOx than most
gasoline engines (with ALL of their emissions controls working, but just
a little below peak efficiency) that are more than a few years old.
Still, without the EGR, they will not meet current emissions standards
for new cars so can't be sold in the US.
I believe that the oxidation CAT used on the later OM60x engines reduces
NOx.
Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 182Kmi, '84 190D 2.2 229Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5
turbo 237kmi
