Exhaust stink

[Rudi Machilek]

The stink is Hydrogen Sulfide (H2S) not Sulfuric Acid (H2SO4).  The sulfur
comes from the fuel (No sulfur in fuel or oil, no rotten egg smell).  You
pretty well need a significant lack of oxygen (real rich burn) to make
Hydrogen Sulfide. The catalytic converter has to be running rich also.  The
problem is only evident when the catalytic converter is not yet lit or
poisoned by lead.  The converter provides a great deal of surface area to
promote undesirable reactions (Harder to smell rotten eggs from a non
converter car).  Some designs are a lot worse than others. As soon as there
is enough oxygen around at temperature, in either the combustion chamber or
catalytic converter, one gets the various oxide forms instead.  These oxide
forms are acid rain and smog problems, but do not smell like rotten eggs.
At very high combustion temperatures (lean burn conditions), thermal NOx is
formed and SOx is formed (in greater abundance) which when combined with
water make Nitric Acid and Sulfuric Acid.  These are also valve burn or at
least high EGT conditions.

ECM content; work on fuel map to keep A/F ratio in range and EGT under
control.  If running cats, keep air pump.  Rotten egg smell is not as much
of an issue with newer ECMs with post cat O2 sensor.

Kept most of the chemistry and thermo out, but I believe accurate enough.

Rudi Machilek
formerly Project Engineer/Manager under contract with EPA, both Stationary
Sources and Mobile Sources, RTP, NC


>> Whats the reason some vehicles STINK from unleaded fuel / cat
>> convertors and others don't
>> Geoff
>>
>