Sun Microsystems MCS 2000 SL - Page 68

Oxides of Nitrogen
Nitrogen
(N)
makes
up approximately
80
% of the
air
we
breath,
the
balance
of
approximately
20
%
is
oxygen.
An
internal
combustion
engine
uses the
oxygen
02 to
operate
and
exhaust
the nitrogen'.
However,
oxides
of
Nitrogen
NOx
are
formed
when
the
combustion
temperature
exceeds
1370
degrees
Celsius.
Although
Nox
compounds
do not
directly
effect
how
the
engine
works,
when NOx
combine with
unburnt
fuel
HC,'in
certain
atmospheric
conditions,
they
are the
basis
of sMoG.
For
this
reason,
Nox
(Measured
in
grams per
mile)
are measured
for
the
type
approval
test.
To reduce
a
part
of
the
Nox,
a
device
called
EGR
(Exhaust
Gas
Regulation)
valve
is
used.
This
valve
provides
lower
combustion
temperatures
by
recirculating
exhaust
gases
back to
the
combustion
chamber.
There
is not
much
what
the
Mechanic/Technician
can
do to control
emissions
except
to make
sure
that
the
engine
and
the
EGR valve
(if
installed)
are functioning
correctly.
It
is not
practical
to measure
NOx
in
the
service
workshop
without
the
use
of
a
dynamometer
and
special
equipment.
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