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according to the Environmental
Protection agency's estimate in 2019
seven percent of the light duty vehicles
in the United States did not comply with
their mandated vehicle emissions
regulations even more astonishing is the
fact that one specific component on
these vehicles account for about 68 of
these compliance failures for many of
that seven percent this light represents
a repair bill that can span anywhere
from 900 to over twenty seven hundred
dollars depending on the vehicle and at
the heart of this statistic is a
mandated component that seemingly adds
no benefit to the performance of the
vehicle it's fitted to the catalytic
converter
though the catalytic converter has
become the primary mechanism of the
automobile industry for controlling
exhaust emissions in internal combustion
engines its origin is a byproduct of
industrialization as a whole during the
turn of the 20th century the smog
created in urban areas by Factory Smoke
Stacks triggered the first concerns for
air quality
as the automobile and the internal
combustion engine became more abundant
their impact on air quality grew more
worrisome
during the 1940s in the United States
the growing problem of urban smog
specifically in the Los Angeles area
prompted the French mechanical engineer
Eugene hujri to take interest in the
problem
who drew was an expert in catalytic oil
refining and had developed techniques
for catalytically refining heavy liquid
tars into Aviation gasoline these
methods were instrumental to U.S wartime
Aviation field production during World
War II following World War II hoodri
founded a company called oxycatalyst
applying his expertise to the air
pollution problem his device called a
catalytic converter or cat was initially
intended for industrial use but would
then be adapted for gasoline engines
eventually resulting in a patented
catalytic converter designed for
automotive use hugeur's design worked by
flowing exhaust gases through a chemical
structure with a high surface area
coated in a catalyst the Catalyst would
induce a chemical reaction in the
exhaust gases causing the primary
pollutants to oxidize into less harmful
chemicals the fundamentals of this
design would carry forward to Modern
catalytic converters as a greater
understanding of air pollution would
bring about drastic regulatory changes
the exhaust gases of all internal
combustion engines used on vehicles is
composed primarily of three constituent
gases nitrogen carbon dioxide and water
vapor in lean operating modes of
gasoline engines and in diesel engines
oxygen is also present diesel engines by
Design generally operate with excess air
which always results in exhausted oxygen
especially at low engine loads the
nitrogen and oxygen are primarily
pastors of atmospheric gases while
carbon dioxide and water vapor are the
direct products of the combustion
process
depending on the engine type and
configuration these harmless gases form
98 to 99 of an engine's exhaust however
the remaining one to two percent of
combustion products comprises thousands
of compounds all of which to some degree
create air pollution
the primary components of these
pollutants carbon monoxide and nitrogen
oxides are formed within the highly
reactive high temperature flame zone of
the combustion cycle while unburned and
partially oxidized hydrocarbons tend to
form near the cylinder walls where the
combustion flame is quenched particulate
matter especially in diesel engines are
also produced in the form of soot in
addition to this engine exhaust also
contains partially burnt lubricating oil
and Ash from Metallica additives in the
lubricating oil and wear Metals Beyond
this a myriad of Trace compounds are
also present for decades it was not
fully understood how these exhaust
products created smog especially during
bright sunny summer months finally in
1948 after collecting samples from the
polluted air of Los Angeles flavor
chemist Ari haugensmith was able to
identify ozone as a primary component of
smog from this Hagen Smith discovered
that nitrogen oxides from Automotive
exhausts and gaseous hydrocarbons from
both vehicles and Industrial processes
when exposed to sunlight would form form
peroxy acyl nitrates and ozone this
process is known as photochemical smog
additionally some of the sulfur dioxide
and nitrogen oxides from exhaust gases
eventually are oxidized in the
troposphere to nitric acid and sulfuric
acid which when mixed with water form
the primary components of acid rain smog
particularly in dense Urban regions is a
major health hazard ground level ozone
sulfur dioxide nitrogen dioxide and
carbon monoxide are especially harmful
to senior citizens children and people
with health and lung conditions the
peroxy acyl nitrates created in the
atmosphere are also powerful respiratory
and irritants several major Studies have
also found links between mortality and
the presence of smog one such study
published in nature magazine found that
over a four year period smog episodes in
the city of Janan in Eastern China were
associated with a 5.87 percent increase
in the rate of overall mortality
in 1970 the United States passed the
clean year act which required all
vehicles to cut their emissions by 75
percent in only five years
one of the most significant objectives
of the cleaner Act was the removal of
the anti-knock agent tetraethyl-led from
most types of gasoline up until this
point lead and fuel had prevented the
use of catalytic converters on vehicles
it tended to cake on the operating
surfaces of a catalytic converter
rendering it ineffective with lead now
removed from Gasoline by 1975 the first
widespread use of catalytic converters
and vehicles began in the United States
modern Automotive catalytic converters
are composed of a steel housing
containing a catalyst Support called a
substrate that's placed in line with an
engine's exhaust stream
because the Catalyst requires a
temperature of over 450 degrees Celsius
to function they are generally placed as
close to the engine as possible to
promote rapid warm-up and heat retention
on early catalytic converters the
Catalyst media was made of pallets
placed in a packed bed these early
designs were restrictive sounded
terrible and wore out easily during the
1980s this design was superseded by a
ceramic-based honeycomb monolithic
substrate coated in a catalyst the
honeycomb structure used is typically
cubic in nature these new cores offer
better flow and because of their much
larger surface area exposed more
Catalyst material to the exhaust stream
the ceramic substrate used is primarily
made of a synthetic mineral known as
cordurite during the manufacturing
process the corduroid crystals are
purposely aligned along one axis in
order to resist cracking from the
thermal cycling of Automotive use in
order to disperse the catalytic material
on the substrate it's suspended within
an aluminum oxide-based wash coat
designed to form a rough irregular
surface this is done to further increase
the catalytically active surface area as
well as to prevent sintering of the
catalytic metal particles at
temperatures above 1000 degrees Celsius
the Catalyst material used is generally
a mix of three precious metals from the
Platinum Group Platinum Palladium and
rhodium the exact composition used is
dependent on the engine displacement and
the type of fuel used
each metal covers one specific type of
reaction rhodium is used as a reduction
Catalyst Palladium is an oxidation
Catalyst and platinum is used both for
reduction and oxidation the first
generation of Automotive catalytic
converters used up until 1981 worked
only by oxidation these were known as
two-way converters as they could only
perform two simultaneous reactions the
oxidation of carbon monoxide to carbon
dioxide and the oxidation of
hydrocarbons to carbon dioxide and water
by 1981 the three-way catalytic
converters had superseded their two-way
predecessor in the United States and
Canada many other countries would also
adopt similar stringent vehicle emission
regulations making their use now a
requirement three-way catalytic
converters induce chemical reactions
that reduce nitrogen oxide to harmless
nitrogen this reaction can occur with
either carbon monoxide hydrogen or
hydrocarbons within the exhaust gas in
order to support the competing reactions
Sirius zirconia is added to three-way
catalytic converters allowing them to
store and release oxygen between them
while three-way catalytic converters are
more efficient at removing pollutants
their effectiveness is highly sensitive
to the air fuel mixture ratio for
gasoline combustion this ratio is
between 14.6 and 14.8 Parts air to one
part fuel furthermore they need to
oscillate between lean and Rich mixtures
within this band in order to keep both
reduction and oxidation reactions
running because of this requirement
computer-controlled closed-loop
electronic fuel injection is required
for their effective use
when the combustion process is made lean
there is more oxygen than is required
this causes the reaction to favor the
oxidation of carbon monoxide and
hydrocarbons excess oxygen is also
stored by the serious zirconia during
the state when the system Cycles back to
running rich there is more fuel than
needed and the reaction now favors the
reduction of nitrogen oxides because the
oxygen in the exhaust stream is now
reduced the oxygen stored within the
Syria zirconia begins to release
stimulating the oxidation reaction these
reactions operate at a constant
imbalance resulting in the system never
achieving 100 efficiency furthermore too
lean of a mixture can cause oxidation
damage to the reduction Catalyst while
too rich of a condition renders the
oxidation reaction ineffective on diesel
engines the damaging effect of the
excess oxygen in their combustion
process limits them to two-way catalytic
converters nitrogen oxides are typically
mitigated with other systems such as
exhaust gastric circular relation and as
of 2010 the use of ammonia to reduce
nitrogen oxides to nitrogen known as
selective catalytic reduction the
ammonia is introduced to the catalytic
system by the injection of a urea
solution called diesel exhaust fluid
into the exhaust stream additionally
newer diesel engines are also fitted
with diesel particulate filters to
supplement their catalytic converters
because air fuel ratios are so critical
to three-way catalytic converters a
mechanism to sense this becomes critical
to their efficacy known as an oxygen
sensor or a Lambda sensor these
electronic devices measure how rich or
lean combustion is within a narrow band
of air fuel ratio from the oxygen
present in the exhaust stream typically
this band aligns with the efficiency
zone of the catalytic converter oxygen
sensors provide a feedback signal to the
fuel injection system creating a closed
loop in which it can closely oscillate
lean and Rich conditions in order to
maximize catalytic converter efficiency
a more sophisticated variant known as a
wideband air fuel sensor is sometimes
used instead to further refine control
of the air fuel ratio an oxygen sensor
is also used to verify the operational
efficiency of a catalytic converter by
comparing the oxygen level Downstream of
the catalytic converter against the
sensor Upstream of it this mechanism is
a key feature of the OBD1 and OBD2
onboard diagnostic standard which
constantly monitors the functionality of
the vehicle's emission control system
alerting faults through a check engine
light it's estimated that on average the
Flow Restriction caused by a modern
catalytic converter system reduces Peak
engine power by roughly one percent and
in exchange the EPA estimates that the
introduction of catalytic converters and
other improvements in air quality have
saved more than one hundred thousand
lives and has led to a 40 percent
reduction of carbon monoxide emitted by
cars trucks and motorcycles
it took careful scientific observation
to connect the dots between cause and
effect with air pollution ultimately
leading to the catalytic converter as a
solution the scientific approach allowed
new ideas to be combined with existing
Technologies to solve a difficult
problem and with brilliant building this
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