How An Automotive Exhaust System Catalytic Converter Works Cat Dynomax Walker


Hi, I’m Joe [inaudible 00:00:09] from Tenneco
and the Walker brand of emission control products. In today’s program, we’re going to examine
a key component in automotive emission systems, the catalytic converter. Most vehicle owners don’t think about their
converters until the check engine light comes on. In many cases, the vehicle’s on-board diagnostic
system has registered a code related to the emissions system. More often than not, the actual problem has
occurred upstream of the converter in the engine, fuel, or ignition system. These issues can affect how well the converter
is able to do its job. So, what is that job? It’s actually pretty interesting. The seemingly simple component is actually
a very sophisticated piece of technology that significantly reduces a vehicle’s emissions
of harmful gases. Let’s take a closer look. Automotive engines run on precisely controlled
amounts of air and fuel, which are fed into the engine’s combustion chamber. This mixture is compressed then ignited. As the mixture burns, it rapidly expands creating
the mechanical force that ultimately drives the wheels. Following combustion, the leftover gases are
forced out of the engine and into the exhaust stream. Among these gases are three primary pollutants,
hydrocarbons or HC, carbon monoxide or CO, and nitrogen oxides or NOx. These gases pass through the catalytic converter,
which utilizes a sophisticated precious metals coated substrate. The coated substrate is used as a catalyst
for converting the pollutants into carbon dioxide and water vapor. Early converters were two-way units meaning
they cleaned up two gases, HC and CO, through a single catalyst process called oxidation. It’s important to understand that the catalyst
chemistry needed to clean up HC and CO works best when the engine is fed an artificially
higher amount of air in the air-fuel mixture. This means the engine is running lean. As emissions regulations became more stringent
in the 1980s, vehicle manufacturers needed to clean up not only HC and CO, but also NOx. But unlike HC and CO, the process of reducing
NOx requires an artificially higher level of fuel rather than air in the combustion
chamber. This condition is called running rich. To clean up all three gases and to create
both lean and rich conditions, engineers developed three-way converters. The earliest form of three-way converters
was known as three-way with air, and you’ll understand why in a second. Engines paired with these converters usually
are set to run rich with the resulting emissions first undergoing a reduction process in the
converter that cleans up NOx. Following this first catalyst process, air
is injected into the remaining gases to create an artificially lean air-fuel mixture better
suited for cleaning up HC and CO. Thanks to today’s sophisticated on-board electronics,
three-way with air converters have been replaced by modern three-way units that don’t require
the addition of air. Instead, modern three-way converters like
this locker unit, feature an advanced catalyst that stores and releases oxygen. It works in conjunction with the engine controls,
which oscillate the air-fuel mixture between lean and rich to ensure the proper reduction
of NOx and oxidation of HC and CO. The converter does this by storing oxygen
when the fuel system is lean and releasing the oxygen when the system switches to rich. Catalytic converters are amazing components
with no moving parts. And it’s important to understand that they
don’t fail on their own. Other issues cause them to fail. So don’t replace the converter until you fix
what killed it. That’s all for now from the Walker garage,
and we’ll be back with in-depth videos covering each step of emissions control diagnostics. Thanks for watching.