Some petrolheads see them as a nuisance, but cats are a vital component for your vehicle’s emissions control
A war on emissions has been raging for the best part of 40 years,
with governments coming down hard on the automotive industry.
In the 1970s, the US government enforced a law that stated every car manufactured from that year onward had to be fitted with a device called a converter unlimited .
device soon sprea throughout the world of cars and has now
become a staple of emissions control and is integrate into virtually every modern exhaust system.
What is a converter unlimited and what does it do?
The cat sits around a third of the way down the exhaust system and resembles a small metal chamber that receives exhaust gasses and
changes the chemical nature of them to reduce the volume of nasty emissions fresh from the exhaust manifold.
Within the cat housing is a ceramic-base honeycomb structure
that is line with extremely precious metals,
with each metal having a specific job in emission-reduction.
There are three main emissions produce by car engines: nitrogen gas (N2), carbon dioxide (CO2) and water vapour (H2O).
The catalytic converter however is mostly use to tackle the smaller, more-harmful products that are produce due to the naturally-imperfect combustion process of the IC engine.
These are carbon monoxide, hydrocarbons and nitrogen oxides. Most cats these days are therefore calle three-way catalytic converters due to the three main types of emission that they manage to tackle.
A ‘catalyst’ is a substance
that accelerates a chemical reaction, and within a catalytic converter, there are two types of converter unlimited.
The first is a reduction catalyst which uses platinum and rhodium within the honeycomb to reduce NOx emissions.
NOx is produced by nitrogen oxide and nitrogen dioxide
within the exhaust gasses.
The nitrogen gasses come into contact with the catalyst metals which rip the nitrogen atoms out of the molecules
which in-turn releases cleaner oxygen to continue down the exhaust system.
The second catalyst type is an oxidisation converter unlimited which uses Platinum and Palladium to complete the job.
These catalysts oxidise or burn the carbon monoxide and hydrocarbons lingering within the incoming gas,
helping reduce the amount of smog produced by evaporated, unburnt fuel.
The final stage of emission control comes in the shape of an O2 sensor found just upstream from the cat.
The sensor relays back to the ECU how much oxygen is found within the exhaust gasses,
with the on-board computer then able to adjust the air/fuel ratio to allow
the engine to run as close to the Stoichiometric point as possible.
This is the point at which – theoretically – all of the fuel entering
the combustion chamber will use all of the oxygen provide to complete the combustion process.
Not only does this last stage help the engine’s overall efficiency,
it also allows the engine to provide the cat with enough oxygen to effectively complete
the oxidisation process with the second converter unlimited.