Catalytic converter


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Want to know what a catalytic converter is and what effect it has on a car? Learn more about a catalyst on this page.

What is a catalytic converter?

The main function of this part (also known as ‘catalyst’) is to transform the exhaust gases produced by the combustion engine in order to minimize the harmful components in the exhaust gas.

Combustion engines mainly produce hydrocarbons, carbon monoxides and nitrogen oxides. These toxic gases are converted or transformed by the cat into the non-toxic substances carbon dioxide, water and nitrogen.

Depending on the operating temperature of the engine and the operating condition of the catalyst, conversion rates of almost 100% can be achieved.

What does a catalytic converter do?

Although catalysts usually differ in shape among different vehicle manufacturers, their internal structure is usually the same.

Structure of a catalytic converter

A conventional catalyst usually consists of a stainless steel housing (there are exceptions, of course). Inside the cat you can find either a metallic (metal cat) or a ceramic (ceramic cat) support.
The carrier (ceramic or metal) is always installed longitudinally, so that the exhaust gases from the exhaust can flow through the carrier. There are many small channels in the carrier, visually comparable to a honeycomb. The many small channels serve to create the largest possible surface area. This is because the larger the surface is, the better the effect of the catalytic converter.
A so-called ‘wash coat’ is applied to the substrate surface by vapor deposition. This is a highly porous layer in which precious metals (palladium, rhodium and platinum) are embedded. These precious metals provide for the transformation of harmful substances within the exhaust gases.

The most common type of catalytic converter made from ceramics. In particular with high-performance vehicles, it may also be the case, that a metal catalyst is used in serial production.

Different types of catalysts

Three-way catalytic converter

The three-way catalytic converter is used only on gasoline engines and is the most common type of catalyst on more modern vehicles.

Once the catalyst has reached its optimum operating temperature, it converts the following substances:

  • Nitrogen oxides (NO2 and N2) in oxygen (02) and nitrogen (N2)
  • Unburned hydrocarbons (HC) in water vapor (H2O) and carbon dioxide (C02)
  • Carbon monoxide (C0) to carbon dioxide (C02)

Since these three conversions take place simultaneously in the catalyst, this converter is also called a ‘three-way catalytic converter’.

In order for the catalyst to show its full effect, a certain exhaust gas composition is required. This mixture during injection is known as the ‘stoichiometric mixture” or “lambda = 1”.

A stoichiometric mixture means that the engine receives exactly 14.7 kg of air in relation to one kilogram of gasoline during combustion.

To achieve precisely this mixture during combustion, a lambda sensor is located in the exhaust between the engine and the catalytic converter. This lambda sensor has the task of measuring the residual oxygen content of the exhaust gas and communicating this information to the engine control unit.

Lambda sensor catalytic converter

If the mixture is not optimal, the engine control unit has several options for changing parameters to restore the optimal mixture or the desired residual oxygen content in the exhaust gas.

As emission standards in many countries have become stricter in recent years, it has also become necessary to further develop catalysts. That is why modern three-way catalytic converters are able to reach their operating temperature within just a few seconds. On the one hand, that is achieved through special coatings. On the other hand, catalysts are increasingly being installed directly in the exhaust manifold so that they heat up more quickly.

Oxidation catalyst:

This type of catalytic converter is only used in diesel vehicles. Diesel engines always operate while having an excess of air. In fact, this means that the fuel mixture is adjusted to the air volume. For this reason, the combustion of a diesel engine produces a high proportion of oxygen in the exhaust gas.

Thus, a reduction of nitrogen oxides (NOX) is not possible compared to the three-way catalytic converter.

The oxidation catalyst is capable of converting the following substances:

  • Hydrocarbons (HC) in carbon dioxide (C02) and water vapor (H20)
  • Carbon monoxide (C0) to carbon dioxide (C02)

Due to the significantly lower exhaust gas temperatures in a diesel engine compared to a gasoline engine, oxidation catalysts are usually located very close to the exhaust manifold.

Unregulated catalyst:

An unregulated catalytic converter is a component in an exhaust system that helps to reduce harmful emissions from a vehicle’s exhaust. Unlike the regulated catalytic converter, which is equipped with sensors and a control unit to continuously monitor and reduce emissions, the unregulated catalytic converter has no such functions. Instead, it relies on a chemical reaction to reduce carbon monoxide, nitrogen oxides and unburned hydrocarbons. The unregulated catalytic converter was first developed in the 1970s and was the most common type of catalytic converter used in cars until the mid-1980s. Today, the unregulated catalytic converter is used less frequently due to stricter emission standards and the availability of more effective technologies. Nevertheless, it has made an important contribution to reducing pollution from cars.

The cost of repairing a catalytic converter

Assessing the cost of repair in connection with a catalyst is very difficult before knowing exactly the source of the issue.

A defect in the lambda sensor or a fault in the mixture preparation can already give an impression that there would be an issue with the catalytic converter. A defective lambda sensor would be the cheapest scenario at approx. US$ 50 – US$ 200. However, if the catalyst itself is defective, the repair (including installation and removal) quickly cost several thousand dollars.

How much is a catalytic converter worth?

The value of this component can vary depending on several factors such as:

  1. Type of vehicle: The value of this part can vary greatly depending on the make, model, and year of the vehicle.
  2. Type of catalytic converter: The value of the catalyst can also depend on the type of catalytic converter, such as a universal fit or a direct-fit catalytic converter specifically designed for a particular make and model.
  3. Precious metal content: The value of a catalytic converter is often based on the precious metal content, such as platinum, palladium, and rhodium, which can be recycled.

On average, a catalyst can be worth anywhere from $50 to $200, but the value can be much higher for catalytic converters with high precious metal content. In some cases, the value can be over $1,000 for high-end vehicles.

It’s important to note that the value of a catalytic converter can fluctuate based on the market price of precious metals, and it’s best to get an estimate from a reputable scrap yard or metal recycling facility.

How to use catalytic converter cleaner

  1. Check the manufacturer’s instructions: Before using the cleaner, it is important to read the instructions carefully to ensure that it is suitable for your vehicle and compatible with your catalytic converter. This information is usually found on the product label or in the product manual.
  2. Park the vehicle: Park your vehicle on level ground and turn off the engine. Ensure that the engine has cooled down completely before proceeding to the next step.
  3. Pour the cleaner into the gas tank: Pour the recommended amount of catalytic converter cleaner into your vehicle’s gas tank. Some cleaners come in a concentrated form that needs to be diluted with fuel. Be sure to follow the instructions on the product label carefully.
  4. Drive the vehicle: After adding the cleaner, start the engine and drive the vehicle normally for at least 15-20 minutes. The cleaner will circulate through the engine and catalytic converter, cleaning and removing any built-up deposits.
  5. Repeat as necessary: Depending on the severity of the build-up, you may need to repeat the process a few times to fully clean the catalytic converter.

Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.

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