The catalytic converter (catalytic converter, catalyst) is a key element of the exhaust gas toxicity reduction system. It provides both afterburning of unburned fuel and recirculation, that is, the return of part of the exhaust gases back to the engine cylinders. In general, the catalyst purifies automobile exhaust. Depreciation of the converter is accompanied by a noticeable increase in fuel consumption and a deterioration in exhaust performance. Replacing the catalyst in the workshop is very expensive, so an independent repair will save you a considerable amount, for this you will need a few simple tools, a jack and supports. Just follow the developed algorithm of actions, and you will succeed.
- reduction of carbon monoxide in exhaust gases,
- reduction of hydrocarbon levels in exhaust gases,
- reduction or complete removal of nitrogen oxides from the exhaust gas composition.
The objective of an automotive catalytic converter is to reduce the amount of harmful substances in exhaust gases. Among them:
- carbon monoxide (CO) - a poisonous gas without color and odor (carbon monoxide)
- hydrocarbons (CH), also known as volatile organic compounds - one of the main components of smog, is formed due to incomplete combustion of fuel
- NOx (NO and NO2) - are also components that cause the formation of smog and acid rain, affect the human mucosa.
Most often, the converter is located immediately after the exhaust pipe, but sometimes it is installed directly on the exhaust pipe. They do this for faster heating, since it only works effectively at temperatures above 300 ° C. However, a big minus of this arrangement is too high temperatures and, consequently, a short catalyst life.
The main substances produced during engine operation are harmless. They are:
- nitrogen (N2) - air consists of 78% of nitrogen,
- water (H2O)
- carbon dioxide (CO2) - in itself is harmless, but it is believed that its oversupply leads to global warming,
However, the combustion process is not perfect and, in addition to harmless substances, toxic and harmful substances are released during engine operation. These substances are:
- hydrocarbons (CHx) - the main component of smog,
- nitrogen oxides (NOx) Is another component of smog,
- carbon monoxide (CO) - a poisonous gas without color and odor,
Modern catalysts are three-component, that is, equipped with three catalytic converters, one for each substance, the amount of which must be reduced. The three-component catalyst is a stainless steel metal housing containing a “honeycomb” structure or, less commonly, a “ceramic bead” type structure. The honeycomb structure is metal or ceramic and is coated with catalyst substances, usually platinum, rhodium or palladium (recently, gold is being used on some models, since it is cheaper than other metal catalysts). Ceramic design is more common, as it is cheaper, however, this design has a big minus - fragility. A small blow is enough for the ceramic honeycombs to crumble. Two types of catalysts are used in catalytic converters: reducing and oxidizing.
The reducing catalyst uses platinum and rhodium to reduce nitrogen oxide emissions. When a molecule of nitrogen oxide or dioxide meets with the molecules of the catalyst, a nitrogen atom separates from it, releasing oxygen. The nitrogen atom also binds to another nitrogen atom, forming gaseous nitrogen.
The oxidizing catalyst reduces the amount of unburned fuel and carbon monoxide by burning (oxidizing) it with platinum and palladium. This catalyst also helps carbon monoxide react with unburned oxygen to form carbon dioxide. In a simplified form, these chemical reactions are as follows:
As a result of these reactions, toxic harmful substances CO, CHx and NOx are reduced or oxidized to harmless water H2O, nitrogen N2 and carbon dioxide CO2 .
The neutralizers used in automobiles require the engine to operate at an excess air ratio (α) of as close as possible a unit. This makes it impossible to use a lean mixture (α> 1) to increase economy and a rich mixture (α Catalysts in diesel engines Edit
Catalytic converters of diesel engines do poorly in reducing NO emissionsx. One of the reasons is that diesel engines themselves operate at lower temperatures than gasoline engines, and the inverters perform better when heated. Some leading experts in the field of "green" automotive industry have come up with a new exhaust system that helps correct this shortcoming. They inject an aqueous urea solution into the exhaust pipe before the gases reach the converter. This causes a chemical reaction that reduces the amount of NOx. Urea, also known as urea, is an organic compound of carbon, nitrogen, oxygen and hydrogen. It can be found in the urine of mammals and amphibians, which explains this name. Urea reacts with NOx with the production of nitrogen and water vapor, reducing the amount of nitrogen oxides in the exhaust gases by more than 90 percent. At the moment, automotive catalysts are actively buying catalyst reception centers for utilization and processing throughout Russia. This is due to the deposition of a platinum group of metals in automotive catalysts.
Catalytic converter (collector)
Such close proximity of the massive and hot catalytic converter to the engine makes it difficult to layout the engine compartment and leads to an increase in temperature in the engine compartment. But then the heating of the active zone of the collector after starting the engine is faster. After all, only a heated catalyst is able to effectively purify exhaust gases. Catalytic reactions are effective only at temperatures above 300 degrees Celsius.
Catalytic converter car Lada Priora
For the correct operation of the system, oxygen sensors (lambda probes) are installed in front of the catalytic unit and immediately after it. The sensor standing before the converter is called the control, and the sensor installed after it is called the diagnostic one.
In world practice, another arrangement of the catalytic converter is also used. Such a scheme with the location of the barrel of the catalytic converter under the bottom of the car appeared at the dawn of applying this method of reducing exhaust gas toxicity and is still used, for example, on Renault cars with Euro-4 and even Euro-5 standards.
Lada 4x4 exhaust system
The catalytic converter is considered to be a reliable element in the construction of a modern car, and manufacturers do not provide for a regulation for its replacement. That is, in their opinion, the service life of the collector or element under the bottom of the car should be equal to the service life of the entire car. Nevertheless, practice has shown that catalytic converters do not always serve flawlessly.
How's the warranty going?
Against the background of this attitude towards the consumer, a sharply negative attitude is caused by the position taken by the Kia concern. In the service book of cars of this brand until the beginning of 2016 there was an inscription that the warranty on the catalytic converter extends up to 1 (!) Thousand kilometers. Roughly speaking, two fueling stations, and then “bad Russian gasoline” can damage the catalytic converter, but the company is no longer responsible for this. However, since 2016 the warranty on the catalytic converter has been extended to 150 thousand km.
According to the author, the guarantee for a catalytic converter should be no less than for a car.
Now let's take a closer look at what should and should not be done by the car owner so that the converter can serve happily ever after.
Reasons for the failure of the catalytic converter:
- Poor fuel quality - most often with a low octane rating. The engine management system switches to late ignition. This causes the mixture to burn out at the outlet and increase the temperature of the exhaust gases.
- Incorrect operation of the ignition system (misfire). The fuel not burnt in one cylinder is immediately ignited and burned in the converter.
- Mechanical damage to the catalytic converter. Increased vibration of the power unit and impacts on the catalyst lead to crumbling of the ceramic block.
- Thermal shock. Instant cooling of a hot catalyst while overcoming a puddle, for example, can cause cracks in the ceramic element.
- Incorrect air-fuel mixture caused, for example, by a malfunction of the oxygen sensor. The same effect will cause leaky, pouring nozzles.
- Adding additives to gasoline. Cocktails from unverified manufacturers or impaired concentration can increase the combustion temperature at the outlet.
- The latest engine designs with minimal toxicity are programmed to quickly warm up the converter. In cold weather, in order to accelerate warming up, at first the engine control units very enrich the mixture, which burns out on the surface of the converter.
- In history, there were frank defects in the design of the converter. For example, Suzuki conducted a revocable campaign for the complete replacement of converters on SX4 vehicles.
But what if the end is?
A failed catalytic converter on a non-warranty machine can be replaced and not everyone will want to. Daboutthis is horn. What are the scenarios?
- Just knock the stuffing out of the converter. This requires a flashing of the control unit so that it “closes its eyes” to the signal from the second oxygen sensor, or the installation of a mechanical or electronic blende. The mechanical one is a sleeve in which a piece of the catalytic converter is fixed, and the electronic one simply simulates the correct signal from the oxygen sensor.
- Knock out the filling and install a flame arrestor in its place. It consists of several chambers with openings that serve to reduce the temperature and pressure of the gases. This somewhat reduces noise and facilitates the operation of other elements of the exhaust system. The "brains" of the car will be deceived, as described above.
- Install a universal repair catalytic converter instead of a ceramic block. Most often on a metal rather than ceramic basis. The degree of purification will be slightly lower, but you will not feel like “pests”.
Tell me, how did your communication with the “monster under the bottom” - the catalytic converter - work, cut, replaced?
You can get acquainted with the “case histories” of cars of past generations by following the link.