What is a catalyst and how does it affect engine performance?-Для чего нужен катализатор и как он влияет на работу двигателя

What is a catalyst and how does it affect engine performance?

The process of combustion of fuel in the cylinders of an automobile engine inevitably leads to the formation of harmful substances. The most dangerous of them:

• CO, carbon monoxide, colorless and odorless poisonous gas;

• CH, hydrocarbons, volatile organic compounds, the main component of smog;

• NOx, nitrogen oxides NO and NO2, also "participants" of smog, in addition, falling out also as part of acid rain.

The task of a catalytic converter (more often called a catalyst) is to convert these substances into other combustion products, which are practically harmless, through chemical reactions:

• CO2, carbon dioxide;

• N2, nitrogen gas, which makes up 78% of the Earth's atmosphere;

• and H2O – water vapor.

The catalytic converter was developed back in the distant 70s, but its mass use began with the introduction of environmental standards - Euro 2 and higher. Today, the catalyst is an integral part of the exhaust system of every car; without it, not only production from the conveyor, but also operation is impossible.

STRUCTURE OF THE CATALYST

The main component of the converter is a catalytic carrier: ceramic or metal honeycombs coated with a thin layer of precious metals: palladium, rhodium or iridium, which have high chemical activity. Exhaust gases, passing through the catalyst and touching the honeycomb deposition, react with metals and chemically bond.

 Most modern catalysts are three-component, that is, they consist of three elements that sequentially purify gases. The first element binds nitrogen oxides, the second removes unburned fuel particles and fights carbon monoxide, and the third contains one of the oxygen sensors that analyzes the composition of gases at the outlet of the converter

and transmitting data to the ECU - the engine control unit. In addition to this oxygen sensor, called a diagnostic one, the system also has a control sensor (lambda probe) installed before the catalyst.

        

Most modern catalysts are three-component, that is, they consist of three elements that sequentially purify gases. The first element binds nitrogen oxides, the second removes unburned fuel particles and fights carbon monoxide, and the third contains one of the oxygen sensors that analyzes the composition of gases at the outlet of the converter and transmits data to the ECU - engine control unit. In addition to this oxygen sensor, called a diagnostic one, the system also has a control sensor (lambda probe) installed before the catalyst.

The catalytic converter is most often an oval (flattened) barrel, embedded in the exhaust system of a car. If the first catalysts were mounted under the front of the bottom, approximately in the middle between the exhaust manifold and the first muffler (resonator), then on machines that meet Euro-4 and Euro-5 toxicity standards, they are already much closer - they are attached to the cylinder head.

Despite the fact that this method significantly complicates the layout of the engine compartment, it increases the cleaning efficiency, since catalytic reactions are possible mainly only at temperatures above 300 ° C, and the closer the converter is located to the engine, the faster it will warm up and start working. But without a catalyst, the complete conversion of CO and CH is possible only at 700-850 ° C, and even then, if there is an excess of oxygen, and the neutralization of NOx is impossible in principle.

CATALYTIC CONVERTER FAULTS

Although car manufacturers usually do not provide for regulations for replacing the catalyst, that is, by default they assume that it is designed for the entire period of operation of the car, the average service life of these parts is 100-150 thousand kilometers. At the same time, catalysts with ceramic honeycombs most often fail earlier than metal ones.

The main faults can be divided into three groups:

1. Reflow. The collector cells are sintered, making it difficult for the passage of exhaust gases. Occurs with an extreme increase in the temperature of gases, above 900 ° C. Although sintering does not initially cover the entire inner diameter, the permeability of the catalyst decreases, which leads to an increase in temperature in it and damage to other honeycombs according to the “domino principle”.

2. Destruction of ceramics. Brittle ceramic honeycombs tend to crumble, which is fraught not only with damage to the catalyst, but also with the ingress of fragments into the working chamber, which can damage other components: for example, a turbine or even a piston group, and, as a result, overhaul or replace the engine. This is especially true when the converter is installed directly on the cylinder head.

3. Blockage. The catalyst is clogged with products of incomplete combustion of fuel and, in some cases, oil, which leads to its obstruction.

You can understand that the converter needs to be replaced by signs such as:

• engine power reduction;

• impossibility to raise the speed to the cut-off even without load;

• too smooth and weak exhaust;

• problems with starting the engine, both cold and

and hot;

• increase in fuel consumption;

• roar under the bottom;

• an unpleasant smell from the exhaust system (hydrogen sulfide, "rotten eggs").

In all these cases, an immediate replacement of the catalytic converter is necessary to avoid problems with other engine components.

REASONS FOR CATALYST FAILURE

How to identify a clogged catalytic converter?

Several factors can lead to catalytic converter malfunctions, here are the main ones:

1. Low-quality fuel. More often - gasoline with a low octane number. In this case, the ECU switches the engine to late ignition, which causes the mixture to burn out at the outlet and an increase in the temperature of the exhaust gases.

2. Misfires. Unburned fuel burns in the converter.

3. Incorrect mixture composition. The effect is the same as in the previous case, but it is caused by malfunctions of sensors or injectors.

4. Mechanical damage to the catalyst. Ceramic honeycombs do not like increased vibrations and impacts on the converter body.

5. Thermal shocks. Rapid cooling of the catalyst with water from a puddle or other water barrier can cause cracks in its body.

6. Adding additives to the fuel. Unwanted additives in gasoline can raise the combustion temperature.

7. Gas. The combustion temperature of the gas and its octane number are higher, which leads to the fact that the gas can partially burn out in the catalyst.

8. Engine design. Oddly enough, sometimes the creators constructively create conditions conducive to the rapid destruction of the catalyst - for example, new engine designs with minimal toxicity are programmed to warm up quickly. In cold weather, the ECU re-enriches the mixture, which leads to its afterburning in the converter.

To avoid problems with the catalyst, you must follow some simple recommendations:

• do not turn the engine for a long time with a starter, so as not to pour fuel;

• do not start the engine "from the pusher";

• do not check the operation of the cylinders by disconnecting the spark plugs.

In addition, it should be remembered that the catalyst heats up to very high temperatures during operation, which can be fraught with fire, and do not drive on dry grass, wooden platforms and other similar places for parking.

REPAIR AND REPLACEMENT OPTIONS

The original catalytic converter is a rather expensive assembly due to the use of expensive materials in it. Therefore, when it fails, some car owners are considering alternative repair options, up to removing the catalyst from the exhaust system. The most common options are:

1. Knocking out honeycombs. The exhaust system is disassembled in such a way as to have access to the insides of the catalyst, after which the ceramic honeycombs are knocked out with a long metal object (for example, a crowbar), and their remains are removed. The disadvantages of such a repair are check engine errors, which are eliminated by flashing the ECU or installing “tricks”: mechanical ones that close oxygen sensors, or electronic ones that send “correct” pulses to the unit. In addition, the environmental class of the car is inevitably reduced, which can cause problems with passing the technical inspection. There are frequent cases of increasing the exhaust volume to an uncomfortable level, as well as local overheating in the catalyst area.

2. Installation of a flame arrester. The defective catalyst is removed, and a part similar to another resonator is installed in its place. A flame arrester (also known as a "stronger"), as a rule, is a cylinder with a two-layer body and a complex (often X-shaped) internal structure. Stronger also, like a standard catalyst, reduces engine noise, slows down and partially cools exhaust gases, but does not neutralize them. Therefore, the installation of a flame arrester entails exactly the same problems with ecology and electronics as in the previous case.

3. Universal catalyst. Of all the ways to save money when replacing a "catalyst", installing a non-original part is the only one that does not cross the "boundaries of good and evil" and, in principle, is recommended for use. In this case, there is no need to interfere with the engine software, and most often there are no problems with environmental standards. The main disadvantage of ersatz catalysts is their low resource compared to the original, which rarely reaches more than 60,000 - 80,000 km.