Until recently, we knew only the following about the catalyst: it is such a thing that it is not clear why it is needed, it is not clear how it works, that our gasoline "kills", in general - some trouble. Cut - and no problem! But gradually we began to get used to the fact that the catalyst is still a useful thing, at least the thought of "surgical intervention" the exhaust system is visited less and less often and fewer heads.
In the spring, when the traffic police begin "fight for clean air", another problem falls on us - we need to adjust CO. Owners of cars equipped with catalysts do not even think about it, and CO check posts pass without trembling in the knees and fear for their wallet. True, the same wallet can decently "lose weight" for a different reason. Fines for exceeding the CO level will seem like a penny compared to the cost of buying and replacing a catalyst if it fails. Therefore, it is not at all harmful to know how to handle it, but for this you must first understand how it is arranged and how it works.
How do they work?
When the working mixture is burned, a number of combustion products harmful to human health are formed, in particular, carbon monoxide (SO), various hydrocarbons (CH) and nitrogen oxides (NO). Although these substances make up only 1% of the total exhaust (the rest is nitrogen, carbon dioxide and water vapor), they are very harmful and require neutralization. There are several ways to deal with harmful emissions - for example, leaning the mixture on which the engine is running or exhaust recirculation - but none of them can compare with the effectiveness of a catalytic converter.
According to experts, a catalytic converter is a simple device in which a complex chemical process takes place. "Inside the stainless steel case is a ceramic or metal "brick", which has a honeycomb structure. This monolith has a huge surface area, and all of it is covered with the thinnest layer of a special alloy - the actual catalyst containing platinum, rhodium and palladium. It is these precious metals that are responsible for the wonderful properties of the catalyst, they also determine its high cost".
Traffic fumes "wash" surface of the monolith, and when the temperature reaches "critical" 270°C, the catalytic reaction starts. Carbon monoxide is converted to dioxide (carbon dioxide), hydrocarbons are converted into water and again carbon dioxide, and nitrogen oxides are converted into water and nitrogen. All this is less harmful to the environment.
Catalytic converters can reduce exhaust toxicity quite effectively, while they do not affect fuel consumption and engine power. In the presence of a catalyst, the exhaust back pressure slightly increases, from which the engine loses 2–3 hp, but this is practically the entire "pay" for exhaust cleaning. However, installing a catalytic converter is not an ideal solution. Theoretically, it should serve indefinitely, since the aforementioned precious metals serve only as a catalyst, which, as you know, is not consumed during a chemical reaction. In practice, the life of the catalyst has its limit...
What is destroying them?
Catalytic converter failure can occur for several reasons, although it is usually a gradual process that cannot be caught without special equipment.
"Core" most catalysts are made of ceramic, a material known for its brittleness. The car can hit a pothole at speed, hit something, or even just "strike" stone catalyst housing, and from this the catalytic "brick" may crack. After this loss "core" their working qualities - a matter of time.
New generation converters containing a metal monolith are not so vulnerable in this regard. Of course, it is possible to break them, but, in any case, it is not so simple.
Enemies of the Catalyst
In addition to physical destruction, there is another common cause of catalyst failure. Fuel. It is extremely sensitive to the composition of the fuel. If gasoline is leaded, then the tetraethyl lead contained in it is deposited on the active surface of the catalytic "brick" and fast "salts" her, from which all reactions stop. It seems that at gas stations, hose ends are of different sizes, and dispensers are painted in different colors, and they write about it on every corner, but still consumers sometimes confuse and fill in the wrong gasoline. But it's enough "burn" half a tank of such gasoline, and the catalyst will die forever.
But not only leaded gasoline is the enemy of the catalyst. Unleaded catalyst can also be destroyed if the engine management system is faulty, the mixture does not burn completely, or the engine is badly worn.
Triple catalytic converters ("triple" because the combination of three precious metals serves as a catalyst) installed only on those machines whose engines are equipped with a closed exhaust control system. An oxygen sensor is installed in front of the catalyst, which monitors the composition of the exhaust and transmits this data to the central processor. Depending on the oxygen content in the exhaust, the BEU regulates the composition of the combustible mixture and ignition so that their optimal values are maintained. This serves as the main protection for the catalyst, as well as fuel economy and engine efficiency. The catalyst does not tolerate large deviations in the composition of the working mixture. A poorly adjusted engine with a high content of hydrocarbons in the exhaust simply ruins the catalyst. If the mixture is too lean, this can cause a sharp overheating of the catalyst, from which the monolith will suffer again, only already "physically". Thus, "life" catalyst depends on the health of the engine management system.
Much depends on the health of the oxygen sensor itself. WITH "age" he becomes "lazy" or completely fails, which affects the composition of the mixture and, accordingly, the serviceability of the catalyst.
The exhaust of a heavily worn engine that burns oil can also spoil the catalyst. It, getting along with the exhaust into the catalyst, "baked" on the surface of the monolith, like varnish, and does not allow the catalyst to work.
There are other harmful factors as well. For example, candles. Unsuitable spark plugs will not give complete combustion, which can cause a detrimental meltdown reaction in the catalyst.
Be very careful when using gasoline or oil additives. Most do not think about this, but additives can also adversely affect the catalyst. If the product does not say: "compatible with catalyst", Better don't risk it.
Another dangerous case is starting the engine by towing. In this case, simply pure gasoline may enter the catalyst. This, firstly, poisons the catalyst, but can also cause an instant reaction and even an explosion. Watch also where you are going - try not to get into deep puddles. The operating temperature of the catalyst is about 900°C. Sudden exposure to water can be fatal.
In general, it has been observed that the service life of the catalyst is affected by operating conditions. Catalysts suffer more on cars operated in urban areas, when the engine is often started. On the other hand, during long high-speed driving on highways, the catalyst also deteriorates due to overheating.
Finally, you will be wise to inspect the entire exhaust system regularly. If brackets are broken or rubber mounts have fallen off, the exhaust pipe will vibrate, transferring unnecessary stress to the catalyst.