A controlled mixture formation device is understood to mean a fuel injection system in which the fuel/air ratio can constantly change depending on operating conditions and the oxygen content in the exhaust gases.
The mixing device receives control commands from the oxygen concentration sensor (lambda probe), which is installed in front of the catalytic converter or in the exhaust manifold and is blown by the exhaust gas flow. The lambda probe is an electrical sensor that registers the residual oxygen content in the exhaust gases and issues a corresponding electrical signal. The value of the signal allows you to draw a conclusion about the composition of the air-fuel mixture. In a fraction of a second, the lambda probe can issue a corresponding signal to the electronic control unit, due to this, the composition of the mixture can be constantly adjusted. On the one hand, this is necessary, since operating conditions are constantly changing (e.g. full throttle, idle), on the other hand, because optimal afterburning occurs in the catalytic converter only if there is a sufficient amount of carbon particles in the exhaust gases (unburned gasoline).
Thus, in order for afterburning to occur in the catalytic converter at a temperature of 300–800°C, the exhaust gases must contain more fuel than is required for complete combustion in the engine cylinders. In this regard, when operating a car equipped with an engine with a catalytic converter, fuel consumption increases by about 5%. The catalytic converter is located in the engine compartment of the car in place of the front muffler. The converter consists of a ceramic honeycomb block coated with a noble catalyst metal - platinum or rhodium. An elastic, heat-resistant wire mesh is used to attach the shock-sensitive ceramic block.
The catalytic converter used is a so-called three-way catalytic converter. This means that carbon monoxide is being oxidized at the same time (SO) and hydrocarbons (CH) and reduction of nitrogen oxides (NOx).
Rules for the operation of vehicles with a catalytic converter in the exhaust system
To avoid damage to the oxygen concentration sensor (lambda probe) and catalytic converter, the following instructions must be observed.
Be sure to use unleaded gasoline.
If leaded fuel was added by mistake, the exhaust manifold and catalytic converter must be replaced. Before installing new elements of the exhaust system, fill the fuel tank completely with unleaded gasoline at least twice.
Starting a warm engine by pushing or towing is unacceptable. An electric cable must be used to start the engine. Unburned fuel, if ignited, can cause the catalytic converter to overheat and eventually fail.
Frequent cold starts following one another should be avoided. Otherwise, unburned fuel collects in the catalytic converter, combusts when heated with an explosion, and the converter is damaged.
If you have difficulty starting the engine, do not let the starter operate for a long time, as fuel is injected during starting. You should find and fix the malfunction, and then start the engine.
In case of interruptions in the operation of the ignition system, do not allow fuel injection when starting the engine until the cause of the malfunction is determined.
Do not check for spark with the spark plug tip removed.
It is impossible to carry out a balance test by disconnecting the high-voltage ignition wire of one of the cylinders. When disconnecting the high voltage ignition wire of an individual cylinder, even with the help of a special tester, unburned fuel will enter the catalytic converter.
In the event of a malfunction in the ignition system, avoid running the engine at a high engine speed. Fix the problem as soon as possible.
Do not park your vehicle on dry leaves or grass. The temperature of the exhaust system at the location of the catalytic converter is very high, and heat radiation occurs even after the engine has been switched off.
When filling engine oil, make sure that the maximum oil level on the dipstick is not exceeded. Otherwise, excess may enter the catalytic converter and damage the coating or completely destroy it.
Useful information and tips
How to save the neutralizer
Replacing a failed converter will cost a lot, so it would be good to know in advance how things are with converters in the auto parts market and what problems arise during their operation. Until recently, we knew only the following about the neutralizer: this is such a thing that it is not clear why it is needed, it is not clear how it works, our gasoline «kills», in general, some trouble. Cut - and no problem! But gradually we began to get used to the fact that the neutralizer 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 neutralizers 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 the converter if it fails. That is why you need to know how to handle it, and for this you first need to figure out how it works and how it works.
How does a neutralizer work?
When the air-fuel mixture is burned, a number of products harmful to human health are formed - carbon monoxide (SO), various hydrocarbons (CH) and nitrogen oxides (NO) etc. Despite the fact that 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 exhaust emissions, such as leaning the mixture on which the engine is running, or exhaust gas recirculation, but none of them compares in efficiency with the result 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» with 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 rare metals that are responsible for the wonderful properties of the neutralizer, they also determine its high cost.
Exhaust gases «wash» surface of the monolith, and when the temperature reaches «critical» value +270°С, the catalytic reaction starts. Carbon monoxide is converted to dioxide (carbon dioxide), hydrocarbons into water and again into carbon dioxide, and nitrogen oxides into water and nitrogen. All this is less harmful to the environment.
Catalytic converters can reduce exhaust toxicity quite effectively, while they practically do not affect fuel consumption and engine power. In the presence of a converter, the exhaust back pressure slightly increases, from which the engine loses 2–3 hp, but this is almost all «pay» for exhaust gas cleaning. However, installing a catalytic converter is not an ideal solution. Theoretically, it should serve indefinitely, since the above-mentioned metals serve only as a catalyst, which, as you know, is not consumed in a chemical reaction. In practice, the life span of the converter has a limit...
Causes of neutralizer failure
Catalytic converter failure can occur for several reasons, although this is usually a gradual process that cannot be caught without special equipment.
«Core» most converters 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 converter body, from which the catalytic «brick» may crack. After this loss «core» their working qualities - a matter of time.
New generation neutralizers 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.
In addition to physical destruction, there is another common cause of catalytic converter 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 «pollutes» 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 gasoline «kill» neutralizer.
But not only leaded gasoline is the enemy of the converter. It can also be destroyed unleaded if the engine management system is faulty, the air-fuel mixture does not completely burn out, or the engine is badly worn.
Triple catalytic converters («triple» because the catalyst is a combination of three metals) installed only on those machines whose engines are equipped with a closed exhaust control system. An oxygen concentration sensor is installed in front of the converter, which evaluates the composition of the exhaust gases and transmits this data to the central unit of the engine's electronic control system. Depending on the oxygen content in the gases, the central unit regulates the composition of the combustible mixture and ignition so that their optimal values are maintained. This serves as the main protection of the converter and provides fuel economy, high engine efficiency. The converter does not tolerate large deviations in one direction or another in the composition of the mixture. A poorly adjusted engine with a high content of hydrocarbons in the exhaust just ruins the converter. Too lean mixture can cause a sharp overheating of the converter, from which the monolith will suffer again, only already «physically». Thus, «life» converter 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 working mixture and, accordingly, the serviceability of the converter.
The exhaust of a heavily worn engine that burns oil can also spoil the converter. The latter, getting along with the exhaust into the converter, «baked» on the surface of the monolith, like varnish, and does not allow the neutralizer to work.
There are other harmful factors as well. For example, candles. Unsuitable spark plugs will not burn completely, which can cause a disastrous meltdown reaction in the catalytic converter.
Be careful when using gasoline or engine oil additives. Most drivers do not think about this, but additives can also adversely affect the converter. If the product does not say «compatible with catalytic converter», Better don't risk it.
Another dangerous case is starting the engine by towing. In this case, pure gasoline may enter the converter. This poisons the neutralizer and can also cause an instant reaction and even an explosion.
Also, watch where you are going, try not to get into deep puddles. The operating temperature of the converter is about +900°C. Sudden exposure to water can be fatal.
In general, it was noted that the operating conditions also affect the service life of the converter. Converters suffer more on cars operated in urban mode, when the engine is often started and stopped. Nevertheless, when driving for a long time at high speed outside the city, the converter also suffers, but already from overheating.
Finally, you will be wise to inspect the exhaust system regularly. If the brackets are broken or the rubber muffler mounts have fallen off, the exhaust pipe will vibrate, transferring unnecessary loads to the converter.