«Kozlevich opened the muffler, and the car let out a train of blue smoke, from which the dogs running after the car started sneezing.».
I. Ilf and E. Petrov
By the way, did you ever think why the heroes of our classics had to open a muffler? The fact is that the muffler created quite a lot of resistance to the exhausted gases, and in order to increase the parameters of low-power engines of that time, people had to open a special damper and release the gases bypassing the muffler.
Solvable problems
It is obvious that in the beginning the exhaust system performed only two functions: it took gases away from the driver and passengers of the car, and also reduced the noise level. Modern systems have to perform also the function of neutralizing harmful components of exhaust gases. Let's take a closer look at the measures provided in all modern cars to meet all system requirements.
The exhaust system extends from the engine, located on the vast majority of cars in the front part, to the rear bumper. During this route, harmful substances are converted to neutral, which requires the presence of a catalytic converter. Further, in several acoustic chambers, pressure pulsations will be smoothed out and the gases temperature will be significantly decreased.
The exhaust gases themselves are quite aggressive; in combination with water vapor they form acids, which are destroying the exhaust system from the inside. With short trips, water does not have time to evaporate, which leads to corrosion of the elements in the lower points, where moisture stagnates. Gas corrosion in high temperatures also cannot be discounted.
All elements of the system work at a very high temperature: any attempts to protect them with paintwork or anticorrosive mastics are doomed to failure. Right after the engine starts, such coatings will be immediately burned. In the same time from the outside all parts are exposed to moisture and reagents that road workers are constantly putting at the streets and highways. And we must not forget that the dirty water causes large temperature jumps - thermal shocks, which clearly do not increase the longevity.
Construction materials
Let's talk about constructive measures that help to increase the system longevity and about materials used for the system parts:
- Stainless steel. This material is expensive, and therefore not widely used in mass car production. Mostly stainless steel parts are made by order. Service life - not less than 10-15 years (except for metal-compensator).
- Aluminized (aluminum coated) steel. Exhaust system parts made from this material are most common among domestic and foreign manufacturers. These mufflers serve usually for 4-7 years.
- Ordinary constructional steel without coating or colored with regular paint. Sometimes it is used to make spare parts for domestic cars. Its service life is low and ranges from six months to three years.
Economical and maintainable schools
A modern exhaust system can be performed in different ways, but always includes an exhaust manifold, a catalytic converter, and an element that allows untying the oscillations of the power unit and the exhaust system. A resonator (additional muffler) and a main noise silencer must also be necessarily present. At the same time in Renault cars, for example, there is used an all-welded design of the exhaust system. The only connection that can be disassembled without an angle grinder is the joint between the exhaust manifold and the rest of the system.
This system is the most simple, cheap and, until damaged by corrosion or accident, it seems absolutely optimal. But it is going to be quite difficult to replace, say, a burnt out muffler. The manufacturer has provided places for the system to be cut, but, for example, on the entire Duster pipe that is four meters in length there are only two places like that.
German and Korean cars can be taken as an example of exhaust system that is much more convenient to repair. So, the Volkswagen Polo system consists of three large parts. In this case, pipes of the additional and main mufflers are connected by a special coupler, similar in design to the Renault repair coupler.
And Korean manufacturers do not hesitate to divide the system into four parts, which, of course, makes repairing much easier. After all, in all modern cars, metal expansion joint is a low-resource element, but here it is allocated to an independent unit.
Perhaps the perfect accuracy of positioning the exhaust system parts is provided by Korean automotive industry. All elements are connected by flanges with high positioning accuracy. And considering this information, it could be very frustrating to realize that the flagship of the domestic car industry - Lada Vesta – has exhaust system pipe connections coming from the “eight” model, presented to the public in far 1984. The scheme with two half-chimneys and a centering ring does not actually center anything, the connection is quite weak and inaccurate, and the diameter of the pipes is very small, as we already mentioned.
At the moment, the exhaust system repair is carried out in most cases by replacing individual parts. Most often metal expansion joints are failing first, and then usually mufflers follow.
Reasons for metal expansion joint failure:
- Increased gas pressure and temperature that happens because of the clogged catalytic converter (if the neutralizer is located behind the metal expansion joint);
- Damage of the corrugation walls under the influence of increased power unit vibration;
- Mechanical damage from the road.
Failed metal expansion joint has to be replaced with a new one, and during welding it is important to sustain not only the length, but also the angular position of the welded element.
As for mufflers, they can be repaired with welding only if there is a mechanical damage from the road surface. Muffler that is covered with rust is not a subject to repair. Most workshops can find for you a universal muffler for reasonable money, while the original for a used car will sometimes cost a quarter of your vehicle price.
Time bomb
Now let's talk about the most complicated, expensive and insidious element of the exhaust system - catalytic converter. It was invented in the last century to reduce the toxicity of exhaust gases of a car engine with spark ignition. Inside catalytic converter there is a porous support material - a ceramic block with honeycomb structure. On the surface of the ceramic block there is an intermediate layer of activators, and over it there would be the catalytically active layer of precious metals (platinum, palladium and rhodium). It is where chemical reactions occur - the toxic substances of exhaust gases (carbon monoxide and nitrogen oxides) are converted to carbon dioxide and elemental nitrogen, and hydrocarbons are converted to carbon dioxide and water vapor. The degree of exhaust gases purification in an efficient neutralizer reaches 98%. In most modern vehicles with Euro-4 and Euro-5 toxicity standards, catalytic converters are located as close as possible to the engine outlets and bolted through the gasket to the cylinder head.
Such close proximity of the massive and hot catalytic converter to the engine makes it difficult to assemble the engine compartment and leads to an increase in the temperature there. But on the other hand the catalytic converter core is warming up much faster after the engine is started. After all, only the properly heated catalytic converter can effectively purify the exhaust gases.
For proper system operation in front of the catalytic unit and immediately behind it there will be installed oxygen sensors (lambda probes). Sensor standing before the neutralizer is called the controller, and the one behind it is called diagnostic.
Catalytic converter is considered by the manufacturers to be a reliable part and so they do not provide any certain regulations for its replacement procedure. That is, the life of catalytic convertor should be equal to the life of the entire car. Nevertheless, practice has shown that catalytic converters do not always serve flawlessly. Substandard gasoline, misfiring, leaking injectors and uncontrolled use of fuel additives - all these may cause damage to the catalytic converter.
There are only two possible scenarios:
- Honeycombs are melting which causes a reduction in the cross section up to complete obstruction of the exhaust tract;
- Small particles of ceramics are crumbling and drifting back into the cylinders, which causes the engine piston group to become unusable.
Broken catalytic converter has to be replaced with the new one, but it may turn out quite costly. Therefore, less conscious car owners are using a flame arrester instead. This is an element that does not in any way reduce the toxicity of the exhaust gases and requires either to reprogram the engine control unit or to install the “dummy”. A more correct, but also more expensive way is to install a repair catalytic unit in your own case or to weld into the pipeline the new catalytic converter in its own new case.
Replacing this part also requires a lot of experience, because this is a very delicate work. If you have done this before, you know that you need to have "steady hands": the wrong handling of repairing equipment may harm the car or some car parts.
In the comments please share some information on the longevity of your car’s exhaust system. Durability records and anti-records. Did you ever have to repair your car on the road?
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