Exhaust manifold

Mainly exhaust manifolds are made of cast iron. On the one hand, the collector is attached directly to the internal combustion engine, on the other, to the catalyst or, if the catalyst is not installed, to the exhaust pipe. Due to the specific location of the collector, it works in fairly extreme conditions. The temperature of the exhaust gas reaches several hundred degrees. Thus, after the engine is turned off, sufficiently fast cooling occurs, followed by an inevitable drop of condensate. As a result, the main problem of the collector is the rapid appearance of rust.

In addition to its main function - the removal of exhaust gases from the combustion chamber, the exhaust manifold helps in blowing the combustion chamber and filling it. This occurs as a result of resonant exhaust waves. When the exhaust valve opens, the gas in the combustion chamber is under pressure, while the pressure in the manifold is normal. Immediately after opening the exhaust valve, a wave is generated due to the pressure difference. Reflecting from the nearest obstacle (which in ordinary cars is a resonator or catalyst), it goes back to the cylinder and, in a certain range of revolutions (usually medium), approaches the cylinder by the time of the next exhaust stroke, “helping” to leave the next portion of exhaust gases cylinder.

Standing waves (resonance) occur in the pipe in a rather wide range of revolutions, since the wave propagates not with the speed of sound, but with the speed of exit from the cylinder, respectively, the higher the engine speed, the faster the gases exit the cylinder, the faster the wave moves and returns, and just manages to return to a shorter (in time, for high revolutions) next cycle.

To create the same and favorable working conditions (release) of each cylinder, the exhaust pipes must be, firstly, personalized for each cylinder (to separate the cylinders and create standing waves at certain revolutions), and secondly, must be the same length as is the reason for the use of a "spider" or "pants" from the pipes.

On tractor diesels, due to the low nominal speed (up to 2000 rpm), common cast iron collectors are used.

As a rule, in order to avoid accidental burns, reduce fire hazard and damage other parts from high temperature, in most cases the collector (receiving pipes) is enclosed with a metal screen.

In the field of motorsport and auto-tuning, this element occupies an important place and much attention is paid to it. In the field of auto tuning in Russia, the exhaust manifold is called a “spider”, due to its appearance.

On some racing cars, there is no exhaust manifold at all - each cylinder has its own exhaust pipe of a clearly defined length, without catalyst and without a muffler. For tuning, many exhaust manifolds with different characteristics are noticeably affecting the operation of the engine. Exhaust manifolds are made of steel, cast iron, stainless steel and titanium. Exhaust manifolds made of stainless steel are not susceptible to corrosion due to exposure to high temperatures and exhaust gases. Due to high temperatures, the outer part of the exhaust manifold changes color to blue ^[1] . Cast iron exhaust manifolds have a high degree of thermal insulation, therefore, if an exhaust manifold of this material is installed, the remaining parts of the car are less susceptible to high temperatures. Titanium collectors are the lightest and are often installed in race cars. Ferrous exhaust manifolds degrade over time because this material is highly susceptible to rust and corrosion. Therefore, as a rule, they are covered with a layer of ceramics, heat-resistant paint or chrome plated. Most exhaust manifolds are made of stainless steel or ceramic. Although ceramic collectors turn out to be much lighter, but with strong heating, followed by cooling, they crack, which instantly affects the quality of the function performed.