The function of the engine intake and exhaust system is to supply fresh air to the engine and discharge the exhaust gas after combustion. The engine intake and exhaust system directly affects the engine's power, economy and emission performance.
1: Intake system
The function of the intake system is to supply combustible mixture or fresh air to each cylinder as much and as evenly as possible to ensure the continuous operation of the engine. The intake system is usually composed of components such as air filter, throttle body and intake manifold, as shown in the figure below.
The main function of the air filter is to filter out impurities in the air and let clean air enter the cylinder.
Most engines use dry paper filter air filters, which are composed of paper filters and filter housings. The filter housing includes a filter cover and a filter housing base.
The function of the throttle body is to control the amount of air entering the engine. During the working process, some impurities in the air will condense on the throttle body when heated, which will cause idle jitter, flameout and other phenomena, so the throttle body should be cleaned regularly.
The intake manifold refers to the intake duct from the throttle body to the cylinder head intake duct. The intake manifold must distribute the air to each cylinder as evenly as possible, so the length of the intake manifold should be as equal as possible.
2: Exhaust system
The vehicle exhaust system refers to the system that collects and discharges exhaust gas, which is mainly composed of exhaust manifold, exhaust pipe, three-way catalytic converter, resonator, muffler, exhaust tail pipe and other components. The automobile exhaust system has the following main functions:
① Lead the exhaust gas to the rear of the vehicle to prevent harmful gases from entering the cab.
② Improve the emission pollution of the engine and reduce the harm to the atmosphere.
③ Reduce the noise of the engine exhaust gas.
Types of exhaust systems
The exhaust system generally has two types: single exhaust system and dual exhaust system. The single exhaust system is used for in-line engines and some V-type engines, and the dual exhaust system is used for V/W engines.
1.Single exhaust system
During the exhaust stroke of an in-line engine, the exhaust gas in the cylinder enters the exhaust manifold through the exhaust valve, then enters the exhaust pipe, three-way catalytic converter and muffler from the exhaust manifold, and finally is discharged into the atmosphere from the exhaust tail pipe, as shown in the figure below. V-type engines have two exhaust manifolds. Most vehicles equipped with V-type engines still use a single exhaust system, that is, two exhaust manifolds are connected to one exhaust pipe through a fork pipe.
2.Dual exhaust system
Some V/W engines use two single exhaust systems, that is, each exhaust manifold is connected to an exhaust pipe, a three-way catalytic converter, a resonator, a muffler and an exhaust tail pipe. This arrangement is called a dual exhaust system, as shown in the figure below. The dual exhaust system reduces the pressure in the exhaust system and makes the engine exhaust smoother.
Composition of the exhaust system
1.Exhaust manifold
The function of the exhaust manifold is to guide the exhaust gas discharged by the engine to the exhaust pipe, as shown in the figure below. An in-line engine has one exhaust manifold, and a V-type engine has one exhaust manifold on each side. Depending on the number of engine cylinders, an exhaust manifold can have 3, 4 or 6 channels, and the other ends of these channels are connected together and then connected to the exhaust pipe.
2.Muffler
When the exhaust valve is just opened, the exhaust pressure and temperature are very high and have a certain amount of energy. At the same time, due to the intermittent nature of the exhaust, exhaust pressure pulsations are generated in the exhaust pipe. If the exhaust gas is discharged directly into the atmosphere, it will inevitably produce strong noise with a relatively complex spectrum. Letting the exhaust pass through the muffler can gradually reduce the exhaust pressure and attenuate the exhaust pulsation, thereby reducing the exhaust noise.
3.Three-way catalytic converter
The three-way catalytic converter is the most important purification device in the exhaust system. It can convert various harmful gases in the exhaust gas into non-toxic gases. When the exhaust gas passes through the three-way catalytic converter, the active substances inside it cause the harmful gases to undergo certain chemical reactions to generate various harmless gases. The three-way catalytic converter is installed behind the engine exhaust manifold and is generally composed of a shell, a heat insulation pad and a catalyst carrier (with a catalyst attached to the surface).
