Air or a fuel-air mixture, depending on the type of engine (diesel, injection or carburetor), enters the cylinders through the intake manifold. The main purpose of the intake manifold is to ensure uniform distribution of air or working mixture between the cylinders. The efficiency of the motor directly depends on this. In addition, other components, such as a carburetor or throttle valve, can be mounted on the manifold.
The principle of its operation is quite simple: air or its mixture with fuel, entering through the inlet, is divided into several streams, according to the number of engine cylinders. The pistons, moving downwards, create a vacuum in the manifold, which can reach large values. This partial vacuum is also used to neutralize crankcase gases. They enter the intake manifold through the engine crankcase ventilation system, mix with the fuel-air mixture or air and are burned in the cylinders.
Until recently, the main materials for the manufacture of the intake manifold were aluminum, iron and cast iron. This created certain difficulties. The fact is that the collector itself gets very hot during engine operation and heats the air that is currently inside it. The air, in turn, expands and enters the cylinders in a smaller volume, as a result of which fuel consumption increases and engine performance deteriorates.
As an alternative to metal, since the late 90s, now the last century, plastic-based composite materials have been used on many cars. Due to low thermal conductivity, such an intake manifold does not heat up as much, as a result, the cylinders are better filled with air, and the engine power per unit of fuel increases.
Purpose of the intake manifold
This part is designed to ensure the supply of air and VTS to the engine cylinders while it is running. In modern power units, additional elements are installed on this part:
- Throttle valve (air valve);
- Air sensor;
- Carburetor (in carburetor modifications);
- Injectors (in injection internal combustion engines);
- A turbocharger whose impeller is driven by the exhaust manifold.
We offer a short video about the features of this element:
Intake manifold: frequently asked questions
The structure of both options
If you exaggerate, the collector is 4 pipes that connect into one. That is, a kind of “pants”, only with four “trouser legs”. It should be noted that there are also “two - three” or even “six” pipes. This device is determined by the number of cylinders in the engine, as we know on the OKA car there were only two cylinders (two pipes), for example, on the new FORD there are options with three (three pipes), and on some executive cars there are six cylinders (six pipes). Moreover, these will be both the intake and exhaust manifolds.
Here is just the top point, where one of their outputs will differ:
Intake - connects to the air or fuel supply system, so at the “top point” there will be either a carburetor or a throttle valve.
Exhaust - connects to the muffler and removes exhaust gases. Nowadays it is often connected to the catalyst.
Now in more detail about each type.
Design and design of the intake manifold
One of the most important factors affecting the efficiency of the motor is the shape of the commutator. It is presented in the form of a series of pipes connected into one pipe. An air filter is installed at the end of the pipe.
The number of taps at the other end depends on the number of cylinders in the engine. The intake manifold is connected to the gas distribution mechanism in the area of the intake valves. One of the disadvantages of the VC is the condensation of fuel on its walls. To prevent this effect of electrostatic reaction, engineers have developed a pipe shape that creates turbulence inside the pipeline. For this reason, the inside of the pipes is deliberately left rough.
The shape of the collector pipes must have specific parameters. Firstly, the path should not have sharp corners. Because of this, fuel will remain on the surface of the pipes, which will lead to clogging of the cavity and change the air supply parameters.
Secondly, the most common intake tract problem that engineers continue to struggle with is the Helmholtz effect. When the intake valve opens, air rushes into the cylinder. After its closure, the flow continues to move by inertia, and then abruptly returns. Because of this, a resistance pressure is created, which interferes with the movement of the next portion in the second pipe.
These two reasons force automobile manufacturers to develop improved manifolds that would ensure smooth operation of the intake system.
About tuning instead of an epilogue
When thinking about the exhaust manifold, one cannot ignore the topic of tuning, because this part quite often ends up on the list of those subject to modification.
As a rule, on the market you can find different configurations of this element for a specific model.
Exhaust manifolds allow you to achieve, for example, good performance at low speeds or in the mid-range - for every taste and color.
And in motorsports, they often do away with exhaust manifolds altogether, connecting the exhaust pipes directly to each cylinder.
Principle of operation
The suction manifold operates according to a very simple scheme. When the engine starts, the air valve opens. As the piston moves to bottom dead center on the suction stroke, a vacuum is created in the cavity. As soon as the intake valve opens, a portion of air moves at high speed into the vacated cavity.
During the suction stage, different processes occur depending on the type of fuel system:
- Single injection - another portion of air comes from the filter. It passes through the carburetor or cavity in which the fuel injector is installed (if the engine is equipped with an injection vehicle). In this cavity, air is mixed with fuel. Due to the vacuum in the cylinder, this portion is sucked through the raised valve of the intake system;
- Multipoint injection - individual fuel injectors are located in each manifold pipe. When the corresponding valve opens, air is supplied through the pipe suitable to it. At the same time, fuel is atomized.
- Direct injection - only air is sucked in. The valve lowers, the piston compresses the air in the cylinder. At the end of the compression stroke, fuel under pressure is supplied through the nozzle into the compressed medium. In diesel internal combustion engines, an identical process occurs, only the air is compressed more strongly.
All modern engines are equipped with an electronic system that controls the supply of air and fuel. Thanks to this, the motor operates more stably. The dimensions of the pipes are selected to match the parameters of the motor at the stage of manufacturing the power unit.
Shape and volumetric efficiency
One of the most important parameters of the intake manifold that determines its efficiency is its shape. The basic rule that all engineers adhere to is that the intake manifold should not have any angular shapes , as this will provoke pressure drops and, as a result, worse filling of the cylinders with air or working mixture. Therefore, all collectors have smooth transitions between segments and rounded shapes.
The vast majority of current collectors use runners. They are separate pipes diverging from the central entrance of the manifold to all available intake channels in the cylinder head. Their task is to use a phenomenon called Helmholtz resonance. The operating principle of the design is as follows.
At the moment when suction occurs, air flows at a very high speed through the open inlet valve. When the valve closes, the air that did not have time to enter the cylinder retains a large impulse, which means it presses on the valve, resulting in a high-pressure zone. Then pressure equalization occurs, with lower pressure in the manifold. Due to the influence of inertial forces, leveling occurs with fluctuations: first, air enters the runner at a pressure lower than in the manifold, then at a higher one. This process occurs at the speed of sound, and before the intake valve opens again, oscillations can occur many times.
The smaller the diameter of the runner, the greater the change in pressure due to resonant air vibrations. As the piston moves down, the pressure at the outlet of the runner decreases. This low pressure pulse then travels to the manifold inlet where it turns into a high pressure pulse that travels in the opposite direction through the runner and valve, after which the valve closes.
To achieve the maximum effect from resonance, the intake valve must open at a strictly defined moment, otherwise the result will be the opposite. This is quite difficult to achieve. The gas distribution mechanism is a dynamic unit, and its operating mode is directly dependent on the crankshaft speed. The pulses are synchronized statically, the synchronization depends on the length of the runners. The problem is partially solved by selecting the length for a certain speed range at which the greatest torque is achieved. Another option is the use of systems for changing the geometry of the intake manifold and electronic timing control.
Collector pipe shape
This is a very important factor, which is given key importance when designing the intake system of a separate modification of engines. The pipes must have a specific cross-section, length and shape. Sharp corners and complex curvatures are not allowed.
