The most effective modern technology which allows to considerably increase power of an internal combustion engine, reduce fuel consumption and toxic emissions, is the system of changing the geometry of inlet manifold. Modern technology is also used in auto recycling:

Changing manifold geometry parameters can be achieved in two cases:

By changing the length of the intake manifold itself;

By changing its cross-sectional area.

In some types of internal combustion engines, the manifold geometry is changed in two ways simultaneously.

Inlet manifold with length change

This type of manifold can be used on diesel and gasoline engines that ensure efficient filling of the combustion chamber with incoming air at working engine speeds.

In order to ensure high torque at sufficiently low engine speeds, a maximum length intake manifold is used. Conversely, at high RPMs, a minimal length intake manifold is used for efficient engine operation.

Such intake manifolds are used in the most well-known geometry changing systems – BMW’s DIVA; Mazda’s VICS and VRIS; and Ford’s DSI.

The inlet manifold length is adjusted by a control valve, which is an integral part of the IMS (Engine Management System).

Operating principle

The principle of the inlet manifold with length adjustment is based on the following. The part of the air mass that remains in the intake manifold after the intake valves are closed performs oscillatory movements with a frequency that is directly proportional to the length of the manifold and the operating speed of the engine.

At some point, the oscillating air mass reaches resonance frequency, which contributes to the supercharging effect. This process is called resonance supercharging. The opening of the intake valves allows high-pressure air to enter the combustion chamber.

In a supercharged engine, there is no need to fiddle with a variable length intake manifold, since the air supply is provided by a turbine or compressor. Therefore, such engines use a short intake manifold, which reduces the size of the combustion engine and, therefore, its cost.

Inlet manifold with section change

Inlet manifold with section change is used on all types of ICE – gasoline, diesel, supercharged.  Increase in speed of air movement, improvement of formation and combustion of fuel and reduction of toxicity of gases is provided due to the reduction of the cross section of the manifold channels.

Some of the most common systems equipped with a variable cross-sectional intake manifold include: Twin Port from Opel; Variable Induction System from Volvo; VIS from Toyota; IMRC and CMCV from Ford.

Such a system has a central intake channel, which is divided into two channels for individual cylinders. One of the channels is closed by a damper, which is driven by a vacuum-type regulator or an electric motor.

If the load in the system is incomplete, the flaps remain closed, the FAM or clean air (depending on the injection system used) is fed into the combustion chambers of the cylinders through a single channel. This creates swirls which improve the mixing process.

Reducing the cross-sectional area of the intake manifold helps to improve the economy of the engine due to the fact that the exhaust (exhaust) gas recirculation system begins to work a little earlier.

If the load is full, in this case the flaps remain open, so there is a maximum supply of fuel (or air) into the combustion chamber with a further increase in combustion engine power.

The geometry change system has a fairly simple principle of operation. Each cylinder has a separate channel for each intake valve. At the same time, any of these channels can be closed by a special flap. The engine management system activates the damper actuator. Depending on the system load, the appropriate volume of fuel (or air) is fed into the combustion chamber.

The main purpose of the system is to improve the efficiency and economy of any internal combustion engine while maintaining the declared power. Such a system also allows to save fuel up to 10-15%, if the system is used in parallel for recirculation of gases formed during combustion of fuel.

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