An important technical parameter of a modern ICE is the compression ratio, which is the ratio of the volume of the operating cylinder when the piston is in the so-called lower dead center (LDC) to the volume of the combustion chamber.

An increase in the compression ratio helps to create the most suitable conditions for ignition of the FAM (fuel-air mixture) in the combustion chamber and, as a result, a more rational use of the energy released in the process. Turning in a car for recycling when it’s being charged several thousand dollars to repair it is also rational:

Features of the Compression Variation System

The compression ratio varies depending on the fuel type used and the operating conditions of the engine. The compression ratio system is designed to compensate for these variations.

In gasoline engines, the compression ratio is limited exclusively to the area in which fuel detonation occurs. At low loads, an increase in compression does not lead to the detonation process, but at higher loads, detonation can reach a critical point.

Reducing compression leads to an increase in engine power and a decrease in fuel mixture consumption. However, it is worth keeping a balance between increasing and decreasing this indicator, since an excessively low compression ratio and low loads can lead to a reduction in the engine’s power and fuel economy.

The system itself is designed to provide increased power and torque, reduced fuel consumption and lower exhaust emissions. The system ensures that the engine runs smoothly on different fuels without reducing the efficiency of the detonation process.

The pioneer in the production of engines with variable compression ratio is SAAB, which 14 years ago introduced the first analogue 5-cylinder engine equipped with Variable Compression. The peculiarity of this engine was that it combined the block head and cylinder liners into a single mechanism.

Such a mechanism combined with a camshaft and a cylinder liner, which gave a displacement of 4 to 5 degrees, which in turn caused a change in compression ratio.

Control over this indicator was carried out by the general control system of the internal combustion engine, taking into account the different degree of load. Thus, at maximum load the compression ratio was minimum, and vice versa, at minimum load the compression ratio was maximum.

Despite the positive results in terms of power and torque, the prototype was never put into production.

In 2010, SAAB presented a new development, a one and a half liter four-cylinder engine with the MCE-5 Development compression system. Such a sample was additionally equipped with a modern system of phase conversion of gas distribution, as well as a direct fuel supply system.

Engine with the MCE-5 compression system

The engine equipped with such a system has a rather complex design, which involves changing the characteristic of the working stroke of the pistons in the cylinders.

The toothed shear enters into interaction with the working piston and the control piston. The rocker arm is connected via a lever to the crankshaft.

The secateurs move under the influence of the control piston. The chamber above the piston begins to fill with oil, the volume of which is strictly controlled by a special valve.

As the secateurs move, the position of the piston’s TMT is changed, and as a consequence, the working volume of the combustion chamber changes at a significant compression interval.

At present the MCE-5 engine has not yet been put into mass production, but it has good prospects for development in the future.

A new concept of an internal combustion engine equipped with a modern compression system was presented by Lotus Cars. This is a unique two-stroke engine called Omnivore that allows using different types of fuel – gasoline, diesel, alcohol, ethanol, etc.

The upper part of the chamber is equipped with a washer, the movement of which leads to a change in the volume of the chamber. This allows the highest degree of compression – 40 to 1.

Despite its efficiency, such a compression system currently does not allow to achieve good indicators regarding fuel economy and environmental friendliness of a two-stroke engine.

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