Turning to FSI gasoline direct injection technology, Audi launched a new generation of engines that, in terms of efficiency. means a huge leap forward. Compared to conventional intake manifold petrol injection engines, the direct injection engine is more dynamic and powerful, delivers more torque and reduces fuel consumption by up to 15 percent.
This became possible, first of all, thanks to the layered charge in the partial load mode. This means that the combustible mixture is needed only near the spark plug, and the rest of the combustion chamber is filled with a significant excess of air. Thanks to this, the engine can not be throttled. In addition, with direct injection, heat losses are reduced. This means that the layers of air around the mixture cloud isolate it from the cylinder and cylinder head.
In contrast to an intake manifold injection engine, fuel is injected directly into the combustion chamber. The nozzle, which is supplied with fuel by means of a single plunger pump and a common fuel line, is located on the side of the cylinder head. The valve injector dispenses fuel with millisecond precision and at pressures up to 110 bar.
The principle of gasoline direct injection: 1 - fuel, 2 - air, 3 - throttle (electronic accelerator pedal). 4 - inlet pipeline, 5 - valve injectors, 6 - engine.
Schematic representation of the Bosch-MED system (electronic control system for engines with direct fuel injection)
Fuel is injected in stratified charge mode on the compression stroke. After that, it is involved in the movement of air, which is admitted into the combustion chamber. The air, in turn, is set in a targeted movement thanks to the movable flap in the intake manifold, the intake duct and the special shape of the piston crown.
After that, the necessary effect of layered distribution of fuel in the charge is achieved: a cloud of fuel, which together with air forms a combustible mixture and spreads within a limited space, is located around the spark plug by the time of ignition. Due to the large jet expansion angle, the fuel cloud almost does not come into contact with the piston crown, in addition, after combustion, an insulating layer of air is located between the ignited mixture and the cylinder wall. As a result, heat dissipation through the cylinder block is reduced, and this increases efficiency. engine.
The cylinder block and dimensions of the first representative of the new generation of engines are identical to the cylinder block and dimensions of the conventional two-liter A4 and A6 units. This engine is equipped with a common rail fuel injection system and a single plunger injection pump. The cylinder head has not five, but four valves, this provides free space for the valve injector.
The variable duct length intake manifold consists of two stages, so it provides two path lengths: for high and low speeds. The permanently acting camshaft adjuster ensures proper control of the valve opening times. On the exhaust side, one of the main components necessary for effective reduction of exhaust gas toxicity is located - the exhaust gas recirculation system. This system works more efficiently than previous systems, diverting up to 30 percent of the exhaust gases to the combustion chamber.
Tumble system
To implement stratified charging, it is necessary that the injection, the air flow inside the cylinder and the geometry of the combustion chamber are optimally matched to each other. The Tumble system is used to control air flow in the intake tract (tumble in English means «somersault, somersault»). Through a special partition, the inlet channel is divided into upper and lower halves. The suction channels are located in the cylinder head, and the special dampers are located on the side of the head, in a flanged multifunctional module. The upstream damper directs the air either through the top only or through the entire cross section.
In order to achieve an intense cylindrical flow in the combustion chamber, a special damper, and with it one of the two channels, closes in the layered charge mode. In this mode, fuel is injected only in the last third of the piston's upward movement, that is, during compression. Thanks to the combination of targeted air flow and the special piston geometry, which has a pronounced combustion chamber cavity, the finely atomized fuel is optimally concentrated around the spark plug and ignites reliably.
The Tumble system, firstly, for the first time made it possible to achieve a combination of an economical layered charge mode and very high power and torque values. At high speeds, the FSI engine operates like a conventional pipe injection engine, but due to the greater compression efficiency. engine increases.
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