With FSI direct petrol injection technology, Audi has launched a new generation of engines that represent a huge leap forward in terms of efficiency. Compared to conventional engines with petrol injection into the intake manifold, the direct injection engine is more dynamic and powerful, delivers more torque and reduces fuel consumption by up to 15 percent.
This is made possible primarily by stratified charging in partial load mode. This means that the combustible mixture is only needed near the spark plug, while the rest of the combustion chamber is filled with a significant excess of air. This means that the engine does not need to be throttled. In addition, direct injection reduces heat loss. This means that the air layers around the mixture cloud isolate it from the cylinder and cylinder head.
Unlike a manifold-injected engine, the fuel is injected directly into the combustion chamber. The injector, which is supplied with fuel via a single-plunger pump and a common fuel line, is located on the side of the cylinder head. The valve injector doses the fuel with millisecond precision and at a pressure of up to 110 bar.
The principle of direct gasoline injection: 1 - fuel, 2 - air, 3 - throttle valve (electronic accelerator pedal). 4 - intake manifold, 5 - valve injectors, 6 - engine.
Schematic representation of the Bosch-MED system (electronic control system for direct fuel injection engines)
The fuel is injected in stratified charge mode during the compression stroke. It is then set in motion by the air that is admitted into the combustion chamber. The air, in turn, is set in targeted motion by a movable flap in the intake manifold, the intake channel and the special shape of the piston crown.
After this, the required effect of layered distribution of fuel in the charge is achieved: the fuel cloud, which together with air forms a combustible mixture and spreads within a limited space, is located around the spark plug at the moment of ignition. Due to the large angle of expansion of the jet, the fuel cloud almost does not touch the piston bottom, in addition, after combustion, an insulating layer of air is located between the ignited mixture and the cylinder wall. As a result, heat removal through the cylinder block is reduced, and this increases the efficiency of the 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 regular two-liter units A4 and A6. This engine is equipped with a fuel injection system through a common fuel line and a single-plunger injection pump. The cylinder head has not five, but four valves, which provides free space for the valve injector.
The variable-length intake manifold consists of two stages, so it provides two lengths of the tract: for high and low speeds. The permanently operating camshaft adjuster ensures the appropriate control of the valve opening time. On the exhaust side is one of the main components necessary for the effective reduction of exhaust gas toxicity - the exhaust gas recirculation system. This system works more efficiently than previous systems, it diverts up to 30 percent of the exhaust gas into the combustion chamber.
Tumble System
To implement a layered charge, it is necessary that the injection, the air flow inside the cylinder and the geometry of the combustion chamber are optimally coordinated with each other. To control the air flow in the intake tract, the Tumble system is used (tumble in English means "somersault, somersault"). By means of a special partition, the inlet channel is divided into upper and lower halves. The suction channels are located in the cylinder head, and special dampers are located on the side of the head, in a flanged multifunctional module. The pre-connected flap directs air either only through the upper part or through the entire cross-section.
In order to achieve an intensive cylindrical flow in the combustion chamber, a special flap is closed in stratified charging mode, and with it one of the two channels. In this mode, the fuel is injected only in the last third of the piston's upward movement, i.e. during compression. Thanks to the combination of a targeted air flow and a special piston geometry, which has a clearly defined combustion chamber cavity, the finely atomized fuel is optimally concentrated around the spark plug and reliably ignited.
The Tumble system firstly made it possible to combine the economical stratified charging mode with very high power and torque values for the first time. At high revs, the FSI engine operates like a conventional engine with intake manifold injection, but thanks to the higher compression, the engine efficiency increases.
(The original article is available on the online resource: AudiManual)