Stratified charge and homogeneous operation
In the stratified-charge operating mode, fuel is injected during the engine's compression stroke and is picked up by the movement of the air that has been drawn into the combustion chamber. A movable flap in the intake manifold, the intake port and the special shape of the piston crown impart a type of movement in the air that is known as "tumble".
The main factor contributing to the engine's efficiency is the stratified-charge principle at part load. In other words, in this operating mode the engine only needs a fuel-air mixture capable of immediate ignition in the area around the spark plug. The remainder of the combustion chamber is filled with a leaner mixture, that is to say one with a considerable degree of excess air. As a result of this, the engine can be run with the throttle valve open. The direct injection engine also benefits from reduced heat losses,
This means that the strata of air around the 'cloud' of ignitable mixture isolate the latter from the cylinder and cylinder head; less thermal energy is lost via the cooling system.
The desired "stratified-charge effect" is obtained in this way: the cloud of fuel which has become swirled with sufficient air to form an ignitable mixture surrounds the spark plug at the moment of ignition.
After combustion, a layer of air insulates the ignited mixture from the cylinder wall. This cuts the amount of heat lost to the engine block and increases the engine's operating efficiency.
In stratified-charge operation, incidentally, significantly higher lambda values related to the combustion chamber as a whole are achieved. This is essential if fuel consumption is to be reduced at low and medium engine speeds.
At full load, the fuel in injected synchronously with the air intake phase. This fills the combustion chamber homogeneously. Here again, this produces a definite reduction in fuel consumption together with higher power-output and torque figures than would be possible with indirect fuel injection. This was demonstrated on the race-winning Le Mans engine, which runs permanently in the homogeneous mixture mode.
Highly effective exhaust emission control
On the exhaust side of the engine there is one of the fundamental elements needed for efficient exhaust emission control, the exhaust gas recirculation system. This operates more efficiently than previous systems, and diverts up to 35 percent of the exhaust gas back to the engine's combustion chambers. Two catalytic converters are provided for exhaust emission control: an underbonnet three-way converter behind the manifold, and a NOx storage-type converter under the floor pan.
The NOx storage converter has been specially designed to suit the needs of a direct injection engine, and has a NOx sensor installed at the discharge end. It is an established fact that the conventional three-way catalytic converter is unable to break down oxides of nitrogen sufficiently in the engine's lean-burn phase; for this, the composition of the exhaust gas must be stoichiometric (14 parts air to one part fuel).
The higher levels of oxides of nitrogen that remain therefore have to be reduced to harmless nitrogen gas. This task is performed efficiently in the storage-type catalytic converter, which has a barium coating with which the oxides of nitrogen combine.
The storage-type converter is controlled by a mapped operating characteristic and by temperature. When the converter is saturated, the engine's mixture is temporarily made richer. As a result of the increase in temperature and the enriched exhaust gas, the nitrogen oxide is released by the barium molecules and reduced to nitrogen.
To make this new form of mixture preparation and the modified combustion process possible, Audi's engine specialists had to develop a large number of new components and assemblies specifically for this purpose. They include the following:
- The common rail fuel injection system with high-pressure injection pump
This array of new features highlights that the new 1.6 FSI engine is far more than simply a refined version of a conventional predecessor. Its production launch in the first half of 2002 lends yet more substance to Audi's proverbial "Vorsprung durch Technik".
Top model in the range: the A2 1.6 FSI
Like the other versions in the A2 model line, the 1.6 FSI represents the sum total of Audi's experience as a pioneer of lightweight design. As a result of its Audi Space Frame ASF, the A2's aluminium body is more than 40 percent lighter than if it had been made using conventional steel techniques. That is why the A2 uses less fuel than other vehicles in this class that are capable of a similar performance. Its low weight makes it particularly agile.
With its striking shape, the A2 moreover reinforces Audi's claim to set new standards in the field of design. The progressive outline also signals the utterly distinctive character of an innovative vehicle concept with which Audi has once again demonstrated its credentials as a technological trendsetter.
For all its compact exterior, which measures just 3.83 metres in length, the A2's interior nevertheless feels "grown-up" in every respect - it is outstandingly spacious, in fact. Its width of 1.67 metres and height of 1.55 metres, and above all its superior space efficiency, mean that there is a surprisingly large amount of space in the A2. The "space floor concept", with a rear footwell that is sunk in relation to the front footwell, provides significantly more space for rear passengers, ensuring that they can maintain a superbly ergonomic, relaxing seated posture.
The increase in engine output compared with the 1.4 version is attributable to various modifications in every department. For instance there is a larger rear spoiler, which adjusts the refined aerodynamics of the A2 body in line with its higher top speed.
The running gear, too, has been modified to reflect the higher performance of the top A2 version. Specially defined spring and damper rates establish a perfect balance between maximum agility and compelling comfort in all driving conditions.
The A2 1.6 FSI also has disc brakes at the rear, to provide effective braking action at any time. And the increased capacity of the fuel tank, which now holds 42 litres, means that the car is capable of an operating range of more than 700 kilometres.
The A2 1.6 FSI is naturally available in a wide array of colour and equipment versions, lending the entire model line an exclusive, sporty flavour.