Audi's catalyst for change

The high-tech A3 range's cleaner-burning engine demonstrates why New Zealand needs to keep reducing the sulphur content in its fuel. Motoring editor ALASTAIR SLOANE reports


The technical people at Audi will not go as far as telling owners of its new three-door A3 hatchback which brand of petrol to use. But they insist the car will run better and "pick up efficiencies" using fuel with the lowest possible sulphur content. In other words, shop around.

Technology in the second-generation A3 - launched in Auckland mid-week - shows why New Zealand must continue to reduce the sulphur content in fuel. Running the car on a richer sulphur diet compromises the role of its direct-injection engine and its three catalytic converters. Other carmakers have run into the same problem. Sulphur gums up the latest high-tech works.

For example, the country's best-selling brand, Toyota, can't import its high-tech V6 diesel four-wheel-drive Prado because it is designed to run on diesel containing a maximum of 50 parts per million of sulphur - not the 500ppm maximum in New Zealand.

The sulphur content of petrol here is limited to 150 parts per million, a mix deemed by Audi boffins to be "only just acceptable" for its 2-litre FSI - fuel stratified injection - engine.

But it is improving. Fuel out of the petrol pumps, says the oil industry, actually contains between 40-110ppm of sulphur. In a few years the limit will be 50ppm. Same with diesel. That's the restriction for both fuels in Europe now. Next year, Europe goes to 15ppm.

Carmakers are building leaner-burning, cleaner engines to meet international emissions regulations.

New Zealand has introduced an emissions standard - but it won't get the benefits until there is cleaner fuel across the board.

Low-sulphur fuel has benefits apart from reducing emissions. It reduces by-products that contaminate oil, thereby making the job of engine oil-makers easier. Engine oils remain cleaner, work more efficiently, and last longer.

The new FSI engine in the A3 is one of Audi's most advanced units. The crankcase and basic engine dimensions are exactly the same as the 96kW aluminium power unit in the bigger A4 sedan.

But the FSI engine comes with direct petrol injection using a common rail injection system and a single-piston high-pressure injection pump. The result is 110kW of power and 200Nm of torque at 3500rpm.

The optimum mix using a traditional fuel-injection system, where petrol goes into the combustion chamber through an inlet port, is 14.7 parts of air to one part of fuel. That was the industry goal as the best burn ratio.

But fuel in the FSI engine is directed straight into the combustion chamber, thereby creating a stratified mix of up to 43 parts of air to one part of fuel - three times leaner than port injection.

Audi says the ratio has been made possible by a new air-guided combustion process, where fuel is not injected until the compression phase.

It is then transported to the spark plug by the air turbulence produced in the combustion chamber. This causes an ignitable mixture to form around the spark plug, with a substantial air surplus in the rest of the combustion chamber. This is the engine's most economical mode.

When the engine is required to work harder under throttle, the fuel/air mix returns to a 14.7:1 ratio.

The FSI engine needs three catalytic converters for efficient exhaust emission management: two in the manifolds and a NOx (nitrogen oxides) storage catalyst under the car. The FSI A3 is one of the few cars in New Zealand with a storage catalyst.

A NOx sensor controls and monitors the function of the storage catalyst. When the catalyst is saturated with undesirable oxides, says Audi, the temperature increases, causing the contaminants to decompose and be expelled through the exhaust as harmless nitrogen.

The new A3 also comes with the Volkswagen Group's new direct-shift gearbox, which combines the advantages of a conventional six-speed manual gearbox with the qualities of a modern automatic transmission.

Basically, DSG allows two gears to be engaged at the same time - a pre-selection process - thereby reducing shift times and providing an almost uninterrupted flow of power; unlike a conventional automatic, where power is lost through the torque converter.

The design was first patented in Germany in 1940, by Rudolf Franke, a professor of engineering.

Audi used a DSG set-up in the legendary Audi Sport quattro back in 1985, with rally champion Walter Rohrl at the wheel.

There are three A3 models on sale: the 2-litre FSI at $53,500 for the five-speed manual and $56,500 for the five-speed automatic, and the 3.2-litre V6 DSG, at $79,900. The V6 develops 184kW and 320Nm of torque between 2500 and 3000 rpm

The new car isn't quite as tall as the outgoing model, but is more elegant inside and out. Handling and ride are said to be greatly improved.

There is more kneeroom in the back and both rows of seats offer significantly more shoulder room (30mm at the rear and 42mm at the front).

A new feature of the Audi A3 is electromechanical steering with speed-related power assistance. It is lighter at parking speeds and heavier and more precise at speed.

The A3 comes with the usual safety systems, including ABS anti-lock brakes and airbags front and rear. For the moment, the A3 is only available as a three-door.

A completely different five-door, called the A3 Sportsback, will be available later.