Diesels clean up

Don't dismiss the diesel, writes Alastair Sloane. Using the latest technology, cleaner, quieter diesel cars are a hit in Europe and could be coming our way.

A BMW technician watching a diesel-powered 3-Series race car lap the Juarez circuit in southern Spain last year offered a glimpse of why car-makers are becoming excited about diesel development.

It was a simple throwaway line in the middle of a conversation about how a diesel engine's torque is suited to endurance racing.

"We have gone about as far as we can with the design of the conventional petrol engine, short of working on improved lean-burn technology," he said.

"But the diesel engine has been around for 100 years and we have hardly touched it. We are starting to realise the enormous potential of diesel."

A few weeks later, the same 2-litre car undergoing testing at Juarez that night won an endurance race in Germany, beating the mostly petrol-powered opposition. A few weeks before, it had finished third behind a diesel-powered Volkswagen Golf.

Diesel wasn't the most important thing on Dr Robert Buechelhofer's mind when he flew into Auckland not long ago to talk about Volkswagen's future in the Asia-Pacific.

Buechelhofer is a member of the Volkswagen AG board and president of the car-maker's Asia-Pacific region.

He knew that, unlike Europe, diesel-powered passenger cars are thin on the ground in New Zealand.

Both petrol and diesel are comparatively cheap here but petrol has a cleaner image. Diesel has suffered in the passenger-car market, mainly because of the appearance of smelly, dirty, used Japanese oil-burners.

Things are different in Europe, although there are certainly some grubby examples. Diesel is enormously popular because, although it is similarly priced, it offers better fuel economy than petrol engines.

Europeans don't seem to have a problem with diesel's image either. Two of the most impressive test vehicles over the past couple of years have been the BMW 320TD and the Alfa Romeo 156JD - both diesels using the very latest high-pressure fuel technology, yet keeping their sporty, luxury images intact.

Indeed, a 320TD gliding through the Andalucian hills of southern Spain last year left its more illustrious stablemate, the petrol-powered 328i, struggling to stay with the pace.

But BMW and Alfa Romeo won't stock the 320TD or 156JD over here. It's the image. Sporty German and Italian cars powered by diesel motors and driven by New Zealanders? Forget it.

But Buechelhofer believes diesel has a future here, where twists and turns and hilly terrain are ideally suited to lazy pulling power, a characteristic of diesel.

"It might not be popular now, but wait until the luxury car-makers start to build sophisticated diesel engines for their top models. Then people will start to take notice. It will have a flow-on effect," he says.

Mercedes-Benz, BMW, Audi and Jaguar have already confirmed the presence of multi-valve V8 diesel engines as an option in their premium models.

In fact, Mercedes-Benz is looking at more diesel options across its fleet.

It unveiled one in New Zealand the other day: the five-door A-Class 170 CDi, powered by a four-cylinder, 1.7-litre engine developing 66kW at 4200 rpm and 180Nm of pulling power between 1600 and 3200 rpm.

The A170 accelerates from zero to 100 km/h in 12.5 seconds, fractionally slower than many similar-sized, petrol-powered cars, and can theoretically cover 1100km on its 54-litre fuel tank.

At the heart of the new technology is a fuel-injection system called "common rail." This lowers fuel consumption and the emission of pollutants, aids ride comfort and suppresses much of the noisy clatter associated with traditional diesel engines.

The first car-maker to import a mainstream diesel into New Zealand was Citroen, with its BXTZD, in 1989. The French car-maker celebrated its 10th diesel birthday the other day with the latest version, the Xantia HDi, powered by a turbocharged, 2-litre, four-cylinder motor using common rail technology.

Briefly, conventional diesels use a mechanical pump to distribute fuel to each injector. But this is a complex procedure and the flow of fuel in the combustion process can't be precisely controlled. Mixing in a combustion chamber a large and irregular amount of fuel with compressed hot air is what made conventional diesels noisier than petrol engines.

Common rail does away with the mechanical pump and uses electronics to pre-heat and filter the fuel in a sealed metal tube called a "rail." The fuel is then electronically injected from the rail into each combustion chamber, using micro-second timing to regulate the combustion process to the point where the loud detonation is converted to a long roar. Consequently, the engine runs much quieter.

Citroen says advances in the engine's electronics have given the HDi engine many advantages over the previous 2.1-litre unit, including a 30 per cent increase in fuel economy, 32 per cent more pulling power in the lower rev range, and 20 per cent fewer emissions.

The 2-litre unit produces 80kW at 4000 rpm and 250Nm of torque at 1750 rpm. Sitting at 100 km/h in fifth gear, the engine is spinning at a lazy 2100 rpm and 95 per cent of maximum torque is on tap, available between 70 and 120 km/h.

This is long-legged cruising at its best, backed up by an Auckland-to-Wellington trip where the Xantia HDi recorded 60 mpg, or about 5 litres of fuel for every 100km.