Diesel focus for Renault

The Renault Laguna and the VW Touareg are two high-end vehicles that come in both diesel and petrol models.

French carmaker Renault has entered a new marketing phase in New Zealand with its facelifted four-cylinder Laguna passenger range - the diesel variant is the premium model.

The company's general manager Robert Nash says that giving the 2.2-litre oil-burning Laguna more equipment and pricing it at $51,990 - $10,000 above the 2-litre petrol model - points to the growth of diesel in New Zealand.

Volkswagen did the same with its hatchback four-cylinder Golf line-up 20 months ago, pricing the 2-litre turbodiesel about $9000 above that of the entry-level 2-litre petrol model.

Said Nash: "Renault sees diesel as the long-term direction for cost-efficient motoring in this country.

"The popularity of diesel sports utility vehicles and the acceptance of diesel at the luxury end of the market is evidence of this.

"We are following the lead and introducing them through our range. We not making them the bargain basement-type models of 20 years ago, where you were basically Mr Scrooge if you wanted a fuel-saving diesel model.

"Today, people want all the features they expect in a European car but they want the savings of diesel and the environmental positives that diesel offers over petrol, particularly with particle filters."

Particle filters have just arrived in New Zealand. The Laguna's 2.2-litre diesel engine has the technology. So does the new 3-litre V6 engine in the VW Touareg, and Peugeot/Citroen diesels.

Diesel engines with particle filters are cleaner-burning than those without. A particle filter traps exhaust soot and burns it off under high temperatures. It is at its most efficient when low-sulphur fuel is used.

High-sulphur fuel clogs the filters, which is why some engines with particle filters in their dedicated exhausts were not available here before New Zealand recently reduced the sulphur content.

Reducing it from 500 parts per million to 50 ppm cuts soot, or sulphur dioxide, emissions by 90 per cent. Up until recently New Zealand allowed a sulphur content of 3000 ppm. Now it's down to a maximum 50ppm, still dirty by new European standards of 5ppm but getting better.

The next step in cleaner, simpler and less expensive diesel engines is the development of pressure-sensing glow plugs. Proponents believe the technology may even allow designers to ultimately dispense with exhaust emissions systems.

Petrol engines use oxygen sensors in the exhaust to measure ignition and fuel for the engine-management system. But diesel control systems can only predict internal conditions. Until now.

Researchers believe pressure-sensing glow plugs can correct tolerances to match the aging of the injection system - and open possibilities of new combustion principles.

The first new glow plugs are expected in Europe in 2008 - two years before new Euro 5 emissions standards will make it much tougher on particulates and nitrogen oxides (NOx), both problem areas for diesels.

Particle filters and and other exhaust emissions treatments increase manufacturing costs by hundreds of dollars.

But pressure-sensing glowplugs could make such after-treatment systems redundant, say developers.

By measuring precise combustion conditions inside each cylinder, diesel engineers could create controls to regulate the combustion process much more precisely. This would let engines run more smoothly, efficiently and cleanly.

Pressure-sensing glowplugs provide feedback to the engine-management system that controls the timing and quantity of fuel injected into the cylinder.

This feedback allows the engine electronics to adjust the injection characteristics so the engine avoids fuel-mixture combinations that generate high levels of emissions.

In this sense, the feedback loop works like the lambda sensors in a petrol engine exhaust system.

Combined with other factors such as lower compression ratios and exhaust-gas recirculation, pressure-sensing glowplugs allow designs that stabilise combustion temperatures. Doing so substantially reduces the level of raw emissions coming from the engine.

German glowplug specialist Beru, owned by US company BorgWarner, has been at the forefront of pressure-sensor development.

"If an engineer knows the pressure, he can optimise the [diesel combustion] cycle," said Bernd Last, head of cold start research and development. "This could even lead to new combustion methods. The main driver for all this is environmental protection."

Siemens VDO, which is also working on integrated glowplug combustion sensors, says that pressure-sensing feedback techniques are an important and necessary step towards new emissions standards.

"The process will help keep the load off the after-treatment system," said spokesman Johannes Winter-hagen. "The benefit is lower cost of compliance, not low cost."

Siemens VDO believes that diesels under two litres will be able to pass new Euro 5 without costly after-treatment.

The potential market for pressure-sensing glowplugs is 20 million units a year for Europe alone.

- Additional reporting, agencies