Rudolf Diesel invented the compression-ignition engine in Germany, and Mercedes-Benz in 1936 put the first diesel engine in a passenger car, but France is home to many key European diesel suppliers.

Faurecia SA is the leader in diesel particulate filters. Rhodia SA supplies the Eolys fluid that regenerates 1.8 million particulate filters on the road in Europe; PSA Peugeot Citroen made particulate filters a selling point well ahead of legal requirements; and Delphi Diesel Systems is one of the leaders in diesel injection systems.

“When you look at the growth of diesel in Europe, it is pretty much the same in all countries, but France believed in diesels long before most other countries, particularly Peugeot,” says André Douaud, director of technology for the French auto maker's association CCFA.

Because Peugeot started with light-vehicle diesels as far back as the 1960s, followed by Renault SA about 10 years later, France has a large number of diesels on the road.

Environmental rules now drive diesel technology, and costs.

Due to the expense of meeting current Euro IV emission rules, diesel systems cost about €1,000 ($1,200) more than gasoline engines. Engineers now are working to meet what they expect to be the even tighter standards of Euro V coming in several years and the even less well-defined rules of Euro VI that could arrive in 2010 or 2011.

The two challenges of diesel engines are particulate emissions — soot — and oxides of nitrogen (Nox).

“The particulate filter is well-proven and meets the norms of Euro V,” says Bertrand Gatellier of the powertrain division at the Institut Franñais du Pétrol. “The only negative is NOx.”

Delphi Corp. bought diesel direct-injection technology from TRW Automotive in 1999 and has 500 engineers at its main diesel technical center in Blois, France, developing injectors, common rails and overall system controls for customers.

“Euro V norms are not yet decided, but the hypothesis of the auto makers is that they will be very severe for particulate emission and relatively mild for NOx reduction,” says Philippe Bercher, deputy technical director for diesel systems at Delphi France.

“We meet Euro IV today with our solenoid injectors and pressures of 1,600 bar (23,000 psi). Euro V will be 1,800 bar (26,000 psi) or 2,000 bar (29,000 psi), according to the motor and the weight of the vehicle.”

Today's injectors, whether solenoid or piezo-driven, actuate a hydraulic circuit to open and close the injector.

“The real revolution will come later,” says Bercher, “with our piezo direct injector that will not involve a hydraulic circuit. We will be able to reduce the time between injections from about 200 milliseconds today to zero and the volume of the injection below 0.5 cu. mm. Our direct piezo will have an advantage on reducing NOx. We are preparing that for 2010, or even before. We already have a development contract.”

But even the cleanest diesel will require aftertreatment. After Euro V forces particulate filters onto all but the smallest cars, Euro VI likely will require adding aftertreatment for NOx.

Faurecia is Europe's leading supplier of particulate filters, which trap soot in a honeycomb mesh that is periodically cleaned out by a flame of super-hot exhaust from the engine.

PSA and Ford use an injection of the catalytic fluid Eolys from Rhodia to reduce the temperature required for this regeneration, and other auto makers use a catalytic coating on the filter.

“Until 2009-2010, we don't see any major changes in the particle filter,” says Dominique Moret, director of marketing for Faurecia exhaust systems.

“Long term, we are studying the injection of diesel fuel directly into the exhaust system, for more frequent, lower-temperature regeneration.”

The disadvantage of a coated filter is cost, but the advantage is that owners have no catalytic fluid to replenish. Working with Inergy, a French-Belgium fuel tank company, Rhodia has doubled the maintenance interval of its Eolys system — and a third generation is in development that will last the life of the car.

“There is no research at the moment on a fourth generation as the ‘fit-for-life’ or ‘service-free’ state has been reached for passenger cars,” says Laurent Rocher, Eolys market development manager for Rhodia Electronics & Catalysis.

Filter regeneration for heavy vehicles is trickier, especially those that stop and go, such as urban buses and garbage trucks. At idle, they create soot but not enough heat for cleanout.

A venture capital company in France, Aaqius & Aaqius, has taken a leading role in this arena by actively helping a French inventor, Jean-Claude Fayard, bring his Exoclean heavy duty filter to market.

Aaqius had already been working with Rhodia, and when Fayard approached Faurecia with his patent, Faurecia suggested he go to Aaqius & Aaqius for help.

“We invest money, and we pay people to bring innovative technology to the market and to accelerate the conditions needed to start a profitable business,” says Aaqius & Aaqius CEO Thierry Seguelong.

Exoclean now is offered in the aftermarket and as an option by Volvo's Renault Truck subsidiary. Last year, Fayard sold 150 truck filters for €6,000 to €9,000 ($7,250 to $10,900) each. Aaqius hopes to develop a system for automobiles, which means dramatic cost reduction. The Rhodia-Inergy system for cars costs about €500 ($604).

Researchers have some time to solve the NOx question.

“For NOx, we don't see a need until Euro VI, which would come in 2010 or 2012,” says Faurecia's Moret. “We think it will be an SCR (selective catalytic reduction) approach, with (liquid catalyst) injection.”

Like particulate filter regeneration, there are two approaches to reduce NOx.

The SCR adds urea, known as AdBlue in Europe, to the exhaust stream to reduce NOx to nitrogen and water.

DaimlerChrysler already offers this system in some Mercedes-Benz trucks and plans to use it for passenger vehicles starting in a few months. The other approach is a NOx trap that captures NOx in nitrate form on an absorbent mass in a catalytic converter, then reduces it with carbon monoxide and hydrocarbons produced in the exhaust stream by running the engine in a rich mode.

Aaqius has three long-term diesel projects aimed at meeting future emissions regulations.

“We don't think one technology can cover 100% of the market,” says Seguelong.