ROUEN, France – PSA Peugeot Citroen plans to add a urea-injection aftertreatment to curb oxides of nitrogen and hydrocarbons on all its diesel engines starting in 2014.

“One technology is the best answer to achieve a big volume” and reduce price, Christian Chapelle, vice president-powertrain and chassis engineering, says at a conference here on the future of the diesel engines sponsored by the SIA French vehicle-engineering society.

The future of diesel engines is in question in Europe because Euro 6 rules on NOx emissions are radically tougher and are coming at the same time as a requirement for increased fuel economy measured in carbon-dioxide emissions. During the diesel-combustion process, although the fuel economy is better, NOx production is worse.

PSA chose to develop a urea-based system of selective catalytic reduction, or SCR, to treat the diesel exhaust, allowing it to tune the engines for maximum fuel efficiency. The auto maker’s strategy for the future is “a clean car for each customer,” says Patrice Marez, who heads PSA’s engine-design department.

The SCR system involves an injection of urea into the NOx catalyst to help the exhaust heat change the compound into harmless nitrogen and water.

This makes sense for PSA. The diesel particulate filters it introduced in 2000 also operate with an injection of an additive that enables the burn-off of trapped carbon particles to take place at about 842° F (450° C), instead of 1,022° F (550° C).

That allows the SCR catalyst to be placed ahead of the particulate filter and closer to the exhaust heat.

With the SCR upstream, its efficiency is about 80%, says Marez. A high NOx conversion rate requires an early light off of the SCR, and if the exhaust passes through the filter first, the thermal resistance of the substrates delays the increase of exhaust-gas temperature.

PSA’s approach allows the engine to be tuned for better fuel efficiency despite the increase in engine-out NOx, resulting in a 2%-5% CO2 reduction, compared with Euro 5. “We can fulfill Euro 6 emissions (standards) and at the same time save on fuel consumption,” Marez says.

The SCR approach is a first step in the French auto maker’s wide-ranging plan to reduce its fleet fuel consumption below 95 g/km of CO2, the equivalent of 59 mpg (3.9 L/100 km) for gasoline engines or 66 mpg (3.6 L/100 km) for diesel.

Other elements include:

  • Support for a generalization of adding 10% biodiesel to diesel fuel at the refinery, which is good for about 5% improvement in CO2 reduction.
  • Reducing mass of its vehicles: 100 kg equals 4 g/km.
  • Reducing aerodynamic drag.
  • Generalizing stop/start technology.
  • Downsizing engines, including 3-cyl. gasoline and diesel engines.
  • Adding diesel hybrids, diesel plug-in hybrids and electric vehicles.

Chapelle says by 2020 PSA expects conventional engines to still hold an 80% share of the market in Europe, with EVs and hybrids accounting for the rest. EVs “will have a place in 2020, but it will be marginal.”

A PSA diesel hybrid will have a 32 to 48 mile (20-30 km) range on electricity, which is enough to cover the main demands of customers in the city during weekdays. “And for weekends, they can go where they want,” he says.

PSA already is a leader in Europe for low emissions, achieving a fleet average 139 g/km in 2008 for cars with an average mass of 2,939 lbs. (1,333 kg), so it need only improve by 8% to reach its 2015 goal of 128 g/km.

The average auto maker in Europe needs to make a 15% improvement to meet the industry target of 130 g/km.

Marez says PSA already offers a Peugeot 207 and Citroen DS3 with diesel engines that produce only 99 g/km of CO2. The auto maker now intends to reach 85 g/km with such cars, using an optimized 4-cyl. diesel meeting Euro 6 rules.

With a 3-cyl. diesel in development, an optimized gearbox and stop/start, PSA can reach 75 g/km. Hybridizing the engine would reduce emissions to 55 g/km and making it a plug-in hybrid would bring a the C3’s emissions down to 45 g/km, or 139 mpg (1.7 L/100 km) of diesel fuel.

PSA will launch an electric car this year; 11 new small gasoline engines starting next year that will allow the 207 to achieve 99 g/km; diesel hybrids next year in the Peugeot 3008 and Citroen DS5; and plug-in versions in 2012.

Beyond that, the auto maker plans to introduce a second-generation of plug-in in 2015, a new global small car in 2015, a family of 3-cyl. diesels in 2015 and a second-generation electric car in 2017.

For its diesel hybrids next year, PSA is using its 1.6L HDi engine with a few minor changes in the hardware, says Olivier Coppin, PSA engineer in charge of alternative drivetrains. To handle vibration from the stop/start transitions, the hybrids will get a reinforced starter system with a specific drive belt and belt-tension system.

An in-cylinder pressure sensor will help monitor the engine and manage injections for quicker starts. In addition, the aftertreatment will be tuned to handle the specific on-and-off transient moments and the temperature of the re-circulated exhaust gas.

Coppin argues a diesel hybrid is the most sensible approach to reducing fuel consumption.

“Until you have a plug-in, all energy in a vehicle comes from the fuel tank, with electricity in a hybrid coming from recuperation (of brake energy). For driving phases requiring power, a lower consumption engine will make the global powertrain efficiency better.”

To achieve a given CO2 output, he says the cost of a diesel hybrid will be less than the cost of a gasoline hybrid, because the gasoline version would need more battery capacity and the battery is the most expensive part.

PSA is working on gasoline hybrids for markets such as China, Russia and Japan, where diesel passenger cars are rare.

“Today, we are using an existing engine” for the hybrids, Coppin says. “But I can say the next-generation engine will be as adapted as best as possible for a hybrid system.”

While PSA’s roadmap is precise, the cost obstacle is not yet surmounted. “You can’t add a lot of technology without thinking of cost,” Marez says.

Under today’s Euro 5 conditions, the average diesel in Europe costs €1,000-€1,500 ($1,200-$1,800) more than a comparable gasoline engine and provides a 30 g/km CO2 advantage.

Under Euro 6, the average CO2 advantage will be only 20 g/km, and the cost could be E2000 ($2,476) extra, “which may be too important to keep the diesel advantage,” Marez says. “Our main priority is to reduce costs and to keep the same CO2 advantage as with Euro 5,” or the customer will choose gasoline.

“It is achievable,” he says. “Progress has already been made, and upstream NOx treatment is a major breakthrough.”