Regulations to Remove Oxides of nitrogen from diesel exhaust and pressure to reduce carbon-dioxide emissions are shrouding the future of compression-ignition engines, and only time and engineering will tell if gasoline is on the verge of having its revenge in Europe.

A study by the Center for Automotive Research in Germany says diesels will decline in Western Europe from the 2007 penetration level of 53.3%.

In Germany, specifically, CAR predicts diesel penetration will fall from its 46% level through April of this year to 20% by 2020. The study cites the rising price of diesel fuel and its E1,000-E1,500 ($1,553-$2,349) extra cost, the arrival of gasoline-hybrid powertrains and new-generation gasoline engines as reasons for diesel's diminishing demand.

However, Global Insight Inc. in London predicts diesel sales will continue to rise on an overall European level to about 62% in 2014, when Euro 6 emissions rules on NOx take effect, then fall a few points before stabilizing at about 59%.

Jean-Philippe Le Denmat, who follows powertrains for the consultant, says suppliers have developed inexpensive particulate filters that will enable auto makers to meet Euro 6 rules for their diesels in 2009.

At Europe's International Conference on Diesel Engines, sponsored by SIA, the French automotive engineering society, engineers describe the approaches they are taking to keep diesel ahead of gasoline.

Christian Chapelle, chief of powertrains at PSA Peugeot Citroen, says the key to diesel engines' future is to improve their efficiency even more. Customers won't pay extra to pollute less, he says, but they will pay more for an engine that consumes less as long as the comfort and drivability remain satisfactory.

To achieve its fuel-efficiency goals, PSA is working on better air boosting; increasing cylinder pressure; finding cost-effective noise and vibration solutions for 2- and 3-cyl. engines; reducing frictional losses; decreasing weight; and applying widespread use of micro-hybrid stop/start systems.

Meeting Euro 6 rules for NOx “will not be neutral in terms of price,” Chapelle warns, noting Euro 6 calls for a 56% reduction in NOx output to 0.08 g/km, compared with the 0.18 g/km level of Euro 5 taking effect next year.

PSA will try to meet the NOx limits on smaller cars without resorting to NOx traps or selective catalytic reduction (SCR) systems that will be needed on larger engines.

PSA engineers are attempting to reduce the temperature of combustion by re-circulating more low-pressure exhaust gas, as higher temperatures favor NOx formation. Along with its suppliers, the auto maker is working on better fuel vaporization by having more, smaller holes in the injectors and higher injection pressures.

Limitations include packaging and corrosion issues for the exhaust-gas recirculation (EGR) system, plus the cost of the technology for improved fuel injection.

Packaging either an EGR system or an SCR system is a special challenge in meeting Euro 6, because the rules apply not only to new vehicles introduced in 2014, but all vehicles sold that year.

“The Euro 6 challenge is in reducing cost,” says Chapelle. “The technologies are available, but they cost too much.”

Scientists and engineers are working in two directions to improve diesels: the engine and the fuel. Demand is increasing the price at the pump, and the amount of diesel available from a given barrel of petroleum is limited.

The French Petroleum Institute (IFP) is working on several projects to introduce ethanol into diesel fuel.

It is participating in a 2007-2009 international consortium called Ethanol for Diesel (E4D), which aims at using ethanol made from biomass in diesel engines.

A second project, part of the French research program PREDIT, is adapting a Citroen C4 diesel to run on an ethanol-methanol-diesel fuel. The first phase of the project has been successful in that the car runs well on the fuel.

“The next step,” says IFP's Philippe Hadida, “is to optimize the engine for NOx reduction.” Results are expected late this year or in early 2009.

Using ethanol to extend the gasoline supply already is well-developed, with only the food vs. fuel argument slowing down implementation. Biodiesel is subject to the same political problems as first-generation ethanol but is behind the curve in development.

The E4D research is important to European diesels, because extending the gasoline supply will only aggravate an imbalance in the global European refining pool. Already, Europe ships excess gasoline to the U.S., which exports diesel fuel to Europe.

Biodiesel, however rare, is helpful to NOx reduction, says Jean Arregle, a researcher at CMT Motores Termicos in Valencia, Spain.

Arregle says he has identified diesel combustion that produces no particulate matter using diesel fuel mixed with rape seed oil, lower temperature EGR and injectors with tiny, tapered nozzles. An absence of soot in the exhaust eliminates the need for a particulate filter.

Arregle suggests other fuel combinations deserve more study. “Why not use a fuel like a water-fuel oil emulsion?” he asks. “The water vapor brings a 20-30 degree drop in temperature.”

Controlling combustion better is another key to less NOx and more efficiency, and suppliers such as Federal- Mogul Corp., Beru AG and Continental Automotive Systems offer pressure sensor/glow plug combinations that bring better information to engine control units. But cost remains the issue.

While General Motors Corp. and Volkswagen AG plan to use a pressure sensor in the cylinder, and some other auto makers have a model-based control, Renault SA engineer Pascal Emery says, “For the moment, our position is between the two.”

Several auto makers already have downsized their diesel engines once. PSA-Ford Motor Co.'s joint venture 1.4L and 1.6L diesel engines, making 68-110 hp, have the same power as the 2.0L mills they replaced but with more low-end torque and less fuel consumption.

There are different approaches to the next level of downsizing: fewer bigger cylinders or more small cylinders.

CMT Motores Termicos is working on a project to turbocharge a 3-cyl. engine, says researcher Jose Galindo, adding the small turbochargers required are difficult.

“The challenge in making engines with less than 4 cylinders is that vibrations are disagreeable,” says Andre Douad, scientific director of the French auto maker association CCFA.

“All the OEs are working on how to make engines with less than 1.0L displacement. They make them powerful with turbocharging, but 4-cyls. have efficiency problems, and 2- or 3-cyls. have better combustion but more NVH problems.”

ACTech AG, a German specialist in foundry prototypes, displays a 2-cyl. at the conference that displaces close to 1.0L.

AVL List GmbH, the Austrian engine developer, is working in both directions. It has developed a large, 1-cyl. diesel engine for motorcycles that will see production, while also working with customers on a 3-cyl. mill.

Diesel Project Manager Michael Weissbaeck says AVL also is working with small cylinders displacing about 0.25L, so that a 4-cyl. engine would displace 1.0L. But AVL's main approach for bigger cars is to hybridize a smaller diesel.

Downsizing a 2.0L diesel to 1.6L and improving the power with a 2-stage turbocharger and EGR would bring a 12% improvement in fuel efficiency, says Weissbaeck. Adding a stop/start micro-hybrid raises the improvement to 17%, and an electric motor attached to the engine or the gearbox would raise the improvement to 24% and 26%, respectively.

He proposes auto makers make a global 1.6L diesel engine, tuning it for fuel quality and regulations in emerging markets, while hybridizing it for Europe.

Even if the engineers win their cost battles for bringing new technologies to market, diesel's share of Europe's future market remains a question.

“For achieving low CO2 emissions, for the heart of the market, the only solution is diesel,” CCFA's Douad says. “But for small cars, the cost of meeting Euro 6 will make diesels prohibitive.”

PSA's Chapelle believes Euro 6 will hurt diesel. “Fuel prices are rising and consequently drivers average fewer kilometers per year. The combination makes it more difficult for drivers to justify the extra cost of a diesel car.

PSA is facing that future by investing in a new 3-cyl., 1.0L gasoline engine due in 2011, producing less than 100 g/km of CO2 in small cars.

Others say the global market for diesels remains a growth possibility. “Penetration of 12% is not unreasonable for the U.S.,” says IFP's Hadida.

Meanwhile, India is developing diesels for passenger cars, with Tata Motor Ltd. introducing its DICOR engine in several new models this year. Japanese leaders are considering opening their streets to diesel cars, but China has decided against diesel passenger cars.

PSA's Chapelle believes diesel fuel in China will be politically directed toward the commercial-vehicle market. However, AVL List's Weissbaeck says his company is working on a diesel for a Chinese passenger car, and that key Chinese politicians will change the current policy.

Diesel's Future

Favorable factors:

  • Financial incentives based on CO2 emissions.
  • Higher resale price (currently).
  • CO2 regulations.
  • Great power/torque; fun to drive.

Unfavorable factors:

  • Convergence of diesel and gasoline prices.
  • Reduction of fuel consumption differences between gasoline and diesel.
  • Reduction in kilometers driven per year.
  • For Euro 5, increased cost especially for small diesel that will continue with Euro 6.
  • Development of turbocharged DGI engines.

Source: PSA Peugeot-Citroen

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