VEHICLE TECHNOLOGY
Injector wars: Piezo vs. solenoid
Automotive suppliers back different technologies to meet Europe's tighter emissions rules
Suppliers of diesel fuel injectors are fighting a technology battle to win new business as tougher European Union emissions rules take effect before the end of the decade.
German suppliers Robert Bosch GmbH and Siemens VDO Automotive and Italian supplier Magneti Marelli say injectors using piezo technology are the only way large diesel engines can meet future Euro 5 rules. But Delphi Corp. says it can improve the performance of conventional solenoid -- or electromagnetic -- injectors enough to avoid investing in piezo injectors.
Denso, of Japan, the fifth and smallest of the leading injector manufacturers, plans to continue developing both technologies.
The injector debate pits a well-established technology being pushed toward its known performance limits against a more costly, undeveloped one with perhaps greater potential.
Suppliers decline to discuss revenues from injectors, but one unit of the complex part is needed for every cylinder in a car engine. That pushes the total European injector volume beyond 80 million units a year.
Until Delphi decided to try extending the use of solenoid injectors, many industry executives expected that Euro 5 standards for oxides of nitrogen (NOx) and particulate emissions would force most manufacturers to switch to piezo injectors.
The initial EU proposal for Euro 5 standards called for reducing NOx emissions to 200 milligrams per kilometer, from 250 milligrams, and particulates to 5 milligrams per kilometer, from 25 milligrams, for diesel engines. But by the time Euro 5 becomes law, possibly in 2008 or 2009, the NOx limit is likely to be 170 milligrams per kilometer.
Improving combustion
If diesel-engine manufacturers want to avoid adding new, expensive systems to clean up the exhaust after combustion, they must improve the diesel combustion process. The best way to do that is with better fuel injectors. Work led by suppliers has focused on new injectors with:
Increased injection pressure.
Multiple-nozzle injection.
Enhanced injection timing.
Suppliers are working on a new generation of diesel injectors with 29,000 pounds per square inch of injection pressure, up from about 23,200 psi, and better vaporization performance.
Siemens VDO has used piezo injectors since 2000 and believes that technology is best for meeting Euro 5 and even tougher standards in the future.
But Delphi says its latest 29,000-psi version of traditional solenoid technology works as well as piezo injectors.
"We compared piezo with solenoid types, and we saw no difference," says Detlev Schoeppe, engineering director of Delphi diesel systems. "Our system is also 20 millimeters more compact."
Delphi's choice has surprised industry sources.
"It is interesting. Cost could be the reason, especially for French carmakers that have tighter margins," says Andrew Fulbrook, manager of powertrain forecasts at CSM Worldwide's office in London. "But NVH (noise, vibration and harshness) could be a disadvantage."
Stefan Geiger, an analyst in the London office of consultant Global Insight, doubts that piezo technology is needed to meet Euro 5. He says it also could be achieved with existing technology, addition filters and adjustments to engine management systems.
"The French had already taken the easy way before, fitting particulate filters rather than optimizing the diesel combustion internally," Geiger says.
Delphi says French automakers had extensively investigated traditional solenoids.
"But some other OEM customers need to be convinced about solenoid advantages," Schoeppe says.
Solenoid injectors are still PSA/Peugeot-Citroen's primary diesel technology, says company spokesman Marc Bocque.
"But we are investigating piezo technology for its direct valve control, more precise timing and metering," he adds.
Denso, which has strong ties to Toyota, is looking to add more European customers. Denso plans to develop both piezo and traditional solenoid injector technology. It has a new advanced piezo injector with three phases and nine injector holes instead of seven.
A technology race
Both systems are likely to meet Euro 5 standards. Many believe piezo technology has an advantage for a possible Euro 6 standard expected by 2014 or 2015, but only research will definitely answer the question.
"To meet stricter limits than Euro 5, (you need) more than just higher pressures," says Shinya Omi, general manager of corporate communications at Denso Europe.
"You need full aftertreatment of exhaust gases, with a NOx catalytic converter and particulate filters."
As operating pressures increase, it becomes more difficult to balance forces, such as preventing backflow of fuel at the end of the injection phase.
Analysts see piezo technology gaining on traditional solenoids, both for diesel and gasoline, because piezo injectors work well for gasoline direct-injection engines, a growth area.
Global Insight estimates diesel's current share of European car production at 47.4 percent, or 10.2 million units, growing slightly to a 48.1 percent share by 2010.
Industry sources estimate 2010 volume for piezo diesel injectors at 20 million to 22 million units, figuring it will capture 45 to 47 percent of the diesel market by then.
Analysts see little change in suppliers' market shares, except that Siemens VDO will gain some at the expense of Bosch because of Volkswagen.
When VW abandoned its proprietary unit-injector diesel system, it entered a joint venture with Siemens VDO to make piezo-type injectors.
Says Siemens VDO spokesman Joachim Toepfer: "Because of that, we will increase our market share somewhat."
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