Honda Motor Co. said on Monday it has developed a new and simple diesel powertrain that is as clean as gasoline-fuelled cars, unveiling plans to mount it on a car for the U.S. market by 2009.

Diesel engines, which now power half of Europe's new cars, are slowly gaining traction with fuel-conscious consumers around the world since they typically get 30 percent better mileage than gasoline cars.

Their weakness has been the higher exhaust levels of nitrogen oxide (NOx), a greenhouse gas, and carmakers are racing to come up with ways to clear the world's strictest emissions regulations, which the United States will usher in next year.

Honda's new diesel drivetrain generates and stores ammonia within a two-layer catalytic converter to turn nitrogen oxide into harmless nitrogen.

Honda engineers said the technology is superior to a process pioneered by Germany's DaimlerChrysler AG because the latter requires a complex system and heavy add-ons to generate ammonia from urea-based additives.

Some technical hurdles remain.

The system would need fine-tuning for the wide-ranging cetane indexes of diesel fuel found in the United States. Honda also needs to develop technology to measure emissions levels according to U.S. On-Board Diagnostic System requirements.

But Japan's third-biggest auto maker said it planned to roll out the advanced diesel engine, first in the United States within three years and later to other regions. DaimlerChrysler, which along with Volkswagen AG already sells diesel cars in the world's biggest auto market, is preparing its next-generation diesel car for a 2008 launch.

Honda has long been at the forefront of green powertrain technology, perhaps most famously with the development in 1973 of the CVCC (Compound Vortex Controlled Combustion) engine which gave the popular Civic its name. The engine was the first to meet U.S. clean air guidelines without a catalytic converter.

Just as we paved the way for cleaner gasoline engines, we will take the leadership in the progress of diesel engines, Honda Chief Executive Takeo Fukui told a news conference.

Honda would be open to considering licensing its new diesel technology once it was perfected, Fukui said.

FUEL CELLS, FLEX-FUEL

In a demonstration of other new power plant technologies at its R&D center in Tochigi, north of Tokyo, Honda also showed off a prototype of its next-generation fuel cell vehicle which runs on a newly developed compact and more powerful fuel cell stack.

The new stack is designed to allow the hydrogen and water formed during electricity generation to flow vertically instead of horizontally, making the component 20 percent smaller and 30 percent lighter than the previous version.

Honda's new FCX fuel-cell car now has a driving range of 570 km (354 miles) - a 30 percent improvement from the 2005 model. Its maximum speed is 160 km (100 miles) per hour, and it can be driven in temperatures as low as minus 30 degrees Celsius (-22 F).

Honda plans to begin marketing the car in limited numbers in 2008 in Japan and the United States.

Honda said it also developed a flexible fuel vehicle system that can operate on any proportion of ethanol to gasoline between 20 percent and 100 percent. That car will be sold in Brazil, the biggest market for ethanol-based vehicles, later this year.

Way out in the future, the ultimate green car will be fuel cell vehicles, Fukui said. But in the meantime, you need a wide range of green technology to meet varying local needs and fuel supply.

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