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Researcher Develops Reaction Model for NOx Aftertreatment for Diesel and Lean-Burn Engines

A Dutch researcher has developed a reaction model describing the activity of new NOx Storage Reduction (NSR) catalytic converters used in conjunction with diesel or lean-burn gasoline engines. The model supports the development of a controller for the engine and emissions aftertreatment systems to optimize fuel consumption and NOx control.

While diesel and lean-burn gasoline engines offer beneficial reductions in fuel consumption compared to conventional gasoline engines, they also generate exhaust gases rich in NOx. One current approach to reducing NOx emissions in such engines is to incorporate trapping components like barium oxide in oxidation catalysts, thus enabling the storage of NOx as nitrates under oxygen-rich conditions for later reduction.

With this new type of NOx Storage Reduction (NSR) catalytic converter, NOx generated during a long oxygen-rich (lean-burn) period is stored in the barium component. When this component becomes saturated, the catalyst is regenerated during the short fuel-rich period. The NOx stored is released and subsequently reduced to nitrogen over a precious metal such as platinum.

Caren Scholz from the Eindhoven University of Technology investigated this NSR mechanism to gain a better understanding of how the storage component functions during the oxygen-rich and fuel-rich periods.

She studied the behavior of the catalyst in detail, analyzing the effect of the various forms in which barium occurs in the catalytic converter, the effect of the presence of carbon dioxide and water in the exhaust gas, and the effect of the various reducing agents, such as carbon monoxide, hydrogen, and ethylene on the NOx storage and reduction.

The research yielded insights into the function of various components in the catalytic converter. Scholz produced a practical mathematical model that describes the various chemical reactions in the device.

Using this reaction model, a controller in the car can determine when the maximum NOx capacity of the catalyst has been reached, followed by the length of time extra fuel must be injected to regenerate the catalyst.

The research was carried out in cooperation with PSA Peugeot Citroen, Toyota and Ford, the car development company PD&E Automotive Solutions, catalytic converter manufacturer Engelhard De Meern (now BASF), and with TNO Automotive, Shell, E.P. Controls and IPCOS.




Here's a short interesting read:

"Diesel cars may be the greenest"
Like hybrids, diesels are very fuel efficient

NANCY MACDONALD | July 2, 2007 |

"Mention diesel engines to most North Americans and it conjures images of noisy, smoke-belching trucks of the past. But all that may soon change. According to analysts at UBS Warburg, by 2008 North American consumers may come to see diesel as the most promising technology for improving fuel economy and reducing greenhouse gas emissions. That, in part, may be why even diesel laggards like Toyota have recently announced plans to beef up their diesel offerings.

A surprising new report co-authored by Swiss bank UBS and the British consultancy Ricardo suggests diesels may be just as energy efficient as gas/electric hybrids, and come at a better price. Diesels offer 30 per cent better mileage than their gasoline counterparts, the equivalent of or better than hybrids. UBS says diesel's biggest advantage comes at the dealership: hybrid buyers take a hit of around US$5,000 for a mid-sized car, and almost $8,000 for a crossover, like the Lexus LX400h. In Europe, the cost premium for a diesel runs an average $2,000 compared to gas models.

Diesel already dominates Europe, where they make up more than half of all cars sold. They are gaining popularity in India and South Korea, but they've barely penetrated North America, the world's biggest car market. But UBS expects that will change by 2008, as consumer options grow. Volkswagen, which sold 20,000 diesels in 2006, is the current American pacesetter. Next-best Mercedes sold 7,000 diesel cars in the U.S. last year, an increase of 60 per cent over 2005. Its high-end competitor, BMW, is planning to launch a diesel car in the U.S. in 2008; Honda is promising one by 2009; and Nissan has announced a diesel version of their Maxima sedan will hit North America by 2010.

By 2012, as worldwide concern over global warming increases, UBS predicts diesel sales will hit 1.7 million, outpacing hybrids' predicted sales of 1.5 million. First, though, it must overcome its image problem. The humming, Hollywood-friendly Toyota Prius hybrid screams green. The diesel VW Golf? Not so much."

Greg Faulkner

I just hope this technology is cheaper than the current, LNT-type, NOx-reducing technology slated to come on line for the new VW four cylinder with common-rail and the 2.2 liter for the Honda Accord. It is said that these systems cost upwards of $1800 per unit, which explains why most auto companies are not too keen about diesels for the U.S.

The Euro 5 and Euro 6 emissions standards will be such that these advanced systems will not be required for anywhere but for the U.S., which makes the marketability of smaller diesel engine designs even less attractive for the U.S., since these systems will not be necessary anywhere but here. Our NOx rules are now even tougher than Japans.

The larger engines (V-6s and above) have a cheaper system, called SCR, but those NOx reducers are consumer intrusive in that they require a urea solution be added to a resevoir about as often as an oil change, and these systems will still cost over $1200 per unit by the time all the EPA-mandated warning and disabling systems are applied to these new diesels.

I hope this new technology has promise to replace both the current LNT systems and SCR systems to make diesels more feasible for our market. Either that or our EPA could just grow a brain and let these 75% cleaner diesels into our markets without an immediate, 90% reduction in NOx. They then could allow technology to catch up to their regulations.

The above attached article does not take these advanced, NOx devices into account when arguing the promise of diesel-powered cars for America versus hybrid cars. Sure, for Europe, no one with a brain would buy a gas-electric hybrid with diesels outperforming and out economizing them, while addtionally having the benefit of being alternative-fuel capable without loss in fuel economy; but in the U.S., the struggle to catch technology up to our anti-diesel biased EPA, it's a different story.

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