BlueTec

BlueTec is Daimler AG's name for its two nitrogen oxide (NO_x) reducing systems, for use in their Diesel automobile engines. One is a urea-based reductant called AdBlue, the other is called DeNO_x and uses an oxidizing catalytic converter and particulate filter combined with other NO_x reducing systems. Both systems are designed to reduce pollutant emissions.

The BlueTec was on the Ward's 10 Best Engines list for 2007 and 2008.

Uses

Mercedes-Benz introduced the systems in the E-Class (using the 'DeNO_x' system) and GL-Class (using 'AdBlue') at the 2006 North American International Auto Show as the E320 and GL320 Bluetec vehicles. This system makes these vehicles 45-state and 50-state legal, respectively in the United States, and is expected to meet all emissions regulations through 2009.

A Jeep Grand Cherokee with the same BlueTec engine is also expected, and Mercedes announced tentative plans for a BLUETEC/electric hybrid S-Class.

Daimler AG has entered into an agreement with Volkswagen and Audi to share BlueTec technology with them in order to increase the Diesel passenger-vehicle market in the US.

Volkswagen introduced the Jetta Clean TDI, the Tiguan concept, and the VW Touareg BlueTDI as part of the BlueTec licensing program. All are expected to be introduced in the American market in 2008. The Jetta and the Tiguan use NOx Adsorbers, while the Touareg uses a Selective Catalytic Reduction catalytic converter.

In August 2007 VW Group announced that cooperation on BlueTec with Daimler AG would end. The reasoning for this change is due to the recognition of the VW TDI branding. VW did not want to use a competitor's branding for a product they would introduce into the market.

Rationale

The BlueTec system was created because the processes that give diesel engines efficient fuel economy also creates extra emissions of certain pollutants. High compression ratios and lean air-fuel mixtures make high combustion temperatures, which results in more nitrogen oxides and Diesel Particulate Matter (also known as soot) being released into the atmosphere. While the particulate matter can be controlled with higher injection pressures and particulate filters, the big challenge is limiting NO_x (Tier 2 regulations in the US are 0.05 grams per mile of NO_x, which is ⅛ of the 0.40 limit in the European Union).
Consisting of many different elements, BlueTec most notably relies upon particulate traps to eliminate soot/smoke throughout the engine's operating range, and upon urea injection from a stored canister (Mercedes calls this AdBlue) into the exhaust stream. AdBlue injection begins a chemical chain reaction which, in conjunction with an additional catalytic converter, converts nearly all remaining NOx into water vapor and nitrogen.

Process

The BlueTec system will use two catalytic converters specifically targeting NO_x. The first converter traps the NO_x, and later releases it to the second converter which then converts it to nitrogen (N₂) and water (H₂O). This will make a diesel car legal in 45 states. But to make it pass the more stringent regulations of California, Maine, Massachusetts, New York and Vermont, AdBlue (NH₄) will have to be introduced into the system, making the conversion more complete.

<math>NH_3 + NO_x \rightarrow \; N_2 + H_2O</math>

The whole exhaust system would work like so:

1. A Diesel oxidation catalyst reduces the amounts of carbon monoxide (CO) and hydrocarbons (HC) released from the exhaust.
2. A DeNO_x catalytic converter begins a preliminary removal of oxides of nitrogen.
3. A particulate filter traps and stores soot particles, burning them off when the filter gets full.
4. If the above are not sufficient to meet the exhaust specifications, a Selective Catalytic Reduction (SCR) catalytic converter will take the remaining nitrogen oxides and convert them to nitrogen and water. AdBlue will be injected into the exhaust gas stream to enable the conversion.

External links

• BLUETEC.COM: The official BLUETEC News Blog by Mercedes-Benz
• The Evolution from Diesel to BLUETEC in Depth
• Mercedes-Benz Global Home
• Official BlueTec website
• greencarcongress.com on BlueTec
• FactsAboutSCR.com, North American SCR Stakeholders Group