BlueTEC is Daimler AG's marketing name for engines equipped with advanced NOx reducing technology for vehicle emissions control in diesel-powered vehicles. The technology in BlueTec vehicles includes a selective catalytic reduction (SCR) system that uses diesel exhaust fluid, and a system of NOx Adsorbers the automaker calls DeNOx, which uses an oxidizing catalytic converter and diesel particulate filter combined with other NOx reducing systems.
Daimler introduced BlueTEC in the Mercedes E-Class (using the DeNOx system) and GL-Class (using SCR) at the 2006 North American International Auto Show. At that time, these BlueTEC vehicles were 45- and 50-state legal, respectively, in the United States (a 45-state vehicle does not meet the more stringent California emission standards that have also been adopted by four other states).
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 United States. VW introduced the Jetta Clean TDI, the Tiguan concept, and the Touareg BlueTDI as part of the BlueTec licensing program. 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.  VW developed their own system, but it failed and they re-programmed the engine control to show false values during pollution tests.
By 2010 a BlueTEC version of the Mercedes Sprinter was released. The BlueTEC systems allowed the elimination of much of the EGR in that vehicle's engine, which as a result gives 188 horsepower (140 kilowatts) compared to the non-BlueTec engine's 154 horsepower (115 kilowatts).
The BlueTEC system was created because the properties of the Diesel cycle that give diesel engines high fuel efficiency also lead to relatively higher emissions of certain pollutants compared to Otto cycle engines. High compression ratios and lean air-fuel mixtures make high combustion temperatures, which results in more nitrogen oxides being produced during the combustion. While the particulate matter can be controlled with higher injection pressures and particulate filters, the big challenge is limiting NOx; Tier 2 regulations in the US are 0.05 grams per mile of NOx, which is ⅛ of the 0.40 limit in the European Union.
The emissions system works in a series of steps:
- A diesel oxidation catalyst reduces the amounts of carbon monoxide (CO) and hydrocarbons (HC) released from the exhaust.
- A DeNOx catalytic converter begins a preliminary removal of oxides of nitrogen.
- A particulate filter traps and stores soot particles, burning them off when the filter gets full.
- If the above are not sufficient to meet the prevailing emissions regulations, a Selective Catalytic Reduction (SCR) catalytic converter will convert the remaining nitrogen oxides to nitrogen and water; so-called diesel exhaust fluid (solution of urea and water) is injected into the exhaust gas stream to enable the conversion. In order to prevent vehicles from breaking emissions regulations, the engine may go into a limp-home-mode if the DEF tank is depleted; drivers are instructed to keep the tank refilled as necessary. Some commercial vehicles are equipped with a request or inhibit switch which allows the DEF injection to be "postponed" as it can reduce power output and increase temperatures temporarily; if the vehicle is climbing a grade, for example, it may be necessary to delay the cycle.
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