The BlueTec technology developed by Mercedes-Benz is based on cutting-edge diesel engines with common rail direct injection and features all the strengths and advantages of this drive principle. BlueTEC is a modular concept for the effective reduction of fuel consumption and emissions in diesel vehicles. It comprises various coordinated technical measures combining technologies inside the engine aimed at reducing untreated emissions with the effective aftertreatment of exhaust gases. All the relevant constituents of emissions are minimised. The employed technology includes an oxidation catalytic converter and a particle filter. The most important objective, however, is to drastically reduce nitrous oxide emissions – the only component of exhaust gases today whose level is higher for diesel engines than the corresponding value for petrol engines.
The clean diesel technology.
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Mercedes-Benz has developed two variants here. The first combines an oxidation catalytic converter and particulate filter with a long-life NOx storage catalytic converter and an additional SCR catalytic converter (SCR = Selective Catalytic Reduction). With the second variant, AdBlue®, a harmless aqueous urea solution, is injected into the exhaust flow. This releases ammonia, which breaks down up to 80% of nitrous oxides into harmless nitrogen and water in the downstream SCR catalytic converter.
The innovative exhaust control technology in detail:
The aim is to optimise the engines and their combustion processes in order to reduce untreated emissions to the greatest extent possible. The technology employed to this end includes electronic engine control, four-valves-per-cylinder design, third-generation common rail direct injection with piezo injectors, turbochargers with variable geometry and exhaust gas recirculation.
Oxidation catalytic converters are used to minimise emissions of carbon monoxide (CO) and uncombusted hydrocarbons (HC).
The particulate filter, which has been fitted as standard in all diesel-powered Mercedes-Benz passenger cars in many countries since the summer of 2005, reduces particulate emissions to barely detectable levels.
Nitrogen oxides are reduced by a NOx storage catalytic converter in conjunction with an SCR catalytic converter or by AdBlue injection in conjunction with an SCR catalytic converter. These extremely effective exhaust aftertreatment methods enable nitrogen oxides in BlueTEC vehicles to be reduced by up to 80%.
Whether a NOx storage catalytic converter or AdBlue injection is employed to reduce nitrogen oxides is determined primarily by the design of the individual vehicle concerned. The AdBlue technology offers advantages for saloons, pick-ups and SUVs because the engine is not required to run at intervals on a rich fuel-air mixture, as is necessary to clean a NOx storage catalytic converter which is used to remove the harmful nitrogen oxides from the exhaust gas. This would be necessary at particularly frequent intervals on heavy vehicles with higher fuel consumption levels, thereby further increasing their fuel consumption.
In order to achieve the best possible results with BlueTEC technology, sulphur-free diesel fuel (sulphur content of less than 15 ppm) is required. Such fuel also improves the emission levels of older diesel engines.
Various BlueTEC models have been available since the autumn of 2009. Practically all of these models already comply with the Euro 6 standard which is to apply for new vehicles as of 2015. Nitrogen oxide emissions are reduced on these models by AdBlue injection in conjunction with an SCR catalytic converter. The AdBlue solution is contained in a separate tank in the vehicle, from where it is conveyed by means of a feed pump to the metering module. As only very little AdBlue is required, it is sufficient to replenish the small tank in the course of regular servicing.