BLUETEC: The Cleanest Diesel in the World

Margo Oge, Head of the Office of Transportation and Air Quality at the US Environmental Protection Agency (EPA) presented the following figures back in March 2004: "If we had a light duty vehicle population that was one third diesels, that could save up to 1.4 million barrels of oil per day in the US, the amount of oil the US currently imports from Saudi Arabia. If we made these vehicles diesel hybrids, the oil savings would about double or up to 2 times the amount of oil Saudi Arabia ships to the US every day."

BLUETEC – the emission-control technology from Mercedes-Benz

The Mercedes-Benz development engineers have been advancing emission-control solutions for a number of years, one of the main aims being to ensure compliance with future emission standards in the US, Europe and Asia. One focus of these activities is devising effective and economical methods for reducing nitrogen oxides ("denoxing"). This technology for the cleanest diesel in the world is called BLUETEC.

In order to bring together all these technologies within a single, appropriate package, Mercedes-Benz is following a graduated plan that includes the following phases: • Optimization of the engines and their combustion processes to minimize untreated emissions. This includes electronic engine management, four valves per cylinder, third-generation common-rail direct injection with piezoelectric injectors, a turbocharger with variable nozzle turbine and exhaust gas recirculation. • Oxidizing catalytic converters to minimize emissions of carbon monoxide (CO) and unburned hydrocarbons (HC). • The particulate filter, fitted as standard in all Mercedes-Benz diesel cars in many countries since summer 2005, reduces particulate emissions by as much as 98 percent, thus easily undercutting even the current EU 4 particulate limits (0.025 g/km). This technology also ensures compliance with the US limits currently in force. • Nitrogen oxides – whose concentration is higher than in the exhaust gases of gasoline engines due to the specific combustion process in diesel engines – are reduced to such an extent that even the world's most stringent exhaust gas limits can be complied with. Here the so-called BLUETEC technology is utilised. This reduction is achieved either with an advanced DeNOx storage catalytic converter, available in the E 320 BLUETEC from autumn 2006, or with the more complex but even more effective AdBlue injection. This, combined with Selective Catalytic Reduction (SCR) creates the most effective method of exhaust gas after-treatment currently available. This enables nitrogen oxide levels to be reduced by up to 80 percent. The Mercedes Benz engineers will be show-casing the combination with AdBlue injection in the Vision GL 320 BLUETEC at the Detroit show and are developing the process for use as a standard system in passenger cars.

The SCR process is based on the injection of the reducing agent AdBlue into the exhaust gas stream. AdBlue is an aqueous urea solution that is carried in a separate tank. Since an average of around 0.1 liters per 100 km (2352.15 mpg or 1 to 3 percent of diesel consumption) is all that is required, the tank can be designed so that it only needs to be refilled when service staff are carrying out regular, scheduled maintenance. When AdBlue is injected into the pre-cleaned exhaust gas, ammonia (NH3) is released, causing the nitrogen oxides to be converted into harmless nitrogen (and water) in a downstream catalytic converter. The decisive factor in ensuring that the catalytic converter works extremely efficiently is precise metering in line with the current engine operating state. Choosing which technological solution to use depends both on the vehicle concept concerned and on the required "denoxing" rate.

BLUETEC already a success in commercial vehicles

However, BLUETEC technology is not altogether new as, in Europe, it has already been employed extremely effectively in Mercedes-Benz commercial vehicles with a GVW above six tonnes. This technology has proved a resounding success in more than 10,000 vehicles such as the Actros, Axor and Atego trucks. In this case, BLUETEC reduces the nitrogen oxide levels considerably, meaning that these vehicles already comply with the emission standards due to come into force for trucks from 2009. In Europe the AdBlue supply network already comprises some 1,500 filling points.