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Motoring made simple -- S. Muralidhar
Mercedes Benz, which has worked on new diesel engine technologies for passenger cars for more than 70 years, had in 2002 developed a new technology platform for lowering diesel engine emissions, particularly NOx. Called BLUETEC, this new technology consists of two systems that focus on NOx reduction, even as these are combined with other technologies to reduce the amount of particulate matter in the emissions.
The award-winning modular BLUETEC technology package includes familiar systems such as the oxidation type catalytic converter and particulate traps, in addition to the optimised, new generation common-rail diesel engines.
From ‘NOxious’ to innocuous
Mercedes’ BLUETEC systems work to break down the NOx emissions into nitrogen and water vapour. A complex catalytic converter system consisting of an improved storage-type nitrogen-oxide catalytic converter and an SCR (selective catalytic reduction) catalytic converter work in conjunction. The BLUETEC systems are already in use in the Mercedes Benz E320 sedan and the car is currently being sold in the US.
Under normal operating conditions, the NOx from the exhaust gas is collected in this storage-type catalytic converter cycle. Through regular adjustment of the fuel-air mixture inside the engine, the combustion process and, thus, the composition of the exhaust gases, is modified for a short period. The NOx is first separated and there is also a particulate filter that collects the soot and burns it off after the filter is full.
The SCR is a complex catalytic converter, but Mercedes has further perfected the system, making it even more effective with the addition of what it calls ‘Adblue’ injection. The process involved here requires the injection of ammonia (liquid urea), into the pre-treated exhaust gas. With the Adblue injection fed into the collected NOx, the ammonia reacts and breaks down the pollutant into harmless nitrogen and water in the downstream SCR catalytic converter. This is currently the most efficient method of exhaust gas after-treatment in diesel engines.
Mercedes Benz has used BLUETEC technology with Adblue injection successfully in its commercial vehicles in Europe. These vehicles are already capable of meeting Euro V emission norms that only come into effect by 2009.
Euro VI emission standard
At this year’s Geneva Motor Show, Mercedes has also showcased a new Vision C220 with BLUETEC technology. This new C-class sedan is capable of meeting the even stricter Euro VI emission standard that will be applicable to all new vehicles Europe-wide only from 2015. The Vision C 220 BLUETEC also continues to live up to the reputation of diesel engines and is extremely economical, consuming only 5.5 litres of diesel per 100 km.
BLUETEC technology can only be effective when ultra low sulphur diesel is used (which means bringing it to India is ruled out). Further, though this new generation diesel engine is very effective in reducing emissions over the long term, it still has a small handicap in that the urea or liquid ammonia reservoir (for Adblue injection) needs refilling at regular intervals.
Mercedes is working on another new technology that can enable its future diesel engines to meet even more stringent emission norms and without the use of an ammonia reservoir.
Next: Honda’s diesel engine Tech.
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