Mercedes is set to break another technical barrier when it becomes the first car maker to sell diesel-engined passenger cars fitted with ‘urea injection’ technology later this year.Ultra-clean Bluetec versions of the revised ML, GL and R-Class will be unveiled at next week’s New York motor show. The car uses a version of the familiar 3.0-litre V6 common-rail diesel, fitted with a system that injects a urea solution into the exhaust. The solution, branded AdBlue by Merc, is stored in an on-board tank and injected into the exhaust system at regular intervals to transform harmful nitrogen oxides into ammonia. Some 80 per cent of this is then reduced into nitrogen and water by a secondary catalytic converter.The new models, which are intended for the American market, are the first diesel-engined cars to conform to the latest US ‘BIN5’ emissions standards, meaning that they can be sold in all 50 US States, including California. They also meet the upcoming EU6 emissions standard, due to come in force in 2014. Mercedes also claims class-leading fuel economy, with the GL managing 29.7mpg on the European combined cycle.The three models will all go on sale in the USA in September. UK sales won’t be before next year, with further refinements being made to reduce CO2 output further according to company insiders.