Are the requirements of Euro 4 and 5 truck and bus emissions legislation best met using SCR (selective catalytic reduction) downstream aftertreatment, or EGR (cooled exhaust gas recirculation) inside the engine? It is a question which has divided opinions amongst Europe's main commercial vehicle builders. DaimlerChrysler had rolled out its Euro 4 and 5 plans, telling the world that all Mercedes-Benz heavy - and later middle- weight - trucks for Europe would be equipped exclusively with SCR. Mercedes engineers remain unequivocal in their championing of SCR's aftertreatment deNOx technology, with its claimed fuel economy improvement of five to six per cent as the key justification for its adoption. They criticise EGR - much as Caterpillar has done in the US - for its 'pollution' of the intake air and the increase in running temperature it creates, both taking their toll on long-term lube oil performance, and with an accompanying need for extra engine cooling. DAF Trucks, Volvo and Fiat-Iveco are broadly supportive of DC's deNOx strategy, opting firmly for the SCR alternative. So too is Cummins, whose 10.8 litre ISMe engines power most ERF and many Foden heavy truck models. In the light-middleweight truck market, 4 and 6 litre Cummins ISBe diesels go into DAF's 6 to 18 tonne LF chassis. In the UK, higher-rated ISBe engines also power Foden 18-tonners and Dennis Elite municipal chassis. All proclaim the fuel consumption benefits of SCR. By dealing with NOx emissions 'downstream', it enables the engine to be programmed for the best balance of fuel consumption and road performance, unhampered by having to restrict the amount of NOx generated by high peak temperatures inside the engine. Injection timing can be re-advanced to roughly where it was in the mid-90s, before timing retardation became the low-cost 'quick fix' method of cutting tailpipe NOx.


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    Title :

    Truck deNOx strategies stir controversy


    Published in:

    Automotive Engineer ; 29 , 8 ; 30-32


    Publication date :

    2004


    Size :

    3 Seiten, 5 Bilder



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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