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Considering future emission legislation for HD diesel engines it is apparent that it will be probably necessary to employ A/T devices to achieve them. The main problem concerns the simultaneous control of both NOx and particulate emissions at an acceptable fuel penalty. Concerning particulate matter the use of particulate traps is considered to be a proven technology while for NOx emission control; various solutions exist mainly being the use of SCR catalysts or LNT devices. But LNT traps require periodical regeneration, which is accomplished by generating reducing agents i.e. CO and H2. The present investigation focuses on the regeneration of LNT devices through the engine operating cycle. This can be achieved using two techniques, additional injection of fuel at the exhaust manifold (external measures) or operation at low lambda values in the range of 1.0 or lower (internal measures).