Lean NOx Trap for Heavy-Duty On-Road Applications - A Feasible Alternative?

The implementation and development efforts of lean NOx trap catalysts for heavy-duty applications decreased a number of years ago. Most heavy-duty engine manufacturers realized that the system complexity as well as the durability of such a system does not allow large volume production without significant risk. The current consensus of the heavy-duty community is that for 2010 the SCR system will be the prime path to meet the 0.2 g/bHPhr NO_x emission standard, although this is subject to adequate infrastructure investment and progress.

As a low volume manufacturer, in order to comply with the 2007 heavy-duty phase-in emission standards, General Engine Products (a subsidiary of AM General LLC) integrated a NO_x adsorber system on the Optimizer 6500 engine. This engine features split combustion chamber design, rotary fuel injection pump and operates with EGR. The engine meets the 2004 heavy-duty emission standards, but does not allow a NO_x reduction through engine internal measures that would allow certification to 2007 emission standards. This fact forced the introduction of an exhaust aftertreatment system with NO_x conversion efficiencies in the 60% range. The developmental results were presented in greater detail in paper 2007-01-0235.

The paper discusses the details of the catalyst system development, the oxygen storage management of the different components and the associated hydrocarbon breakthrough during DNT regenerations as well as the durability results of the DF testing.