Lean NOx Trap Catalysis for NOx Reduction in Natural Gas Engine Applications

Reliable power generation and distribution is a critical infrastructure for the public and industry. Large-bore spark-ignited natural gas reciprocating engines are a reliable source of power generation. Lean operation enables efficient operation, and engines can conveniently be placed wherever natural gas resources are located. However, stricter emission regulations may limit the installation and use of more natural gas reciprocating engines if emissions cannot be reduced. Natural gas engine emissions of concern are generally methane, carbon monoxide, and oxides of nitrogen (NOx). Methane and carbon monoxide can be controlled by oxidation catalysts; however NOx emissions are difficult to control in lean exhaust conditions. One method of reducing NOx in lean exhaust conditions is lean NOx trap catalysis. Lean NOx trap technologies (also known as NOx adsorber catalysts, NOx storage and reduction catalysts, etc.) have demonstrated >90% NOx reduction for diesel reciprocating engines and natural gas turbines. In the work presented here, the feasibility of a lean NOx trap catalyst for lean burn natural gas reciprocating engines will be studied. Tests were conducted on a Cummins 8.3-liter engine on a dynamometer. The lean Nox trap catalyst was controlled in a valved exhaust system that utilized natural gas as the catalyst reductant. Oxidation and reformer catalysts were used to enhance utilization of methane for catalyst regeneration. The feasibility of this approach will be discussed based on the observed NOx reduction and associated fuel penalties.