Selective NO_x Recirculation for Stationary Lean-Burn Natural Gas Engines

NO_x control in a lean burn natural gas engine is typically achieved with appropriate management of air/fuel ratio and ignition timing. A novel approach for further reduction involves the capture of NO_x by first adsorbing the NO_x from the exhaust stream, followed by the periodic desorption of NO_x from an aftertreatment medium. Then, by passing the desorbed NO_x gas into the intake air stream and back through the engine, a percentage of the NO_x will be converted to harmless gases during the combustion process. The objective of this paper is to report the NO_x conversion phenomenon during a lean combustion process. The results of this testing will be used to develop an optimal system for the conversion of NO_x with a NO_x adsorber. A 1993 Cummins L10-G spark ignited natural gas engine was used to conduct the experiments. Commercially available nitric oxide (NO, 98.8% purity) was injected into the engine intake to mimic the NO_x stream from the desorption process to obtain NO conversion rates at various steady-state engine operating points. The NO injection system was capable of injecting NO at varying flow rates and time intervals. NO was injected into the intake manifold for ten and twenty second periods, and the conversion rates were calculated. When the injected NO amount increased from 0.22 g/s to 1.2 g/s and engine loads varied from 200ft-lb to 400ft-lb at 800 RPM, the NO conversion rates increased from 5% to 47%. It was observed that the air/fuel ratio, injected NO quantity and the engine load greatly effected the NO conversion rates. It was also noted that engine speed had a negligible affect when the intake NO concentration was held constant.