Emissions regulations on stationary, natural gas fired reciprocating engines are becoming increasingly tighter throughout the United States. In addition to lower NOx, CO and hydrocarbon limits, regulation of HAP (Hazardous Air Pollutant) emissions has become more prevalent. Rich burn (stoichiometric) natural gas engines are widely used in the oil and gas industry, as well as in distributed power generation. Due to the low oxygen content in the exhaust, these engines are suitable for 3-Way catalyst, which simultaneously reduces NOx and oxidizes CO and hydrocarbons. A series of 3-Way catalyst tests were conducted on a small natural gas engine at the VTT Technical Research Centre in Espoo, Finland. The overall goals of the testing were to determine the ability of various 3-Way catalysts to meet California emissions regulations and to gather data on HAPs emission reductions. The testing was carried out in two phases. In phase 1, several fresh catalysts were tested at the NOx/CO crossover point (i.e., the point where CO and NOx reduction percent is approximately equal) by using an air/fuel ratio controller to keep the exhaust oxygen level constant. Detailed emissions measurements of both regulated and unregulated emissions were taken. The measurements included NOx, CO, hydrocarbon species, CH2O, N2O, NH3, and H2. In phase 2, the effects of exhaust lambda variation on NOx and CO were studied in more detail, with aged catalyst. Also, different engine loads were tested to vary the space velocity and temperature. This paper describes the testing in more detail and presents some of the resulting data.

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