Investigation of Inlet Air Humidity Effects on a Large-Bore, Two-Stroke Natural Gas-Fired Engine
The natural gas transmission industry has in service over 8000 large-bore natural gas engines of various makes and vintages for compressing natural gas. Many of these engines are operated in high relative humidity conditions of the Gulf and East Coast regions of the United States. Significant change in emissions are often observed with changing ambient conditions and can be related to a combination of inlet air temperature as well as humidity effect. In an effort to investigate the humidity parameter, a project was sponsored by the American Gas Association to study humidity effects at the Colorado State University Large Bore Engine Test Bed. In this project, an inlet air humidification system was constructed to deliver a known amount of entrained water vapor to a Cooper-Bessemer GMV test engine. Due to the amount of instrumentation and controls available on the engine, it was possible to isolate the effects of humidity on engine performance and emissions. Feedback control was accomplished through humidity sensors located in the inlet air duct. In this paper, the direct effects of changing the humidity of the inlet air on engine performance and emissions are presented. Test data and theory are used to demonstrate the effects of varying inlet air humidity on the formation of oxide of nitrogen (NOx), hydrocarbons (THC), carbon monoxide (CO), and air toxic (formaldehyde) emissions from the engine.