In 1998 EPA promulgated new emissions regulations that phase in more restrictive NOx standards for locomotives. This, combined with rising diesel fuel costs, confronts railroads with challenging tradeoffs between fuel economy and compliance with emission standards. Greater locomotive fuel economy can be achieved with leaner fuel mixtures, but leaner mixtures increase NOx emissions. Currently, railroads do not have a convenient instrument for measuring NOx emissions, so optimizing fuel use while meeting EPA standards has to be based on guess work and indirect measurements such as cylinder temperature.
This project investigated a locomotive emissions analyzer that could be mounted on a locomotive and continuously monitor exhaust emissions. Ion Mobility Spectrometry (IMS) was selected for the sensor technology because of its rapid response time, low cost, and small size. IMS sensors consist of a reaction tube and a drift tube, separated by a shutter grid. Exhaust gas entering the reaction tube is ionized, and the ions afe gated into the drift tube through the shutter grid. The ions are drawn down the drift tube toward a Faraday cup where they impact a metal plate and transfer their charge, creating an electric current. This current is amplified and digitized, and the analysis of this signal can be translated into concentrations of NOx. The analyzer output would be used to continuously control engine settings such as injector timing to achieve the optimum balance between engine efficiency and exhaust emissions.
