Infrared diode laser exhaust gas analyser for trace components

We report on a four-component TDLS system for highly sensitive real time car exhaust gas analysis, based on infrared diode laser absorption spectroscopy. Four lead-salt diode lasers, one for each gas species, are operated simultaneously in a fast multiplex mode. A long optical path of up to 100 m in a multiple reflection arrangement and a short path of 15 cm are provided. The optical absorption cell is kept at 190 degree C with a gas sample pressure of 50 hPa. The total system response time of appr. 2 s is determined by cell volume and pumping speed. The system is designed for the analysis of a number of "unregulated pollutants" like formaldehyde, ethene or methanole at detection limits in the 10 ppb range, in correlation to major constituents as carbon monoxide, carbon dioxide or nitric oxide. First results obtained in a dynamometer test facility are presented.