FAST MONITORING OF MOTOR EXHAUST COMPONENTS BY RESONANT MULTIPHOTON IONIZATION AND TIME-OF-FLIGHT MASS-SPECTROMETRY

A new analytical procedure is provided by the combination of two types of spectroscopy. Resonant ionization of selected compounds by multiph oton ionization is based on results of absorption spectroscopy for the compound molecules of interest and time-of-flight mass spectrometry s erves for the unambigious detection of these compounds. An interesting application of this method is the fast exhaust gas analysis. In the d evelopment of future combustion engines, the management of dynamic mot or processes becomes predominant because by more than 90% of all the d angerous exhaust pollutions are produced in instationary motor phases such as fast speed or load changes. The investigation of dynamic proce sses however, requires fast analytical procedures with millisecond tim e resolution together with the capability to measure individual compon ents in a very complex gas mixture. The objectives for a development p roject of such an instrument were set by the Research Association for Combustion Engines (Forschungsvereinigung Verbrennungskraftmaschinen, FVV, Germany): Up to ten substances should be monitored synchroneously with a time resolution of about 10 milliseconds, with concentration l imits of 1 part per million and with a precision better than 10% relat ive standard deviation. Such a laser mass spectrometer for fast multi- component automotive exhaust analyses has been developed in a joint re search project by Bruker-Franzen Analytik GmbH, Dornier GmbH and the T echnical University of Munich.The system has been applied at a motor t est facility to investigate the emissions of the aromatic hydrocarbons benzene, toluene and xylene, of nitric oxide and acetaldehyde in stat ionary and dynamic engine operation. These measurements demonstrate th at strong emission of these pollutants takes place at instationary eng ine operation and in particular that these compounds are emitted at di fferent times, giving new information about the processes in the combu stion chamber and in the exhaust pipe.