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Infrared microsystem for polluting emission control on cars


Emerging fires on manned space stations or in aircrafts could lead to hazardous situations for the passengers and the crew on board. Furthermore complex and valuable spacecraft or aircraft equipment needs to be protected for safety reasons. Today’s fire detection systems are providing reliable fire alarm information. But for new concepts like the long haul operations of aircrafts or the large-scale space stations new approaches are needed. Reasonable features of such fire detection modules are further reduction of the false alarm probability, self-test and pre-warning capabilities. This article presents recent results on possible pre-warning strategies. Today’s fire detection modules rely on stray light detection. Soot particles arisen from burning fires can be detected. This effect leads to a reliable fire-warning signal but a prediction of fire events cannot be given. This new concept is using a signature analysis of possible fire precursors and the metabolism oriented gases. Fire precursors are gaseous products emerging from incomplete combustion e.g. hydrogen, hydrocarbons and carbon monoxide. Typical metabolism oriented gases are carbon dioxide and water vapour. An infrared system was built up in order to measure the above mentioned gases and to verify the measurement strategy.
Two prototypes were evaluated during the project against hydrocarbons detection. The first one was more dedicated for research and studies on synthetic gas bench to determine the potential of the HC emitter such as, limit of detection, interference, selectivity, response time etc. The second prototype, as close as possible to a production system, was evaluated both on synthetic gas bench and chassis dynamometer. Results show that HC emitter at 3.3µm is able to detect hydrocarbons as the whole and the behaviour of the output signal is in accordance with classical HC gas analyser (FID technology) used in the automotive field. Because of the fast response time, the IMPECC prototype should be compatible with cylinder individual measurements. In gasoline application, the IMPECC prototype has demonstrated the possibility in up-stream and down-stream three way catalyst measurements in order to give information about the diagnostic of the catalytic converter. Because of the low HC concentration in common rail Diesel exhaust, limit of detection has to be enhanced. The prototype has survived several hours under Diesel raw exhaust without any clogging.
Among different cavity designs for producing infrared microcavity based light emitters, a configuration bringing a strong improvement in terms of optical properties has been found. It relies on a specific etch stop layer used during the fabrication of the microcavity. By using such an etch stop layer optical losses can be minimized and thus optical output power maximized.