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NIR sensor gives car makers a boost

29 Sep 2005

A laser-based temperature probe that fits into a spark plug could lead to more efficient vehicle engines.

A miniature optical temperature sensor that can be installed in a spark plug could help car makers develop a new generation of low emission, highly fuel efficient engines say its inventors. The device is the result of a collaboration between Japanese automotive firm, Nissan, US technology developer, Physical Sciences Incorporated (PSI) and Stanford University, US.

Operating in real-time, the instrument measures in-cylinder gas temperatures over a 300 - 1050 K range and will be used by vehicle engineers to study engine combustion. The sensor features 10 mW diode lasers emitting at two wavelengths in the near-infrared and works by monitoring the absorption strength of water vapour in the cylinder.

"The absorption strength depends on the internal energy distribution within the water vapour molecule, which is governed by the gas temperature," PSI's Mark Allen told Optics.org. "This general two-wavelength absorption measurement of temperature has been published before, but never at the high pressures associated with the automotive engine."

Stanford University scientists provided the high-pressure, high-temperature water vapor spectroscopy know-how, with the optical probe's design and engine vibration isolation determined by Nissan. PSI's role in the project was to develop the unit's ultra-high-speed signal processing that enables real-time temperature monitoring.

"The response time [of the device] is 130 micro-seconds, with a temperature resolution and accuracy of around 20K, depending on the in-cylinder pressure," said Allen. "Extensions to the unit's temperature measurement range are being studied now to cover higher post-combustion temperatures."

The sensor's spark-plug compatible design is said to make it much easier to implement compared with competing methods. These include attaching sensors inside the cylinder wall or estimating the temperature from camera images obtained in a specially modified engine.

According to Allen, the automotive engine testing market is worth around $60 million per year worldwide to instrumentation suppliers. Nissan plans to release further project details early next year at an upcoming Society of Automotive Engineering event.

Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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