Optical linear array from Melexis turns the spotlight to real-time fuel quality sensing

October 20, 2011 - Tessenderlo, Belgium. Melexis: Near IinfraRed (NIR) spectroscopy using the company’s 3rd generation of Optical Linear Array, the MLX75306 enables real-time fuel quality sensing for engine management. Working with petrochemical and other researchers, the company has decoded the optical fingerprint of different types of fuel available in the market. A cost effective and robust spectrum analyzer is realized with LED light, optical filters and the MLX75306. Measurement of fuel type, mixtures and contaminants provides engine control systems an important new input for optimizing efficiency and emissions.

Refined fuel quality analysis capabilities are useful for several reasons. At present, automotive OEMs supply different specification engines to different continents because of variances in fuel quality. Direct molecular fuel analysis offers vehicle manufacturers the ability to develop a single, real-time programmable engine that is suitable for all regions, as opposed to the current situation whereby engines are developed per fuel region. More accurate fuel analysis techniques can also be used to respond to new and emerging fuel types like Flex Fuel. As fuel price rises globally, fuel adulteration practices have become common in some countries, providing additional justification for technologies that can identify the compounds and concentration of certain additives and, if necessary, alert the driver. Increasingly tight emissions regulations also support the provision of better information about a fuel’s intrinsic quality as it can be used to help the engine run in an optimal and therefore more emissions-friendly way.

The MLX75306 comprises a 142 x 1 array of photodiodes, associated charge amplifier circuitry and a pixel data-hold function to provide simultaneous integration start and stop times for all pixels. With an integrated AD converter and full SPI control, the MLX75306 is a highly digital optical linear array. The package design allows for close integration with a linear variable filter covering the entire near-infrared band, supplied by a partner company. Notably, in response to market demand, Melexis has begun advanced development on an integrated solution that marries the linear array and a wideband near infrared filter inside a standard automotive CMOS process.

For all automotive applications, temperature range and mechanical dimensions are key parameters. The MLX75306’s narrow body SO16 package allows it to be placed in a variety of locations, whilst its availability in an automotive temperature range means that it can be fitted close to the fuel lines. As fuel is also used as a “recirculation cooling liquid” its temperature can easily exceed 85oC, thus ruling out consumer grade parts. The bill-of-materials for the system is completed with microprocessors and LEDs with different wavelengths that can be readily found off-the-shelf in automotive temperature grades.