Exhaust gas measurement

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Long wavelength infrared sensors can be used for gas analysis, such as exhaust gas of cars. Traditionally exhaust gas analysis has been done in the test facilities, using big IR spectrometers with lamps. The new challenge is now to shrink this measurement down and make it precise and reliable enough for an in-car measurement.

Since the 1st of September 2015, all new passenger vehicles from the EU Member States are subject to the exhaust gas regulation Euro 6. Other worldwide governmental regulations also include, EPA ‘2010 /‘2013 (Japan/USA), NS4 and upcoming NS5 (China) force the development of environmental sensors.

In particular, these regulations set new emission limits (mg/km) for nitrogen oxides (NOx), but also for CO, HC and particulate matters (PM). Previous standard targets could be achieved via chemical sensors, but for detection of low levels of gas with a high precision then optical sensor is definitely the next generation answer for exhaust gas measurement.

Pollution is minimized when the engine is burning fuel correctly, and the well-known Lambda sensor is usually maintaining the optimum fuel - air ratio by measuring the amount of Oxygen in exhaust gases. However, the sensor cannot quantify pollutants such as CO, hydrocarbons and oxides of Nitrogen in exhaust gas. This is an inconvenience as per the Euro 6 standard, car-makers have to look to extract the exact concentration information.

Thus, in addition to the merits of a fuel quality sensor or “FQS” (uphill analysis), additional measurements have to be conducted for exhaust gas (downhill analysis), in order to accurately monitor the levels of NOx, CO, HC and particulate matters.

As for FQS, the optical methods can be wavelength dispersive or not, but are almost exclusively longwave infrared oriented for an all-in-one optical sensor.

Thus, mid IR components such as InAsSb photodiodes associated LEDs in the range of 3 to 5µm and Thermopile sensors are the right optical choices.

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