Nanosized soot particles are a serious health hazard in urban air. They can penetrate deep into the lungs and their fat solubility makes possible their accumulation in other organs such as the brain. Legislation has therefore continuously reduced the allowable emission levels and raised requirements for reporting the status of the exhaust system (OBD, on board diagnostics) in diesel powered vehicles.
In this project we developed a sensor based on thermophoresis (patent filed) to enhance soot deposition on the sensor.
Thermophoresis is a force acting on particles located in a temperature gradient, such that a sensor held at lower temperatures than the surrounding exhaust gas will obtain enhanced deposition of submicron particles.
Sensors with finger electrodes (width/gap, 150/100 μm) and a heater for burn off of collected soot, were fabricated on one end of alumina substrates (90x5x1 mm). Thermal simulations initiated the construction of a sealed metal tube around the sensor rod (patent filed), which drained heat from the sensor surface allowing a temperature gradient of 50-100°C with respect to the exhaust gas temperature. This sensor layout showed preliminary good results in two runs of testing in diesel exhausts.
An aerosol based soot generation system was constructed which generates controlled soot atmosphere possible to use for testing and calibration of soot sensors in the lab.
The work from this project will be continued in the SootSens II project. In this one year follow-up project, which has been partially financed by the Nordic Innovation Centre through the Nordic MINT III call for proposals , the project participants will quantify and improve the thermophoresis effect, optimize the sensitivity of the soot sensor, test transistor devices and optimize the aerosol calibration system.
Project duration: October 2007 - December 2010