Vehicle exhaust system could reduce soot emissions

Greenhouse-gas emissions from diesel-powered vehicles could fall thanks to a new exhaust-monitoring system co-developed by Volvo.

The sensor is placed inside the exhaust system to measure soot levels when the vehicle is on the road, something that has previously been a major challenge, according to its developers at Norwegian research institute Sintef.

Particles of black carbon, a major component of soot, make a substantial short-term contribution to global warming, and reducing soot emissions would immediately begin to protect the climate, according to a UN report released last week.

The importance of cutting soot emissions is likely to lead to demands for better monitoring of vehicle exhaust gases, said Andreas Larsson, Sintef’s project manager for the device.

The challenge in creating the device was in collecting enough soot particles after the exhaust had passed though a particle filter to monitor emissions.

To do this, the researchers used a principle known as thermophoresis. ‘Basically it means if you have some particles in a gas, they will be drawn to cold areas,’ Larsson told The Engineer.

‘What we wanted to do was put the sensor as far as possible into the centre of a very hot gas and make it as cold as possible to collect as many of the soot particles as we can.’

The team had to keep the sensor at least 50ºC colder than the gas, which can reach temperatures of 300ºC, but without making the device so cold as to create condensation and without actively cooling it.

To do this, the team fitted a heat-conducting shield around the sensor with a layer of air in between acting as insulation.

‘The heat energy will travel through the path of least resistance,’ said Larsson. ‘The air has a very high thermal resistance so the heat prefers to go through the heat shield.’

More research is needed before the sensor can be commercialised but initially it will be used for diagnosing technical faults in vehicle exhaust systems, such as cracks in the particle filter.

Eventually it might play a role in reducing energy consumption if it can provide live information and demonstrate changes to the exhaust as they happen.