Finding faults in exhaust gas systems

After three years of development, Norwegian scientists can now measure the soot content of a vehicle's exhaust while it is actually on the road. The new sensor measures soot particles in the exhaust gas after it has passed the particle filter, rather than before. Project manager Andreas Larsson, a scientist at SINTEF, believes that continuous measurements of emissions will be in demand in the future. "Stricter emission limits for CO₂ and other pollutants will lead to demands for better monitoring of vehicle exhaust gases," he says.

Measures "scrubbed" exhaust

Measuring soot when a vehicle is actually on the road has been a major challenge, but by applying a principle known as thermophoresis, the scientists have managed to measure soot concentrations in clean, or "scrubbed" exhaust.

"Thermophoresis is a physical phenomenon that draws microscopic soot particles in the exhaust gas towards cold particles or regions in the gas. When soot particles collide with high-energy hot particles, they are forced towards colder, less energy-intensive regions. In other words, particles are transported from hot to cold parts of the system," says Larsson.

The sensor itself is installed in the middle of the gas flow, so that it is exposed to the high-temperature exhaust gas. If the sensor is kept cold enough, solid particles in the exhaust gas will be attracted to the cold surface of the sensor, where they can be measured.

Temperature-sensitive

A further challenge was therefore to reduce the sensor temperature by 50 to 70 degrees relative to the hot exhaust, which can reach temperatures as high as 100 to 300 degrees Celsius.

The scientists solved this problem by fitting a heat-conducting shield around the sensor. Between the heat shield and the sensor is a heat-conducting air layer that prevents heat from reaching the sensor.

Several applications

SINTEF patented the cooling principle in 2009. A good deal of research still needs to be done before it can be brought into commercial use, but so far, the results are promising. The primary field of application will be diagnosing technical faults in vehicle exhaust systems, such as cracks in the particle filter.

The scientists believe that in the longer term, the sensor will also be able to lower vehicle energy consumption, and thus help to reduce emissions of the greenhouse gas CO₂ and other pollutants such as NO_x and particles.

Volvo Technology, which is a central partner in the project, has applied for a patent on the method together with Volvo Car Corporation.