Robust sensor yields cleaner car exhaust

Emissions from cars have to be reduced further in order to meet today’s environmental demands. A new and robust exhaust sensor developed by researchers at Linköping University in Sweden has proven to meter the consistency of exhaust gases extremely well and is now on its way to the market.

It’s a tiny electronic component, no larger than the head of a pin. It has been tested both at LiU and in cars at its collaborating auto-makers, Volvo Cars in Gothenburg, Sweden, and Ford Motor Company in Detroit, Michigan. The results are reported in a dissertation by Helena Wingbrant, a doctoral student at the S-SENCE center of excellence.

The component is used to meter the amount of air in the fuel mixture, or the content of ammonia in diesel exhaust. The former is important to be able to reduce emissions from gasoline cars during cold starts, the latter to regulate the exhaust purification system that is under development for diesel cars. The sensor has proven to perform these tasks extremely well­-so well that the Linköping company AppliedSensor now wants to take it to market.

All cars already have a component that regulates the amount of air in the fuel mixture so the catalytic converter can function optimally. However, it can’t be used for the first few minutes after the engine has started, since a hot sensor might crack if it is hit by the tiny droplets of water that occur in the exhaust from a cold engine. During that time, the exhaust purification system doesn’t function satisfactorily.

The new component is made of more robust material, silicon carbide, and works from the instant the engine starts.

The ammonia sensor is for use in regulating the exhaust purification system in diesel cars, where it’s a matter of reducing the amount of nitrogen oxide. In the new system, ammonia is added to react with the nitrogen oxide, so only water and nitrogen gas are emitted. The job of the sensor is to regulate the ammonia content.

Laws targeting the emission of environmentally harmful substances from cars are becoming more and more stringent. In 2008 the amount permitted will be zero, which places demands on new technologies for cleaning exhaust.