February 26, 2007
Delphi launches ammonia sensor for diesel engines
Luxembourg – Delphi Corporation says it has developed the world’s first automotive ammonia sensor, which will allow direct closed-loop control of the Selective Catalytic Reduction (SCR) systems used on an increasing number of diesel vehicles to reduce NOx.
By directly measuring tailpipe ammonia, the sensor allows for optimum injection of urea, an ammonia-rich compound required by the SCR system, along with a reduction in ammonia emissions. Control of urea injection is expected to become a rapidly-increasing priority as SCR levels increase to meet new emissions regulations in light- and heavy-duty diesel markets.
Atmospheric ammonia reacts with airborne compounds such as nitric acid to create dust-sized airborne particles, which can create a smog-like haze. SCR systems inject ammonia, in the form of liquid urea, into the exhaust stream ahead of the NOx reduction catalyst. The ammonia reacts with the gas and converts it to nitrogen and water.
SCR technology is already well-established in the European heavy-duty truck market, and will become increasingly important in the U.S. market, which must comply with new heavy-duty regulations to be mandated from 2010. SCR will also be used on U.S. passenger cars to help deliver compliance with Tier II Bin 5 regulations for light-duty vehicles.
Currently, SCR systems are an open loop, so the urea dose is estimated by the engine control unit. To accurately control the dose, systems must be closed-loop, which will require either a NOx or ammonia sensor, but Delphi says that the NOx sensor technology is cross-sensitive to NOx and ammonia and can confuse the two, leading to inappropriate dosing decisions.