23 February 2007
Delphi Corporation announced the world’s fist ammonia sensor for automotive selective catalytic reduction (SCR) systems. By directly measuring tailpipe ammonia, the sensor allows the injection of urea to be optimized and ammonia emissions reduced.
Control of urea injection is an increasing priority as SCR systems must provide increasing NOx reduction efficiency to meet future emissions regulations in both light and heavy duty diesel markets. A vehicle’s SCR system injects ammonia precursor, in the form of urea solution, into the exhaust stream ahead of the SCR catalyst. Over the catalyst, the ammonia reacts with NOx, converting it into nitrogen and water. Unreacted ammonia, known as “ammonia slip”, is expelled with the exhaust gasses.
Today’s SCR systems use an open loop control, where the urea dose is estimated by the engine control unit based on the engine speed and load using predictive algorithms, such as a look-up table. To control urea dose more precisely, future systems will need to use closed loop control, which will require a post-catalyst sensor to measure NOx, ammonia, or both gases. One of the issues with existing NOx sensors has been their cross-sensitivity to ammonia. Delphi did not comment whether its new ammonia sensor is cross-sensitive to NOx.
Delphi’s sensor has been developed based on the company’s expertise in oxygen sensors. A new ammonia sensitive material, developed at the Delphi Research Laboratories in Troy, MI, is deposited onto a thick film ceramic substrate similar to the one in oxygen sensors. The sensor is then mounted in a compact stainless steel package also based on Delphi’s oxygen sensor technology. The new sensor detects ammonia in the exhaust gas within a range of zero to 100 ppm. Series production of the sensor will commence in 2010.
The use of SCR is expected to increase dramatically both in light-duty and heavy-duty applications. The technology is already well established in the European heavy-duty truck market and will become increasingly important in the US market to deliver compliance with the EPA 2010 emission standards for heavy-duty diesel engines. SCR will also be used on passenger cars in the United States to meet Tier 2 Bin 5 standards for light-duty vehicles. The technology may be also used in Europe to help meet Euro 6 regulations to be mandated from 2014.