Delphi Corp., Troy, Mich., says it has developed the first automotive ammonia sensor. It should improve closed-loop control of selective catalytic-reduction (SCR) systems used in an increasing number of diesel vehicles to reduce NOx. The sensor measures tailpipe ammonia so the converter knows how much urea to inject.
Controlling urea injection should become increasingly important, as SCRs must meet new emissions regulations in both light and heavy-duty diesel markets. SCRs inject ammonia, in the form of liquid urea, into the exhaust ahead of the NOx reduction catalyst. Ammonia converts the gas into nitrogen and water. Unreacted ammonia, known as "slip," escapes with the exhaust gases.
"With the growth of vehicles using SCRs, ammonia emissions are a potential problem that we want to address before it becomes an environmental issue," says Guy Hachey, president of Delphi Powertrain.
In the atmosphere, ammonia reacts with compounds such as nitric acid to create dust-sized particles, which can create smoglike haze. Ammonia emissions from vehicles, however, are only a small portion of total ammonia emissions. The biggest sources are livestock and factories.
SCRs will also be used on passenger cars in the U.S. to help comply with Tier II Bin 5 regulations for light-duty vehicles. Delphi is working with vehicle manufacturers in Asia, North America, and Europe on the new ammonia sensor, which is expected to reach production in 2010.