Ammonia Measurement Investigation Using Quantum Cascade Laser and Two Different Fourier Transform Infrared Spectroscopy Methods

Most diesel engine exhausts have been fitted with SCR (Selective Catalyst Reduction) in order to reduce NO_X (Oxides of Nitrogen) by using NH₃ (ammonia). However, both NO_X and NH₃ have been classified as compounds hazardous for the environment and human health. If the reaction between NO_X and NH₃ is unbalanced during treatment, it can lead to either NO_X or NH₃ being released into the environment. Accurate measurement is thus necessary. QCL (Quantum Cascade Laser) and FTIR (Fourier Transform InfraRed) are two methods that have been used to measure NH₃ and NO_X directly in diesel engine exhausts. However, only a few studies have compared those two methods of NH₃ measurement, mainly from diesel engine exhausts. The aim of this paper is to compare the QCL and 2 different FTIR specifications for NH₃ measurement directly from diesel engine exhausts under well-controlled laboratory conditions. Researchers have found that as NH₃ is reactive, it is absorbed inside the exhaust pipe if the probe location is some distance away from the SCR. The results reported here contradict this and show that the probe location has only a small impact on NH₃ measurement inside the exhaust pipe. Furthermore, both instruments gave comparable results with the necessary regulatory precision. The outcome from this paper will have an impact on the discipline of NH₃ measurement and industry in the way NH₃ from diesel engines is measured.