Development of a Real-time NH3 Gas Analyzer Utilizing Chemi-luminescence Detection for Vehicle Emission Measurement

Recently, after-treatment techniques for diesel engine emission have made remarkable progress with the development of suitable De-NOx catalysts. The urea-injection SCR system is one of the candidates for a high efficiency De-NOx method for diesel engine emissions. This system reduces NOx through a reaction with ammonia (NH₃) that is generated from injected urea. In this system, it is very important to control the amount and timing of the urea injection so as to minimize the NH₃ gas slip. Therefore, NH₃ gas measurement is becoming important during the development of NOx after-treatment systems even though NH₃ is not a target component of the current emission regulations. In this paper, a new NH₃ gas analyzer utilizing a chemi-luminescence detection (CLD) method has been developed. The new NH₃ analyzer consists of dual detectors (DCLDs) and a furnace for a NH₃ oxidization catalyst. Real-time concentration of NH₃ can be calculated from the difference of NOx readings of two detectors. Basic performances such as response time and interference effect have been discussed here. Additionally, NH₃ measurement in exhaust gas from a diesel engine vehicle with a urea-SCR system, as well as a lean burn gasoline engine vehicle with a three-way catalyst will be presented. Comparisons with conventional methods for NH₃ measurement, such as fourier transform infra-red (FTIR) gas analyzer and soft ionization mass spectrometer (SIMS), are also described.