Shigeru Nakatani

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.

NH 3 Measurements for Advanced SCR Applications

Since the introduction of Euro IV legislation [1, 2], Selective Catalytic Reduction (SCR) technology using liquid urea injection is (one of) the primary methods for NOx reduction in many applications. Ammonia (NH3) is the reagent and key element for the SCR system and its control calibration to meet all operational requirements. TNO and Horiba are highly motivated to facilitate a correct interpretation and use of emissions measurement data. Different hypotheses were defined to investigate the impact of temperatures and flow rates on urea decomposition. These parameters are known to strongly affect the urea decomposition process, and thus, the formation of NH3. During a test campaign, different SCR catalyst feed gas conditions (mass flow, temperature, species and dosing quantities) were applied. Three Horiba FTIR gas analyzers were installed to simultaneously sample either all upstream or all downstream of the SCR brick. Both steady-state and dynamic responses were evaluated. When undecomposed urea is present, the application of sampling system conditioning above the thermolysis temperature of 133°C can result in additional conversion of urea into NH3. The NH3 concentration reading then does not correctly represent the in-situ condition. It is concluded that a lower sampling system temperature will result in the more accurate and physically sound NH3 measurement. This is an important observation to enable fundamental understanding or development of catalyst and control models. For tailpipe NH3 measurements on full-size SCR systems and typical urea dosing conditions, e.g. type approval measurements, same accuracies are expected for 113oC and 191oC sampling system conditioning.

Measurement of automobile N2O from bag and continuous stream by quantum cascade laser spectroscopy

N2O emission from automobile has been regulated by the United States Environment Protection Agency due to its higher global warming potential compared to CO2. Responding to this, an instrument for fast sensing of ultra-low concentration of N2O from automobile has become an urgent need. In this study, an instrument based on the quantum cascade laser spectroscopy has been developed and applied for certification testing of ultra-low N2O in automobile exhaust. The pulsed quantum cascade laser can emit coherent lights in the mid-infrared region where N2O shows strong absorption and better control of wavelength. Therefore, a very low detection limit can be achieved and interference of co-existing gases can be avoided using a super fine resolution of the mid-infrared spectrum. The US Code of Federal Regulations Parts 1065/1066 allows measuring N2O from sample storage bags, from a continuous dilute stream or a raw exhaust stream. Typically, batch (bag) sampling has better accuracy and repeatability, but continuous sampling is more efficient in terms of test cell running time and provides test-mode emissions. In this study, the quantum cascade laser analyzer has been applied to investigate correlations between bag sampling and continuous dilute exhaust sampling using a fleet of vehicles with a wide range of N2O emission levels all meeting United States Environment Protection Agency emission standards. Very good correlation between these two sampling methods was observed for the majority of tests conducted and in best case the difference was less than ±1%. The direct injection gasoline vehicle emits higher N2O than conventional port injection gasoline vehicles. The quantum cascade laser analyzer has been successfully applied for United States Environment Protection Agency N2O certification test.