Browse Topic: Selective catalytic reduction (SCR)
Selective Catalytic Reduction (SCR) is an optimized technology developed to encounter current BS6 Emission Regulations. AdBlue is the reductant used in the SCR Dosing system to eliminate NOx in the Exhaust gas. In order to ensure engine emissions compliance, insufficient or improper reductant in tank required to be detected. The right AdBlue concentration of 32.5% is highly necessary to attain the higher NOX conversion efficiency. Low concentration of the reductant will drastically reduce the NOx conversion in the system. Hence monitoring the AdBlue concentration in the tank itself is more important as per the OBD legislation. This implies on a physical quality sensor in the tank for detecting the reductant concentration. The functionalities of the quality sensor can also be instituted via a virtual software modelling called Improper Reductant Detection (IRD). IRD logic is highly robust and work competently to meet the BS6 stage 2 legislation’s NOx target. The reductant is suspected
Urea-NH3 dosed Selective Catalytic Reduction is a powerful reaction system to ensure NOx reduction in the exhaust gases by minimizing ammonia slip. When the dosed ammonia exceeds the actual request than the required, NH3 to NOx ratio is potentially high, the unused ammonia is limited to 10ppm corresponding to experimental result of every World Harmonic Transient Cycle. The dosage estimation depends on the NOx sensors which has this drawback of high cross-sensitivity to ammonia that can affect the measurement of NOx and compromise the SCR-ASC closed loop strategies. This paper aims to resolve the complexity in prediction of ammonia slip to resolve the cross-sensitivity of tailpipe NOx sensor in the SCR system by a closed loop estimation of NOx and ammonia slip to ensure high NOx conversion efficiency. The focus is to develop a simplified model-based solution for estimating ammonia slip, because of the limitations in the real drive conditions in SCR system. This model approach is
This study presents the development of newly proposed SCR mixer for diesel engine that improves vehicle NOx emission without rebound of the exhaust pressure loss. Unique SCR mixer structure which produces multiple vortices can realize lower NOx emission due to the highly uniform mixing of NH3 generated from the SCR spray and the exhaust gas, compared to the conventional mixer which produce a single vortex. Through its unique mixer structure constructed with some blades that generate multiple vortices. In order to study the mixer structure in a short period of time, 2 steps design process have been studied by separating parametric study in flow analysis and performance confirmation in the dual-phase flow analysis. Consequently, this newly proposed SCR mixer realize excellent mixing performance without increasing the exhaust pressure loss
This study shows the newest results of a near-series pre-turbo-catalyst (PTC) system reaching lowest emissions for electrified diesel passenger cars to address future emission legislation. The PTC system is developed using a state-of-the-art tool chain containing 1D & 3D simulation approaches and testing near-series exhaust gas aftertreatment systems under real-driving boundary conditions. The innovative concept of a selective catalytic reduction (SCR) PTC and a PTC bypass path solve the challenge of a thermal handshake between PTC and underfloor SCR System as well as the challenge of a particular filter regeneration. The development of adaptive PTC bypass path operation strategies based on exhaust gas and catalyst conditions enables lowest NOx and NH3. Using this concept, zero-impact NOx emissions, that don’t impact cities air quality, can be reached in a wide range of operating scenarios while sustaining full drivability and highest efficiency. Advanced catalyst technologies enable a
Diesel oxidation catalyst (DOC) is one of the critical catalyst components in modern diesel aftertreatment systems. It mainly converts unburned hydrocarbon (HC) and CO to CO2 and H2O before they are released to the environment. In addition, it also oxidizes a portion of NO to NO2, which improves the NOx conversion efficiency via fast SCR over the downstream selective catalytic reduction (SCR) catalyst. HC light-off tests, with or without the presence of NOx, has been typically used for DOC evaluation in laboratory. In this work, we aim to understand the influences of DOC light-off experimental conditions, such as initial temperature, initial holding time, HC species, with or without the presence of NOx, on the DOC HC light-off behavior. The results indicate that light-off test with lower initial temperature and longer initial holding time (at its initial temperature) leads to higher DOC light-off temperature. Depending on the types of HC used, the presence of NOx can also influence HC
Aftertreatment system meeting BS-VI emission regulations for diesel engines led to a decrease in NOx emissions to a low level. Selective catalyst reduction (SCR) is the most prominent and mature technology used to reduce NOx emissions. Initially, the UWS injection layout was designed without any mixer which resulted in low NH3 uniformity on SCR monolith with reduced UWS conversion efficiency, leading to concentrated wall spray loads. A dual-stage static mixer was designed and introduced to enhance the proper mixing of UWS droplets with exhaust gas upstream, to accelerate UWS breakup and evaporation of droplets. The mixer blades enhance the local turbulence, which resulted in a high mixing degree of droplets with the exhaust gas stream, thus reducing the crystallization risk at the mixer and the surrounding area. Mixers also extend the evaporation path, residence time, and thermal decomposition for droplets. Mixer shape was optimized with various design parameters with good structural
To reach close to zero tailpipe NOx emissions, a double-SCR (selective catalytic reduction) system is proposed. In that, the first SCR unit would be placed upstream of the diesel particulate filter (DPF) and the second SCR unit downstream of DPF. This study focused on the experiments of the first SCR unit. The experiments were conducted utilizing a new, 4.4-liter heavy duty diesel engine that was connected to a research facility for studying after-treatment systems in controlled environment. Three different SCR’s: a vanadium-based SCR (V-SCR), a copper-based SCR (Cu-SCR) and a vanadium-based SCR including an ammonia slip catalyst (V-SCR+ASC) were studied. Studies were done at different exhaust temperatures from 215°C to 350°C. Emissions of NO, NO2, NH3, N2O, CO, CO2 and hydrocarbons were measured by FTIR. Particulate emissions (PM, PN) were studied as a part of the experiments. The results showed that the three SCR units performed differently. The performance of the V-SCR catalyst was
Engines have improved a lot and reached a new state of the art in terms of combustion technology, but they alone still fall short in achieving emission limitations without any trade-off on performance. Selective Catalytic Reduction (SCR) is the key technology used to meet the increasingly strict Nitrogen Oxides (NOx) emission regulations. The injection of Urea Water Solution (UWS—32.5% urea solution) upstream the catalyst is currently the leading technique for reducing the emission of NOx from the exhaust (DeNOx). A uniform distribution of the spray droplets is very crucial to achieve a good conversion efficiency. Therefore, the size and velocity distribution of the droplets are of high importance in deciding the fate of the DeNOx process. This article describes an approach of modelling the UWS spray and its validation against experimental data collected under realistic exhaust-like conditions. Droplet size distributions and velocities were recorded using Phase Doppler Anemometry (PDA
Selective catalyst reduction (SCR) using cordierite honeycomb substrate is generally used as a DeNOx catalyst for diesel engines exhaust in both on-road and commercial off-highway vehicles to meet today’s worldwide emission regulations. Worldwide NOx emission regulations will become stricter, as represented by CARB2027 and EuroVII. Technologies which can achieve further lower NOx emissions are required. Recently, several technologies, like increased SCR catalyst loading amount on honeycomb substrates, and additional SCR catalyst volume in positions closer to the engine are being considered to achieve ultra-low NOx emissions. However, undesirable pressure drop increase and enlarging after treatment systems will be caused by adopting these technologies. Therefore, optimization of the material and honeycomb cell structure for SCR is inevitable to achieve ultra-low NOx emissions, while minimizing any system drawbacks. Since the SCR catalyst generally being used in the market today is
During the past decades, the Nitrogen Oxides (NOx) emission limitations have become stricter, promoting the development of after-treatment systems like Selective Catalytic Reduction (SCR) for emission reduction purposes. The Urea-Water Solution (UWS) spray characteristics can directly have an effect on the SCR efficiency. To understand the droplet breakup and mixing of the UWS with the surrounding air under different operating conditions, a computational campaign has been set up. The main objective of the present study is to recreate the spray injection process, as well as the chemical processes that the UWS spray undergoes, and to analyze the optimal injection angle to maximize the amount of ammonia generated during the injection process by means of Computational Fluid Dynamics (CFD). A Eulerian-Lagrangian framework has been employed to track the evolution of the injected droplets within a Reynolds-Averaged Navier-Stokes (RANS) turbulence formulation. Typical injection pressures have
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