A Study on the Factors Affecting the Formation of Urea Crystals and Its Mitigation for SCR After-Treatment Systems

Jain, Abhilash; Barman, Jyotirmoy; Patchappalam, Kumar; Gedela, Srikanth

doi:10.4271/2017-26-0132

Cited by 7 publications

(5 citation statements)

References 12 publications

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“…Hence, a proper urea injection system is important. Jain, et al [20] performed the numerical analysis and observed that the injection angle had a key impact on urea decomposition. Chen, et al [21] performed experimental and numerical analysis to reduce the urea deposits formation.…”

Section: Review Of Recent Workmentioning

confidence: 99%

3-D Numerical Study of Effect of Urea Injector Location and Intake Cone Geometry on SCR Performance

Bhosale¹,

Patil²,

Dhepe³

et al. 2022

ijirss

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In response to current strict laws aiming to reduce motor vehicle emissions, more and more research projects are being carried out in order to enhance the flow of automotive catalysts. There have been substantial efforts to further refine the SCR technology (selective catalytic reduction) for diesel-powered vehicles. Furthermore, only a little distance from the catalytic input between the exhaust system is available for a mobile SCR system. This therefore leads to an insufficient urea residence period, and evaporation and thermolysis at the catalyst entry cannot therefore be completed. This can lead to substantial secondary ammonia and isocyanic acid emissions. Therefore, fast thermolysis, effective ammonia blend with exhaust gas and reduction of ammonia slip are crucial factors for the deployment of SCR technology on cars. The Computational Fluid Dynamics (CFD) approach is used for optimizing the exhaust gas flow inside the existing catalyst by changing intake cone designs which is intended to be used on Euro VI/Bharat Stage-VI emissions legislation compliant heavy-duty diesel engines in India. This study is divided in to two parts. The first part of the study deals with finding the optimized ammonia injector location, and in the second part, the proposed inlet cone design’s flow velocity uniformity index is estimated and compared with that of the existing SCR catalyst model.

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Section: Review Of Recent Workmentioning

confidence: 99%

3-D Numerical Study of Effect of Urea Injector Location and Intake Cone Geometry on SCR Performance

Bhosale¹,

Patil²,

Dhepe³

et al. 2022

ijirss

View full text Add to dashboard Cite

show abstract

“…The transient operating parameters like mass flow rate of exhaust gas, NO x content, temperature of exhaust gas, ambient temperature, UWS spray properties, and UWS dosage have their effect on deposit formation. Further, the design parameters such as the position of urea injector, mounting positions and wall interaction along with the spray or drop trajectory have a strong influence on deposit formation (Jain et al 2017). Some of the above studies have been done for urea decomposition in open-air conditions and for a fixed mass of urea (Schaber et al 2004).…”

Section: Factors Affecting Deposit Formation During Transient Running Conditionmentioning

confidence: 99%

Effects of thermal treatments on characteristics and morphological variations in the deposits of urea-SCR systems

Natesan²,

Nayak

2021

Environ Sci Pollut Res

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Selective catalytic reduction (SCR) systems are employed by automobile manufacturers for the abatement of environmental pollutants like oxides of nitrogen (NOx) emitted from exhaust gases of diesel engines. In SCR, the urea-water solution (UWS) is injected to exhaust gases in the form of a spray to generate the reducing agent NH3. Deposit formation at lower temperatures is a major concern with this technology. The deposits not only create backpressure but also leak NH3 to the environment as they deplete. It is very important to know the depletion characteristics of deposits formed at lower temperatures in order to assess the NH3 leakage to the environment when the engine exhaust gases attain higher temperatures. In the present work, deposits formed at a low-temperature range of 150–200°C for continuous run along with UWS injection were investigated. Additionally, they were aged at 300°C in the absence of UWS to check the variation in characteristics with the rise of temperature. By gravimetric analysis, it is inferred that the deposits formed at higher pre-age temperatures are less prone to depletion as the temperature increases. The elemental analysis using energy-dispersive X-ray spectroscopy (EDX) indicates slight variation in carbon, nitrogen and oxygen compositions for all the pre-age conditions. As an extended study, the byproducts at pre-age and post-age conditions were investigated through X-ray diffraction (XRD). The compounds like cyanuric acid (CYA) and biuret were not observed when pre-age samples were aged at 300°C. Instead, the compounds like ammelide, ammeline, triuret and melamine were observed. Scanning electron microscope (SEM) study revealed morphological changes in both pre-age and post-age samples. Further, the crystallinity variations were also observed for the changes in the heating cycles during deposit formation. The gravimetric analysis of deposits in pre-age and post-age conditions helps in predicting the amount of deposits for transient load cycles.

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“…Under actual engine operating conditions, due to the changing operating conditions, the formation characteristics of crystallization are different from those under steady-state conditions. Transient exhaust temperature, ambient temperature, and urea injection amount have different effects on the formation of crystallization [18]. Sadashiva studied the effect of temperature changes on the total amount of crystallization by increasing the temperature of crystals generated under stable low-temperature conditions (150 °C-250 °C).The results showed that at the same injection amount, intermittent and continuous injection at low temperatures (150 °C) had a small impact on the total amount of crystallization, but intermittent temperature rise could eliminate the crystals generated during the period of no injection, thereby reducing the total amount of crystallization [19].…”

Section: Introductionmentioning

confidence: 99%

Study on Urea Crystallization Risk Assessment and Influencing Factors in After-Treatment System of Diesel Engines

Sun,

Zhang,

Zhao

et al. 2024

Applied Sciences

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In order to meet the increasing pollutants discharge standard, the selective catalytic reduction (SCR) module in the diesel engine after-treatment system is an important means to reduce nitrogen oxide (NOx) emissions. SCR systems are prone to urea crystallization at lower temperatures, especially during the cold-start conditions of diesel engines. In this study, we use the diesel engine after-treatment system test bench to obtain the boundary parameter of the simulation modules, and the urea crystallization risk assessment model of the diesel SCR system is established. Comparing the computational fluid dynamics (CFD) results with the test bench results, it is shown that the predicted urea film distribution of the assessment model is in good agreement with the experimental results. In order to clarify the various factors that affect the urea crystallization risk, this paper conducts a simulation analysis on a nozzle and mixer structure and operating parameters. The CFD results indicate that the increase in urea spray time will increase the maximum urea film thickness on the SCR system mixer surface. Exhaust temperature is the most important influencing factor. When the diesel engine exhaust temperature increases from 190 °C to 300 °C, the maximum urea film thickness decreases by 32 and the urea film mass accumulation decreases by 5%. Exhaust flow has a small impact on urea crystallization risk. When the exhaust flow increases from 300 kg/h to 600 kg/h, the maximum urea film thickness decreases by 39% and the urea film mass accumulation decreases by about 1%. In addition, urea spray rate, nozzle numbers, spray angle, and spray cone angle are also factors that affect urea crystallization risk.

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A Study on the Factors Affecting the Formation of Urea Crystals and Its Mitigation for SCR After-Treatment Systems

Cited by 7 publications

References 12 publications

3-D Numerical Study of Effect of Urea Injector Location and Intake Cone Geometry on SCR Performance

3-D Numerical Study of Effect of Urea Injector Location and Intake Cone Geometry on SCR Performance

Effects of thermal treatments on characteristics and morphological variations in the deposits of urea-SCR systems

Study on Urea Crystallization Risk Assessment and Influencing Factors in After-Treatment System of Diesel Engines

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