Ammonia Uniformity Research Articles

Optimization of the Uniformity Index Performance in the Selective Catalytic Reduction System Using a Metamodel

The significance of the selective catalytic reduction system in vehicles increases in line with the high standards of emission control and enhanced selective catalytic reduction efficiency. This study aims to improve the performance of the selective catalytic reduction system through an optimization method using a metamodel. The objective function is defined as the ammonia uniformity index, and the design parameters are defined in relation to the pipe length and mixer related to the chemical reaction of the urea solution. The range of design parameters has been designated by a trial-and-error method in order to maintain the overall design drawings of the selective catalytic reduction system and prevent modeling errors. Three algorithms, namely, ensemble decision tree, Kriging, and radial basis function, are employed to develop the metamodel. The accuracy of the metamodel is verified based on three indicators: the normalized root mean square error, root mean square error, and maximum absolute error. The metamodel is generated using the Kriging model, which has the highest accuracy among the algorithms, and optimization is also performed. The predicted optimization results are confirmed by computational fluid dynamics numerical analysis with a 99.83% match. The ammonia uniformity index is improved by 1.38% compared to the base model, and it can be said that the NOx purification efficiency is improved by 30.95%. Consequently, optimizing the uniformity index performance through structural optimization is of utmost importance. Furthermore, this study reveals that the design variables related to the mixer play a crucial role in the performance. Therefore, using the metamodel to optimize the selectively catalytic reduction system’s structure should be considered significant. Finally, in the future, the analysis model can be validated using test equipment based on the findings of this study.

Numerical and Experimental Investigation of Ammonia Uniformity in a Compact Selective Catalytic Reduction System

Numerical and Experimental Investigation of Ammonia Uniformity in a Compact Selective Catalytic Reduction System

Study of Ammonia Concentration Characteristics and Optimization in Broiler Chamber during Winter Based on Computational Fluid Dynamics

Poultry breeding is one of the most significant components of agriculture and an essential link of material exchange between humans and nature. Moreover, poultry breeding technology has a considerable impact on the life quality of human beings, and could even influence the survival of human beings. As one of the most popular poultry, broiler has a good economic benefit due to its excellent taste and fast growing cycle. This paper aims to improve the efficiency of raising broilers by understanding the impact of ammonia concentration distribution within a smart broiler breeding chamber, and the rationality of the system’s design. More specifically, we used computational fluid dynamics (CFD) technology to simulate the process of ammonia production and identify the characteristics of ammonia concentration. Based on the simulation results, the structure of the broiler chamber was reformed, and the ammonia uniformity was significantly improved after the structural modification of the broiler chamber and the ammonia concentration in the chamber had remained extremely low. In general, this study provides a reference for structural optimization of the design of broiler chambers and the environmental regulation of ammonia.

Optimisation design of short pitch spiral hybrid SCR structure for improving the exhaust performance

As exhaust emission standards become increasingly stringent, the requirements for diesel exhaust post-treatment systems become increasingly demanding. This research focuses on the optimisation of a new hybrid structure to improve the performance of exhaust post-treatment systems. First, a short pitch spiral mixing chamber with sufficient mixing space and low temperature loss was designed to improve the evaporation of liquid droplets. Additionally, a conical plate mixer was used to conduct secondary mixing of the gas to improve the flow characteristics further. The ammonia uniformity and crystallisation risk of the new hybrid structure were simulated using Computational Fluid Dynamics, and the optimal hybrid structure was verified by tests. The results showed that ammonia leakage, low temperature crystallisation and NOX conversion efficiency could effectively be improved by optimally designing the new hybrid structure. This research is of great significance for reducing exhaust pollution and optimising diesel exhaust post-treatment systems.

A study on the high-efficiency mixer of the SCR system

A new mixer for a diesel engine after-treatment system is developed to meet the requirements of China VI emission regulation. As for the structure of the mixer, it is surrounded by spiral blades, and the center is staggered with small blades, which is conducive to the crushing of urea droplets and can make the droplets fully mixed with air, improve the conversion efficiency of nitrogen oxides (NOx) and reduce ammonia leakage. The numerical analysis, engine bench test, and vehicle road test were carried out on the after-treatment system equipped with the new mixer. The numerical calculation results show that the velocity uniformity index of the selective catalytic reduction (SCR) carrier can reach 0.98, as well as the ammonia uniformity can reach 0.95, meanwhile, the low wall film height shows excellent anti-crystallization properties. engine bench test results are consistent with numerical results. The crystallization status of the mixer after the vehicle durability test is acceptable and well performed.

Optimization of the Urea Injection Angle and Direction: Maximizing the Uniformity Index of a Selective Catalytic Reduction System

The uniformity of ammonia is very crucial for reducing the NOX emissions in a selective catalytic reduction system since the uniformity highly affects the chemical reaction between the ammonia and NOX emission. However, increasing ammonia uniformity in a short time period while injecting a urea solution is not a trivial task. Therefore, in this study, the uniformity of various urea injector designs is compared and an optimal design for the urea injector angle and direction is selected. The uniformity index (UI) was calculated using numerical analysis and compared with experimental result to achieve high reliability. The boundary condition of the analysis is extracted from the dominant operating region of the non-road transient cycle (NRTC) to guarantee a realistic analysis result. The design candidates were generated from the combination of three urea injection angles and eight urea injection directions and thoroughly compared to provide an insightful analysis. The conclusion is that injecting urea in the opposite direction to the main stream of exhaust gas increases the kinetic energy and thus the uniformity is highly increased. For example, urea injection in the opposite direction and angle to the mainstream flow could increase the UI to 0.966, which is a 16.7% improvement compared to the same direction and angle injection.

Investigation of Urea Uniformity with Different Types of Urea Injectors in an SCR System

Heavy-duty diesel engines in highway use account for more than 40% of total particulate and nitrogen oxide (NOx) emissions around the world. Selective catalytic reduction (SCR) is a method with effective results to reduce this problem. This research deals with problems in the urea evaporation process and ammonia gas distribution in an SCR system. The studied system used two types of urea injectors to elucidate the quality of ammonia uniformity in the SCR system, and a 12,000-cc heavy-duty diesel engine was used for experimentation to reduce NOx in the system. The uniformity of the generated quantities of ammonia was sampled at the catalyst inlet using a gas sensor. The ammonia samples from the two types of urea injectors were compared in experimental and simulation results, where the simulation conditions were based on experimental parameters and were performed using the commercial CFD (computational fluid dynamics) code of STAR-CCM+. This study produces temperatures of 371 to 374 °C to assist the vaporization phenomena of two injectors, the gas pattern informs the distributions of ammonia in the system, and the high ammonia quantity from the I-type urea injector and high quality of ammonia uniformity from the L-type urea injector can produce different results for NOx reduction efficiency quality after the catalyst process. The investigations showed the performance of two types of injectors and catalysts in the SCR system in a heavy-duty diesel engine.

A study effects of injection pressure and wall temperature on the mixing process of NOx and NH3 in Selective Catalytic Reduction system

Diesel engines are commonly used for public transportation on-road and off-road applications. Growth production of the diesel engine is very significant from year to year. Nitride Oxide (NOx) from diesel engine was one of the major sources of air pollution. Selective Catalytic Reduction (SCR) has been successfully used to reduce NOx from a diesel engine with a chemical reaction from ammonia (NH3). The mixing reaction between NOx and NH3 reaction can produce steam (H2O) and Nitrogen (N2). However, ammonia uniformity pattern usually not homogenization and the ammonia was difficult to mix with NOx. The constant air flows incomplete to assist the spray injector to spread NH3 to all corners of SCR. The impact study of turbulent phenomena and standard k-epsilon Low-Reynolds Number model to the mixing process in the SCR system using STARCCM+. The simulation studies are conducted under different pressure (4 to 6 bars), the injection rate (0.04 g/s) and temperature (338 K – 553 K) and the high pressure and high velocity magnitude creating turbulent swirl flow. The ammonia decomposition process and mixing process with NOx were investigated using a box with optical access. The simulation and numerical study results validated using back pressure value and the distribution of NOx concentration value from the catalyst outlet. The wall temperature will increase the urea evaporation to generate ammonia and gas pressure will increase the mixing process and chemical process in the SCR system. These reactions enable to optimize the SCR system technology which eventually able to reduce the NOx quantity from a diesel engine.

A Fast Modeling Approach for the Numerical Prediction of Urea Deposit Formation

<div class="section abstract"><div class="htmlview paragraph">The permanently tightening emission regulations for NOx pollutants force further development of automotive exhaust aftertreatment systems with selective catalytic reduction (SCR). Of particular interest is the long-term reliability of SCR systems with regard to unfavorable operating conditions, such as high injection rates of urea water solution (UWS) or a low exhaust gas temperature. Both of them may lead to formation of solid deposits which increase backpressure and impair ammonia uniformity.</div><div class="htmlview paragraph">A fast modeling approach for numerical prediction of deposit formation in urea SCR systems is desired for optimization of system design. This paper presents a modified methodology for the modeling of deposit formation risk. A new determination of the initial footprint of the spray, where the deposit formation is inhibited, is proposed. The threshold values for the evaluation of the film transport were validated based on experimental results. To achieve a more realistic simulation in terms of wall wetting and cooling, the impingement heat transfer as well as the impingement model were modified based on optical investigations.</div><div class="htmlview paragraph">In order to accomplish the modeling of deposit formation with typical time ranges of several minutes, a recently developed injection source approach was applied. The substitution of the Lagrange-particles with source terms of mass, momentum and energy allowed to reduce simulation time by a factor of 30. The presented modeling approach was validated against both, the experimental data from an optical box and an exhaust aftertreatment system. The comparison of measured and simulated results shows the capability of the presented modeling approach to predict the position and the severity of solid deposits.</div></div>

Deposit Formation from Urea Injection: a Comprehensive Modeling Approach

Long-term reliability is one of the major requirements for automotive exhaust aftertreatment systems with selective catalytic reduction (SCR) using urea water solution (UWS) as NH3 carrier fluid. A high injection rate of UWS or unfavorable operating conditions may lead to formation of solid deposits, which decrease system efficiency by increasing backpressure and impairing ammonia uniformity. A reliable numerical prediction of deposit formation in urea SCR systems is desired for optimization of system design. However, comprehensive modeling of physical and chemical processes in the tailpipe as well as different time scale phenomena represents a challenging task. This study presents a comprehensive approach for modeling UWS injection, droplet impingement, liquid film and deposit formation based on CFD-simulation. An existing kinetic model for urea decomposition is integrated into the CFD code to predict solid by-product formation from wall films. Physical simulation time is extensively increased by substituting the Lagrange-particles with source terms of mass, momentum and energy reducing simulation time by a factor of 20. The comparison of measured and simulated results shows the capability of the presented modeling approach to predict position and chemical composition of solid deposits.

Application Study on a New Hybrid Canning Structure of After-Treatment System for Diesel Engine

Based on the airflow rotation concept, a new packaging structure was designed to meet the performance requirements of China-VI stage emission regulations. The new structure is a hybrid structure of spiral space with small blades and conical plates. The Computational Fluid Dynamics (CFD) simulation was used to analyze the velocity uniformity and ammonia uniformity of the flow field, and the results showed that velocity uniformity and ammonia uniformity were higher than 0.95, and the possibility of crystallization risk was very low. The actual performance of the new structural prototype was verified by means of engine bench testing. The test results were excellent and the conversion efficiency reached 0.96. The new selective catalytic reduction (SCR) urea mixed structure design greatly improved the conversion efficiency of the after-treatment system and has excellent anti-crystallization performance.

Effects of Urea Injection Timing on Predicting NoX Conversion In SCR Systems

The most undesired diesel engine pollutants are nitride oxide (NOX), particulate matter (PM), carbon monoxide (CO), and unburned hydrocarbon (HC). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully employed to remove NOX from diesel emissions via chemical reactions to yield steam (H2O) and nitrogen (N2). However, the ammonia homogenization process is usually incomplete and difficult to mix with NOX. This reaction affected from the urea injection process in the system when the condition is not suitable for urea decomposition process. Therefore, a study on the effects of urea injection timing to predict the NOX reduction efficiency was needed in order to identification the suitable condition based on temperature, flow mass, pressure, etc. In this study, the experiments and simulations were conducted to obtain constant and stable conditions in the SCR system, as constant conditions can optimize the uniformity of ammonia distribution in the system. The engine conditions in the experiment were computed from turning an engine on to determine the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. The temperatures used for processing ammonia uniformity in diesel SCR systems were investigated with operation at ambient temperature (298 K) and inlet gas temperature (686 K). Numerical results were validated using the experimental results of ammonia concentration distribution.

Ammonia Uniformity to Predict NOx Reduction Efficiency in an SCR System

The automotive industry has been restricted by several regulations to reduce nitrogen oxide emissions from diesel engines. To adhere to the emission regulation, advanced engine technology aims to control oxygen access, compression, and ignition engine, while achieving both reduced fuel consumption and lowering unburnt HC, CO2, and CO levels. However, it is difficult to meet the NOx limits of the European standard (EURO VI) and American standard (US TIER 2 BIN 5). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully employed to remove NOx from diesel engines. However, uniform ammonia distribution is usually difficult to achieve. Therefore, a study on ammonia uniformity to predict NOx reduction efficiency in SCR systems is needed. The engine utilized in the experiment was turned on for a few minutes to obtain the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. This study was performed at engine operating conditions of 1500 rpm, 2000 rpm, and 3000 rpm; simulation was performed with a fixed pressure and velocity, as in the experiment, thus creating a similar turbulent swirl flow in the SCR system. Numerical results were validated using experimental results of ammonia concentration distribution.

Numerical Investigation of SCR Mixer Design Optimization for Improved Performance

The continuous increase in the number of stringent exhaust emission legislations of marine Diesel engines had led to a decrease in NOx emissions at the required level. Selective catalyst reduction (SCR) is the most prominent and mature technology used to reduce NOx emissions. However, to obtain maximum NOx removal with minimum ammonia slip remains a challenge. Therefore, new mixers are designed in order to obtain the maximum SCR efficiency. This paper reports performance parameters such as uniformity of velocity, ammonia uniformity distribution, and temperature distribution. Also, a numerical model is developed to investigate the interaction of urea droplet with exhaust gas and its effects by using line (LM) and swirl (SM) type mixers alone and in combination (LSM). The urea droplet residence time and its interaction in straight pipe are also investigated. Model calculations proved the improvement in velocity uniformity, distribution of ammonia uniformity, and temperature distribution for LSM. Prominent enhancement in the evaporation rate was also achieved by using LSM, which may be due to the breaking of urea droplets into droplets of smaller diameter. Therefore, the SCR system accomplished higher urea conversion efficiency by using LSM. Lastly, the ISO 8178 standard engine test cycle E3 was used to verify the simulation results. It has been observed that the average weighted value of NOx emission obtained at SCR outlet using LSM was 2.44 g/kWh, which strongly meets International Maritime Organization (IMO) Tier III NOx (3.4 g/kWh) emission regulations.

A study of urea injection timing to predict the NOx conversion in SCR systems

The automotive industry has been restricted by several regulations to reduce pollutant from diesel engines. To fulfill the emission regulation, advanced engine technology purposes to control pollutant reduction and lowering the unburnt HC, CO2 and CO level. However, it is difficult to meet the NOx limits of the world standard like a European standard (EURO VI) and American standard (US TIER 2 BIN 5). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully to remove NOx from diesel engines. However, uniform ammonia distribution is usually difficult to achieve. Therefore, a study on the effects of urea injection timing to predict NOx reduction efficiency is needed. In this study, the simulations and experimental work to obtain constant and stable conditions in the SCR system were conducted. Because the constant condition can optimize the ammonia uniformity. The engine in experiment was compute from engine turned on to find the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. The numerical results were validated using experimental results of ammonia concentration distribution.

Study on Ammonia Uniformity and DeNOx Analysis in the Urea-SCR System for Construction Machinery

Study on Ammonia Uniformity and DeNOx Analysis in the Urea-SCR System for Construction Machinery

Simulation and Experimental Study of SCR Injection System

Abstract According to actual engineering test, we design a linear controlled spray ammonia grille, and apply it to the SCR injection system of ship tail gas treatment. In this paper, the geometric model of ammonia injection grid was built in the flue of diesel engine, and the effects of spray atomization, ammonia uniformity and urea droplet distribution on spray atomization were simulated. Then the test bench was set up to observe the injection status of the ammonia injection grille. The NOx content of the outlet was measured by the original data of the flue gas, and the experimental data were processed. We calculate the denitrification rate by taking the average value to verify the correctness of the spray ammonia grid scheme.

Multiphase injector modelling for automotive SCR systems: A full factorial design of experiment and optimization

Advances in emission control technologies have seen the introduction of Selective Catalyst Reduction (SCR) systems as a method for NOx decontamination in light and heavy duty vehicles. SCR systems make use of a urea–water solution (UWS) injected directly into the exhaust gas stream for the reduction of NOx contaminants to Nitrogen (N2) over a monolith catalyst [2]. The effectiveness of an SCR system depends on many factors including the type of catalysts, the injection and mixing pattern of the UWS, temperature and more [1].Spray analysis involves multi-phase flow phenomena and requires the numerical solution of the conservation and transport equations for the gas and the liquid phase simultaneously. Spray/wall interaction mechanisms such as droplet splash, spread, rebound or stick are complex to model and directly affected by the injection parameters [4]. The accurate modelling of the UWS injector can help in the prediction of phenomena such as wall film formation, droplet evaporation and urea crystallization [7].This study presents a series of multi-phase numerical analyses, computed with the commercial software AVL Fire 2014 v, to measure the impact of injection velocity, spray angle and droplet size, in the overall performance of an SCR system. The analysis consisted of a completely mixed turbulent flow, solved using a two equations turbulence model (k−zeta−f). The interaction of the injected particles was solved with an Euler/Lagrange approach, the liquid phase calculation was based on the statistical Discrete Droplet Method interacting with the numerical solution of the conservation equations of the flow pattern.It was found that the injection parameters had an impact on the final results of the ammonia uniformity index (NH3UI) and wall film formation on the SCR system. The method applied in this work successfully predicted the performance of an SCR system. Moreover, a series of response surfaces were created based on a linear regression model which allowed for further design optimization outside of the initial experimental space.

박용 탈질 시스템의 혼합기 적용에 따른 요소수용액 분무 및 혼합특성 수치적 연구

Among various De-NOx technologies, Urea-based Selective Catalytic Reduction (SCR) systems are known to be the most effective in marine diesel applications. The spraying and mixing behavior of the urea-water solution has a decisive effect on the system's net efficiency. Therefore, in this study, the spray behavior and ammonia uniformity with and without a static mixer were analyzed by CFD in order to optimize the SCR system. The results showed that the static mixer significantly affected the uniformity of velocity and ammonia concentration. Static mixers may be especially suited for marine SCR systems with space constraints.