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    <title>Transport Research International Documentation (TRID)</title>
    <link>https://trid.trb.org/</link>
    <atom:link href="https://trid.trb.org/Record/RSS?s=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" rel="self" type="application/rss+xml" />
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    <language>en-us</language>
    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
    <image>
      <title>Transport Research International Documentation (TRID)</title>
      <url>https://trid.trb.org/Images/PageHeader-wTitle.jpg</url>
      <link>https://trid.trb.org/</link>
    </image>
    <item>
      <title>Effect of urea on the thixotropic behavior of mixtures containing calcium aluminate cement and Portland cement</title>
      <link>https://trid.trb.org/View/2643528</link>
      <description><![CDATA[This study investigates influence of urea utilization on the rheological and thixotropic properties of Portland and calcium aluminate cementitious system. In each cementitious system, a total of eight different paste mixtures were prepared with 2.5%, 5% and 10% replacement of cement weight with urea. Thixotropic behavior was evaluated using the step change and the loop methods. The use of urea in cementitious systems, independent of the type of cement, was found to result in a decrease in dynamic shear stress and viscosity values, in other words, an increase in flow performance. The addition of urea was observed to increase the formation of thixotropic structure, and this effect is more pronounced in Portland cement mixtures. The Herschel–Bulkley model is more consistent with the rheological data obtained in Portland cement mixtures. In Portland cement mixtures, the values of structural build-up are observed to be higher compared to the values of structural breakdown, while in calcium aluminate cement mixtures, the opposite has been observed. The viscosity after rest value decreased by 95% with the addition of 10% urea to the mixture containing Portland cement, and this value decreased by 76% with the addition of 10% urea to the mixture containing calcium alumina.]]></description>
      <pubDate>Sat, 07 Feb 2026 16:21:02 GMT</pubDate>
      <guid>https://trid.trb.org/View/2643528</guid>
    </item>
    <item>
      <title>Effect of using substitution urea on fresh and hardened state properties of cementitious systems</title>
      <link>https://trid.trb.org/View/2643610</link>
      <description><![CDATA[It is well known that to ensure the durability of concrete throughout its service life, the search for alternative materials continues. The durability of concrete is enhanced by industrial urea. This study investigated the effect of urea on various fresh and hardened cementitious systems, focusing on durability performance. The durability of concrete is enhanced by industrial urea. This study investigated the effect of urea on various fresh and hardened cementitious systems, focusing on durability performance. Two series of paste and mortar mixtures were prepared for the research, and the replacement of water and cement was determined as 10%, 20% and 30% of the binder volume. The study investigated several properties of the produced cement paste and mortar mixes, including drying shrinkage, time-dependent flow, compressive strength, microstructural analysis, freeze-thaw resistance, carbonation depth, ultrasonic pulse velocity and water absorption. The results of the study showed that urea substitution increased the freeze-thaw resistance by up to 20% and reduced the drying shrinkage behavior by up to 49%. The use of urea reduced the carbonation depth of mortar mixtures by 35%. It was also observed that the use of urea improved flowability.]]></description>
      <pubDate>Thu, 15 Jan 2026 14:31:04 GMT</pubDate>
      <guid>https://trid.trb.org/View/2643610</guid>
    </item>
    <item>
      <title>Multi-objective optimization of an electrical injector in Urea-SCR system</title>
      <link>https://trid.trb.org/View/2617140</link>
      <description><![CDATA[Electrical injector is mainly used in non-air-assisted urea dosing systems to atomize and inject urea water solution. It consists of solenoid switch valve and injector. A good performance of the electrical injector can improve dosing precision of urea dosing system. To investigate dynamic characteristics of the electrical injector, an equivalent magnetic circuit model of the solenoid valve was established and magnetic field of the solenoid valve was also simulated using a three-dimensional finite element model. The results show that the calculation error of the two models is 6%, demonstrating that the equivalent magnetic circuit model can effectively predict the magnetic characteristics of the solenoid. Taking opening time, closing time, and coil area of the electrical injector as objective functions, a multi-objective optimization algorithm was used to optimize the design parameters of the electrical injector. Opening and closing processes of the optimized electrical injector under different pressures and driving voltages were measured through laser triangulation sensor. The experimental results showed that calculation results of the proposed theoretical model were close to the measurement results. The opening time of the optimized injector has been reduced by 11%, the response of the injector has significantly improved.]]></description>
      <pubDate>Fri, 21 Nov 2025 08:44:19 GMT</pubDate>
      <guid>https://trid.trb.org/View/2617140</guid>
    </item>
    <item>
      <title>Experimental and 2-D simulation studies on urea pulse strategies to investigate chemical reactions in Cu-Chabazite SCR catalysts</title>
      <link>https://trid.trb.org/View/2586828</link>
      <description><![CDATA[To meet the stringent emission regulation of future diesel engines, it is essential to develop innovative aftertreatment systems, especially selective catalyst reduction (SCR) systems. NOₓ emissions are purified in the SCR systems using urea water injection to the catalyst surface. The SCR system can convert NOₓ efficiently under a wide temperature range. However, its conversion performance deteriorates at exhaust gas temperatures T ≤ 200°C. Therefore, urea pulse injection strategy improves SCR conversion rate under low exhaust temperatures. This work aims to develop a more precise numerical model that follows the engine test results. Therefore, firstly the radial temperature distributions are recorded to decide the model boundary conditions. The measured engine test data are then used for validation on the simulation model under exhaust gas temperature of T = 200°C (constant and pulse supply). Additionally, the reaction rate of T = 300°C was compared with validation of chemical reaction rate. The model was able to predict the NOₓ conversion processes reasonably, which leads to a further understanding of the production rate of major gas and solid species in the Cu-chabazite SCR system. The effect of reaction rate parameters on NO and NO₂ emissions are also reported.]]></description>
      <pubDate>Fri, 26 Sep 2025 13:39:56 GMT</pubDate>
      <guid>https://trid.trb.org/View/2586828</guid>
    </item>
    <item>
      <title>Droplet–Wall Interaction Dynamics during Urea Dosing in an
                    Aftertreatment System</title>
      <link>https://trid.trb.org/View/2578238</link>
      <description><![CDATA[
                
                Urea–water solution (UWS) is sprayed during selective catalytic reduction (SCR)
                    in the aftertreatment system of a diesel engine. UWS decomposes to ammonia and
                    reacts with harmful nitrogen oxides present in exhaust gas to convert it to
                    harmless nitrogen and water vapor. The interaction of UWS spray droplets with
                    the hot wall of the aftertreatment system plays a crucial role in the
                    performance and life of the aftertreatment system used in modern diesel engines
                    for emission control. We report here a comprehensive experimental investigation
                    on the normal impact of UWS droplets on the heated wall of stainless steel
                    (SS410), mimicking the droplet–wall interaction in an SCR aftertreatment system.
                    We have built a regime map underlying the possible outcomes under operating
                    conditions encountered in an SCR system. The transition zones are identified,
                    and the complex transition dynamics from one regime to another are discussed.
                    Finally, we investigate and discuss the universality of the non-dimensional
                    parameters used to characterize drop impingement on a heated wall. Present study
                    will help to develop strategies to avoid the urea deposits on the walls of an
                    SCR system.
            ]]></description>
      <pubDate>Wed, 23 Jul 2025 09:12:57 GMT</pubDate>
      <guid>https://trid.trb.org/View/2578238</guid>
    </item>
    <item>
      <title>Analysis of N₂O Emissions and Design Optimization for Urea-SCR System</title>
      <link>https://trid.trb.org/View/2556917</link>
      <description><![CDATA[It is known that Nitrous oxide (N₂O) is produced as a by-product during the process of purifying NOₓ from diesel exhaust gas using urea-SCR. Because the global warming potential of N₂O is 273 times higher than that of CO₂, reducing N₂O emission is required. From the viewpoint of system design, N₂O emission is affected multiple factors, such as catalyst performance, catalyst volume and urea supply control. In this study, to reduce by-product of N₂O in urea-SCR system, the authors carried out the optimization of five design parameters by using simulation tool of diesel after-treatment. From the simulation results, response surface models (RSM) were created with the design parameters as explanatory variables and NOₓ, N₂O, and NH₃ emissions as objective variables. Analysis of designs to reduce N₂O emissions without increasing NOₓ and NH₃ emissions shows that system optimization is effective in reducing N₂O from ASC but has little effect on reducing N₂O from SCR. This indicates that further improvements in catalyst performance are necessary in addition to system optimization to reduce N₂O by-production in urea-SCR system.]]></description>
      <pubDate>Wed, 25 Jun 2025 16:34:26 GMT</pubDate>
      <guid>https://trid.trb.org/View/2556917</guid>
    </item>
    <item>
      <title>Efficient Modeling of SCR Urea Deposits Formation Using ANSYS Fluent</title>
      <link>https://trid.trb.org/View/2539467</link>
      <description><![CDATA[This paper presents recent developments of the Euler/Lagrange wall film model which allow the efficient simulation of complete Selective Catalytic Reduction (SCR) systems, used for exhaust gas aftertreatment in diesel and newly designed H₂ engines. Since release 2024R2, ANSYS Fluent is equipped with a chemistry model from recent literature to predict homogeneous chemical reactions in the film and heterogeneous reactions between gas and film occurring in SCR systems operating with aqueous urea solutions. The implementation of the chemistry model is first validated against results from Thermo–Gravimetric Analysis (TGA) measurements. The SCR–specific chemistry, combined with the Lagrangian Wall Film (LWF) model employing an improved wall–film convective heat transfer model, is then compared favorably with experimental SCR test rig measurements of urea deposits for fifty injection cycles, followed by a relaxation period. The full simulation completes significantly faster due to a new numerical algorithm for the LWF which reduces the number of wall film particles by consolidating groups of particles into a single particle that produces the same overall effect.]]></description>
      <pubDate>Thu, 05 Jun 2025 11:59:53 GMT</pubDate>
      <guid>https://trid.trb.org/View/2539467</guid>
    </item>
    <item>
      <title>Breakup dynamics in a pressure-swirl injector for urea-water solution applications: A computational study</title>
      <link>https://trid.trb.org/View/2521717</link>
      <description><![CDATA[The co-optimization of in-cylinder combustion and after-treatment technology has become a major aspect in engine design and development, with the goal of meeting the increasingly restrictive emission regulations in the transportation industry. Selective Catalytic Reduction is a robust technology to control the emission of NOₓ, and the injection of urea in water solution is the exhaust tailpipe is a key aspect of its operation. The proposed work uses high-fidelity Computational Fluid Dynamics to characterize the atomization dynamics of the liquid jet in relevant cross-flow conditions. The study focuses on a commercial low-pressure (9 bar) pressure-swirl injector which is characterized in its internal geometry through high-resolution X-ray micro-computational tomography. The internal two-phase flow has been modeled according to the volume-of-fluid approach in a large eddy simulation framework and validated against near-nozzle X-ray radiography measurement. Moreover, characterizing the breakup dynamics for the swirling hollow cone formation, and assessing the influence of the cross-flow in the breakup dynamics was completed. The results have been reported proposing Re-Oh maps and probability density functions of the spray kinematics. Higher cross-flow momentum generates an increase in the jet intact length and a reduction of the liquid droplet diameters. The axial momentum of the jet is affected by the cross-flow already in the near-nozzle region, determining a relevant deviation of the spray velocities. This work aims to inform the initialization of Eulerian-Lagrangian spray models through the assignment of droplet kinematics and static one-way coupling between volume-of-fluid results and Lagrangian spray parcels, to be used for system-size domain simulations.]]></description>
      <pubDate>Wed, 28 May 2025 12:01:52 GMT</pubDate>
      <guid>https://trid.trb.org/View/2521717</guid>
    </item>
    <item>
      <title>Consideration on Understanding the NOₓ Purification Performance of Urea SCR Catalyst installed in Heavy-duty Vehicles during the Use Process</title>
      <link>https://trid.trb.org/View/2505967</link>
      <description><![CDATA[Data on the NOₓ purification performance of copper-based zeolite SCR catalysts installed in vehicles that comply with the 2016 exhaust gas regulations was collected continuously by conducting chassis dynamometer tests and actual road driving tests as the accumulated mileage increased. Using these, the NOₓ purification rate, space velocity, etc. were used as analytical indices to consider the NOₓ purification performance of the urea SCR catalyst during the use process. As a result, when the NOₓ purification performance of the urea SCR catalyst decreases during use, it was found that the NOₓ purification rate decreased significantly as the space velocity increases.]]></description>
      <pubDate>Tue, 25 Mar 2025 16:57:55 GMT</pubDate>
      <guid>https://trid.trb.org/View/2505967</guid>
    </item>
    <item>
      <title>Influence of urea solution condition on NOx reduction in marine diesel engines</title>
      <link>https://trid.trb.org/View/2437650</link>
      <description><![CDATA[This study aims to provide a clear relationship of how the storage status and duration of the urea affect the efficiency and performance of the selective catalytic reduction (SCR) system. Focusing on the marine environment, the research compares nitrogen oxides (NOx) emissions using new urea solution versus urea solution stored for 5 years on ships. The results indicate that using new urea solution reduces NOx emissions by an average of 30%. Additionally, the study confirms that the impact of the SCR system on the combustion process is negligible. These findings the importance of regular urea solution replacement to optimize the performance of SCR systems installed to meet environmental regulations. Currently, there are no detailed procedures or regulatory standards for urea management and replacement on ships. Considering the strict NOx emission regulations and harsh storage conditions in ship, the study proposes the establishment of effective urea replacement cycles and management procedures.]]></description>
      <pubDate>Thu, 12 Dec 2024 16:58:18 GMT</pubDate>
      <guid>https://trid.trb.org/View/2437650</guid>
    </item>
    <item>
      <title>Improving the Stability of Sandy Soils by Using Urease Enzyme in Soybean Plants</title>
      <link>https://trid.trb.org/View/2445188</link>
      <description><![CDATA[In recent years, the urease enzyme has been used to accelerate the natural precipitation of calcium carbonate (EICP) as a potential method of soil improvement. Optimizing the costs and scale-up is the main pitfall in facilitating the application of this method. Here, the efficiency of crude soybean extract as an alternative substance for purified enzymes has been investigated to reduce costs and achieve an environmentally friendly process. The urease activity of the soybean aerial organ was 9.355 × 10(⁻³), and for the soybean root was 6.056 × 10(⁻³). The ideal buffer for extracting the plant is phosphate buffer. The effect of time of adding reactants (CaCl₂ and Urea) to the plant extract was investigated for the calcium carbonate precipitation process and the amount of sediment obtained. The highest uniaxial compressive strength of the improved soil sample obtained using the soybean aerial organ extract was equal to 380 kPa. The results of energy-dispersed X-ray spectroscopy and scanning electron microscopy indicate the effective binding of soil particles by calcium carbonate deposits. In conclusion, the crude plant extract can be a proper alternative to pure enzymes in the EICP method to improve soil.]]></description>
      <pubDate>Mon, 09 Dec 2024 09:56:53 GMT</pubDate>
      <guid>https://trid.trb.org/View/2445188</guid>
    </item>
    <item>
      <title>Quantitative Analysis of Urea Deposit Formation Process in the Urea SCR System</title>
      <link>https://trid.trb.org/View/2434034</link>
      <description><![CDATA[In compression ignition engines, the urea selective catalytic reduction system is used to reduce NOₓ in the exhaust gas. However, under low exhaust gas temperature conditions, the urea water solution (UWS) film forms on the wall where the spray impinges and changes chemically to the solid deposit. Since this solid deposit prevents the NH₃ formation and its homogeneous dispersion, it is necessary to understand the detailed chemical reaction process under actual engine conditions. In this study, the chemical reaction process of the UWS film was measured by Raman spectroscopy in an experimental system simulating the actual exhaust system. As a result, the UWS film evaporated and decomposed at all gas temperatures, and finally solid deposits remained on the wall, with different mass and composition at each gas temperature. Immediately after the UWS was put in, the urea mass decreased, and the wall surface temperature also decreased due to the vaporization latent heat. Thereafter, the rate of decrease of urea mass becomes smaller as the surface temperature of the wall surface decreases.]]></description>
      <pubDate>Fri, 25 Oct 2024 13:58:45 GMT</pubDate>
      <guid>https://trid.trb.org/View/2434034</guid>
    </item>
    <item>
      <title>Analysis of Flash Boiling Spray by Heating Urea Water Solution in Urea Selective Reduction Catalyst Systems</title>
      <link>https://trid.trb.org/View/2434030</link>
      <description><![CDATA[In compression ignition engines, the urea selective catalytic reduction (SCR) system is used to reduce NOₓ in the exhaust gas. However, under low exhaust gas temperature conditions, the urea is not decomposed completely, leading to a decreased NOₓ purification rate. In this study, the temperature of the urea water solution (UWS) was controlled to promote atomization, evaporation, and the chemical reaction of the UWS spray. To understand the effect of the degree of superheat on UWS spray characteristics, the urea SCR nozzle tip was electrically heated, and the UWS spray was optically measured at different temperatures. The Super High Spatial Resolution Photography (SHSRP) method, which allows for whole spray imaging while maintaining the spatial resolution of small droplets, was applied, and the UWS droplet size distribution in quiescent conditions was analyzed. By applying a phase change model of flash boiling with energy balance, the vapor mass fraction at the nozzle outlet of the heated UWS spray was analyzed. Assuming a low-temperature exhaust gas flow field, the mass fraction of UWS spray droplets following the gas flow, the adhesion mass on the wall, and the location of water evaporation were estimated. The efficiency of UWS heating in urea SCR systems was discussed.]]></description>
      <pubDate>Wed, 23 Oct 2024 15:52:15 GMT</pubDate>
      <guid>https://trid.trb.org/View/2434030</guid>
    </item>
    <item>
      <title>Electrically Heated Mixer for Near-Zero Urea Deposit</title>
      <link>https://trid.trb.org/View/2367613</link>
      <description><![CDATA[When used with injecting urea-water solution forming ammonia, Selective Catalytic Reduction (SCR) catalyst is a proven technology for greatly reducing tailpipe emission of nitrogen oxides (NOx) from Diesel engines. However, one major shortcoming of an SCR-based system is forming damaging urea deposits (crystals) in low temperature exhaust operations, especially exacerbated during higher injection rates. Deposits reduce SCR efficiency, damage exhaust components, and induce high concentration ammonia slips.We describe here an Electrically Heated Mixer (EHM™) demonstrated on a Diesel engine markedly inhibiting deposit formation in urea SCR systems, both in low (near 200 °C) and higher exhaust temperature operations and for both low and high urea injection rates in various, realistic engine operations. Engine test runs were conducted in long durations, 10 to 20 hours each, for a total of nearly 100 hours. In nearly all operation modes, EHM maintained deposits below 1% of the total injected DEF mass; most were below 0.5%, practically non-existent, including when in higher injection rates. To further gain confidence in and validate the deposit-free outcome due to the EHM impact, CFD simulations of the same exhaust conditions were performed, which further confirmed EHM’s capability in substantially inhibiting urea deposits observed on the engine.Along with prior publications, this work forms a trilogy demonstrating EHM enabling rapid heat-up making available several-fold lower tailpipe NOx, meeting ultra-stringent NOx regulations (e.g., Californian/EPA 2027 meeting 0.02 gr/bhp.hr), reducing tailpipe NOx in various regulatory and non-regulatory cycles [Frontier, 2022] while enabling highly efficient NOx conversion in low-load cycles and in fast transients [Topics in Catalysis, 2022, COMVEC, 2022].]]></description>
      <pubDate>Wed, 08 May 2024 09:32:46 GMT</pubDate>
      <guid>https://trid.trb.org/View/2367613</guid>
    </item>
    <item>
      <title>Numerical Modeling of Liquid Film Boiling, Urea Deposition and Solidification in SCR Applications</title>
      <link>https://trid.trb.org/View/2367380</link>
      <description><![CDATA[The proposed Euro 7 regulation aims to substantially reduce the NOx emissions to 0.03 g/km, a trend also seen in upcoming China 6b and US EPA regulations. Meeting these stringent requirements necessitates advancements in Urea/Selective Catalytic Reduction (SCR) aftertreatment systems, with the urea deposit formation being a key challenge to its design. It’s proven that Computational Fluid Dynamics (CFD) can be an effective tool to predict Urea deposits. Transient wall temperature prediction is crucial in Urea deposit modeling. Additionally, fully understanding the kinetics of urea decomposition and by-products solidification are also critical in predicting the deposit amount and its location. In this study, the authors introduce (i) a novel film boiling model (IFPEN-BRT model) and (ii) a new urea by-product solidification model in the CONVERGE CFD commercial solver, and validate the results against the recent experiments. The IFPEN-BRT model handles the spray-wall heat transfer in various boiling regimes, and the urea by-product solidification model separates solid deposits from liquid film parcels and renders them inert on the walls. The authors couple the by-product solidification model with the detailed decomposition model for urea. The authors use surface morphing feature developed in CONVERGE to enable realistic representation of solid surface topology once the solid deposits are formed on the testing plate. Multiple acceleration schemes have been employed to achieve a faster turnaround time while maintaining high fidelity. Additionally, the fixed flow approach has been used to accelerate the simulation and reach the time scale required for appreciable deposit formation. The simulations, incorporating both the IFPEN-BRT model and the urea by-product solidification model, matches the experiments very well on several fronts: the wall temperature contours, the temporal evolution of wall temperature profiles, and film/deposit patterns. The simulations also correctly predict cyanuric acid (CYA) as the primary solid deposit, aligning with experimental findings after 20 minutes real time simulation.]]></description>
      <pubDate>Sun, 05 May 2024 17:28:32 GMT</pubDate>
      <guid>https://trid.trb.org/View/2367380</guid>
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