Academic literature on the topic 'Code Kiva II'

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Journal articles on the topic "Code Kiva II"

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Blunsdon, C. A., Z. Beeri, W. M. G. Malalasekera, and J. C. Dent. "Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part I: Buoyant Diffusion Flames." Journal of Energy Resources Technology 118, no. 1 (March 1, 1996): 65–71. http://dx.doi.org/10.1115/1.2792695.

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A modified version of the computational fluid dynamics code KIVA-II was used to model the transient behavior of buoyant turbulent diffusion flames burning in still air. Besides extensions to the range of permitted boundary conditions and the addition of buoyancy terms to the turbulence model, KIVA-II was augmented by a version of the coherent flame-sheet model, Tesner’s soot generation model, Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model that included both banded and continuum radiation. The model captured many of the features of buoyant turbulent flames. Its predictions supported experimental observations regarding the presence and frequency of large-scale pulsations, and regarding axial distributions of temperature, velocity, and chemical species concentrations. The radial structure of the flame was less well represented. The axial radiative heat flux distribution from the flame highlighted deficiencies in the soot generation model, suggesting that a model of soot particle growth was required.
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Choi, C. Y., and R. D. Reitz. "A Numerical Analysis of the Emissions Characteristics of Biodiesel Blended Fuels." Journal of Engineering for Gas Turbines and Power 121, no. 1 (January 1, 1999): 31–37. http://dx.doi.org/10.1115/1.2816309.

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Computer simulations were conducted to study the combined effects of methyl soyate (biodiesel) blends with no. 2 diesel fuel on diesel engine (D.I.) performance. Diesel engine emissions and heat release rates were some of the parameters studied. The results from the computer simulations were compared against previously published results (Choi et al., 1997) from engine tests conducted on a single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. The experiments and simulations were performed over a range of injection timings allowing particulate versus NOx trade-off curves to be a generated. Phillips 66 certified no. 2 diesel fuel was used as the baseline; mixtures of 20 percent and 40 percent by volume of methyl soyate with the baseline no. 2 diesel fuel were used as the biodiesel blends. The multidimensional KIVA-II code (ERC version 2.4) was used to better understand the factors controlling the formation of NOx and soot. KIVA-II modeled the high load, single injection combustion of the baseline #2 diesel fuel and the biodiesel blends. The code was changed to account for different fuel effects and the computational results were then compared against the experimental data. It is concluded that the increased NOx observed with the use of biodiesel fuels (in spite of their lower heats of combustion) is due to increased local temperatures as a result of enhanced fuel/air mixing and increased spray penetration. The increased spray penetration results from the higher fuel viscosity of the biodiesel blended fuels which leads to reduced injection durations.
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Emery, P., F. Maroteaux, and M. Sorine. "Modeling of Combustion in Gasoline Direct Injection Engines for the Optimization of Engine Management System Through Reduction of Three-Dimensional Models to (n × One-Dimensional) Models." Journal of Fluids Engineering 125, no. 3 (May 1, 2003): 520–32. http://dx.doi.org/10.1115/1.1570859.

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Gasoline direct injection (GDI) spark ignition engines may be able to run over a wide range of operating conditions. The GDI process allows combustion with lean mixtures which may lead to improved fuel economy and emissions relative to homogeneous spark ignition (SI) engines. To satisfy the different modes of operation, the tuning of GDI engines requires a large number of engine tests which are time-consuming and very expensive. To reduce the number of tests, a model with a very short computational time to simulate the engines in the whole operating range is needed; therefore the objective of this paper is to present a reduced model to analyze the combustion process in GDI engines, applied to a homogeneous stoichiometric mode. The objective of the model is to reproduce the same tendencies as those obtained by three-dimensional models, but with a reduced computational time. The one-dimensional model is obtained thanks to a reduction methodology based on the geometry of the combustion front computed with three-dimensional models of the KIVA-GSM code, a modified version of KIVA-II code including a CFM combustion model. The model is a set of n one-dimensional equations (i.e., for n rays), taking into account a thin flame front, described with the flamelet assumption. It includes a CFM combustion model and a (k,ε)-model including the mean air motions (swirl and tumble). The results of the one-dimensional model are compared to those obtained by the KIVA IIGSM under different engine conditions. The comparison shows that the one-dimensional model overestimates the maximum cylinder pressure, which has an insignificant effect on the net indicated work per cycle. The results obtained by the numerical simulations are close to those given by the three-dimensional model, with a much reduced computation time.
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Beeri, Z., C. A. Blunsdon, W. M. G. Malalasekera, and J. C. Dent. "Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part II: High-Momentum Reactive Jets." Journal of Energy Resources Technology 118, no. 1 (March 1, 1996): 72–76. http://dx.doi.org/10.1115/1.2792696.

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This paper describes the application of computational fluid dynamics (CFD) to the prediction of the characteristics of high-momentum vertical and horizontal flames in ambient air flows. The KIVA-II code has been modified by extending the range of boundary conditions and by the addition of the following: a version of the coherent flame-sheet model, Tesner’s soot generation and Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model. To assess the accuracy of the complete model for prediction purposes, results are compared with experimental data. Predictions of temperature and flame profiles are in good agreement with data while predictions of radiative heat transfer are not entirely satisfactory.
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Cao, Jianming. "On the Theoretical Prediction of Fuel Droplet Size Distribution in Nonreactive Diesel Sprays." Journal of Fluids Engineering 124, no. 1 (August 8, 2001): 182–85. http://dx.doi.org/10.1115/1.1445140.

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Droplet size distribution function and mean diameter formulas are derived using information theory. The effects of fuel droplet evaporation and coalescence within combustion chamber on the droplet size are emphasized in nonreactive diesel sprays. The size distribution function expressions at various spray axial cross sections are also formulated. The computations are compared with experimental data and KIVA-II code. A good agreement is obtained between numerical and experimental results. Droplet size distribution and mean diameter at various locations from injector exit and at various temperature conditions are predicted. The decreases of droplet number and variations of mean diameter are computed at downstream and higher temperature.
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Shih, L. K., and D. N. Assanis. "Effect of Ring Dynamics and Crevice Flows on Unburned Hydrocarbon Emissions." Journal of Engineering for Gas Turbines and Power 116, no. 4 (October 1, 1994): 784–92. http://dx.doi.org/10.1115/1.2906886.

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A significant source of unburned hydrocarbon emissions from internal combustion engines originates from the flow of unburned fuel/air mixture into and out of crevices in the piston-cylinder-ring assembly. During compression, fuel vapor flows into crevice regions. After top dead center, the trapped fuel vapor that returns into the cylinder escapes complete oxidation and contributes to unburned hydrocarbon emissions. In this work, the crevice flow model developed by Namazian and Heywood is implemented into KIVA-II, a multidimensional, reacting flow code. Two-dimensional, axisymmetric simulations are then performed for a 2.5 liter gasoline engine to investigate the effects of engine speed and selected piston-ring design parameters on crevice flows and on unburned hydrocarbon emissions. Results suggest that engine-out unburned hydrocarbon emissions can be reduced by optimizing the ring end gap area and the piston-cylinder side clearance.
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Lebre`re, L., M. Buffat, L. Le Penven, and B. Dillies. "Application of Reynolds Stress Modeling to Engine Flow Calculations." Journal of Fluids Engineering 118, no. 4 (December 1, 1996): 710–21. http://dx.doi.org/10.1115/1.2835500.

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To improve the prediction of turbulence inside internal combustion engines, a Reynolds stress turbulence model is implemented in the Kiva-II code. After a rapid description of the Launder-Reece-Rodi model (noted LRR), two validation test cases (the plane channel flow and the flow over a backward facing step) are presented. The advantages of a second order closure and the shortcomings of the LRR model are then analyzed. Finally, a simulation of an intake and compression stroke using both the standard k – ε model and the LRR model is described. As a precise knowledge of the velocity and turbulent fields near TDC is necessary for the prediction of the mixing and the combustion processes, we have analyzed the influence of the turbulence model on the flow field. Results are compared with experimental data and show a strong influence of the turbulence model even on the mean flow, especially at the end of the compression stroke (TDC).
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Ambari, Ade Meidian, Budhi Setianto, Anwar Santoso, Basuni Radi, Bambang Dwiputra, Eliana Susilowati, Fadilla Tulrahmi, Annemiek Wind, Maarten Jan Maria Cramer, and Pieter Doevendans. "Randomised controlled trial into the role of ramipril in fibrosis reduction in rheumatic heart disease: the RamiRHeD trial protocol." BMJ Open 11, no. 9 (September 2021): e048016. http://dx.doi.org/10.1136/bmjopen-2020-048016.

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IntroductionRheumatic heart disease (RHD) is a major burden in developing countries and accounts for 80% of all people living with the disease, where it causes most cardiovascular morbidity and mortality in children and young adults. Chronic inflammation and fibrosis of heart valve tissue due to chronic inflammation in RHD will cause calcification and thickening of the impacted heart valves, especially the mitral valve. This fibrogenesis is enhanced by the production of angiotensin II by increased transforming growth factor β expression and later by the binding of interleukin-33, which is known to have antihypertrophic and antifibrotic effects, to soluble sST2. sST2 binding to this non-natural ligand worsens fibrosis. Therefore, we hypothesise that ACE inhibitors (ACEIs) would improve rheumatic mitral valve stenosis.Methods and analysisThis is a single-centre, double-blind, placebo-controlled, randomised clinical trial with a pre–post test design. Patients with rheumatic mitral stenosis and valve dysfunction will be planned for cardiac valve replacement operation and will be given ramipril 5 mg or placebo for a minimum of 12 weeks before the surgery. The expression of ST2 in the mitral valve is considered to be representative of cardiac fibrosis. Mitral valve tissue will be stained by immunohistochemistry to ST2. Plasma ST2 will be measured by ELISA. This study is conducted in the Department of Cardiology and Vascular Medicine, Universitas Indonesia, National Cardiac Center Harapan Kita Hospital, Jakarta, Indonesia, starting on 27 June 2019.Ethics and disseminationThe performance and dissemination of this study were approved by the ethics committee of National Cardiovascular Center Harapan Kita with ethical code LB.02.01/VII/286/KEP.009/2018.Trial registration numberNCT03991910.
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"99/03581 Spray characteristics of non-reacting diesel fuel spray by experiments and simulations with KIVA II code." Fuel and Energy Abstracts 40, no. 6 (November 1999): 380. http://dx.doi.org/10.1016/s0140-6701(99)98787-8.

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Li, Juncheng, Zhiyu Han, Cai Shen, and Chia-fon Lee. "A Study on Biodiesel NOx Emission Control With the Reduced Chemical Kinetics Model." Journal of Engineering for Gas Turbines and Power 136, no. 10 (May 2, 2014). http://dx.doi.org/10.1115/1.4027358.

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In this paper, the effects of the start of injection (SOI) timing and exhaust gas recirculation (EGR) rate on the nitrogen oxides (NOx) emissions of a biodiesel-powered diesel engine are studied with computational fluid dynamics (CFD) coupling with a chemical kinetics model. The KIVA code coupling with a CHEMKIN-II chemistry solver is applied to the simulation of the in-cylinder combustion process. A surrogate biodiesel mechanism consisting of two fuel components is employed as the combustion model of soybean biodiesel. The in-cylinder combustion processes of the cases with four injection timings and three EGR rates are simulated. The simulation results show that the calculated NOx emissions of the cases with default EGR rate are reduced by 20.3% and 32.9% when the injection timings are delayed by 2- and 4-deg crank angle, respectively. The calculated NOx emissions of the cases with 24.0% and 28.0% EGR are reduced by 38.4% and 62.8%, respectively, compared to that of the case with default SOI and 19.2% EGR. But higher EGR rate deteriorates the soot emission. When EGR rate is 28.0% and SOI is advanced by 2 deg, the NOx emission is reduced by 55.1% and soot emission is controlled as that of the case with 24% EGR and default SOI. The NOx emissions of biodiesel combustion can be effectively improved by SOI retardation or increasing EGR rate. Under the studied engine operating conditions, introducing more 4.8% EGR into the intake air with unchanged SOI is more effective for NOx emission controlling than that of 4-deg SOI retardation with default EGR rate.
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Dissertations / Theses on the topic "Code Kiva II"

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Leborgne, Hervé. "Modélisation de l'évaporation à haute pression de gouttes multicomposants dans le code Kiva II." Rouen, 1999. http://www.theses.fr/1999ROUES046.

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Nous présentons dans ce mémoire une modélisation numérique de l'évaporation de gouttes multicomposants adaptée à la haute pression. La prise en compte de l'influence de la pression sur l'évaporation et d'une phase liquide a plusieurs constituants permet en effet d'améliorer la simulation des moteurs à injection directe. Nous avons dans le premier chapitre rappelé les caractéristiques du modèle d'évaporation du code Kiva II, utilisé dans cette étude, en mettant en évidence ses points faibles pour une utilisation à pression élevée. Suite à une synthèse bibliographique des modèles existants, nous avons développé un modèle d'évaporation haute pression en modifiant le calcul des transferts de masse et de chaleur, en prenant en compte les effets de la pression et du mélange vapeur/gaz ambiant dans le calcul des propriétés physiques du film de diffusion, et en considérant un gaz réel dans le calcul de l'équilibre thermodynamique à l'interface liquide/vapeur. Ce modèle a été validé dans le troisième chapitre où nous avons également montré l'influence de chaque modification par rapport à l'ancien modèle. Deux applications du modèle d'évaporation sont présentées dans les quatrième et cinquième chapitres. La première concerne l'évaporation d'une goutte isolée (configuration de Kadota-Hiroyasu) ou nous avons mis en évidence l'influence de chaque paramètre et la seconde celle d'un spray (configuration de Sommerfeld) où nous avons montré l'influence du choix du modèle sur la prédiction de la répartition de la vapeur. Dans le sixième chapitre, nous avons complété le modèle d'évaporation haute pression en introduisant un traitement multicomposants de la phase liquide dont la principale différence avec les modèles existants provient de la prise en compte d'un coefficient de diffusion d'une espèce dans le mélange gazeux diffèrent pour chaque espèce. Ce modèle a été validé et appliqué à l'évaporation d'une goutte à deux et à trois composants.
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Himdi, Morjane. "Contribution à la simulation numérique des écoulements de fluides compressibles et peu compressibles par le code de calcul Kiva-II." Lille 1, 1993. http://www.theses.fr/1993LIL10113.

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L'objectif de cette thèse est d'apporter une contribution à la modélisation des écoulements de fluides compressibles et peu compressibles en utilisant le code de calcul kiva-ii. La première partie est consacrée à l'aspect théorique du problème, conduisant à une formulation mathématique adéquate. On y montre notamment les difficultés de la résolution numérique des équations de Navier-Stokes dans le cas des écoulements de fluides dits peu compressibles (écoulements à faible nombre de mach). Ces difficultés sont dues essentiellement à la grande disparité qu'il y a entre le temps caractéristique de la propagation des ondes acoustiques et celui lié à la convection. Une méthode est alors développée, elle consiste à utiliser l'hypothèse de faible nombre de mach pour éliminer les ondes acoustiques présentes dans l'écoulement et qui sont sans intérêts dans ce cas. Dans la deuxième partie, nous avons abordé l'étude des différentes méthodes numériques utilisées dans le code kiva-ii, ainsi que la caractérisation des algorithmes de résolution dont ils font appel. Une discussion concernant ce code, et les principales modifications dont il a fait l'objet sont présentées dans la troisième et la quatrième partie. La cinquième partie est consacrée à la présentation des cas tests que nous avons traités pour valider les différentes méthodes adoptées. Dans la sixième partie, nous avons abordé les modèles physiques pour la turbulence. Trois modèles de fermeture (modèle longueur de mélange, modèle à une équation de transport et modèle à deux équations de transport) sont alors étudiés et comparés
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Emtil, Hassane. "Implantation et validation de sous-modèles de délai et de suie et modélisation du rayonnement dans le code Kiva-II." Ecully, Ecole centrale de Lyon, 1994. http://www.theses.fr/1994ECDL0037.

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Le but de cette thèse est l'étude du rayonnement dans le code kiva-ii pour un moteur diesel. Elle comprend une présentation du code kiva-ii, puis de l'étude expérimentale ayant servi de base de données pour la confrontation aux calculs numériques. Puis sont présentés les modèles d'auto-inflammation qui ont été testés et discutés. Apres la validation de la pression par le modèle de combustion turbulente de Magnussen, nous modélisons selon trois méthodes la quantité de suie dans la chambre de combustion que nous comparons aux résultats des mesures expérimentales. L'aboutissement des différentes phases précédentes est la modélisation du rayonnement par la méthode des zones et la quantification de l'énergie à la paroi. Le rayonnement étant l'un des moyens d'analyser in situ la production des suies.
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Affad, El Houssin. "Modélisation de la combustion turbulente dans les moteurs à allumage commandé avec prise en compte d'une cinétique complexe. Prédiction des polluants." Rouen, 1995. http://www.theses.fr/1995ROUES011.

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Les travaux de modélisation de la combustion et des phénomènes chimiques dans les moteurs à combustion interne revêtent une grande importance pour la prédiction des polluants chimiques (CO, NOx) émis par les moteurs à allumage commandé. Dans les codes de calcul complet existants pour prédire l'aérodynamique interne des chambres de combustion (Kiva, Speed,) la chimie est traitée de façon très simplifiée et donne des prédictions très approximatives des espèces principales. Le but de cette thèse était de: choisir après une série de validations, un schéma cinétique réduit fiable dans le domaine de fonctionnement d'un moteur à allumage commandé (haute pression et température). Réaliser un couplage entre un modèle utilisant des pdf présumées et un modèle eulérien-lagrangien pour la modélisation de la combustion turbulente, puis implanter ce modèle dans le code Kiva II. Des comparaisons des résultats numériques avec des résultats expérimentaux concernant la propagation d'une flamme en milieu confiné machine à compression rapide (expérience de l'arc-moteur) et les émissions des polluants émis par un moteur à allumage commandé ont été satisfaisantes
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Conference papers on the topic "Code Kiva II"

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Belardini, P., C. Bertoli, F. E. Corcione, and G. Valentino. "In-Cylinder Flow Measurements by LDA and Numerical Simulation by KIVA-II Code." In International Congress & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1992. http://dx.doi.org/10.4271/920155.

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Lebrère, Laurent, and Bruno Dillies. "Engine Flow Calculations Using a Reynolds Stress Model in the Kiva-II Code." In International Congress & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1996. http://dx.doi.org/10.4271/960636.

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YING, S., RAMA GORLA, and KRISHNA KUNDU. "The promising chemical kinetics for the simulation of propane-air combustion with KIVA-II code." In 29th Joint Propulsion Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-2189.

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Mariani, Francesco, and Lucio Postrioti. "Modeling Diesel Engine Using KIVA II 3D-Code: Validation of a New Global Combustion Model and its Sensitivity to the Spatial Discretization." In International Congress & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1996. http://dx.doi.org/10.4271/960872.

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Yang, Wenming, Hui An, Jing Li, Dezhi Zhou, and Markus Kraft. "Impact of Urea Direct Injection on NOx Emission Formation of Diesel Engines Fueled by Biodiesel." In ASME 2015 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/icef2015-1059.

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There are many NOx removal technologies: exhaust gas recirculation (EGR), selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), miller cycle, emulsion technology and engine performance optimization. In this work, a numerical simulation investigation was conducted to explore the possibility of an alternative approach: direct aqueous urea solution injection on the reduction of NOx emissions of a biodiesel fueled diesel engine. Simulation was performed using the 3D CFD simulation software KIVA4 coupled with CHEMKIN II code for pure biodiesel combustion under realistic engine operating conditions of 2400 rpm and 100% load. To improve the overall prediction accuracy, the Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) spray break up model was implemented in the KIVA code to replace the original Taylor Analogy Breakup (TAB) model for the primary and secondary fuel breakup processes modeling. The KIVA4 code was further modified to accommodate multiple injections, different fuel types and different injection orientations. A skeletal reaction mechanism for biodiesel + urea was developed which consists of 95 species and 498 elementary reactions. The chemical behaviors of the NOx formation and Urea/NOx interaction processes were modeled by a modified extended Zeldovich mechanism and Urea/NOx interaction sub-mechanism. Developed mechanism was first validated against the experimental results conducted on a light duty 2KD FTV Toyota car engine fueled by pure biodiesel in terms of in-cylinder pressure, heat release rate. To ensure an efficient NOx reduction process, various aqueous urea injection strategies in terms of post injection timing and injection rate were carefully examined. The simulation results revealed that among all the four post injection timings (10 °ATDC, 15 °ATDC, 20 °ATDC and 25 °ATDC) that were evaluated, 15 °ATDC post injection timing consistently demonstrated a lower NO emission level. In addition, both the urea/water ratio and aqueous urea injection rate demonstrated important roles which affected the thermal decomposition of urea into ammonia and the subsequent NOx removal process, and it was suggested that 50% urea mass fraction and 40% injection rate presented the lowest NOx emission levels.
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Cao, L., Huimeng Liu, Yongchang Liu, and Q. Huang. "Numerical Prediction to Effects of Manifolds Configuration on Flow in Swirling Flow Exhaust Pipe System." In ASME 2001 Internal Combustion Engine Division Spring Technical Conference. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/ices2001-136.

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Abstract Compared to conventional Modular Pulse Converter (MPC) system with the typical structure of symmetrical T-junction, a novel swirling flow exhaust pipe system has its advantages especially in reducing collision loss of high-speed gases near junction and having interference-free scavenging and higher energy utilization. The initial junction configuration in swirling flow exhaust system was determined with reference to T-junction in MPC. In order to analyze and compare its flow behaviors, 3D-flow fields of manifold-type junctions in swirling flow exhaust pipe system were performed with the revised KIVA II code. A non-linear algebraic Relynolds stress (ASM) model was considered in this study and comparisons were made with the standard κ–ε turbulence model. For many cases of parametric studies considered, it is found that junction’s configurations have significant influence on the velocity distribution and swirl intensity. 30° swirling flow junction is found to be unreasonable, 45° junction with oblate rectangular type contraction area is recommended in swirl flow pipe exhaust pipe system. 3D-Particle Dynamic Analyzer (PDA) measurement was introduced to measure the axial and tangential velocity components of swirling flow in main pipe. Comparisons of computed and measured velocities reveal that model predictions are in generally reasonable agreement with the measurements, indicating validity of computational code and reliability of prediction model.
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Zhou, Dezhi, Wenming Yang, Hui An, Jing Li, and Markus Kraft. "An Enhanced PRF Mechanism Considering Conventional Fuel Chemistry in Engine Simulation." In ASME 2015 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/icef2015-1057.

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A compact and accurate primary reference fuel (PRF) mechanism which consists of 46 species and 144 reactions was developed and validated to consider the fuel chemistry in combustion simulation based on a homogenous charged compression ignition (HCCI) mechanism. Some significant reactions were updated to ensure its capabilities for predicting combustion characteristics of PRF fuels. To better predict laminar flame speed, the relevant C2-C3 carbon reactions was coupled in. This enhanced PRF mechanism was validated by available experimental data references including ignition delay times, laminar flame speed, premixed flame species concentrations in jet stirred reactor (JSR), rapid compression machine and shock tube. The predicted data was calculated by CHEMKIN-II codes. All the comparisons between experimental and calculated data indicated high accuracy of this mechanism to capture combustion characteristics. Also, this mechanism was integrated into KIVA4-CHEMKIN. The engine simulation data (including in-cylinder pressure and apparent heat release rate (HRR)) was compared with experimental data in PRF HCCI, partially premixed compression ignition (PCCI) and diesel/gasoline dual-fuel engine combustion data. The comparison results implied that this mechanism could predict PRF and gasoline/diesel combustion in CFD engine simulations. The overall results show this PRF mechanism could predict the conventional fuel combustion characteristics in engine simulation.
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