Control-oriented modelling and diagnostics of diesel after-treatment catalysts

[ES] Esta tesis doctoral abarca el desarrollo de algoritmos orientados a mejorar el sistema de control de emisiones en motores Diesel. Para este propósito, la inclusión en el vehículo de sensores embarcados como los de temperatura, los de NOx o el de NH3 permite realizar diagnóstico a bordo de los sistemas de post-tratamiento foco de este trabajo, los cuales son el DOC y el SCR. Así pues, el objetivo es el de satisfacer las normativas de diagnóstico a bordo para mantener las emisiones por debajo del umbral permitido por la normativa a lo largo del tiempo. Los tests experimentales, incluyendo las medidas con analizador de gases, permiten tener una visión más amplia de las especies en la línea de escape. Complementariamente, se utilizan unidades nuevas y envejecidas para tener el efecto experimental del envejecimiento en los catalizadores. De esta manera, se analiza el efecto de la temperatura, el gasto de escape, las concentraciones de las especies y el envejecimiento en el DOC y en el SCR, así como la evaluación de algunas de las medidas relevantes realizadas por los sensores. Las temperaturas tienen una influencia destacada en el funcionamiento de los catalizadores, por lo que se requiere la evaluación de las medidas de los sensores de temperatura, junto con el desarrollo de modelos de transmisión de calor, para alimentar las funciones a continuación desarrolladas. En este sentido, la medida lenta del sensor aguas arriba del DOC se mejora en condiciones transitorias mediante una técnica de fusión de la información basada en un filtro de Kalman. Luego, se presenta un modelo de transmisión de calor 1D y un modelo agrupado 0D, en los cuales se evalúan las entradas aguas arriba según el uso del modelo. Por otra parte, se presenta una técnica para estimar el incremento de temperatura debido a la oxidación de los pulsos de post-inyección en el DOC. Se proponen modelos para ambos DOC y SCR para estimar el efecto del envejecimiento en las emisiones, en los cuales el factor de envejecimiento es modelado como un parámetro sintonizable que permite variar desde estados nuevos a envejecidos. Por una parte, un modelo agrupado 0D es desarrollado para el DOC con el propósito de estimar el desliz de HC y CO, el cual es validado en un WLTC para después ser usado en simulación. Por otra parte, un modelo 1D y un modelo 0D se desarrollan para el SCR, los cuales se usan a continuación para alimentar la estrategia de diagnóstico y para simulación. Finalmente, las estrategias de diagnóstico se presentan para fallo total o retirada de DOC, así como para la estimación de la eficiencia en DOC y SCR. Por una parte, la primera estrategia se divide en pasiva y activa, en la que se usan post-inyecciones en la activa para excitar el sistema y confirmar el fallo total si es el caso. A continuación, la eficiencia del DOC se estima a través de una técnica indirecta en la que la temperatura de activación se detecta y se relaciona con el incremento de emisiones a través del modelo. Por otra parte, se desarrolla un observador para estimar el estado de envejecimiento del SCR, el cual está basado en un filtro de Kalman extendido. Sin embargo, para evitar asociar baja eficiencia del catalizador debido a pobre calidad de la urea inyectada, a envejecimiento del SCR, un indicador de la calidad de la urea se ejecuta en paralelo.[CA] Esta tesi doctoral abasta el desenvolupament d'algoritmes orientats a millor el sistema de control d'emissions en motors Diesel. Per a este propòsit, la inclusió en el vehicle de sensor embarcats com els de temperatura, els de NOx o el d'NH3 permet realitzar el diagnòstic a bord dels sistemes de post-tractament focus d'este treball, els quals són el DOC i el SCR. Així doncs, l'objectiu és el de satisfer les normatives de diagnòstic a bord per a mantindre les emissions per baix de l'umbral permés per la normativa al llarg del temps. Els tests experimentals, incloent les mesures amb analitzador de gasos, permeten obtindre una visió més àmplia de les espècies en la línia d'escapament. Complementàriament, s'utilitzen unitats noves i envellides per tal de tindre l'efecte experimental de l'envelliment en els catalitzadors. D'aquesta manera, s'analitza l'efecte de la temperatura, la despesa d'escapament, les concentracions de les espècies i l'envelliment en el DOC i en el SCR, així com l'avaluació d'algunes mesures rellevants realitzades pels sensors. Les temperatures tenen una influència destacada en el funcionament dels catalitzadors, pel que es requerix l'avaluació de les mesures dels sensors de temperatura, junt amb el desenvolupament de models de transmissió de calor, per a alimentar les funcions a continuació desenvolupades. En este sentit, la mesura lenta del sensor a l'entrada del DOC es millora en condicions transitòries mitjançant una tècnica de fusió de la informació basada en un filtre de Kalman. Després, es presenta un model de transmissió de calor 1D i un model agrupat 0D, en els quals s'avaluen les entrades a l'entrada segons l'ús del model. Per altra banda, es presenta una tècnica per a estimar l'increment de temperatura degut a l'oxidació dels polsos de post-injecció en el DOC. Es proposen models per a DOC i SCR per a estimar l'efecte de l'envelliment en les emissions, en els quals es modela el factor d'envelliment com un paràmetre sintonitzable, que permet variar des d'estats nous a envellits. Per altra banda, un model agrupat 0D _es desenvolupat per al DOC amb el propòsit d'estimar la relliscada de HC i CO, el qual és validat en un WLTC per a després ser usat en simulació. Per altra banda, un model 1D i un model 0D es desenvolupen per al SCR, els quals s'usen a continuació per a alimentar l'estratègia de diagnòstic i per a simulació. Finalment, les estratègies de diagnòstic es presenten per a la fallada total o retirada del DOC, així com per a l'estimació de l'eficiència en DOC i SCR. Per altra banda, la primera estratègia es divideix en passiva i activa, en la que s'utilitzen post-injeccions en la activa per a excitar el sistema i confirmar la fallada total si es dona el cas. A continuació, l'eficiència del DOC s'estima a través d'una tècnica indirecta en la que la temperatura d'activació es detecta i es relaciona amb l'increment d'emissions a través del model. Per altra banda, es desenvolupa un observador per a estimar l'estat d'envelliment del SCR, el qual està basat en un filtre de Kalman extés. No obstant això, per a evitar associar baixa eficiència degut a pobre qualitat de l'urea injectada a l'envelliment del SCR, un indicador de la qualitat de l'urea s'executa en paral·lel.[EN] This dissertation covers the development of algorithms oriented to improve the emission control system of Diesel engines. For this purpose, the inclusion of on-board sensors like temperature, NOx and NH3 sensors allows performing on-board diagnostics to the after-treatment systems focus of this work, which are the DOC and the SCR system. Then, the target is to meet on-board diagnostics regulations in order to keep emissions below a regulation threshold over time. Experimental tests, including gas analyzer measurements, allow having a wider view of the species in the exhaust line. Complementary, new and aged units are used in order to have the experimental effect of ageing on the catalysts. Then, the effect of temperature, exhaust mass flow, species concentrations and ageing is analyzed for DOC and SCR, in combination with the assessment of some relevant sensors measurements. As a result, the characteristics, opportunities and limitations extracted from experimental data are used as the basis for the development of models and diagnostics techniques. The assessment of temperature sensors measurements, along with the development of heat transfer models is required to feed temperature dependent functions. In this sense, the slow measurement of the DOC upstream temperature sensor is improved in transient conditions by means of a data fusion technique, based on a fast model and a Kalman filter. Then, a 1D and a 0D lumped heat transfer models are presented, in which the upstream inputs are assessed in relation to its use. On the other hand, a technique to estimate the temperature increase due to post-injection pulses oxidation is also presented. Both DOC and SCR models are proposed in order to estimate the effect of ageing on emissions, in which an ageing factor is modelled as a tunable parameter that allows varying from new to aged states. On the one hand, a 0D lumped model is developed for DOC in order to estimate the HC and CO species slip, which is validated in a WLTC and is then used for simulation. On the other hand, a 1D and a 0D models are developed for SCR, which are then used to feed the diagnostics strategy and for simulation. Finally, diagnostics strategies are presented for total failure or removal of DOC, as well as for efficiency estimation of DOC and SCR. On the one hand, the former strategy is separated into passive and active diagnostics, in which post-injections are used in active diagnostics in order to excite the system and confirm a total failure, in case. Then, the DOC efficiency estimation is done by means of an indirect technique in which the light-off temperature is detected and an emissions increase is related by means of the DOC ageing model. On the other hand, an observer to estimate the SCR ageing state is developed, which is based on an extended Kalman filter. However, in order to avoid associating low SCR efficiency to ageing, an indicator of the injected urea quality is developed to run in parallel.Mora Pérez, J. (2018). Control-oriented modelling and diagnostics of diesel after-treatment catalysts [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115937TESI

Experimental Study of the Urea-Water Solution Injection Process

[ES] La industria y la comunidad investigadora están trabajando para desarrollar herramientas y tecnologías que contribuyan a la reducción de emisiones contaminantes. Uno de los sectores afectados por la normativa anticontaminación es el transporte. Nuevas tecnologías están evolucionando, especialmente componentes de los sistemas de inyección, diseño de cámaras de combustión, elementos de postratamiento, la hibridación, entre otros. Los sistemas de reducción catalítica selectiva (SCR) han sido una de las claves para alcanzar los objetivos de las normativas de emisiones, especialmente de Óxidos Nitrosos (NO). La tecnología SCR se emplea para eliminar los NO presentes en los gases de escape de un motor. El proceso de inyección de la solución de urea-agua (UWS) determina las condiciones iniciales para la mezcla y evaporación del fluido en el sistema de reducción catalítica selectiva. Para un correcto funcionamiento, el inyector UWS debe dosificar una cantidad adecuada de líquido en el tubo de escape para evitar la formación de depósitos y garantizar la eficiencia del post-tratamiento. Esta tarea requiere la caracterización hidráulica del inyector y de la evolución del spray. El objetivo de esta tesis es la comprensión de los procesos de inyección de solución urea-agua en condiciones de funcionamiento realistas, similares a las que se encuentran en un tubo de escape de motor. Para ello, este trabajo se centra en el desarrollo de nuevas instalaciones experimentales que permitan realizar la caracterización hidráulica combinando medidas de flujo de cantidad de movimiento y masa inyectada. Posteriormente, el chorro de UWS se visualiza aplicando técnicas ópticas a varios niveles de temperatura y flujo másico de aire, en un banco de pruebas diseñado para este propósito. En cuanto a la caracterización hidráulica del inyector de UWS, el método se basa en medir el flujo de cantidad de movimiento para comprender la influencia de diferentes variables como el fluido inyectado, la presión de inyección, entre otros. Las medidas se realizaron utilizando una instalación experimental desarrollada en CMT-Motores Térmicos para la determinación del flujo de cantidad de movimiento, la cual fue modificada para cumplir con los requisitos de operación de estos inyectores. Además, la masa inyectada se obtiene experimentalmente para las mismas condiciones de funcionamiento. La metodología propuesta permitió calcular el flujo másico de estos atomizadores de baja presión, así como el coeficiente de descarga, que son datos útiles para futuras actividades de modelado. Se diseñó una instalación experimental para estudiar la atomización del fluido UWS en condiciones similares a las del tubo de escape del motor. La evolución del spray se caracterizó desde el punto de vista macroscópico, desarrollando una metodología para la determinación de la penetración y del ángulo del chorro. El método se basa en la configuración óptica conocida como diffused-back-light en una configuración de campo lejano. La penetración del spray se dividió en dos zonas: el inicio del chorro y el cuerpo principal. Se observó que la parte inicial del spray inyectado no se ve particularmente afectada por la presión de inyección sino más bien por la temperatura de la camisa de enfriamiento del inyector. El proceso de atomización se investigó mediante la misma técnica de diagnóstico óptico, diffused-back-lighting, acoplado a una lente microscópica especial. Se cuantificó la distribución del diámetro de las gotas y la velocidad de las gotas (en los componentes axial y tangencial) del chorro, en diferentes niveles de presión de inyección y flujo de aire. Se empleó una cámara de alta velocidad para capturar las imágenes de la fase líquida, comparando las gotas de líquido atomizado en tres regiones diferentes del chorro. Como resultado de este estudio, se puede observar que una mayor presión de inyección produce más gotas con diámetros menores favoreciendo el proceso de atomización.[CA] Noves tecnologies estan evolucionant, especialment components dels sistemes d'injecció, disseny de cambres de combustió, elements de posttractament, la hibridació, entre altres. Els sistemes de reducció catalítica selectiva (SCR) han sigut una de les claus per a aconseguir els objectius de les normatives d'emissions, especialment d'Òxids Nitrosos (NO). La tecnologia SCR s'empra per a eliminar els NO presents en els gasos de fuita d'un motor. El procés d'injecció de la solució d'urea aigua (UWS) determina les condicions inicials per a la mescla i evaporació del fluid en el sistema de reducció catalítica selectiva. Per a un correcte funcionament, l'injector UWS ha de dosar una quantitat adequada de líquid en el tub d'escapament per a evitar la formació de depòsits i garantir l'eficiència del post-tractament. Aquesta tasca requereix la caracterització hidràulica de l'injector i de l'evolució de l'esprai. L'objectiu d'aquesta tesi és la comprensió dels processos d'injecció de solució urea-aigua en condicions de funcionament realistes, similars a les que es troben en un tub d'escapament de motor. Per a això, aquest treball se centra en el desenvolupament de noves instal·lacions experimentals que permeten realitzar la caracterització hidràulica combinant mesures de flux de quantitat de moviment i massa injectada. Posteriorment, el doll de UWS es visualitza aplicant tècniques òptiques a diversos nivells de temperatura i flux màssic d'aire, en un banc de proves dissenyat per a aquest propòsit. Quant a la caracterització hidràulica de l'injector de UWS, el mètode es basa a mesurar el flux de quantitat de moviment per a comprendre la influencia de diferents variables com el fluid injectat, la pressió d'injecció, la contrapressió i la temperatura del sistema sobre les característiques del flux. Les mesures es van realitzar utilitzant una instal·lació experimental desenvolupada en CMT-Motores Térmicos per a la determinació del flux de quantitat de moviment, la qual va ser modificada per a complir amb els requisits d'operació d'aquests injectors. A més, la massa injectada s'obté experimentalment per a les mateixes condicions de funcionament. La metodologia proposada va permetre calcular el flux màssic d'aquests atomitzadors de baixa pressió, així com el coeficient de descàrrega, que són dades útils per a futures activitats de modelatge. Es va dissenyar una instal·lació experimental per a estudiar l'atomització del fluid UWS en condicions similars a les del tub d'escapament del motor. L'evolució de l'esprai es va caracteritzar des del punt de vista macroscòpic, desenvolupant una metodologia per a la determinació de la penetració i de l'angle del doll. El mètode es basa en la configuració òptica coneguda com diffusedback-light en una configuració de camp llunyà. La penetració de l'esprai es va dividir en dues zones: l'inici del doll i el cos principal. Es va observar que la part inicial de l'esprai injectat no es veu particularment afectada per la pressió d'injecció sinó més aviat per la temperatura de la camisa de refredament de l'injector. El procés d'atomització es va investigar mitjançant la mateixa tècnica de diagnòstic òptic, diffused-back-lighting, acoblat a una lent microscòpica especial. Es va quantificar la distribució del diàmetre de les gotes i la velocitat de les gotes (en els components axial i tangencial) del doll, en diferents nivells de pressió d'injecció i flux d'aire. Es va emprar una càmera d'alta velocitat per a capturar les imatges de la fase líquida, comparant les gotes de líquid atomitzat en tres regions diferents del doll: la primera prop de l'eixida de la tovera i les altres dues a la regió desenvolupada de l'esprai, una alineada amb l'eix de l'injector i l'altra en la perifèria del mateix. Com a resultat d'aquest estudi, es pot observar que una major pressió d'injecció produeix més gotes amb diàmetres menors afavorint el procés d'atomització.[EN] One of the sectors affected by the anti-pollution regulations is the transportation, since it is responsible for around 20% of the green house gases emissions production. New technologies are evolving, especially subsystems as fuel injection components, combustion design, after-treatment and hybridization. The SCR has been one of the most important to reach the emission targets, specially for Nitrous Oxides (NO). The SCR technology is employed in the elimination of the NO present in the exhaust gases of a combustion engine. The injection process of the urea-water solution (UWS) determines the initial conditions for the mixing and evaporation of the fluid in the selective catalytic reduction system. For a proper operation, the UWS injector must dose an adequate amount of liquid into the exhaust pipe to avoid deposit formation and to guarantee the SCR system efficiency. This task requires the knowledge of the performance of the injector and the evolution of the spray. The goal of this thesis is the comprehension of the urea-water solution injection processes under realistic operating conditions, similar to those of an engine exhaust pipe. To this end, this work focuses on the development of new experimental facilities that enable to perform the hydraulic characterization combining momentum flux measurements and injected mass. Afterwards, the UWS jet is visualized by applying optical techniques at various levels of air temperature and mass flow, in a novel test rig designed for this purpose. Regarding to the hydraulic performance of the UWS injector, the approach is based on measuring the spray momentum flux in order to understand the influence of different variables as injected mass, injection pressure, back pressure and cooling temperature on the flow characteristics. The measurements were carried out using an experimental facility developed at CMT-Motores Térmicos for the determination of spray momentum flux, where the configuration of the system was customized to fulfill the injector operation requirements. Also, the injected mass is obtained experimentally for the same operating conditions. The proposed methodology allowed to calculate the mass flow rate of this low pressure atomizers and the discharge coefficients, which are useful data for future computer modeling activities. A dedicated test facility was designed to study UWS spray under conditions that resemble those of the engine exhaust pipe. The liquid spray evolution is characterized from the macroscopic point of view, developing a methodology for the determination of the spray penetration and spreading angle. The method is based on the optical setup known as back-light in a far-field configuration. The spray penetration was divided in two zones, the spray burst and the body, where it was observed that the initial part of the injected spray is not particularly affected by the injection pressure but was rather influenced by the cooling temperature of the injector. Besides, the liquid atomization process of the UWS dosing system is investigated using optical diagnosis through back-light imaging coupled with a special lens. The droplet diameter distribution and the droplet velocity (in the injector axial and tangential components) of the liquid spray are quantified under different air flow and injection pressure levels. A high-speed camera was used for capturing the liquid phase images, comparing the atomized liquid drops in three different regions of the plume: the first one near the nozzle exit, and the other two in the developed region of the spray, one aligned with the injector axis and the other at the spray periphery. The results of this study demonstrated that injection pressure produces more droplets with smaller diameters favoring the atomization process.Moreno, AE. (2022). Experimental Study of the Urea-Water Solution Injection Process [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/181637TESI

DYNAMIC MODEL BASED STATE ESTIMATION IN A HEAVY DUTY DIESEL AFTERTREATMENT SYSTEM FOR ONBOARD DIAGNOSTICS AND CONTROLS

Estimating un-measurable states is an important component for onboard diagnostics (OBD) and control strategy development in diesel exhaust aftertreatment systems. This research focuses on the development of an Extended Kalman Filter (EKF) based state estimator for two of the main components in a diesel engine aftertreatment system: the Diesel Oxidation Catalyst (DOC) and the Selective Catalytic Reduction (SCR) catalyst. One of the key areas of interest is the performance of these estimators when the catalyzed particulate filter (CPF) is being actively regenerated. In this study, model reduction techniques were developed and used to develop reduced order models from the 1D models used to simulate the DOC and SCR. As a result of order reduction, the number of states in the estimator is reduced from 12 to 1 per element for the DOC and 12 to 2 per element for the SCR. The reduced order models were simulated on the experimental data and compared to the high fidelity model and the experimental data. The results show that the effect of eliminating the heat transfer and mass transfer coefficients are not significant on the performance of the reduced order models. This is shown by an insignificant change in the kinetic parameters between the reduced order and 1D model for simulating the experimental data. An EKF based estimator to estimate the internal states of the DOC and SCR was developed. The DOC and SCR estimators were simulated on the experimental data to show that the estimator provides improved estimation of states compared to a reduced order model. The results showed that using the temperature measurement at the DOC outlet improved the estimates of the CO , NO , NO2 and HC concentrations from the DOC. The SCR estimator was used to evaluate the effect of NH3 and NOX sensors on state estimation quality. Three sensor combinations of NOX sensor only, NH3 sensor only and both NOX and NH3 sensors were evaluated. The NOX only configuration had the worst performance, the NH3 sensor only configuration was in the middle and both the NOX and NH3 sensor combination provided the best performance

Investigation on Lean NOx Trap Regeneration Using Alcohol Fuels

The impacts of automotive pollutants on local air quality, human health, and climate change are a major concern worldwide. Therefore, the internal combustion engine (ICE) powered automobiles are expected to be able to meet the increasingly stringent emission and fuel efficiency standards. The reduction in oxides of nitrogen (NOx) in lean burn and diesel-fueled compression ignition (CI) engines is a major challenge. In this research, the use of alcohol fuel such as n-butanol and ethanol is studied in a CI engine. With the application of moderate exhaust gas recirculation (EGR), low engine-out NOx and soot emissions are achieved simultaneously. However, to meet NOx emission regulations, the use of only alternative fuels is not sufficient for a wide range of engine operating conditions. Therefore, lean NOx trap (LNT) after-treatment system is used for further NOx reduction using a reductant. In this study, an investigation on the performance of long breathing LNT is performed using ethanol, n-butanol, and diesel as reductants. The LNT regeneration experiments are conducted on a heated flow bench under simulated engine exhaust like conditions. Ethanol and n-butanol are found to be more effective compared to diesel as a reductant in terms of NOx conversion, ammonia (NH3) slip, nitrogen dioxide (N2O) slip, and hydrogen (H2) formation, during the LNT regeneration period at the tested conditions. The formation of NH3 and N2O during the LNT regeneration is not desired. Albeit, the NH3 generated during the LNT regeneration can be utilized to further reduce NOx using a selective catalytic reduction (SCR) convertor downstream of the LNT catalyst. In this study, the combined LNT-SCR tests are performed to investigate overall NOx reduction using n-butanol as a reductant

Microscopic Imaging Spray Diagnostics under High Temperature Conditions: Application to Urea–Water Sprays

The quantitative investigation of droplet laden turbulent flows at high temperature conditions is of great importance for numerous applications. In this study, an experiment was set up for investigation of evaporating urea-water sprays, which are relevant for the effective reduction of nitrogen oxide emissions of diesel engines using Selective Catalytic Reduction. A shadowgraphy setup is pushed to its limits in order to detect droplet diameters as small as 4µm and droplet velocities up to 250m/s. In addition, the operating conditions of the gaseous flow of up to 873K and 0.6MPa are an additional challenge. Due to the high temperature environment, image quality is prone to be compromised by schlieren effects and astigmatism phenomena. A water-cooled window and an astigmatism correction device are installed in order to correct these problems. The results to be presented include characteristics of the turbulent gas flow as well as detailed spray characteristics at different positions downstream of the atomizer. It is demonstrated that the velocity of the gas can be approximated by the velocity of the smallest detectable droplets with sufficient accuracy. Furthermore, the statistical analysis of velocity fluctuations provides data for predicting the turbulent dispersion of the droplets

Light off temperature based approach to determine diesel oxidation catalyst effectiveness level and the corresponding outlet NO and NO2 characteristics

According to the latest EPA emission regulations, the NOx (Nitrogen oxide compounds) emissions from heavy duty compression ignition engines need to see a dramatic reduction. The current technology used for this purpose is the selective catalytic reduction (SCR) system, which achieves NOx reduction of around 90% [9]. This involves urea injection which is influenced by the NO: NO2 ratio at the inlet to the SCR. Thus, the role of the DOC (Diesel Oxidation Catalyst) where most of the oxidation of the NOx compounds takes place, comes to fore. The focus is also on the effectiveness of the catalyst as it thermally ages. Therefore, the aim of this research project is to correlate the aging in the DOC with the light off temperature of the catalyst and subsequent variation in the NO and NO2 concentration at the outlet of the DOC. This shall be achieved through means of a model developed after extensive experimental procedures. Also, further exhaustive experiments to validate the model over multiple aging cycles of the catalyst shall be undertaken. ^ The DOC was subjected to 2 rigorous kinds of experiments aimed at determining the light off temperature shift as the catalyst aged and to determine the NO and NO2 concentrations at the DOC outlet as it aged. Exhaust stream compounds were measured using exhaust analyzers and DOC temperatures were determined using thermocouples installed inside the DOC and at its inlet and outlet. ^ The data thus obtained was then analyzed and 2 separate models were developed, one for the light off experiments, and the other for the NOx experiments. Aging procedures were carried out at an oven according to prescribed techniques and the DOC was subjected to similar experiments again. Analysis was carried out on the data. From the light off experiments and the model analysis, a clear positive shift in light off temperatures was observed from one aging level to another across the range of set points. It was also observed that even after subjecting the DOC to three thermal aging exercises, its conversion efficiency went up to 90%. Also, as the DOC aged, the NO concentration at the DOC outlet showed a downward trend which was observed across the spectrum of engine set points and aging levels. These experiments were repeated for consistency so that the models could be rendered more useful

Estimation of Entropy Generation in a SCR-DeNOx System with AdBlue Spray Dynamic Using Large Eddy Simulation

In this work, the entropy generation analysis is extended to the multi-phase fluid flow within a Large Eddy Simulation (LES) framework. The selected study case consists of a generic selective catalytic reduction (SCR) configuration in which the water/AdBlue is injected into a cross-flow of the internal combustion (IC) engine exhaust gas. The adopted numerical modules are first assessed by comparing with experimental data for film thickness in the case of AdBlue injection and then with H₂O mass fraction and temperature for water injection case. Subsequently, the impact of heat transfer, fluid flow, phase change, mixing and chemical reaction due to AdBlue injection on the entropy generation is assessed. Hence, the individual contributions of viscous and heat dissipation together with the species mixing, chemical reaction during the thermal decomposition of urea into NH₃ and dispersed phase are especially evaluated and analysed. In comparison to the shares of the viscous and mixing processes, the entropy generation is predominated by the heat, chemical and dispersed phase contributions. The influence of the operating parameters such as exhaust gas temperature, flow rate and AdBlue injection on entropy generation is discussed in details. Using a suitable measures, the irreversibility map and some necessary inferences are also provided

디젤 엔진에서 가상 질소산화물 센서에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2013. 8. 민경덕.thus, this model can be applied to engines and after-treatment systems as a useful tool to control the engine-out NO without the use of a NOx sensor. In addition to being a virtual NO sensor, the estimation model can be applied to 1-D simulations, such as GT-SUITE and AMESIM, and demonstrate improved NO estimation results as the model is able to predict the NO level as same standard as the 3-D CFD simulation. Then, a newly developed NO estimation model was implemented on the embedded system bypassed from a conventional engine control unit for real-time estimation of NO during steady-states and transient engine operations. The results of the model were compared to real-time measurement of engine-out NO of a conventional Diesel engine at representative steady state operating points which cover the entire NEDC region. Also, EGR rate and main injection timing were varied to verify the predictability of the model under various conditions. The results showed that the model predicts steady state results well with R2 value of 0.96 for 76 HP-EGR cases. In addition, to verify transient estimation of NO, the engine-out NO was measured by a fast NO analyzer and compared with the results of the model during simple ramp transition conditions. Additionally, the engine-out NO emissions measured by a fast NOx analyzer and the estimated NO emissions were compared during ECE-15 and EUDC cycles. Furthermore, to extend the NO model to a complete NOx estimation model, an empirical NO2 estimation model was proposed based on the experiments under steady-state conditions. The in-house EGR estimation model was also applied in the NOx estimation model for accurate cycle-by-cycle estimation and used as an input during transient engine operations. This systematic research on the development of a virtual NOx sensor contributes to real-time NOx monitoring for transient NOx control and after-treatment system control.however, there were several limiting factors, such as complexity of the model for a real-time application, the necessity of various calibration constants, fitting processes for empirical equations and the demand for training for numerical models. In this study, to overcome the limits of previous studies, a real-time nitric oxide estimation model was developed based on the in-cylinder pressure and on data available from the ECU. As computational fluid dynamics can describe the process of NO formation which is not directly obtainable from experiments on a physical basis, the NO formation model was developed based on both the analysis of CFD results as well as on a physical model. Furthermore, the in-cylinder pressure is used to predict the amount of NO formation under various engine operating conditions as the pressure reflects the change in the combustion characteristics. The estimation model consisted of a simple calculation processTo meet the stringent emission regulations on diesel engines, engine-out emissions have been lowered by adapting new combustion concepts such as low-temperature combustion and after-treatment systems have also been used to reduce tailpipe emissions. To optimize the control of both in-cylinder combustion and the efficiency of an after treatment system to reduce NOx, the amount of real-time NOx emissions should be determined. Thus, many studies on a virtual NOx sensor using physical and phenomenological models have been reported. Previous studies have shown reliable NOx estimationstherefore, the model could predict the cycle-by-cycle NO in real-time. The validation results show that the model presented can predict engine-out NO well디젤 엔진에 대한 배기 규제가 강화됨에 따라 새로운 연소 기법을 이용하여 엔진 자체의 배출물을 줄이거나 후처리 장치 등을 이용하여 최종 배출물을 줄이는 등의 노력이 이루어지고 있다. 특히, 질소 산화물 (NOx) 감소를 위한 실린더 내 연소제어, 동시에 후처리 장치의 효율을 최적화하기 위해서는 실시간으로 배출되는NOx 배출량에 대한 정보가 필요하다. 따라서 물리적, 현상학적 모델을 사용한 가상 NOx 센서에 대한 많은 연구가 보고되고 있다. 기존 연구들은 비교적 정확하게 NOx 배출량을 예측하고 있지만 실시간 애플리케이션으로써 활용하기에는 현재 차량에 장착 중인 엔진 제어 장치의 계산 능력에 비해 모델이 너무 복잡하거나, 경험식을 피팅하기 위해 많은 보정 상수가 사용되고, 통계적 수학적 모델 등의 경우에는 많은 트레이닝이 필요한 등의 여러 가지 제한 요인이 있었다. 본 연구에서는 선행 연구의 한계를 극복하기 위해 실시간 실린더 압력과 ECU에서 얻을 수 있는 데이터에 기반한 실시간 NOx 예측 모델을 개발하였다. CFD 는 실험 과정에서 직접 얻을 수 없는 NO의 형성 과정을 자세히 설명 할 수 있기 때문에, 물리적 분석과 함께 CFD 결과의 분석을 통해 모델을 개발하였다. 또한 실린더 내 압력이 엔진 연소특성의 변화를 잘 반영하기 때문에, 다양한 엔진의 작동 조건에서 NO의 배출량을 예측할 수 있도록 연소압력이 사용되었다. 개발된 NO 예측 모델은 간단한 계산 과정으로 이루어졌기 때문에 실시간으로 사이클 별 NO를 예측할 수 있었다. 검증 결과는 제안된 모델이 엔진에서 배출되는 NO 를 잘 예측하는 것을 보여주었고, 따라서 개발된 모델이 NO센서 대용으로써 엔진과 후처리 장치의 제어를 위한 유용한 도구로써 시스템에 적용될 수 있음을 확인하였다. 가상 NO 센서로 사용될 수 있는 것 이외에도, 개발된 NO 예측 모델은 GT-SUITE와 AMESim 과 같은 1 차원 시뮬레이션에 적용되어CFD 모델과 동일한 수준으로 NO 수준을 예측할 수 있는 가능성을 가지고 있다. 이후, 개발 된 NO예측 모델은 정상 상태와 과도 엔진 작동 상태에서 NO의 실시간 추정을 위한 기존의 엔진 제어 장치를 우회한 임베디드 시스템에 구현되었다. 모델의 결과는 NEDC 전 영역을 커버하는 대표적인 정상 상태의 동작 점에서 엔진에서 배출되는 실시간 NO 측정값과 비교되었다. 또한 다양한 조건에서 모델의 예측성을 검증하기 위해 배기가스 재순환율과 주분사시기를 베이스 조건 대비 변화시켰다. 정상상태 검증 결과 HP-EGR 76 케이스에서 실험 결과와 R2=0.96 의 높은 예측 정도를 확인할 수 있었다. 또한 과도상태에서의 NO 예측 정도를 검증하기 위해 고속 NOx 분석기를 사용하여 엔진 속도, 부하 변경 등의 간단한 램프 조건에서 모델 결과와 비교하였다. 또한 유럽의 배출가스 측정 모드인 ECE-15 와 EUDC 사이클에서 고속 NOx 분석기 결과를 사용하여 모델을 검증하였다. 추가적으로, NO 만이 아닌 전체 NOx를 예측할 수 있도록 정상상태 실험 결과 기반의 경험식을 사용한 NO2 예측 모델을 제안하였다. 실시간 NOx 예측 모델에 정확한 과도상태 EGR 값을 제공하기 위해 실험실에서 개발된 EGR 예측 모델 또한 적용 되었다.Acknowledgements iii Abstract iv Contents vii List of Tables x List of Figures xi Acronym xiv Chapter 1. Introduction 1 1.1 Background and Motivation 1 1.1.1 Nitrogen oxides formation 1 1.1.2 The effect of nitrogen oxides on health and environment 2 1.1.3 Nitrogen oxides emission from diesel engines 3 1.1.4 Emission regulations for NOx from diesel engines 4 1.1.5 NOx reduction technologies and challenges in diesel engines 6 1.2 Literature Review on virtual NOx sensors 23 1.3 Objectives 28 Chapter 2. Development of NO estimation model with in-cylinder pressure measurement 29 2.1 Computational model and validation 30 2.1.1 Computational model for the CFD simulation 30 2.1.2 Validation of the computational models 30 2.2 NO estimation model 36 2.2.1 Basic assumptions for the NO estimation model 36 2.2.2 Physical model for NO formation 36 2.2.3 Determination of the duration of NO formation 39 2.2.4 Determination of averaged NO formation rate 39 2.2.5 Calculation of the maximum NO formation rate 40 2.2.6 Summary of the NO estimation model 43 2.3 Model validation with CFD results 53 Chapter 3. Experimental Apparatus 55 3.1 Engine setup 55 3.2 In-cylinder pressure measurement 61 3.3 EGR measurement 63 3.4 NO and NOx measurement 65 3.5 Real-time calculation of NO 68 Chapter 4. The effect of EGR rate on NO estimation model 72 4.1 Sensitivity analysis 72 4.2 Cylinder-to-cylinder measurement of EGR 74 4.3 EGR estimation model 76 Chapter 5. NO estimation during steady state and simple ramp transition using a real-time virtual NO sensor 82 5.1 Experimental cases 83 5.1.1 Steady state cases 83 5.1.2 Simple ramp transition cases 83 5.2 Experimental results 85 5.2.1 Steady state results 85 5.2.2 Simple ramp transition results 85 5.2.2.1 EGR rate change 85 5.2.2.2 Engine speed change 86 5.2.2.3 Simultaneous engine speed and load change 86 5.2.3 Source of error 86 5.2.4 Improvement of model accuracy using modified R and k 87 5.2.5 Cycle-by-cycle & cylinder-by-cylinder NO estimation 89 Chapter 6. NOx estimation during transient state using a real-time virtual NOx sensor 99 6.1 Extend to NOx (NO2) estimation model 100 6.2 Experimental conditions 105 6.3 Results and discussions 107 Chapter 7. Conclusion 113Docto

Advances and challenges of ammonia delivery by urea-water sprays in SCR systems

Over the past decades, selective catalytic reduction (SCR) using aqueous urea sprays as ammonia precursor has become the prevalent technique for NO$_{X}$ emission control in mobile applications. Preparation of ammonia from urea water sprays still represents a challenge in aftertreatment engineering as complex interactions of multi-phase physics and chemical reactions have to be handled. Increasingly stringent emission legislations and the ongoing development of fuel-efficient engines and close-coupled aftertreatment systems raise high demands to SCR systems. Due to highly transient conditions and short mixing lengths, incomplete spray evaporation can result in liquid/wall contact and formation of solid urea deposits lowering ammonia selectivity and homogeneity. This article reviews the ongoing development of SCR systems with focus on the efficient evaporation and decomposition of the injected spray for a homogeneous ammonia distribution in front of the SCR catalyst. Critical aspects of spray evaporation and impingement, liquid film and deposit formation are pointed out and potentials for system optimization are discussed