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

Development of an Ammonia Reduction After-Treatment Systems for Stoichiometric Natural Gas Engines

Three-way catalyst (TWC) equipped stoichiometric natural gas vehicles have proven to be an effective alternative fuel strategy that shows significant low NOx emissions characteristics. However, recent studies have shown the TWC activity to contribute to elevated levels of tailpipe ammonia (NH 3) emissions. Although a non-regulated pollutant, ammonia is a potent pre-cursor to ambient secondary PM formation. Ammonia is an inevitable byproduct of fuel rich operation that results in lowest NOx slip through the TWC after-treatment system.;The main objective of the study is to develop a passive Ammonia Reduction Catalyst (passive-ARC) based NH3 reduction strategy that results in an overall reduction of ammonia as well as NOx emissions. The study investigated the characteristics of Fe-based and Cu-based zeolites SCR catalysts in storage and desorption of ammonia at high exhaust temperature conditions, that are typical of stoichiometric natural gas engines. Continuous measurements of NOx and NH3 before and after the SCR systems were conducted using a Fourier Transform Infrared Spectrometry (FTIR) gas analyzer. Results of the investigation showed that both, the Fe- and Cu zeolite SCRs adsorbed above 90% of TWC generated NH3 emissions below 350--375 °C SCR temperatures. Desorption or slipping of NH3 was observed at exhaust gas temperatures exceeding 400 °C. In terms of NOx conversions, Fe-zeolite showed efficiency between 50--80% above temperatures of 300--350 °C while Cu-zeolite performed well at lower SCR temperature from 250 °C and above with a conversion efficiency of greater than 50%.;In order to efficiently reduce both NOx and NH3 simultaneously over longer durations it was found that an engine-based air fuel ratio operation strategy for the passive-ARC system must be developed. To this extent, the study extended its objectives to develop an engine-based control strategy that results in stoichiometric ammonia production operation followed by brief lean operation to regenerate the saturated ammonia reduction catalyst using high NOx slip through TWC. The study presents comprehensive results of ammonia storage characteristics of SCRs pertaining to stoichiometric natural gas engine exhaust as well as an advanced engine control strategy approach to simultaneously reduce both NOx and NH3 using an alternating air -fuel ratio approach

On-Board Sensor-Based NO x Emissions from Heavy-Duty Diesel Vehicles

Real-world nitrogen oxides (NOx) emissions were estimated using on-board sensor readings from 72 heavy-duty diesel vehicles (HDDVs) equipped with a Selective Catalytic Reduction (SCR) system in California. The results showed that there were large differences between in-use and certification NOx emissions, with 12 HDDVs emitting more than three times the standard during hot-running and idling operations in the real world. The overall NOx conversion efficiencies of the SCR system on many vehicles were well below the 90% threshold that is expected for an efficient SCR system, even when the SCR system was above the optimum operating temperature threshold of 250 °C. This could potentially be associated with SCR catalyst deterioration on some engines. The Not-to-Exceed (NTE) requirements currently used by the heavy-duty in-use compliance program were evaluated using on-board NOx sensor data. Valid NTE events covered only 4.2–16.4% of the engine operation and 6.6–34.6% of the estimated NOx emissions. This work shows that low cost on-board NOx sensors are a convenient tool to monitor in-use NOx emissions in real-time, evaluate the SCR system performance, and identify vehicle operating modes with high NOx emissions. This information can inform certification and compliance programs to ensure low in-use NOx emissions

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

The state of the art in selective catalytic reduction control

Selective Catalytic Reduction (SCR) is a leading after treatment technology for the removal of nitrogen oxide (NOx) from exhaust gases (DeNOx). It presents an interesting control challenge, especially at high conversion, because both reagents (NOx and ammonia) are toxic, and therefore an excess of either is highly undesirable. Numerous system layouts and control methods have been developed for SCR systems, driven by the need to meet future emission standards. This paper summarizes the current state-of-the-art control methods for the SCR aftertreatment systems, and provides a structured and comprehensive overview of the research on SCR control. The existing control techniques fall into three main categories: traditional SCR control methods, model-based SCR control methods, and advanced SCR control methods. For each category, the basic control technique is defined. Further techniques in the same category are then explained and appreciated for their relative advantages and disadvantages. Thus this paper presents a snapshot of the current state of the art for the research area of SCR control. This is a very active field, and it is hoped that by providing a better understanding of the different control strategies already developed for SCR control, future areas of interest will be identified and developed with the ultimate aim of satisfying the increasingly stringent emissions legislation. Copyright © 2014 SAE International

DEVELOPMENT OF A HIGH-FIDELITY MODEL AND KALMAN FILTER BASED STATE ESTIMATOR FOR SIMULATION AND CONTROL OF NOX REDUCTION PERFORMANCE OF A SCR CATALYST ON A DPF

Reduction of emissions and improving the fuel consumption are two prime research areas in Diesel engine development. The present after-treatment systems being used for emissions control include diesel oxidation catalyst (DOC) for NO, HC and CO oxidation along with catalyzed particulate filters for PM (particulate matter) and selective catalytic reduction (SCR) for controlling NOx emissions. Recently an after-treatment system called SCR catalyst on a DPF capable of simultaneously reducing both NOx and PM emissions has been developed in order to reduce the overall size of the after-treatment system. The goal of this proposed research is to create a state estimator that is capable of estimating the internal states of temperature distribution, PM distribution, NH3 storage faction as well as pressure drop across the filter and outlet concentration of NO, NO2 and NH3 for different operating conditions. This would help in achieving an optimal urea dosing strategy during NOx reduction as well as an optimum fuel dosing strategy during active regeneration for the SCR catalyst on a DPF. The motivation for this research comes from the desire to quantify the interaction of SCR reactions and PM oxidation in the SCR catalyst on a DPF and to use the mathematical model created in the process to develop a state estimator that can provide optimal control and onboard diagnostics of combined SCR catalyst on a DPF devices. In the initial phase of the research a high-fidelity SCR-F model is being developed in MATLAB/Simulink which is capable of predicting the filtration efficiency, temperature distribution, PM distribution, pressure drop across the filter and outlet concentrations of NO, NO2 and NH3. This model will be calibrated using experimental data collected on a Cummins 2013 ISB SCRF®. After the validation of the SCR-F model, the high-fidelity SCR-F model developed will be used with an existing 1D SCR model to perform NOx reduction studies on a system consisting of SCRF® + SCR using experimental data. This step will be followed by development of a reduced order SCR-F model using a coarser mesh (e.g. 5x5 vs 10x10) and simplified governing equations which will also be used as the mathematical model for the state estimator. SCR-F state estimator will be developed to accurately predict the internal states of NH3 coverage fraction, temperature distribution, PM distribution and pressure drop across the SCR catalyst on the DPF. The estimator will be validated using experimental data

Model-Based Ammonia Slip Observation for SCR Control and Diagnosis

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] The control of selective catalytic reduction (SCR) systems, via NH3 injection, requires from a precise estimation of the SCR load in order to ensure NOx reduction by minimizing ammonia slip. This article aims to resolve the cross-sensitivity of current NOx sensors at the outlet of the SCR, by providing the control unit with an estimation of NOx and ammonia slip. The problem of discerning between NOx and ammonia slip is solved by identifying an intermediate variable representing the SCR load. The SCR load is estimated by combining the mass conservation principle between the inlet and the outlet of the SCR and a NOx reduction model, via an extended Kalman filter. Current models and observers have several limitations to represent the real behavior of the SCR along all the operating conditions; on one hand, when relying on the mass conservation, small errors at models are integrated, leading to important bias on the SCR load and on the other hand, the dynamics at the SCRmust be preciselymodelled for an adequate adaptation of the model. The main focus of the developed algorithm is to use a simplified model which might be used for ammonia slip estimation, being aware of current limitations of SCR models in real operation. Experimental results in a EURO 6 compression ignited (CI) engine show the potential of such observation in transient conditions and an adequate correlation with external ammonia measurements provided by additional sensors available on the test bench.This work was supported by the Spanish Ministerio de Economia, Industria y Competitividad under project TRA2016-78717-R.Guardiola, C.; Pla Moreno, B.; Bares-Moreno, P.; Mora, J. (2020). Model-Based Ammonia Slip Observation for SCR Control and Diagnosis. IEEE/ASME Transactions on Mechatronics. 25(3):1346-1353. https://doi.org/10.1109/TMECH.2020.2974341S1346135325

Ageing on commercial automotive catalysts, a structure reactivity study

Increasingly stringed regulations for diesel engine emissions have a significant impact on the required efficiency of DOC. Lowered DOC oxidation efficiency due to thermal aging effects influences the efficiency of the exhaust aftertreatment systems downstream of the DOC. In this work carried out in the Jean Le Rond d’Alembert Institute the effect of hydrothermal aging on the reactivity and structure of a commercial DOC was investigated. The characterization of the catalytic performance was carried out on a synthetic gas bench using carrots catalyst under conditions close to the realistic conditions i.e. using a synthetic gas mixture, representative of the exhaust gases from diesel engines. Different structural characterization techniques were performed: textural and morphological proprieties were analyzed by BET and TEM, the characterization of the presented crystallographic phases was performed by DRX and the determination of the number of reducible species was possible by TPR. TEM results shown, an increase of the metal particle size with the aging caused by the agglomeration of metal particles, revealing the presence of metal sintering. DRX results also suggest the presence of support sintering. Furthermore, DRX and BET results unexpectedly reveal that the most drastic aging conditions used actually activated the catalyst surface. As expected, the aging affected negatively the catalyst performance on the oxidation of methane and CO, however an improvement of the NO oxidation performance with the aging was observed. Nevertheless, for the aging conditions used, catalytic activity results show that the influence of aging in DOC performance was not significant, and therefore, more drastic aging conditions must be used

No And No2 Modeling For Diesel Oxidation Catalyst At Different Thermal Aging Levels

Different DOC modeling methods are analyzed and compared. Detailed reaction mechanisms of DOC reaction are discussed and a new NO and NO2 modeling technique is proposed. Experiments are conducted measuring downstream DOC NO and NOx . DOC out NO and NO2 concentrations are modeled as a function of DOC temperature. A robust model is built such that with the input of real time NOx and DOC temperature information, DOC-out NO and NO2 concentrations can be precisely predicted. As is true with many catalysts, the DOC thermally ages as it operates, which reduces the thermal effectiveness level of the catalyst. This directly reduces the amount of HC, CO and NO it is able to oxidize, increasing the DOC-out NO percentage. In this thesis, aged DOC model is recalibrated in modeling DOC-out NO and NO 2concentrations. Correlations between HC light-off temperature shift and DOC-out NO and NO2 concentration shift are discovered and analyzed. A preliminary model of NO and NO2 concentrations as a function of HC light-off temperature and DOC temperature is built and validated against actual data