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

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

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

Development of an Activity-based Windowing Approach to Evaluate Real-World NOx Emissions from Modern Medium and Heavy-Duty Diesel Trucks

The introduction of in-use emissions regulations by the United States Environmental Protection Agency (U.S.EPA) requires medium-duty (MD) and heavy-duty (HD) engine manufacturers to demonstrate emissions compliance during in-fleet operation. In the United States (U.S.), the Not-to-Exceed (NTE) method is used to evaluate real-world emissions compliance from on-highway MD and HD trucks. Regulatory agencies, engine manufacturers and research entities have identified that the NTE method incorporates numerous exclusions and evaluates emissions compliance only under selective operating conditions that are favorable for the selective catalytic reduction (SCR) system to reduce oxides of nitrogen (NOx) emissions efficiently. Such operation is typically encountered only by vocations that experience sustained highway driving operation, which is not entirely representative of actual highly diverse real-world operation experienced by the engine/aftertreatment system. Evaluation of real-world driving emissions (RDE) plays a critical role in monitoring and ensuring the performance of emissions control systems. Portable emissions measurement system (PEMS) serves as a robust tool to assess emissions levels during real-world operation. However, utilization of PEMS for large-scale deployment is time-consuming, labor-intensive, and expensive. As a vision of potential elements for a next-tier of in-use NOx monitoring systems, there is an actively growing research and regulatory interest to evaluate the feasibility of using existing on-boardNOx sensors for HD on-board NOx compliance. However, research studies have highlighted that NOx sensor measurements are also subjected to cross-sensitivity from other species in the exhaust stream. The global objective of the study was to develop an alternative approach that attempts to bridge the gap between current in-use certification procedures and highly diverse real-world operation for evaluation of in-use NOx emissions. The study outlines a vehicle activity-based windowing (ABW) approach that provides an event-based bifurcation of the engine and aftertreatment operational conditions. The thermal boundary bin exhibits bin boundary conditions favorable for SCR catalytic activity. Results of the study show that the 90th percentile of ABW bin-1a bsNOx emissions (i.e., on average of the individual vehicle datasets) was below the current NTE NOx limit. In terms of data usage, the ABW approach provides a unique opportunity of utilizing ~95% and 83% (Phase-1 and Phase-2) of test activity acquired from valid ABW trips. In comparison, the current NTE approach evaluated over a diverse in-use test activity collected as part of the HDIUT program exhibits utilization of only a sparse amount (i.e., less than 10%) of in-use test activity for emissions compliance evaluation. In light of using existing on-board NOx sensors for the screening of in-fleet activity, the study evaluates measurement thresholds of NOx sensors under real-world operating conditions. In the absence of a substantial amount of ammonia (NH3), it was observed that the average measurement deviation was within ±10% for NOx concentration levels between 10 ppm and 200 ppm. However, statistical principal component analysis (PCA) indicates a hypothetic relation between NOx sensor measurements and rapid changes in water (H2O) concentrations

Optimization of a retrofit urea-SCR system

Oxides of nitrogen (NOx) emissions from legacy diesel engines are often many times over currently mandated standards, contributing significantly to degradation of air quality and negative environmental impact. A retrofit urea-SCR (selective catalytic reduction) aftertreatment system offers a viable solution for reducing NOx emissions from older diesel engines. A stand-alone retrofit urea-SCR aftertreatment system was previously developed by West Virignia University (WVU) engineers, implementing a pre-SCR NOx sensor, open-loop feed-forward control, and stoichiometric NOx reduction logic. During experimental testing at WVU, the urea-SCR system demonstrated NOx reductions of 2% to 53%, depending on the test cycle. In order to optimize the system, this dissertation considered additional control configurations. To evaluate the emissions performance of each control strategy, a neural network heavy-duty diesel engine model was developed along with separate four-state chemical and thermal SCR catalyst models. Each model component was validated with experimental data recorded from the WVU Engine and Emissions Research Laboratory (EERL). The following control configurations were considered: (1) pre-SCR NOx sensor, open-loop feed-forward control, (2) post-SCR NOx sensor, closed-loop feed-back proportional-derivative (PD) control, (3) pre- and post-SCR NOx sensors, closed-loop feed-back proportional-integral-derivative (PID) control, (4) pre-SCR NOx sensor, model-based control.;The evaluation process considered differences between a highly instrumented and highly engineered system. Emissions performance was evaluated over two transient on-road test cycles (FTP, ACES HHDDT_S) and one steady-state marine test cycle (ICOMIA E5), implying broad applicability of the aftertreatment system. The evaluation process was characterized by overall NOx reduction percentage, maximum ammonia slip in parts per million (ppm), and average ammonia slip (ppm). The complexity of the sensor configuration and control strategy calibration were evaluated, as well as how adaptable a given configuration was to variations in engine behavior and sensor measurement accuracy. Finally, total cost was compared between each control configuration, considering system capital, maintenance, operation, control strategy engineering, and system calibration. A final cost per ton of NOx reduced was presented for each control configuration, assuming a six year operational cycle in marine and on-road applications. Based on the collective emissions, complexity, and cost analyses, a configuration implementing pre- and post-SCR NOx sensors and closed-loop PID control was identified as optimal for a retrofit application. Model results demonstrated NOx reductions of 44%, 53%, and 47% over FTP, ICOMIA, and ACES High-Speed Cruise (HHDDT_S) cycles, respectively. The total annual NOx reduction cost was {dollar}8,800 per ton of NOx reduced for an on-road application and {dollar}3,651 per ton of NOx reduced for a marine application

A SCR Model based on Reactor and Engine Experimental Studies for a Cu-zeolite Catalyst

A NOx reduction efficiency higher than 95% with NH3 slip less than 30 ppm is desirable for heavy-duty diesel (HDD) engines using selective catalytic reduction (SCR) systems to meet the US EPA 2010 NOx standard and the 2014-2018 fuel consumption regulation. The SCR performance needs to be improved through experimental and modeling studies. In this research, a high fidelity global kinetic 1-dimensional 2-site SCR model with mass transfer, heat transfer and global reaction mechanisms was developed for a Cu-zeolite catalyst. The model simulates the SCR performance for the engine exhaust conditions with NH3 maldistribution and aging effects, and the details are presented. SCR experimental data were collected for the model development, calibration and validation from a reactor at Oak Ridge National Laboratory (ORNL) and an engine experimental setup at Michigan Technological University (MTU) with a Cummins 2010 ISB engine. The model was calibrated separately to the reactor and engine data. The experimental setup, test procedures including a surrogate HD-FTP cycle developed for transient studies and the model calibration process are described. Differences in the model parameters were determined between the calibrations developed from the reactor and the engine data. It was determined that the SCR inlet NH3 maldistribution is one of the reasons causing the differences. The model calibrated to the engine data served as a basis for developing a reduced order SCR estimator model. The effect of the SCR inlet NO2/NOx ratio on the SCR performance was studied through simulations using the surrogate HD-FTP cycle. The cumulative outlet NOx and the overall NOx conversion efficiency of the cycle are highest with a NO2/NOx ratio of 0.5. The outlet NH3 is lowest for the NO2/NOx ratio greater than 0.6. A combined engine experimental and simulation study was performed to quantify the NH3 maldistribution at the SCR inlet and its effects on the SCR performance and kinetics. The uniformity index (UI) of the SCR inlet NH3 and NH3/NOx ratio (ANR) was determined to be below 0.8 for the production system. The UI was improved to 0.9 after installation of a swirl mixer into the SCR inlet cone. A multi-channel model was developed to simulate the maldistribution effects. The results showed that reducing the UI of the inlet ANR from 1.0 to 0.7 caused a 5-10% decrease in NOx reduction efficiency and 10-20 ppm increase in the NH3 slip. The simulations of the steady-state engine data with the multi-channel model showed that the NH3 maldistribution is a factor causing the differences in the calibrations developed from the engine and the reactor data. The Reactor experiments were performed at ORNL using a Spaci-IR technique to study the thermal aging effects. The test results showed that the thermal aging (at 800°C for 16 hours) caused a 30% reduction in the NH3 stored on the catalyst under NH3 saturation conditions and different axial concentration profiles under SCR reaction conditions. The kinetics analysis showed that the thermal aging caused a reduction in total NH3 storage capacity (94.6 compared to 138 gmol/m3), different NH3 adsorption/desorption properties and a decrease in activation energy and the pre-exponential factor for NH3 oxidation, standard and fast SCR reactions. Both reduction in the storage capability and the change in kinetics of the major reactions contributed to the change in the axial storage and concentration profiles observed from the experiments

Development of an Emissions Monitoring Methodology Using On-Board NOx Sensors and Revision to Current In-Use Emissions Regulatory Protocols

Measurement of in-use emissions from heavy-duty (HD) vehicles under real-world operation has been widely performed by using portable emissions measurement system (PEMS). PEMS serve as an accurate and lightweight emissions measurement system to evaluate in-use emissions from HD vehicles. However, emissions measurement using PEMS instrumentation can be time consuming and labor intensive. Advantage of utilizing already existing on-board sensors such that they can potentially provide an alternative measurement methodology to the PEMS. A successful implementation of an on-board NOx sensor-based methodology for assessing in-use NOx emissions will allow for a cost-effective and simplified approach to monitor real-world, NOx emission rates. The technology of on-board NOx sensors is in its initial stages to be used to monitor in-use NOx emissions and the ability of the sensor to measure NO x concentration during selective catalytic reduction (SCR) activity period is of concern. Furthermore, the on-board NOx sensors are also subject to various cross-sensitivity and durability concerns.;The primary objective of this dissertation is to compare the on-board NOx sensor response and accuracy against laboratory grade instrumentation that include PEMS using Non-Dispersive Ultra-Violent (NDUV) and Fourier transform infrared spectroscopy (FTIR) measurement to assess the measurement thresholds of on-board NOx sensors. The study compares the cross-sensitivity of the NOx sensors to ammonia (NH3) concentration in the exhaust. NH3 slip from SCR is believed to interfere with NO x measurements using Zirconium oxide sensors and this study will discuss NH3-NOx cross sensitivity on on-board NO x sensors during real-world HD vehicle activity. Results from this study will compare on-board NOx sensor measurement capabilities and they will be assessed at different power levels related to different SCR conversion efficiency and different NOx concentration levels related to measurements obtained from a laboratory grade emissions measurement system FTIR. The secondary objective of this work is to explore and modify boundary conditions for the Not-to-exceed (NTE) and (Work-based window) WBW regulatory protocols due to deficiencies of current protocols in appropriately characterizing regulated emissions especially during the port drayage and urban activity, characterized by low-load engine operation. Thus, new revised regulatory protocols for a wide range of driving activity are needed for an accurate characterization of in-use NOx emissions

An on-engine method for dynamic characterisation of NOx concentration sensors

An on-engine method for dynamic characterisation of automotive NOx concentration sensors is presented. Steps in start of injection on a diesel engine are employed to achieve step-like NOx concentration variations on exhaust flow. On the basis of the sensor response, delay and dynamic response can be easily identified; the paper shows a simple least squares procedure although other models and identification techniques could be used. Application data is presented for three NOx sensors: a research-grade chemiluminescence exhaust gas analyser, and two different commercial ZrO2-based sensors. © 2010 Elsevier Inc.The authors thanks R. Lujan and G. Couture for their valuable contribution in the experimental part of the present work. This work has been partially supported by Ministerio de Ciencia y Tecnologia through Project PLANUCO No. TRA2006-15620-C02-02.Galindo, J.; Serrano Cruz, JR.; Guardiola, C.; Blanco-Rodriguez, D.; Cuadrado, I. (2011). An on-engine method for dynamic characterisation of NOx concentration sensors. Experimental Thermal and Fluid Science. 35(3):470-476. https://doi.org/10.1016/j.expthermflusci.2010.11.010S47047635

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

Selective catalytic reduction: testing, numeric modeling, and control strategies

Department Head: Allan Thomson Kirkpatrick.2010 Spring.Includes bibliographical references (pages 96-99).Selective Catalytic Reduction (SCR) catalysts respond slowly to transient inputs, which is troublesome when designing ammonia feed controllers. An experimental SCR test apparatus was installed on a Cooper Bessemer GMV-4 natural gas engine. Transient data was taken of commercially available SCR Catalysts. These transient tests are used to quantify SCR catalyst response. Space velocity, catalyst temperature, inlet NOx concentration, and ammonia to NOx molar feed ratio were varied. A Simulink numeric model was created to examine the SCR transient phenomena. The Simulink numeric model showed in-catalyst ammonia and NOx concentration as a function of length in the direction of exhaust flow. This helped explain the SCR transient results. Transient testing showed a fifteen minute delayed response in NOx reduction from ammonia transitions. Ammonia slip succeeded ammonia transitions by thirty minutes. Simulink modeling revealed that these delays are caused by large quantities of ammonia stored in the catalyst. Due to ammonia storage, ammonia waves propagate through the catalyst, front to back. Emission of these constituents through the catalyst is delayed because the wave takes time to propagate through the entire catalyst length. Ammonia feed rate control testing was done on the experimental setup to improve ammonia and NOx emissions from the catalyst. Three control algorithms were used: feed forward control, using a pre ammonia injection ceramic NOx sensor; a feed forward plus feedback control, using a pre ammonia injection ceramic NOx sensor and post catalyst ceramic NOx sensor to generate feed signals; and a feed forward plus feedback algorithm that used a pre ammonia injection ceramic NOx sensor and a mid catalyst ceramic NOx sensor to generate feed forward and feedback signals. The feed forward controller used molar ratio as the control variable, and the feedback system used a technique that minimized the post catalyst ceramic NOx sensor signal. Ammonia to NOx molar ratio was stepped every five or fifteen minutes, and the algorithm made decisions, based on the catalyst response to the step. The decisions were made to minimize the post catalyst ceramic NOx sensor. Feed forward testing revealed that the lack of pressure compensation on ceramic NOx sensors causes errors in feed forward NOx readings, and sub optimal ammonia feed. Feedback testing revealed that a minimization technique can be used successfully with a feedback step rate of one step per fifteen minutes, and a step size of 5% ammonia to NOx molar ratio. The feedback algorithm, with the feedback ceramic NOx sensor located one third the way through the catalyst length, worked poorly. The technique approached a lean ammonia to NOx molar ratio, and stabilized slower than the post catalyst feedback ceramic NOx sensor technique. These phenomena are explained with the Simulink numeric model