Abstract : Selective catalytic reduction (SCR) systems along with a NH3 slip control catalyst (ASC) offers NOx conversion efficiency >90 % with NH3 slip 90 % with NH3 slip 95 %. A downstream SCR catalyst substrate can be used to get additional NOx conversion by using the SCRF® outlet NH3 to increase the cumulative NOx conversion of the system. In this study, NOx reduction, NH3 slip and PM oxidation performance of a Cu-zeolite SCRF® with a downstream Cu-zeolite SCR were investigated based on engine experimental data at steady state conditions. The experimental data were collected at varying SCRF® inlet temperatures, space velocities, inlet NOx concentrations, NO2/ NOx ratios at ammonia to NOx ratios (ANR) between 1.02 to 1.10. The results demonstrated that the SCRF® with downstream SCR together can achieve NOx conversion efficiency > 98% at ANRs between 1.02 - 1.10 (which may have been due to measurement inaccuracies in downstream SCRF 98% at ANRs between 1.02 - 1.10 (which may have been due to measurement inaccuracies in downstream SCRF®/SCRdata), for the inlet temperature range of 200 - 370°C, space velocity in the range of 10 to 34 k/hr and inlet NO2/ NOx in the range of 0.3 - 0.5. However, NH3 slip from the SCRF® decreases and NOx concentration downstream of the SCRF® increases with the oxidation of PM in the SCRF®. The PM oxidation kinetics are affected by the deNOx reactions, hence, the SCRF® with urea dosing showed ~80 % lower reaction rates during passive oxidation when compared to the production CPF. The effect of varying fuel rail injection pressure on the primary particle diameter and on the Elemental Carbon (EC) and Organic Carbon (OC) fraction of the total carbon was also studied. The primary particle diameter was found to be in the range of 28-30 nm with no effect of the variation in fuel rail injection pressure on it. The OC part of the Total Carbon (TC) did not vary significantly with fuel rail injection pressure. The EC content increased with decrease in fuel rail injection pressure.

Abstract : The heavy-duty diesel engines use a Diesel Oxidation Catalyst (DOC), a Catalyzed Particulate Filter (CPF), a Selective Catalytic Reduction (SCR) with urea injection and a Ammonia Oxidation Catalyst (AMOX), to meet the US EPA 2010/2013 particulate matter (PM) and NOx emission standards. However, it is not possible to achieve the 2015 California low NOx standards with this arrangement. Hence, there is a need to improve the existing aftertreatment system. This can be achieved by coating the SCR catalyst on a diesel particulate filter (DPF), thus combining the PM filtration and NOx reduction functionality into a single device. This reduces the overall volume/weight of the system and provides opportunity for packaging flexibility and improved thermal management along with the possibility of higher NOx reduction with a downstream SCR system. The SCR catalyst on a DPF used in this study is known as a SCRF℗ʼ which was supplied by Johnson Matthey and Corning. Previous research on the CPF and SCRF℗ʼ at MTU highlighted that the reactivity of PM retained in the CPF and SCRF℗ʼ is higher during loading conditions compared to passive oxidation conditions i.e. when the flow rate of PM entering the CPF or SCRF℗ʼ is higher in loading conditions compared to the low flow rate and higher PM reaction rate during passive oxidation conditions. A 2013 Cummins ISB engine with a DOC-SCRF℗ʼ arrangement was used to perform twelve tests (eight tests without urea injection and four tests with urea injection) in order to determine the NO2 assisted passive oxidation performance of the SCRF℗ʼ under loading conditions with and without urea injection. The primary focus of this study was to carry out Loading Tests with and without Urea injection and measure species concentrations, PM mass retained, exhaust flowrates, substrate temperature distributions, pressure drop across the filter, and to determine the kinetics of NO2 assisted PM oxidation under loading conditions and compare it with kinetics under passive oxidation conditions. The NO2 assisted passive oxidation performance of the SCRF℗ʼ was experimentally studied by running the engine at 2400 RPM and four different loads at nominal and reduced rail pressure for 5.5 hours in two stages of loading. These conditions were intended to span the SCRF℗ʼ inlet temperatures in the range of 264-364oC and inlet NO2 concentrations in the range of 52-120 ppm. Four conditions out of these eight conditions were repeated with the injection of urea in the form of diesel exhaust fluid at a target ammonia to NOx ratio of 1.0 to investigate both the NOx reduction performance, as well as the effect of urea on the NO2 assisted passive oxidation performance. From the conclusions of the study based on the experimental data, it was found that the cumulative percentage of PM oxidized in the SCRF℗ʼ increases with the increase in engine load due to higher SCRF℗ʼ temperatures and NO2 concentrations. On average, the reactions rates with urea injection during loading conditions in the SCRF℗ʼ are 25% lower compared to the reaction rates without urea injection. The reactivity of PM under loading conditions with and without urea injection is higher compared to the reactivity of PM under passive oxidation with and without urea injection. For a lumped PM oxidation model, a higher pre-exponential for NO2 assisted oxidation is needed for loading as compared to passive oxidation conditions. It was not possible to determine the kinetics of NO2 assisted oxidation of PM under loading conditions from the experimental data using a standard Arrhenius model which lead to the development of a different model for PM oxidation. A PM oxidation model was developed based on the shrinking core model which keeps the identity of the incoming PM masses in the SCRF℗ʼ as compared to SCR-F model being developed at MTU which is lumped model for PM oxidation. The PM oxidation model was calibrated to simulate PM oxidation in the SCRF℗ʼ with a single set of kinetics under wide range of conditions including loading and passive oxidation conditions. The reaction rate results from the PM oxidation model were then applied to the SCR-F model to simulate the pressure drop across SCRF℗ʼ and the PM retained in the SCRF℗ʼ for the loading conditions used in this study. The SCR-F model was calibrated using experimental data from Loading Tests w/o Urea to simulate the PM retained within ℗ł2 g and pressure drop across SCRF℗ʼ within ℗ł0.5 kPa of the experimental data at the end of the test. The calibrated SCR-F model was also used to estimate the cake, wall and channel pressure drop and the PM retained in the cake and wall for the Loading Tests w/o Urea to check the integrity of experimental data and the consistency of the model. The NO2 assisted kinetics for PM oxidation in the SCRF℗ʼ without urea injection using the SCR-F model resulted in an activation energy of 96 kJ/gmol and pre-exponential factor of 2.6 m/K-s for the cake and 1.8 m/K-s for the wall. An analysis of the results from the SCR-F model suggests that for all the conditions, 84-92% of the total PM retained was in the PM cake layer and the oxidation in the PM cake layer accounted for 72-84% of the total PM mass oxidized during loading.

Abstract : The study of NOx reduction across the SCRF® is presented in this report to understand the inlet and outlet NO, NO2, NH3 species from the SCRF®. The SCRF® is a prototype SCR catalyst on a Diesel Particulate Filter (DPF) that reduces NOx and PM at the downstream location. The SCRF® reduces the packaging volume of the aftertreatment components in order to reduce the cost, volume and weight of the aftertreatment system. A total of 12 experiments were performed on a Cummins ISB 2013 280 hp engine and the aftertreatment system. The tests were performed to investigate the NOx reduction performance of the SCRF® under various Particulate Matter loading. The loading phase has been divided into two stages: Stage 1 and Stage 2. Stage 1 begins after all the PM has been removed from the SCRF®, which is then followed by Stage 2 loading. The engine is run at 2400 rpm and 200 Nm load with different fuel rail pressures for a duration to achieve PM loadings of 0, 2, and 4 g/L (grams of PM per volume of the SCRF®) in the SCRF®. For the testing of the SCRF® without PM loading, a Catalyzed Particulate Filter (CPF) was placed before the SCRF®. After the loading phase, NOx reduction stage was run at different engine conditions. The engine speed and load conditions were selected for the NOx reduction stage, named as test points 1, 3, 6, and 8, in order to attain a wide range in space velocities, inlet temperatures and NO2/NOx ratios in the SCRF®, which are the major parameters determining NOx reduction efficiency in the SCRF®. The exhaust temperature varied from 206 to 443 °C, inlet NO2/ NOx ratio varied from 0.22 to 0.46, and space velocity varied from 13.5 to 48.2 k/hr. Urea was dosed in the decomposition tube before the SCRF® to determine the NOx conversion efficiency at different ammonia to NOx ratio (ANR) values. The ANR values considered for the NOx reduction and NH3 slip were 0, 0.8, 1, 1.2, and 1.2 repeat. The ANR of 1.2 was repeated in the urea dosing cycle. It was found that the NOx conversion efficiency across the SCRF® is maximum for test points 3 and 6 i.e. for the temperature range of 300-350°C. The NO2/NOx ratio at those points was around 0.42-0.46. It is observed that the loading in the SCRF® does not affect the NOx conversion efficiency at low (205 °C) and high (440 °C) temperature points but affects in between. The NOx conversion efficiency improved with PM loading until 300 °C SCRF® inlet temperature and decreased (with PM loading) after 350 °C. There is noticeable ammonia oxidation at temperatures above 400 °C in the SCRF® that affects NOx conversion efficiency [1]. At higher temperature of about 440 °C, NH3 slip is observed varying with PM loading in the SCRF®. With PM loading, NO2 assisted oxidation increases the concentration of NO [2] and affects the NOx conversion efficiency. It is concluded from the results that the NO2 concentration across the SCRF® decreased with PM loading and SCRF® temperature due to NO2 assisted PM oxidation. The impact of PM loading on NOx reduction in the SCRF® was insignificant below 300 °C. NOx conversion decreased by 3 - 5 % above 350 °C with increase in PM loading from 0 to 2 and 4 g/L, due to consumption of NO2 via passive oxidation of PM. The NOx concentration is not completely converted across the SCRF® at temperatures above 350 °C even if dosed with an ANR value of 1.2.

Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts presents a complete overview of the selective catalytic reduction of NOx by ammonia/urea. The book starts with an illustration of the technology in the framework of the current context (legislation, market, system configurations), covers the fundamental aspects of the SCR process (catalysts, chemistry, mechanism, kinetics) and analyzes its application to useful topics such as modeling of full scale monolith catalysts, control aspects, ammonia injections systems and integration with other devices for combined removal of pollutants.

Engineers, applied scientists, students, and individuals working to reduceemissions and advance diesel engine technology will find the secondedition of Diesel Emissions and Their Control to be an indispensablereference. Whether readers are at the outset of their learning journey orseeking to deepen their expertise, this comprehensive reference bookcaters to a wide audience.In this substantial update to the 2006 classic, the authors have expandedthe coverage of the latest emission technologies. With the industryevolving rapidly, the book ensures that readers are well-informed aboutthe most recent advances in commercial diesel engines, providing acompetitive edge in their respective fields. The second edition has alsostreamlined the content to focus on the most promising technologies.This book is rooted in the wealth of information available on DieselNet.com, where the “Technology Guide” papers offer in-depth insights. Eachchapter includes links to relevant online materials, granting readers accessto even more expertise and knowledge.The second edition is organized into six parts, providing a structuredjourney through every aspect of diesel engines and emissions control: Part I: A foundational exploration of the diesel engine, combustion, andessential subsystems. Part II: An in-depth look at emission characterization, health andenvironmental impacts, testing methods, and global regulations. Part III: A comprehensive overview of diesel fuels, covering petroleumdiesel, alternative fuels, and engine lubricants. Part IV: An exploration of engine efficiency and emission controltechnologies, from exhaust gas recirculation to engine control. Part V: The latest developments in diesel exhaust aftertreatment,encompassing catalyst technologies and particulate filters. Part VI: A historical journey through the evolution of dieselengine technology, with a focus on heavy-duty engines in the NorthAmerican market. (ISBN 9781468605693, ISBN 9781468605709, ISBN 9781468605716, DOI: 10.4271/9781468605709)

Abstract : 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.

Abstract : This research focuses on modeling and control of PM and NOx in diesel engine exhaust using an SCR catalyst on a Diesel Particulate Filter (SCR-F). A 2D SCR-F model was developed that is capable of predicting internal states: 2D temperature, PM and NH3storage distributions and filtration efficiency, pressure drop, PM mass retained in the PM cake and substrate wall and outlet NO, NO2 and NH3concentrations. The SCR-F model was used to simulate a DOC + SCR-F + DOC + SCR ultra-low NOx system that can achieve > 99.5% NOx conversion efficiency. 99.5% NOx conversion efficiency. The model was calibrated with experimental data from a Johnson Matthey SCRF® with a Cummins 2013 ISB engine. The impact of SCR reactions on passive PM oxidation rate and PM loading on SCR reactions was determined. A comparison of the experimental and model data for different ammonia to NOx ratios, PM loading, and passive oxidation conditions is presented. A 2D SCR-F state estimator was developed by combining a simplified version of the 2D SCR-F model with pressure drop, outlet thermocouple and NOx sensormeasurements using an Extended Kalman Filter. The temperature, PM mass retained and NH3coverage fraction states were predicted which can be used to develop fuel dosing and urea dosing strategies for the SCR-F. A 2D SCR-F + 1D SCR system model was used to simulate the experimental data collected on a SCR-F + SCR system from a Cummins 2013 ISB engine. The NO2/NOxratioat the SCR-F and SCR inlet was found to be limiting factor for NOx conversion efficiency of this system. An ultra-low NOxsystem was developed with a DOC downstream of the SCR-F that maintains an optimum NO2/NOxratio of 0.5 at the downstream SCR inlet by using 2 urea injectors. This system was simulated with a combination of 1D DOC, 2D SCR-F, and 1D SCR models and it was found to be capable of > 99.5% NO 99.5% NOxconversion efficiency, a 90% increase in PM oxidation rate compared to an SCR-F + SCR system with 1 injector for typical engine operating conditions.