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Model-Based Approaches in Developing an Advanced Aftertreatment System: An Overview

SAE International Journal of Advances and Current Practices in Mobility

Cummins Inc.-Changsheng Su, Joseph Brault, Achuth Munnannur, Z. Gerald Liu, Sean Milloy, Arvind Harinath, David Dunnuck, Ken Federle
  • Journal Article
  • 2019-01-0026
Published 2019-01-15 by SAE International in United States
Cummins has recently launched next-generation aftertreatment technology, the Single ModuleTM aftertreatment system, for medium-duty and heavy-duty engines used in on-highway and off-highway applications. Besides meeting EPA 2010+ and Euro VI regulations, the Single ModuleTM aftertreatment system offers 60% volume and 40% weight reductions compared to current aftertreatment systems. In this work, we present model-based approaches that were systematically adopted in the design and development of the Cummins Single ModuleTM aftertreatment system. Particularly, a variety of analytical and experimental component-level and system-level validation tools have been used to optimize DOC, DPF, SCR/ASC, as well as the DEF decomposition device. The highlights of this work can be summarized as follows: a). internal dosing is more efficient than external dosing to control HC slip; High CPSI DOCs show better HC oxidation performance at high SV due to enhanced mass transfer; b). the adopted advanced DPF technologies enable greater ash capacity for long maintenance intervals; c). SCR performance was optimized with the use of a hydrothermally robust Cu-Zeolite catalyst coated on high CPSI substrates.
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CFD Modeling of Tailpipe NOx Sensor Accuracy

SAE International Journal of Engines

Cummins Emission Solutions-Apoorv Kalyankar, Achuth Munnannur, Z. Gerald Liu
  • Journal Article
  • 03-11-04-0029
Published 2018-08-08 by SAE International in United States
In a modern diesel aftertreatment system, a sensor for nitrogen oxides (NOx) placed downstream of the selective catalytic reduction (SCR) catalyst is necessary to determine if the tailpipe NOx concentration remains below the applicable On-board diagnostic (OBD) threshold. Typically the same NOx sensor also provides feedback to the dosing control module to adjust diesel exhaust fluid (DEF) dosing rate thereby controlling tailpipe NOx and ammonia emissions. However, feedback signal sent by the tailpipe NOx sensor may not always be accurate due to reasons including non-uniformity in NOx and ammonia distributions at SCR outlet. Flow based metrics from computational fluid dynamics (CFD) analyses, that are typically used to qualitatively assess NOx sensor accuracy in different designs are often inadequate. In this work, an improved CFD analysis procedure has been developed for assessing NOx sensor accuracy. This approach enables a direct comparison of NOx sensor accuracy between different sampling probe and sensor designs. This improved modeling approach was first validated against test data without spray effects by injecting gaseous NOx in a 5″ pipe. The impact of…
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Predictive Modeling of Impact of ANR Non-Uniformity on Transient SCR System DeNOx Performance

Cummins Emission Solutions-Apoorv Kalyankar, Achuth Munnannur, Z. Gerald Liu
Published 2015-04-14 by SAE International in United States
Selective catalytic reduction (SCR) is a promising technology for meeting the stringent requirements pertaining to NOx emissions. One of the most important requirements to achieve high DeNOx performance is to have a high uniformity of ammonia to NOx ratio (ANR) at the SCR catalyst inlet. Steady state 3D computational fluid dynamics (CFD) models are frequently used for predicting ANR spatial distribution but are not feasible for running a transient cycle like Federal Test Procedure (FTP). On the other hand, 1D kinetic models run in real time and can predict transient SCR performance but do not typically capture the effect of non-axial non-uniformities. In this work, two 3D to 1D coupling methods have been developed to predict transient SCR system performance, taking the effect of ANR non-uniformity into account. First is a probability density function (PDF) based approach and the second is a geometrical sector based approach. Steady state 3D CFD spray simulations are run under multiple test points and the effect of varying ANR uniformity index (UI) is taken into account adaptively while running transient…
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Thermal and Fluid Dynamic Considerations in Aftertreatment System Design for SCR Solid Deposit Mitigation

Cummins Emission Solutions-Achuth Munnannur, Mihai Chiruta, Z Gerald Liu
Published 2012-04-16 by SAE International in United States
Selective Catalytic Reduction (SCR) of oxides of nitrogen (NOx) with ammonia gas has established itself as an effective diesel aftertreatment technology to meet stringent emission standards enforced by worldwide regulatory bodies. Typically, in this technology, aqueous urea solution of eutectic composition - known as Diesel Exhaust Fluid (DEF) - is injected into hot exhaust gases leading to a series of thermal, fluid dynamic and reactive processes that eventually produces the ammonia necessary for NOx reduction reactions within monolithic catalytic substrates. Incomplete decomposition of the injected urea can lead to formation of solid deposits that adversely affect system performance by increasing the engine back pressure, reducing de-NOx efficiency, and lowering the overall fuel economy. In the present study, fundamental thermal and fluid dynamic factors that affect deposit formation and removal, and their relation to design and operating considerations of aftertreatment systems were explored using both simulations and experiments. Lagrangian Drop - Eulerian Fluid spray models were used to assess the deposit formation propensity, and to arrive at strategies that minimize the probability of formation of solid…
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Development of Flow Uniformity Indices for Performance Evaluation of Aftertreatment Systems

SAE International Journal of Engines

Cummins Emission Solutions-Achuth Munnannur, Christopher M. Cremeens, Z. Gerald Liu
  • Journal Article
  • 2011-01-1239
Published 2011-04-12 by SAE International in United States
With the on- and off-road diesel engine emission regulations getting more stringent across the world, diesel aftertreatment systems are expected to deliver outstanding performance and reliability. These objectives should be met by fulfilling tight packaging constraints and incurring only modest material and testing costs. A major strategy for meeting these often conflicting requirements is the effective use of simulation tools such as computational fluid dynamics (CFD) in system design and performance evaluation. Prerequisites for using this CFD analysis-led-design approach, however, are knowledge of the confidence level of the predictions and knowledge of the appropriate transfer functions that establish the relationships between the measured performance parameters and model predictions. The primary aim of the present work is to develop statistically and physically relevant measures that assess the uniformity of flow in aftertreatment systems. Most commonly, a flow distribution index based on L1 norm has been used for quantifying flow uniformity. The index proposed in the present work is based on the L2 norm thereby making it more sensitive to flow maldistribution. Key statistical advantages of the…
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Development and Validation of a Predictive Model for DEF Injection and Urea Decomposition in Mobile SCR DeNOx Systems

Cummins Emission Solutions-Achuth Munnannur, Z. Gerald Liu
Published 2010-04-12 by SAE International in United States
Selective catalytic reduction (SCR) of oxides of nitrogen with ammonia gas is a key technology that is being favored to meet stringent NOx emission standards across the world. Typically, in this technology, a liquid mixture of urea and water - known as Diesel Exhaust Fluid (DEF) - is injected into the hot exhaust gases leading to atomization and subsequent spray processes. The water content vaporizes, while the urea content undergoes thermolysis and forms ammonia and isocyanic acid, that can form additional ammonia through hydrolysis. Due to the increasing interest in SCR technology, it is desirable to have capabilities to model these processes with reasonable accuracy to both improve the understanding of processes important to the aftertreatment and to aid in system optimization. In the present study, a multi-dimensional model is developed to simulate DEF spray processes and the conversion of urea to ammonia. The model is then implemented into a commercial CFD code. Multicomponent DEF particles are tracked in the Lagrangian framework and separate laws are defined for the heat and mass exchange between each…
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Use of a Pressure Reactive Piston to Control Diesel PCCI Operation - A Modeling Study

Engine Research Center, University of Wisconsin-Madison-Achuth Munnannur, Neerav Abani, Rolf D. Reitz
Published 2006-04-03 by SAE International in United States
The heavy-duty diesel engine industry is required to meet stringent emission standards. There is also the demand for more fuel efficient engines by the customer. In a previous study on an engine with variable intake valve closure timing, the authors found that an early single injection and accompanying premixed charge compression ignition (PCCI) combustion provides advantages in emissions and fuel economy; however, unacceptably high peak pressures and rates of pressure-rise impose a severe operating constraint. The use of a Pressure Reactive Piston assembly (PRP) as a means to limit peak pressures is explored in the present work. The concept is applied to a heavy-duty diesel engine and genetic algorithms (GA) are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to provide an optimized set of operating variables. Different sets of PRP parameters (viz. preload, spring constant, damping coefficient and crown mass) were used in an optimization study and the effects of intake valve closure timing, start-of-injection timing, injection duration and exhaust gas recirculation were investigated. The results show that in cases when the…
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Performance Optimization of Diesel Engines with Variable Intake Valve Timing Via Genetic Algorithms

Engine Research Center, University of Wisconsin-Madison-Achuth Munnannur, Song-Charng Kong, Rolf D. Reitz
Published 2005-04-11 by SAE International in United States
The strategy of variable Intake Valve Closure (IVC) timing, as a means to improve performance and emission characteristics, has gained much acceptance in gasoline engines; yet, it has not been explored extensively in diesel engines. In this study, genetic algorithms are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to investigate the optimum operating variables for a typical heavy-duty diesel engine working with late IVC. The effects of start-of-injection timing, injection duration and exhaust gas recirculation were investigated along with the intake valve closure timing. The results show that appreciable reductions in NOx+HC (∼82%), soot (∼48%) and BSFC (∼7.4%) are possible through this strategy, as compared to a baseline diesel case of (NOx+HC) = 9.48g/kW-hr, soot = 0.17 g/kW-hr and BSFC = 204 g-f/kW-hr. The additional consideration of double injections helps to reduce the high rates of pressure rise observed in a single injection scheme. In this context, an illustration of a modified prioritization of the emission targets in optimization studies, which may be crucial to attaining aggressive emission standards, is also provided.…
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