Control Design of an Automotive Urea SCR Catalyst

2002 ◽  
Author(s):  
Devesh Upadhyay ◽  
Michiel Van Nieuwstadt
Keyword(s):  
Ammonia Oxidation ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Control Design ◽  
Reaction Rates ◽  
Lumped Parameter Model ◽  
Lean Burn ◽  
Ammonia Sensing ◽  
Injection Process ◽  
Lean Nox

The leading aftertreatment technologies for NOx removal from the exhaust gas of lean burn engines, Diesels in particular, are urea based Selective Catalytic Reduction (SCR), Lean NOx Traps (LNT) and Active Lean NOx Catalysts (ALNC). It is generally believed that the SCR technique has the potential of providing the best NOx conversion efficiency relative to the other techniques. Nonetheless, it is crucial that the high conversion efficiencies be achieved with a minimum slippage of unreacted ammonia as tail pipe emissions. This necessitates a precise control over the urea injection process. The complex behavior of the catalyst substrate with respect to adsorption and desorption of ammonia in conjunction with a lack of “stored ammonia” sensing capabilities makes the control problem challenging. In this paper we present a model-based control design approach using a lumped parameter model of an SCR system that includes the essential dynamics of the plant. The model includes the adsorption, desorption and surface coverage dynamics, along with the NOx reduction and ammonia oxidation dynamics based on the relevant chemical reaction rates.

Model Based Analysis and Control Design of a Urea-SCR deNOx Aftertreatment System

2005 ◽  
Vol 128 (3) ◽  
pp. 737-741 ◽  
Author(s):  
Devesh Upadhyay ◽  
Michiel Van Nieuwstadt
Keyword(s):  
Sliding Mode ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Control Design ◽  
Observer Design ◽  
Lumped Parameter Model ◽  
Control Synthesis ◽  
Model Based ◽  
Ammonia Slip ◽  
Controllability And Observability

In this paper we tackle issues relevant to model based control design for a Urea based Selective Catalytic Reduction (SCR) process relevant to automotive applications. A three state, control oriented, lumped parameter model of the system is used to investigate essential controllability and observability properties of the Urea-SCR plant. Results from the controllability and observability analysis of both nonlinear and linearized models are shown to have realistic implications. Observer design for predicting gas phase ammonia slip is outlined and results presented. An altered definition of the catalyst efficiency is used in control design. It is shown that this altered definition lends itself readily to control synthesis in the Sliding Mode framework while satisfying the dual control objectives of maximizing NOx reduction and minimizing ammonia slip.

Configuration and Control Design for a Passive SCR System With NOx Storage Capability

2018 ◽  
Author(s):  
Qinghua Lin ◽  
Pingen Chen ◽  
Vitaly Y. Prikhodko ◽  
James E. Parks
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Cost Effective ◽  
Nox Storage ◽  
Lean Burn ◽  
Gasoline Engines ◽  
Generation Cost ◽  
Lean Nox ◽  
Scr System ◽  
Passive Scr

Passive selective catalytic reduction (SCR) systems have been considered as a promising technology for reducing NOx emissions for highly-efficient lean burn gasoline engines. Since passive SCR requires intermittent rich operation for self-generating ammonia (NH3) for NOx reduction in the lean phase, the fuel penalty associated with NH3 generation may be significant. To address this issue, a new prototype passive SCR system with NOx storage capability was recently investigated. The three-way catalyst (TWC) with added NOx storage capability is able to enhance NH3 production rate by utilizing pre-stored NOx and thus reduce the fuel cost related to NH3 production. The main purpose of this study is to reduce the ammonia generation cost by: 1) proposing a new passive SCR system architecture that includes two TWC stages; and 2) developing and optimizing a novel non-uniform cylinder-to-cylinder combustion (NUCCC) control. Optimization results based on the experimental data from a physical engine platform, demonstrate that the new passive SCR system (with NOx storage components on TWCs), in conjunction with optimized NUCCC control, is capable of reducing ammonia specific fuel consumption (ASFC) by 30.2%, when compared to a uniform cylinder-to-cylinder combustion (UCCC)-controlled baseline passive SCR system. Such a novel NUCCC control and innovative passive SCR configuration, will be very instrumental in creating cost-effective lean NOx emission control solutions for lean-burn engines in the future.

Effect of Butanol on the Performance of DeNOx Aftertreatment Systems of a Diesel Vehicle Under WLTC Driving Conditions

2021 ◽  
Author(s):  
Alejandro Calle-Asensio ◽  
Juan José Hernández ◽  
José Rodríguez-Fernández ◽  
Víctor Domínguez-Pérez
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Climatic Conditions ◽  
Transport Sector ◽  
Lean Nox Trap ◽  
Diesel Vehicles ◽  
Medium Speed ◽  
Emission Regulations ◽  
Lean Nox ◽  
Light Duty Vehicles

Abstract Advanced biofuels and electrofuels, among which are medium-long chain alcohols, have gained importance in the transport sector with the enforcement of the EU Renewable Energy Directive (2018/2001). In parallel, last European emission regulations have become much more restrictive regarding NOx, so vehicle manufacturers have been forced to incorporate lean NOx trap (LNT) and/or selective catalytic reduction (SCR). Thus, the combination of modern DeNOx devices and the upcoming higher contribution of sustainable biofuels is a new challenge. In this work, two Euro 6 diesel vehicles, one equipped with LNT and the other with ammonia-SCR, have been tested following the Worldwide harmonized Light-duty vehicles Test Cycle (WLTC) at warm (24°C) and cold (−7°C) conditions using conventional diesel fuel and a diesel-butanol (90/10% vol.) blend. While the effect of butanol on the LNT efficiency was not significant, its influence on the SCR performance was notable during the low and medium-speed phases of the driving cycle, mainly under warm climatic conditions. Despite of the lower NOx concentration at the catalyst inlet, the worst efficiency of the SCR with butanol could be attributed to hydrocarbons deposition on the catalyst surface, which inhibits the NOx reduction reactions with ammonia. Moreover, the LNT was not sensitive to the ambient temperature while the SCR performance greatly depended on this parameter.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

2016 ◽  
Author(s):  
Amin Reihani ◽  
Brent Patterson ◽  
John Hoard ◽  
Galen B. Fisher ◽  
Joseph R. Theis ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Pulse Frequency ◽  
Oxygen Storage ◽  
Passenger Cars ◽  
Catalyst Composition ◽  
Nox Conversion ◽  
Lean Nox ◽  
Lean Nox Traps

Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (Diesel NOx aftertreatment by Adsorbed Intermediate Reductants) [1]. There is a vast parameter space that needs to be explored in order to maximize the NOx conversion at high temperatures and flow rates while minimizing the fuel penalty associated with the hydrocarbon injections. Four parameters were identified as important for RPR operation: (1) the flow field and reductant mixing uniformity; (2) the pulsing parameters including the pulse frequency, duty cycle, and rich magnitude; (3) the reductant type; and (4) the catalyst composition, including the type and loading of precious metal, the type and loading of NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. A novel injection and mixer system was designed that allowed for the investigation of previously unexplored areas of high frequency injections up to f = 100Hz. Under RPR conditions, H2, CO, dodecane, and C2H4 provided approximately 80% NOx conversion at 500°C, but at 600°C the conversions were significantly lower, ranging from 40 to 55%. The NOx conversion with C3H8 was low across the entire temperature range, with a maximum conversion of 25% near 300°C and essentially no conversion at 600°C. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of temperature between 280°C and 630°C. Among the hydrocarbons, this suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

Enhanced transport in washcoated monoliths: Application to selective lean NOx reduction and ammonia oxidation

2019 ◽  
Vol 377 ◽  
pp. 119734 ◽  
Author(s):  
Pritpal S. Dhillon ◽  
Michael P. Harold ◽  
Di Wang ◽  
Ashok Kumar ◽  
Saurabh Y. Joshi
Keyword(s):  
Ammonia Oxidation ◽  
Nox Reduction ◽  
Lean Nox Reduction ◽  
Lean Nox

NOx Reduction: The Challenge for Innovative Concepts in Europe

2011 ◽  
Author(s):  
Ralf Koralewska
Keyword(s):  
Catalytic Reduction ◽  
Catalytic Converter ◽  
Nox Reduction ◽  
Waste Incineration ◽  
Reaction Rates ◽  
Limit Values ◽  
Average Value ◽  
Ammonia Slip ◽  
Emission Limit ◽  
The Eu

During combustion, most of the waste’s nitrogen content is transferred to the flue gases as nitrogen oxide, NOx. The EU Waste Incineration Directive defines a maximum emission limit value for NOx of 200 mg/Nm3 as a daily average value referred to 11% O2. Based on National Emission Ceilings (NEC) defined by the Gothenburg Protocol, it can be expected that the limit values for NOx in the EU will become even more stringent. In some European countries (e.g. The Netherlands, Austria, Switzerland) a lower emission limit has already been introduced. Selective Catalytic Reduction (SCR) technologies are used in many cases to achieve the above-mentioned NOx limits. However, there are drawbacks to SCR systems such as high investment cost. Operation cost is also quite high due to the energy consumption necessary for the reheating of the flue gas as well as the increased pressure loss. Innovative technologies are therefore required to make it possible to reconcile both requirements: reduced emissions and increased energy efficiency. Selective Non-Catalytic Reduction (SNCR) systems are based on the selective reaction of ammonia or urea injected into the upper furnace. In many cases SNCR technologies are limited by the ammonia slip which increases in case of more stringent NOx requirements. According to the relevant BREF document, an ammonia slip limit of 10 mg/Nm3 is generally required at the stack. In order to achieve reduced NOx values, it is necessary to implement measures to reduce ammonia slip, by means of either a wet scrubber or a High-dust catalytic converter. EfW plants in Mainz (Germany) and Brescia (Italy) are examples of operational plants combining SNCR with such a catalytic converter type. In addition R&D activities are carried out on the development of simplified reaction mechanisms to be implemented in Computational Fluid Dynamics (CFD) codes. With these tools it will be possible to describe the interaction between turbulent mixing, radiation and chemical reaction rates. Another option to achieve low NOx values (below 100 mg/Nm3) is the reduction of NOx by so-called primary measures, e.g. the Very Low NOx process (VLN), which has been developed by MARTIN jointly with its cooperation partners. The VLN process is based on a grate-based combustion system. The “VLN gas” is drawn off at the rear end of the grate and is reintroduced into the upper furnace in the vicinity of the SNCR injection positions. NOx will be reduced significantly, ensuring low NOx emission values at the stack as required, at low values for ammonia slip. The new EfW plant in Honolulu (USA) will be equipped with the VLN process. In Coburg (Germany), the VLN process will be retrofitted in an existing installation. This paper documents the potential and the limitations of different measures for NOx reduction as well as examples of recent innovative EfW plants in Europe using MARTIN technologies successfully.

scholarly journals Measures to Reduce the N2O Formation at Perovskite-Based Lean NOx Trap Catalysts under Lean Conditions

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 917
Author(s):  
Sabrina I. Ecker ◽  
Jürgen Dornseiffer ◽  
Stefan Baumann ◽  
Olivier Guillon ◽  
Henny J. M. Bouwmeester ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Operation Mode ◽  
Oxidation Catalyst ◽  
Lean Nox Trap ◽  
N2o Emissions ◽  
Incipient Wetness Impregnation ◽  
N2o Formation ◽  
Lean Burn ◽  
Nox Storage Capacity ◽  
Lean Nox

The net oxidising atmosphere of lean burn engines requires a special after-treatment catalyst for NOx removal from the exhaust gas. Lean NOx traps (LNT) are such kind of catalysts. To increase the efficiency of LNTs at low temperatures platinised perovskite-based infiltration composites La0.5Sr0.5Fe1-xMxO3-δ/Al2O3 with M = Nb, Ti, Zr have been developed. In general, platinum based LNT catalysts show an undesired, hazardous formation of N2O in the lean operation mode due to a competing C3H6-selective catalytic reduction (SCR) at the platinum sites. To reduce N2O emissions an additional Rh-coating, obtained by incipient wetness impregnation, besides the Pt coating and a two-layered oxidation catalyst (2 wt.% Pd/20 wt.% CeO2/alumina)-LNT constitution, has been investigated. Though the combined Rh-Pt coating shows a slightly increased NOx storage capacity (NSC) at temperatures above 300 °C, it does not decrease N2O formation. The layered oxidation catalyst-LNT system shows a decrease in N2O formation of up to 60% at 200 °C, increasing the maximum NSC up to 176 µmol/g. Furthermore, the NSC temperature range is broadened compared to that of the pure LNT catalyst, now covering a range of 250–300 °C.

NO2 Reaction Pathways With NH3 on an Fe-Zeolite SCR Catalyst

2011 ◽  
Author(s):  
Michael A. Smith ◽  
Christopher D. Depcik ◽  
Stefan Klinkert ◽  
John W. Hoard ◽  
Stanislav V. Bohac ◽  
...  
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalyst System ◽  
Lean Nox Trap ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Lean Nox ◽  
System Part

One approach for nitrogen oxides (NOx) emission control of medium duty diesel engines is through the use of a combination Lean NOx Trap and Selective Catalytic Reduction (LNT-SCR) catalyst system. In this system, part of the NOx conversion occurs via an NH3 SCR catalyst that is dependent on the NO2 to NOx ratio of the feed gas with NO2 being a more advantageous oxidizer. One benefit of using this system is the conversion of NO to NO2 over the LNT which increases the NO2:NOx ratio of the feed gas to the SCR catalyst. An experimental study has been performed to investigate the NO2-NH3 reaction for an Fe-based zeolite SCR catalyst using a bench top flow reactor. The increase in NO2 concentration at the inlet of the SCR results in the formation of large quantities of N2O from 200°C to 400°C. Further experiments determined that N2O and NH3 react above 350°C. This has led to a hypothesis that one primary SCR reaction (Slow SCR) can be replaced with two reaction steps featuring NH3, NO2, and N2O. As a result, this paper proposes five NOx reduction reactions as part of a global mechanism, which would account for the observed experimental behavior.

A Torque Balance Method for Multi-Cylinder Gasoline Engines With Non-Uniform Cylinder-to-Cylinder Combustion Strategies

2019 ◽  
Author(s):  
Qinghua Lin ◽  
Pingen Chen
Keyword(s):  
Catalytic Reduction ◽  
Control Strategies ◽  
Fuel Efficiency ◽  
The United States ◽  
Nox Emission ◽  
Successful Implementation ◽  
Lean Burn ◽  
Gasoline Engines ◽  
Engine Model ◽  
Lean Nox

Abstract Lean burn gasoline engines have attracted more and more attentions over the past two decades. One of the main challenges in commercializing lean burn gasoline engines in the United States is lean NOx control to meet the stringent NOx emission regulation. Several types of lean aftertreatment systems including passive selective catalytic reduction (SCR) systems and lean NOx traps (LNTs), have been intensively investigated to meet the NOx emission requirements without triggering significant penalties on fuel efficiency. One of the most promising technologies to achieve this goal is non-uniform cylinder-to-cylinder combustion (NUCCC) control strategies. However, successful implementation of NUCCC strategies are challenging tasks since it may cause cylinder-to-cylinder torque imbalance and thus deterioration of drivability. The purpose of this study is to propose and evaluate a systematic method for generating the references of fuel quantity and air quantity for different cylinders to simultaneously achieve cylinder-to-cylinder torque balance and non-uniform cylinder-to-cylinder air/fuel ratio (AFR) for multi-cylinder engines in various scenarios. To validate the effectiveness of the proposed method, simulation studies were carried out using a multi-zone engine model. The simulation results show that, the proposed references, if successfully tracked, can lead to torque balance across the cylinders as well as non-uniform cylinder-to-cylinder AFR.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Amin Reihani ◽  
Brent Patterson ◽  
John Hoard ◽  
Galen B. Fisher ◽  
Joseph R. Theis ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Passenger Cars ◽  
Catalyst Composition ◽  
Nox Conversion ◽  
Lean Nox ◽  
Adsorbed Intermediate ◽  
Lean Nox Traps

Lean NOx traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based selective catalytic reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400 °C needs to be improved. Rapidly pulsed reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) (Bisaiji et al., 2011, “Development of Di-Air—A New Diesel deNOx System by Adsorbed Intermediate Reductants,” SAE Int. J. Fuels Lubr., 5(1), pp. 380–388). Four important parameters were identified to maximize NOx conversion while minimizing fuel penalty associated with hydrocarbon injections in RPR operation: (1) flow field and reductant mixing uniformity, (2) pulsing parameters including the pulse frequency, duty cycle, and magnitude, (3) reductant type, and (4) catalyst composition, including the type and loading of precious metal and NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150 °C and 650 °C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. Under RPR conditions, H2, CO, C12H26, and C2H4 provided approximately 80% NOx conversion at 500 °C; however, at 600 °C the conversions were significantly lower. The NOx conversion with C3H8 was low across the entire temperature range. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of 280–630 °C. This suggested that the high-temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

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