Browse Topic: Lean NOx traps

Items (101)
Find
First-Principles Research on Adsorption of NOx on Pt Cluster and BaO Cluster Supported by γ-Al 2 O 3 (110) Surface2020-01-03574/14/2020
Lean NOx trap (LNT) is a great potential NOx abatement method for lean-burn gasoline engines in consideration of exhaust aftertreatment cost and installation space. NOx firstly is adsorbed on storage sites during the lean-burn period, then reduced to N2 under catalysis of the catalyst sites in the rich-burn phase. There must be a spillover of NOx species between both types of sites. For a better understanding of this spillover process of NOx species between Pt (as the catalytic center) and BaO sites (as storage components in commercial catalyst), this work focused on the vital first step of spillover, the adsorption of NOx on clean substrate surface (γ-Al2O3 (110) surface) and Ba\Pt cluster supported by the surface. Based on first principles software VASP (Vienna Ab-initio Simulation Package), the most stable adsorption structures of NO with Pt3 clusters and (BaO)3 clusters on carrier γ- Al2O3 (110) surface were confirmed and the adsorption energy of these structures were compared. Meanwhile electronic structure analysis of these adsorption systems was investigated by analyzing DOS (density of state), Bader charge, charge density difference and COHP (crystal orbital Hamilton population). From electronic structure analysis methods mentioned above, a better view of electron transfer and bond formation between gas phase NOx molecules and supported BaO or Pt cluster was obtained. This work has laid a good foundation for the further research of NOx adsorption and reduction of LNT by providing a more microscopic explanation of NOx species spillover mechanism.
Li, Shilong, Zhang, Yanke, zhao, Jin
Calibration and Parametric Investigations on Lean NOx Trap and Particulate Filter Models for a Light Duty Diesel Engine2020-01-06574/14/2020
To comply with the stringent future emission mandates of light-duty diesel engines, it is essential to deploy a suitable combination of emission control devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and DeNOx converter (LNT or SCR). Arriving at optimum size and layout of these emission control devices for a particular engine through experiments is both time and cost-intensive. Thus, it becomes important to develop suitable well-tuned simulation models that can be helpful to optimize individual emission control devices as well as arrive at an optimal layout for achieving higher conversion efficiency at a minimal cost. Towards this objective, the present work intends to develop a one-dimensional Exhaust After Treatment Devices (EATD) model using a commercial code. The model parameters are fine-tuned based on experimental data. The EATD model is then validated with experiment data that are not used for tuning the model. Subsequently, the model was used for studying the effects of geometrical parameters of the after-treatment devices like diameter and length on the conversion efficiency and the pressure drop. The experimental investigations are done in a single-cylinder light-duty diesel engine currently used in Indian market fitted with a Lean NOx Trap (LNT), Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF). From the Indian Driving Cycle (IDC) cycle, 8 representative operating conditions were chosen and experiments were conducted at steady state at these conditions. The chemical kinetic parameters, friction loss and heat transfer coefficient of the one-dimensional model were tuned using five of the 8 experimental data sets. The remaining three data sets were used to validate the predictions with no further tuning. The model could predict the conversion efficiency, pressure drop and outlet temperature with better accuracy. The calibrated model was then used to predict the effect of geometrical parameters. The effects of varying length and diameter of the EATD were studied with this calibrated model. The results obtained show that increasing the diameter is more effective than increasing the length for enhanced conversion efficiency and reduced pressure drop across LNT. For LNT, increasing the diameter by 5% and reducing the length by 10% compared to the existing design, results in a 1% reduction in volume, an 11% increase in pressure drop with 1.6% higher conversion efficiency. For cDPF, increasing the diameter by 10% and reducing the length by 10% results in a 9% increase in volume, a 17% reduction in pressure drop with 1.5% higher conversion efficiency. Thus, the current model and methodology can be used for optimizing the size of EATD.
Bagavathy, S. Suresh, Ramesh, A, Krishnasamy, Anand, Pandian, Senthur
Diesel Vehicle with Ultra-Low NOx Emissions on the Road2019-24-01459/9/2019
The gap between diesel vehicle emissions in laboratory tests compared to those in use has been addressed by the introduction of the Real Driving Emissions (RDE) requirements. Modern diesel technology now demonstrates low emissions on the road over a wide range of driving conditions. This paper further demonstrates that consistent low nitrogen oxide (NOx) and particle number (PN) emissions can be achieved over a wide range of driving conditions beyond Euro 6d RDE requirements, with emission control technologies combined in an integrated approach. An LNT (Lean NOx Trap) is combined with a dual-dosing SCR (Selective Catalytic Reduction) system. Low-load NOx control is achieved by the LNT in combination with a close-coupled SCR coated on the Diesel Particulate Filter (SDPF). High load conditions, on the other hand, are covered by the underfloor SCR system with a second AdBlue® injector. A P0 48V mild-hybrid system is also available to support the NOx control and to ensure good driving performance and fuel efficiency. An advanced control strategy is implemented to ensure optimal interaction between all emission control functionalities. The system was implemented on a C-segment demonstrator vehicle. The paper discusses the emissions tests performed and the results achieved. A combination of tests on the road and in the lab were carried out to cover a wide range of driving conditions. Special attention was paid to the robustness of the emission performance under urban and motorway driving conditions. Results demonstrate that each aftertreatment component contributes to achieving consistently low NOx emissions under all driving conditions. Particulate emissions are effectively controlled by the DPF.
Demuynck, Joachim, Favre, Cecile, Bosteels, Dirk, Bunar, Frank, Spitta, Joachim, Kuhrt, Andreas
Engine-Aftertreatment in Closed-Loop Modeling for Heavy Duty Truck Emissions Control2019-01-09864/2/2019
An engine-aftertreatment computational model was developed to support in-loop performance simulations of tailpipe emissions and fuel consumption associated with a range of heavy-duty (HD) truck drive cycles. For purposes of this study, the engine-out exhaust dynamics were simulated with a combination of steady-state engine maps and dynamic correction factors that accounted for recent engine operating history. The engine correction factors were approximated as dynamic first-order lags associated with the thermal inertia of the major engine components and the rate at which engine-out exhaust temperature and composition vary as combustion heat is absorbed or lost to the surroundings. The aftertreatment model included catalytic monolith components for diesel exhaust oxidation, particulate filtration, and selective catalytic reduction of nitrogen oxides (NOx) with urea. Both the engine and aftertreatment models have been calibrated with dynamometer measurements from a commercial 2010-certificated 15-L Cummins diesel engine. The fuel consumption engine map with the reduced data is attached in the appendix. Simulations with the combined engine and aftertreatment models above appear to reveal important trends among the fuel efficiency, emissions control, power demand for HD trucks under realistic drive cycle conditions. Thus, this type of computational simulation appears to have significant value in choosing among options for HD vehicle design and operation.
Gao, Zhiming, Deter, Dean, Smith, David, Pihl, Josh, Daw, C. Stuart, Parks, James
Model-Based Approaches in Developing an Advanced Aftertreatment System: An Overview2019-01-00261/15/2019
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.
Su, Changsheng, Brault, Joseph, Munnannur, Achuth, Liu, Z. Gerald, Milloy, Sean, Harinath, Arvind, Dunnuck, David, Federle, Ken
Catalyst-Based BS VI Stage 2 Emission Control Solutions for Light Duty Diesel2019-26-01411/9/2019
Various types of after-treatment system for BS VI Stage 1 are being assessed for the Light Duty Diesel (LDD) segment. For BS VI Stage 2, Real Driving Emission (RDE) assessment will be newly introduced, which will require more robustness in emission control system capability. Although the detailed requirements for India BS VI stage 2 are still being discussed, a reasonable assumption is that similar systems to those being developed for Euro 6d, will work for India BS VI. This paper describes typical system designs for Euro 6d and also reveals newly developed SCRF® (Selective Catalytic Reduction Filter) based systems, which demonstrate excellent RDE emissions. In addition, newly developed Lean NOx Trap (NSC) coatings, which focus on low temperature NOx control used with SCRF® (NSC + SCRF®) also show excellent emission control capability as demonstrated in this case on the ARTEMIS Cycle. These systems have potential as promising LDD solutions for India BS VI stage 2.
Sumiya, Satoshi, Kumar, Abhishek, Wylie, James, Bergeal, David
Experimental Analysis of LNT/DPF after Treatment System on a Passenger Car for Indian Road Condition2019-26-01551/9/2019
The Lean NOx Trap (LNT) / Diesel Particulate Filter (DPF) system has been developed as one of key technologies to comply with BS VI regulations. For DPF system it is necessary to prevent excessive soot accumulation and high temperature which can lead to eventual DPF failure. For LNT system it is necessary to maintain the NOx conversion efficiency to meet the required BS VI norms. Considering the Indian road condition a methodology was developed to evaluate the soot, de-NOx and de-SOx regeneration for development of optimized LNT/DPF system. The study was carried on >1500cc, LNT/DPF equipped Euro VI diesel passenger car to evaluate the effect of regeneration characteristics in real Indian driving condition. The study was carried on different conditions such as traffic [urban mode and rural mode] and ambient condition like temperature and weather on the regeneration behavior of LNT/DPF. A concurrent study was conducted on the regeneration frequency, timing, temperature, success rate on the above mentioned methods which affects the life of the post-treatment system. The paper shows the correlation between the active & passive regeneration and Indian road condition for the development of BS VI. The focus of the study was on the system components and the information based on which regeneration is triggered. The paper will report on failure regenerations under several extreme conditions.
Tiwari, Rahul Kumar, Balagangatharan, Balamuralitharan
Impact of Demanding Low Temperature Urban Operation on the Real Driving Emissions Performance of Three European Diesel Passenger Cars2018-01-18199/10/2018
In Europe, the development and implementation of new regulatory test procedures including the chassis dynamometer (CD) based World Harmonised Light Duty Test Procedure (WLTP) and the Real Driving Emissions (RDE) procedure, has been driven by the close scrutiny that real driving emissions and fuel consumption from passenger cars have come under in recent times. This is due to a divergence between stated certification performance and measured on-road performance, and has been most pointed in the case of NOx (oxides of nitrogen) emissions from diesel cars. The RDE test is certainly more relevant than CD test cycles, but currently certification RDE cycles will not necessarily include the most extreme low speed congested or low temperature conditions which are likely to be more challenging for NOx after-treatment systems. To build understanding of the emissions and fuel consumption performance of the latest available diesel passenger cars, Concawe has conducted a study of the performance of three vehicle types. Two of the vehicles featured urea-dosed Selective Catalytic Reduction (SCR) after-treatment, whilst the third was fitted with a Lean NOx Trap (LNT) and a downstream passive SCR catalyst (pSCR). For each vehicle, triplicate tests were conducted over a moderate RDE on-road cycle, as well as CD testing of the Transport for London (TfL) Urban Inter Peak (UIP) cycle, developed directly from real-driving trips in the City of London, UK. The TfL UIP is considered a severe urban cycle and was run over ambient temperatures ranging from −15 °C to 23 °C. After the initial 2-3 minute warm up period, the SCR-equipped vehicles were effective at controlling NOx, while the LNT-equipped vehicle was more effective in the initial minutes of running. The data generated provides insights into the emissions performance of Euro 6 diesel passenger cars, and their after-treatment systems, in extreme congested cold urban conditions including, and beyond, the most demanding likely to be encountered under regulatory RDE testing.
Williams, Rod, Andersson, Jon, Hamje, Heather, Ziman, Pauline, Kar, Kenneth, Fittavolini, Corrado, Pellegrini, Leonardo, Gunther, Garry, Oliva, Fermin, Van de Heijning, Paul
Supervisory Controller for a Light Duty Diesel Engine with an LNT-SCR After-Treatment System2018-01-17679/10/2018
Look ahead information can be used to improve the powertrain’s fuel consumption while efficiently controlling exhaust emissions. A passenger car propelled by a Euro 6d capable diesel engine is studied. In the conventional approach, the diesel powertrain subsystem control is rule based. It uses no information of future load requests but is operated with the objective of low engine out exhaust emission species until the Exhaust After-Treatment System (EATS) light off has occurred, even if fuel economy is compromised greatly. Upon EATS light off, the engine is operated more fuel efficiently since the EATS system is able to treat emissions effectively. This paper presents a supervisory control structure with the intended purpose to operate the complete powertrain using a minimum of fuel while improving the robustness of exhaust emissions. A supervisory controller assisted by look ahead information, and using a supervisory control interface that works in concert with low level local controllers, can make subsystems operate near optimal. The look ahead parametrized supervisory control calculates the set-points for the subsystems: Internal Combustion Engine (ICE), Lean NOx Trap (LNT) and the Selective Catalytic Reduction (SCR) based on the Emission Equivalent Fuel Consumption minimization strategy (EEFC). The controller performance is analyzed for the World wide harmonized Light vehicles Test Cycle (WLTC) and randomly sequenced WLTCs under different initial conditions. This paper extends upon the earlier work where an LNT-SCR EATS supervisory control structure was proposed that optimizes based on the EEFC strategy. The future work will focus on extending the approach to more subsystems and characterizing the look ahead information.
Velmurugan, Dhinesh, McKelvey, Tomas, Lundberg, Daniel
Study of an Aftertreatment System for HLSI Lean-burn Engine2018-01-09454/3/2018
Lean-burn is an effective means of reducing CO2 emissions. To date, Homogenous Lean Charge Spark Ignition (HLSI) combustion, which lowers emissions of both CO2 and NOx, has been studied. Although HLSI realizes lower emission, it is a major challenge for lean-burn engines to meet SULEV regulations, so we have developed a new aftertreatment system for HLSI engines. It consists of three types of catalysts that have different functions, as well as special engine control methods. As the first stage in achieving SULEV emissions, this study focused on enhancing performance under lean conditions. HLSI engine exhaust gases contain high concentrations of hydrocarbons, including a large amount of paraffin, which are difficult to purify, rather than low concentrations of NOx. Therefore, the key point in low emissions is to purify not only NOx, but also high concentrations of paraffin at the same time. Other issues include maintaining high performance under stoichiometry operation and reducing N2O emissions. To resolve these issues, it is important to focus on the division of catalyst roles and their arrangement, and the modification of catalyst material. In this study, an aftertreatment system with three catalysts was developed. TWC was applied for the first catalyst to purify stoichiometry exhaust gases, and a new type of catalyst was used for the second and third catalysts in order to purify hydrocarbon and NOx under lean conditions. The new catalyst was an improvement based on a lean NOx trap catalyst, and was added to a paraffin purification material that highly enhances PGM activity by suppressing oxygen poisoning in PGMs, which hinders paraffin oxidation. The approach to enhancing NOx purification and reducing N2O emissions is to arrange the second and third catalysts with the optimal temperature properties in each position. This layout covers a wide temperature range for NOx performance and reduces N2O emissions. This system was evaluated on an engine bench using a steady lean-rich cycle test. High performance under lean conditions was confirmed.
Takeori, Hiroki, Wada, Katsuji, Matsuo, Yuichi, Morita, Tomoko, Konomoto, Takashi, Murata, Yuichiro, Kimura, Munekazu, Miyauchi, Atsuhiro
Robust DPF Regeneration Control for Cost-Effective Small Commercial Vehicles2017-24-01239/4/2017
Small commercial vehicles (SCV) with Diesel engines require efficient exhaust aftertreatment systems to reduce the emissions while keeping the fuel consumption and total operating cost as low as possible. To meet current emission legislations in all cases, a DOC and DPF and some NOx treatment device (e,g. lean NOx trap or SCR) are required. Creating a cost-effective SCV also requires keeping the cost for the exhaust aftertreatment system as low as possible because the contribution to total vehicle cost is high. By using more sophisticated and more robust operating strategies and control algorithms, the hardware cost can be reduced. To keep the calibration effort at a low level, it is necessary to apply only algorithms which have a time-efficient calibration procedure. This paper will focus on the active regeneration of the DPF. For safe and efficient DPF regeneration, a very reliable and stable DOC out temperature control is required. DOC characteristics and design are often limited by cost and available space but also strongly influence the control requirements and thus the performance. This leads to more sophisticated and more robust control algorithms. In this paper an advanced control algorithm for DOC outlet temperature control for a SCV is presented. The control algorithm applies model-based control and gain-scheduling techniques. An overview over the control algorithm is given and its performance is evaluated on engine test bench, chassis dynamometer and on the public road and compared to the traditional concept which was used before. The results and experiences are presented and analyzed.
Eck, Christopher, Nakano, Futoshi
Technology Challenges and Strategies for BS-VI in Commercial Vehicles2017-28-19377/10/2017
Air Pollution is a major concern in our country due to which Indian Government has taken a decision to move from BS-IV to BS-VI which is nearly 90% reduction in NOx and 50% in particulate matter along with addition of particulate number regulation for BS-VI in comparison to BS-IV norms in very short span of time. Vehicle manufacturers are also having the challenge to produce low cost and fuel efficient product with BS-VI solution in order to meet tightening emission regulations and increasing needs of lower fuel consumption. Detailed study is done with different approaches to meet BS-VI emission which is elaborately explained in different aspect of engine design and after treatment parameter with its pros and cons. After Treatment selection plays an important role in engine development to meet stringent emission legislations and customer demands. Strategies for BS-VI were described with the advantage and drawbacks for after treatment selection. The cost of after treatment and its durability is also the major challenge to establish the BS-VI solution in the market. The injection pressure and turbo charger also play the vital role for strategic decision from the base engine side. Comparative study is done with different aspects of after treatment and base engine design aggregates to meet the emission for BS-VI.
Barman, Jyotirmoy, Arora, Prateek, Patchappalam, Kumar
NO 2 /NOx Ratio and NH 3 Storage Estimation of Automotive SCR Multi-Brick Systems2017-01-09723/28/2017
Many control approaches for selective catalytic reduction (SCR) systems require knowledge of ammonia storage (NH3 storage) to dose urea accurately. Currently there are no technologies to directly measure internal NH3 storage in a vehicle, so it can only be inferred from hardware sensors located upstream, downstream, or in the catalyst. This paper describes an application of extended Kalman filter (EKF) state estimator used as a virtual sensor for urea injection control of a multi-brick aftertreatment system. The proposed estimator combines mean-value physics-based models of combined SCR and diesel particulate filter (SCR/DPF), SCR and clean-up catalyst (CUC). It uses hardware sensors at the inlet and outlet of the aftertreatment system, and includes no sensors between the catalysts. Performance of the proposed estimator was validated in simulations against a high-fidelity model of the aftertreatment system. The algorithm provides accurate estimates of the dominant gaseous species NOx and NH3 as well as NH3 storage for a feedback model predictive control (MPC) control of urea injection. Moreover, the algorithm is able to estimate upstream NO2/NOx ratio from provided constant reference. The proposed estimator is a link in the model-based control design toolchain aimed for post-EURO 6 RDE-compliant light-duty vehicle design. Together with the MPC controller they are capable of running in real-time on current production hardware.
Figura, Jiri, Pekar, Jaroslav, Krejza, Pavel, Mracek, David, von Wissel, Dirk, Zhang, Tianran
Performance Studies and Correlation between Vehicle- and Rapid- Aged Commercial Lean NOx Trap Catalysts2017-01-09403/28/2017
Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.
De Abreu Goes, Jesus Emmanuel, Olsson, Louise, Berggrund, Malin, Kristoffersson, Annika, Gustafson, Lars, Hicks, Mikael
Development of Advanced Ultra-Low PGM DOC for BS VI DOC+CDPF+SCR System2017-26-01421/10/2017
Stricter regulatory standards are continuously adopted worldwide to control heavy duty emissions, and at the same time, fuel economy requirements have significantly lowered exhaust temperatures. The net result is a significant increase in Precious Group Metal (PGM) usage with current Diesel Oxidation Catalyst (DOC) technology. Therefore, the design and development of advanced DOC with ultra-low PGM to achieve highly beneficial emission performance improvement is necessary. The advanced DOC is synergized PGM (SPGM) with Mixed Metal Oxide (MMO). The presence of MMO in SPGM is responsible for NO oxidation to NO2 which is critical for the passive regeneration of the downstream filter and SCR function. This paper outlines the development of MMO for application in modern DOCs and addresses some specific challenges underlying this application. Lab and flow reactor data demonstrates MMO by itself owns great oxidation properties with high surface area available for NO oxidation reaction. In addition, SPGM DOC with reduced PGM levels indicated thermal resistance and sensitivity to type of hydrocarbon in gas stream. This paper summaries the results of engine dyno and on-road testing of SPGM DOC versus OEM DOCs. The engine testing indicated high level of NO2 production at significantly reduced PGM levels. On-road testing on DOC/CDPF/SCR system showed no change or deterioration of the system performance after the switch OEM DOC to SPGM DOC. Field data logging during on-road testing showed identical exotherms for both systems and great NOX conversion and enough NO2 formation when ultra-low SPGM used as advanced DOC. Specific challenges remain in the development of the SPGM DOC which is under investigation based on formulation and mechanism of MMO.
Nazarpoor, Zahra, Golden, Steve, Liu, Ru-Fen
Analysis of a Diesel Passenger Car Behavior On-Road and over Certification Duty Cycles2016-01-232810/17/2016
Precise, repeatable and representative testing is a key tool for developing and demonstrating automotive fuel and lubricant products. This paper reports on the first findings of a project that aims to determine the requirements for highly repeatable test methods to measure very small differences in fuel economy and powertrain performance. This will be underpinned by identifying and quantifying the variations inherent to this specific test vehicle, both on-road and on Chassis Dynamometer (CD), that create a barrier to improved testing methods. In this initial work, a comparison was made between on-road driving, the New European Drive Cycle (NEDC) and World harmonized Light-duty Test Cycle (WLTC) cycles to understand the behavior of various vehicle systems along with the discrepancies that can arise owing to the particular conditions of the standard test cycles. The engine controller of a 2.0L diesel vehicle with active de-NOx and a particulate filter (DPF) has been monitored over 13,700km of driving. The engine speed/torque operating points showed that both the NEDC and WLTC fail to capture the complete static and dynamic usage observed on the road, and are ill-equipped to capture any driver to driver variations. A cyclic analysis of the DPF is proposed, showing up to 70% variation in soot loading at the point of regeneration. This variation can be explained by the controller waiting for favorable driving conditions for regeneration. NEDC and WLTC are poor cycles for capturing DPF effects as the former presents insufficient engine powers to trigger and the later insufficient time to complete a regeneration event. Along with understanding the general contrasts between standard CD cycles and road conditions, this is a key finding for the project overall as understanding and managing DPF loading and regeneration will enable improvements to be made in test precision.
Chappell, Edward, Burke, Richard, Lu, Pin, Gee, Michael, Williams, Rod
Development of Ultra-Low Synergized PGM as Diesel Oxidation Catalyst for Heavy-Duty Applications2016-01-232110/17/2016
Stricter regulatory standards are continuously adopted worldwide to control heavy duty emissions, and at the same time, fuel economy requirements have significantly lowered exhaust temperatures. The net result is a significant increase in Precious Group Metal (PGM) usage with current Diesel Oxidation Catalyst (DOC) technology. Therefore, the design and development of synergized precious metal (SPGM) in which ultra-low PGM is synergized with mixed metal oxide (MMO) to achieve highly beneficial emission performance improvement, is necessary. The presence of MMO in SPGM is responsible for NO oxidation to NO2 which is critical for the passive regeneration of the downstream filter and SCR function. This paper presents an initial study outlining the development of MMOs for application in modern DOCs and addresses some specific challenges underlying this application. Lab and flow reactor data in this study demonstrated SPGM DOCs thermal resistance and sulfur poisoning resistance. In addition, SPGM DOC with reduced PGM levels indicated the increase of NO2 production at T>250 °C compared to OEM benchmarks. This paper outlines the results of engine dyno, transient dyno and on-road testing of SPGM DOCs versus OEM DOCs. The engine testing indicated high level of NO2 production at significantly reduced PGM levels. On-road testing showed no change or deterioration of the system performance after the switch to SPGM for a heavy duty DOC and filter system. Field data logging during on-road testing showed identical exotherms for the same active regeneration calibration, which results in equivalent DPF regeneration. Disclosed SPGM for on-road heavy-duty applications is consistent with sufficient CO and HC conversion and superior warmed up NO2 make. Specific challenges remain in the development of the SPGM DOC which is under investigation based on formulation and mechanism of mixed metal oxides.
Nazarpoor, Zahra, Golden, Steve, Launois, Maxime, Kitazumi, Sen, Xie, Dianyong, McConnell, Campbell
Rapidly Pulsed Reductants in Diesel NOx Reduction by Lean NOx Traps: Effects of Mixing Uniformity and Reductant Type2016-01-09564/5/2016
Lean NOx Traps (LNTs) are one type of lean NOx reduction technology typically used in smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package . However, the performance of lean NOx traps (LNT) 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 a LNT in order to expand its operating window to higher temperatures and space velocities. This approach has also been called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) by Toyota. There is a vast parameter space which could be explored to maximize RPR performance and reduce the fuel penalty associated with injecting hydrocarbons. In this study, the mixing uniformity of the injected pulses, the type of reductant, and the concentration of pulsed reductant in the main flow were investigated. We found that all of these parameters are important for the RPR system performance. To obtain a uniformity of flow with the injected species to approach that of a plug flow, we developed a design using specific mixers to maximize the performance of RPR. The initial hypothesis for the required mixing process was to uniformly mix the injected reductants with the main flow in the radial direction, while keeping the axial mixing as low as possible. This goal was achieved by incorporating different mass transport processes, i.e. advection in the radial direction, and diffusion in the axial direction. Numerical investigation of the mixing of high frequency pulsed gaseous hydrocarbons into the main exhaust flow was performed to design an effective mixer to satisfy the desired mixing conditions. This mixing process and a fast injection system (down to 1ms pulse duration) was shown to have uniform radial mixing and axially separated pulses of reductants that gave the optimal mixing condition and achieved the highest RPR NOx conversion performance. Employing the designed mixer, a range of reductants (H2, CO, C2H4, C3H6, and C3H8) were tested under similar operating conditions over a Pt/Rh LNT. The effectiveness of different reductants for NOx conversion in different temperature regimes was found to be as follows: T < 270°C: H2 > CO > C3H6 > C2H4; 270°C < T < 500°C: C3H6 > H2 > CO > C2H4; T > 500°C: C3H6 > C2H4 >H2 ∼ CO. In terms of the selectivity of converted NOx, H2 resulted in significant ammonia formation at low temperatures, but overall, the N2 selectivity was as follows: CO ∼ C3H6 > C2H4 >> H2. Generally, it was concluded that hydrocarbon reductants provided higher NOx conversion in the mid-range and especially higher temperature ranges with relatively high nitrogen selectivity. However, it was observed that the reactivity of hydrocarbons and the availability of oxygen had a significant influence on their performance, especially as the pulsing frequency was increased and reduction reaction time became more limited. In this study we have shown that the use of rapidly pulsed reductants (RPR) can be studied in the laboratory with the equipment and methods presented here. In studies with a LNT catalyst, the variations in NOx performance with several reductants at reasonably high frequencies were shown. This suggests that this system should be able to provide useful information for optimizing the performance of LNT catalysts at high temperatures.
Reihani, Amin, Corson, Benjamin, Hoard, John W., Fisher, Galen B., Smirnov, Evgeny, Roemer, Dirk, Theis, Joseph, Lambert, Christine
Impact of Rh Oxidation State on NOx Reduction Performance of Multi-Component Lean NOx Trap (LNT) Catalyst2016-01-09474/5/2016
Typical Lean NOx Trap (LNT) catalyst composition includes precious metal components (Pt, Pd, and/or Rh), responsible for NO oxidation during lean operation and NOx reduction during rich operation. It was found that redox history of commercial LNT catalyst plays a significant role on deciding its NOx conversion under Lean/Rich cyclic condition. Further test had shown that fully formulated LNT catalyst being pre-reduced had shown much better NO reduction activity during the temperature-programmed reduction (TPRx) of NO than the same LNT catalyst being oxidized. The following study with Rh-only and Pt-only catalyst had demonstrated that Rh plays a key role on the large variation of the NO reduction function due to oxidation state change over LNT catalyst. Kinetic analysis of the NO reduction was performed in an attempt to elucidate the underlying mechanistic relationship, where it was found that NO reduction over reduced Rh can be well described by an Arrhenius equation with first-order dependence on NO concentration while the oxidized catalyst had been changing its surface redox state during NO reduction. The activation energy of the NO reduction process over reduced fully formulated LNT catalyst was found to be ∼180±14kJ/mol, which is consistent with Rh-only catalyst but very different from Pt-only catalyst. The observed apparent activation energy of NO reduction on LNT catalyst was independent of the reductant used or the degree of hydrothermal aging either from field-aging or lab aging. These findings are consistent with NO dissociation being the rate-limiting step in the NO reduction process. The hydrothermal aging, redox state as well as the reductant type would only change the total number of sites available, active sites accessible as well as the surface coverage, respectively.
Li, Junhui, Currier, Neal, Yezerets, Aleksey, Chen, Hai-Ying, Hess, Howard, Mulla, Shadab
Adapting Design for Six Sigma (DFSS) Methodology for Diesel Lean NOx Trap (LNT) Catalyst Screening2016-01-09534/5/2016
In order to meet LEV III, EURO 6C and Beijing 6 emission levels, Original Equipment Manufacturers (OEMs) can potentially implement unique aftertreatment systems solutions which meet the varying legislated requirements. The availability of various washcoat substrates and PGM loading and ratio options, make selection of an optimum catalyst system challenging, time consuming and costly. Design for Six Sigma (DFSS) methodologies have been used in industry since the 1990s. One of the earliest applications was at Motorola where the methodology was applied to the design and production of a paging device which Consumer Reports called “virtually defect-proof”.[1] Since then, the methodology has evolved to not only encapsulate complicated “Variation Optimization” but also “Design Optimization” where multiple factors are in play. In this study, attempts are made to adapt the DFSS concept and methodology to identify and optimize a catalyst for diesel applications. Lean NOx Trap (LNT) was selected as the catalyst of choice as it could become a development choice in future aftertreatment architecture for above-mentioned emission levels and cold start improvements. Catalysts from multiple washcoat manufacturers’ current production were acquired. Factors such as washcoat type, PGM loading, ratio and component aging were investigated. Catalyst performance was optimized under a specific set of testing conditions. The study proved that the DFSS methodology is a powerful tool that can be adapted for screening large number of catalysts in a relatively short period of time with reduced number of tests, under identical conditions with promising results.
Ahari, Homayoun, Smith, Michael, Zammit, Michael, Walker, Brad
Virtual Test of Manufacturing Process Effect on Injector Design2015-01-27949/29/2015
Diesel exhaust after treatment solutions using injection, such as urea-based SCR and lean NOx trap systems, effectively reduce the emission NOx level in various light vehicles, commercial vehicles, and industrial applications. The performance of the injector is crucial for successfully utilizing this type of technology, and a simulation tool plays an important role in the virtual design, that the performance of the injector is evaluated to reach the optimized design. The virtual test methodology using CFD to capture the fluid dynamics of the injector internal flow has been previously developed and validated for quantifying the dosing rate of the test injector. In this study, the capability of the virtual test methodology was extended to determine the spray angle of the test injector, and the effect of the manufacturing process on the injector internal nozzle flow characteristics was investigated using the enhanced virtual test methodology. Several variations of injector key geometric features caused by the manufacturing process were tested, and the impacts on the dosing rate and the spray angle of test injectors were realized. The virtual test results indicated that the manufacturing process effect must be taken into account in the early product development stage for the optimization of injector design, and tolerances in the manufacturing process should be properly defined.
Lu, Meng-Huang, Lacin, Figen, McAninch, Daniel, Yang, Frank
SAE Fuel Consumption Test Procedure (Engineering Method)J1526_201509 (Historical)9/17/2015
This document describes a fuel-consumption test procedure that utilizes industry accepted data collection and statistical analysis methods to determine the difference in fuel consumption between vehicles with a gross vehicle weight of more than 10,000 pounds. This test procedure can be used for an evaluation of two or more different vehicles but is not to be used to evaluate a component change. Although on-road testing is allowed, track testing is the preferred method because it has the greatest opportunity to minimize weather and traffic influences on the variability of the results. All tests shall be conducted in accordance with the weather constraints described within this procedure and shall be supported by collected data and analysis. This document provides information that may be used in concert with SAE Recommended Practices J1264, J1252, J1321, and J2966 as well as additional current and future aerodynamic and vehicle performance SAE standards.
Truck and Bus Aerodynamics and Fuel Economy Committee
Identifying Limiters to Low Temperature Catalyst Activity2015-01-10254/14/2015
The drive to more fuel efficient vehicles is underway, with passenger car targets of 54.5 mpg fleet average by 2025. Improving engine efficiency means reducing losses such as the heat lost in the exhaust gases. However, reducing exhaust temperature makes it harder for emissions control catalysts to function because they require elevated temperatures to be active. Addressing this conundrum was the focus of the work performed. The primary objective of this work was to identify low temperature limiters for a variety of catalyst aftertreatment types. The ultimate goal is to reduce catalyst light-off temperatures, and the knowledge needed is an understanding of what prevents a catalyst from lighting off, why, and how it may be mitigated. Collectively these are referred to here as low temperature limiters to catalyst activity. This paper describes the work performed to identify low temperature limiters to catalyst activity for gasoline Three Way Catalyst (TWC), Diesel Oxidation Catalyst (DOC), Cu-Z Selective Catalytic Reduction (SCR), Fe-Z SCR and V SCR, Lean NOx Trap (LNT), Ammonia Oxidation Catalyst (AMOx) and Natural Gas Oxidation Catalyst (NGOx).
Bartley, Gordon J.
OBD Diagnostic Strategies for LEVIII Exhaust Gas Aftertreatment Concepts2015-01-10404/14/2015
Upcoming motor vehicle emission regulations, such as California's LEVIII, continue to tighten emission limitations in diesel vehicles. These increasingly challenging emission requirements will be met by improving the combustion process (reducing engine-out emissions), as well as improving the exhaust gas aftertreatment efficiency. Furthermore, intricate On-Board Diagnostics (OBD) systems are required to properly diagnose and meet OBD regulation requirements for complex aftertreatment systems. Under these conditions, current monitoring strategies are unable to guarantee reliable detection of partially failed systems. Additionally, new OBD regulations require aftertreatment systems to be diagnosed as a whole. This paper covers potential OBD strategies for LEVIII aftertreatment concepts with regard to regulation compliance and robustness, while striving to use existing sensor concepts.
Nanjundaswamy, Harsha K., Deussen, Joel, Van Sickle, Roger, Tomazic, Dean, Szailer, Tamas, Franke, Michael, Kotter, Matthias, Koerfer, Thomas
A Study of LNT & Urea SCR on DPF System to Meet the Stringent Exhaust Emission Regulation2014-01-281010/13/2014
In diesel engine development, the new technology is coming out to meet the stringent exhaust emission regulation. The regulation demands more eco-friendly vehicles. Euro6c demands to meet not only WLTP mode, but also RDE(Real Driving Emission). In order to satisfy RDE mode, the new technology to reduce emissions should cover all operating areas including High Load & High Speed. It is a big challenge to reduce NOx on the RDE mode and a lot of DeNOx technologies are being developed. So the new DeNOx technology is needed to cover widened operating area and strict acceleration / deacceleration. The existing LNT(Lean NOx Trap) and Urea SCR(Selective Catalytic Reduction) is necessary to meet the typical NEDC or WLTP, but the RDE mode demands the powerful DeNOx technology. Therefore, the LNT & Urea SCR on DPF was developed through this study. This complex new technology consists of new catalysts(to reduce emissions), insulation(to improve fuel economy, and catalytic performance), and logical controller(to control DeNOx and DePM strategy). This new technology is to improve the weak DeNOx performance and fuel penalty of LNT, and the fast heat-up issue of Urea SCR system. As this technology gathers the strong points of LNT and the Urea SCR system, it is able to meet the strengthened exhaust emission regulation. This study is the result to meet RDE mode and to make sure of fuel economy.
Joo, Kihyung, Park, Jin Woo, Lee, Jin-ha, Kim, Seok-Jae, Yoo, Seungbeom
Virtual Test of Injector Design Using CFD2014-01-23519/30/2014
Diesel exhaust aftertreatment solutions using injection, such as urea-based SCR and lean NOx trap systems, effectively reduce the emission NOx level in various light vehicles, commercial vehicles, and industrial applications. The performance of the injector plays an important role in successfully utilizing this type of technology, and the CFD tool provides not only a time and cost-saving, but also a reliable solution for extensively design iterations for optimizing the injector internal nozzle flow design. Inspired by this fact, a virtual test methodology on injector dosing rate utilizing CFD was proposed for the design process of injector internal nozzle flows. For a low-pressure (less than 6 bar) injector application, the characteristic Reynolds number based on the diameter and mass flow rate of the inlet, return flow outlet, and nozzle exit of the injector might range from 2000 to 20000, therefore, employing a flow-physics based viscous model for building up a virtual test methodology is critical to properly capture the fluid dynamics of injector internal nozzle flow. In this study, a transition three-equation eddy-viscosity model was used to calculate the dosing rate for injectors that have different configuration features, and the computational results of the proposed virtual test methodology were validated with the test data measured in the Tenneco Injector Flow Lab. The results also demonstrated the virtual test methodology can accurately predict the fluid dynamics of boundary layer development and calculate the onset of the transition to cope with the transitional flow behavior. Several design iterations were studied using the validated virtual test methodology to investigate the impacts of injector key geometric parameters on the dosing rate.
Lu, Meng-Huang, Lacin, Figen, McAninch, Daniel, Yang, Frank
Development and Implementation of a Mapless, Model Based SCR Control System2014-01-90507/1/2014
Various engine platforms employ Selective Catalytic Reduction (SCR) technology to reduce the tail pipe emissions of oxides of nitrogen (NOx) from diesel engines as part of an overall strategy to comply with the emission regulations in place in various countries. High levels of NOx conversion (greater than 98%) in SCR aftertreatment may provide operating margin to increase overall fuel efficiency. However, to realize the potential fuel efficiency gains, the SCR technology employed should achieve high NOx conversion with limited reductant slip over transient application cycles in addition to steady state operation. A new approach to SCR controls was developed and implemented. This approach does not rely on any maps to determine the amount of urea solution to be dosed, thus significantly reducing calibration and development time and effort when implementing the SCR technology on multiple engine platforms and applications. In addition, the controls technique is completely model based and was able to achieve high NOx conversion efficiencies through the SCR system, while ensuring limited ammonia slip due to sharp transient events in the application cycle. This ability allows the system to extract the maximum performance from the SCR catalyst, enabling the catalyst size to be optimized for space and cost constraints. The successful implementation of this control technique requires an SCR model with prediction accuracies greater than that typically achieved in practical implementation. Therefore, a real time correction technique was used to enhance the model accuracy to the desired levels for use in the controls algorithm.
Chavannavar, Praveen
Development of New Lean NOx Trap Technology with High Sulfur Resistance2014-01-15264/1/2014
In this study several NOx storage materials have been investigated to see their NOx storage properties. And sulfur release properties of these materials have been also investigated. Based on these findings, new LNT catalyst was developed. In this new LNT catalyst Barium is supported on one basic material, and Strontium is coated in the whole catalyst with high dispersion. And it shows higher NOx storage performance against conventional LNT one even though 10g/L of sulfur was introduced to the catalysts. According to analysis results of new LNT catalyst after sulfur poisoning, it was found that sulfur was mainly adsorbed on Strontium selectively, and then it formed sulfate compound as SrSO4. On the other hand, another sulfate compounds could be hardly observed. And regarding Barium on basic material some analysis measurement said that it has not only better NOx storage function, but also better sulfur release function. The assumption why new LNT catalyst has high sulfur resistance is that Strontium works like scavenger effect against sulfur, therefore it enables to keep higher NOx storage performance by Barium even if it contains much sulfur amount in the catalyst.
Umeno, Takahiro, Hanzawa, Masaya, Hayashi, Yoshiyuki, Hori, Masao
Secondary Fuel Injection Characterization of a Diesel Vaporizer for Active DPF RegenerationSAE-PAPER-2014-01-14944/1/2014
Secondary fuel injection is applied to facilitate active soot management of the particulate filter within diesel aftertreatment systems, avoiding concerns with fuel delivery via in-cylinder post-injection. System performance is dependent on the thermo-fluid interactions of the injected fuel with the exhaust stream, with the intent of having more fully vaporized fuel and a well-mixed air-fuel mixture at the inlet of the oxidation catalyst for uniform thermal distribution as it exothermically reacts. Pre-heating the fuel with a diesel vaporizer prior to its delivery into the exhaust enables improved system performance, reducing droplet sizes and mixing demands. A diesel vaporizer is applied within the exhaust of a medium duty truck application, and the response of the catalyst is characterized across a variety of conditions. Cross-sectional measurements at the catalyst and filter outlet are described, including gas velocity, temperature, and HC concentration, and the effect of poor fuel vaporization is demonstrated. The system is installed in a medium-duty truck with a 4.8L engine and characterized on a chassis dynamometer across various steady-state and transient conditions. Performance is measured while applying closed loop fuel dosing control algorithms, demonstrating control capabilities similar to injectors. Adequate thermal distribution is achieved with minimal HC slip, and recommendations are offered to further demonstrate system integration benefits and risks of diesel vaporizers.
Hein, Eric, Kotrba, Adam, Inclan, Tobias, Bright, Andrew
De-NOx Performance of Combined System of Reforming Catalyst and LNT for a DME Engine2013-01-259210/14/2013
Dimethyl ether(DME) is easily reformed into H2, since the chemical structure of DME does not feature direct C-C bonds, in contrast to diesel fuel. We have researched reforming catalysts for effectively generating H2 from the exhaust gases of a DME engine. The objective of this study is to evaluate the de-NOx performance of a combined system of RC(Reforming Catalyst) and LNT(Lean NOx Trap) for a DME engine according to reforming catalysts. The H2 generation of the reforming catalyst was observed under various conditions. CAT-A, CAT-B and CAT-C were prepared as reforming catalysts, and OC(Oxidation Catalyst) and LNT (Lean NOx Trap) were examined as commercial catalysts. The CAT-A catalyst has a higher amount of acid sites compared to the CAT-B and CAT-C catalysts. The CAT-A which is a mixing of mordenite and γ-Al2O3, has the highest H2 yield. However, the H2 yield decreased in the reforming reaction when CO2, NO and O2 coexisted. The NOx conversions of the combined system of fresh and hydrothermally aged CAT-A+LNT are higher by about 8% and 6% than those of the LNT. The NOx conversion over the combined system of CAT-A+LNT applied to the DME engine has been improved at high rpm-load conditions compared to the LNT.
Choi, Byung-Chul, Park, Syungyong, Lee, Young-Jae
Simulated Fuel Economy and Emissions Performance during City and Interstate Driving for a Heavy-Duty Hybrid Truck2013-01-10334/8/2013
We compare the simulated fuel economy and emissions for both conventional and hybrid class 8 heavy-duty diesel trucks operating over multiple urban and highway driving cycles. Both light and heavy freight loads were considered, and all simulations included full aftertreatment for NOx and particulate emissions controls. The aftertreatment components included a diesel oxidation catalyst (DOC), urea-selective catalytic NOx reduction (SCR), and a catalyzed diesel particulate filter (DPF). Our simulated hybrid powertrain was configured with a pre-transmission parallel drive, with a single electric motor between the clutch and gearbox. A conventional heavy duty (HD) truck with equivalent diesel engine and aftertreatment was also simulated for comparison. Our results indicate that hybridization can significantly increase HD fuel economy and improve emissions control in city driving. However, there is less potential benefit for HD hybrid vehicles during highway driving. A major factor behind the reduced hybridization benefit for highway driving is that there are fewer opportunities to utilize regenerative braking. Our aftertreatment simulations indicate that opportunities for passive DPF regeneration are much greater for both hybrid and conventional trucks during highway driving due to higher sustained exhaust temperatures. When passive DPF regeneration is extensively utilized, the fuel penalty for particulate control is virtually eliminated, except for a 0.4%-0.9% fuel penalty due to a slightly increased exhaust backpressure.
Daw, C. Stuart, Gao, Zhiming, Smith, David E., Laclair, Tim J., Pihl, Josh A., Edwards, K. Dean
Comparative Urban Drive Cycle Simulations of Light-Duty Hybrid Vehicles with Gasoline or Diesel Engines and Emissions Controls2013-01-15854/8/2013
We summarize results from comparative simulations of hybrid electric vehicles with either stoichiometric gasoline or diesel engines. Our simulations utilize previously published models of transient engine-out emissions and models of aftertreatment devices for both stoichiometric and lean exhaust. Fuel consumption and emissions were estimated for comparable gasoline and diesel light-duty hybrid electric vehicles operating over single and multiple urban drive cycles. Comparisons between the gasoline and diesel vehicle fuel consumptions and emissions were used to identify potential advantages and technical barriers for diesel hybrids.
Gao, Zhiming, Daw, C. Stuart, Smith, David E.
Adaptive Temperature Control for Diesel Particulate Filter Regeneration2013-01-05174/8/2013
The regeneration process of a Diesel Particulate Filter (DPF) consists of an increase in the engine exhaust gas temperature by using post injections and/or exhaust fuel injection during a period of time in order to burn previously trapped soot. The DPF regeneration is usually performed during a real drive cycle, with continuously changing driving conditions. The quantity of post injection/exhaust fuel to use for regeneration is calculated using a combination of an open loop term based on engine speed, load and exhaust gas flow and a closed loop term based on an exhaust gas temperature target and the feedback from a number of sensors. Due to the nature of the system and the slow response of the closed loop term for correcting large deviations, the authority of the fuel calculation is strongly biased to the open loop. However, the open loop fuel calculation might not be accurate enough to provide adequate temperature tracking due to several disturbances in the system. This paper discusses a novel methodology for temperature control of the DPF during regeneration. A correction factor, which is a function of fuel computed by open loop and closed loop methods, is defined. This factor is used to generate an adaptive fuel correction map which updates during every regeneration event. At the end of the drive cycle, the map is stored within the Non Volatile Memory of the engine control unit, for use in the next regeneration cycle. The strategy is validated using rapid prototyping tools. This control strategy results in improved temperature control during regeneration of the DPF which will increase the average quality of the regeneration events.
Castellano, Javier, Chaudhari, Anita, Bromham, Jim
Design of Durable Vanadium - SCR Catalyst Systems for Heavy - Duty Diesel Applications2013-26-00491/9/2013
The emission regulations for mobile applications become stricter in Euro-IV to Euro-VI levels. Carbon monoxide and hydrocarbon can be removed by efficient Diesel Oxidation Catalysts (DOC) but Particulate Matter (PM) and NOx are more demanding requiring the use of active methods (urea-SCR and DPF) which will be world-wide implemented in the 2010's. Durable, coated V-SCR catalysts are based on stabilized raw materials and tailored preparation methods. Coated V2O5/TiO2-WO3 catalysts (ceramic 300/400 cpsi and metallic 500/600 cpsi) were evaluated by laboratory and engine bench experiments. Traditional V-SCR catalysts are durable up to about 600°C and have a high efficiency at 300°C-500°C. SCR activities were tailored to be higher also at 200°C-300°C or 500°C-600°C. The use of thermal stabilizers or the vanadium loading variation enabled the changes in operation window and stability. The stabilized V-SCR catalyst kept the SCR activity also after ageing at 600°C-650°C when the reference lost partly the activity. NOx conversions (DOC+SCR, 300 cpsi ceramic) without NH3 slip were above 95% in steady engine points (250°C-530°C, 19.000-51.000 h−1). DOC with a low Pt loading (25 g/cft) was efficient to reach target NO2 promotion (>30% NO2 at 250°C-300°C) needed at low temperatures. The promotion by hydrolysis catalysts on SCR was demonstrated by full and partial flow designs. The development for hydrolysis catalyst coating resulted in lower HNCO formation and better SCR selectivity. The NOx conversions with defined NH3 slip (<10-20 ppm) by catalyst volumes and controlled urea dosing were used for dosing strategy design over the life-time (>500.000 km) of the system. The target NOx conversion (80%-95%) has a crucial effect on required catalyst volumes and dosing strategy marginal, which principles were analyzed based on urea-dosing experiments.
Maunula, Teuvo, Viitanen, Arto, Kinnunen, Toni, Kanniainen, Kauko
Development of an Urea Supply System for the SCR Catalyst2013-26-00471/9/2013
The increase in the fuel price and more stringent regulations on greenhouse gases (CO2) make the engine compression ignition technology even more attractive in the context of internal combustion engines. This is because the modern turbocharged direct injection engines, with the common rail fuel system, are characterized by high combustion efficiency and power density, that make them particularly suitable both for applications on and off road. On the other hand, the compression ignition engines are subject to a heavy technological developments to meet the more stringent regulations on emissions of exhaust pollutants, especially PM and NOx. The adopted technologies have two main approaches, on the combustion and on the exhaust gas aftertreatment. The measures applied for combustion can reduce emissions, but with the risk of penalizing the other engine performances, such as noise, power output and fuel consumption. Instead, the technologies of exhaust gases treatment may allow the over coming of this conflict. In particular using a Selective Catalytic Reduction (SCR) catalyst, a NOx reduction can be reached at least up to 95%. The present article describes the activities to define and optimize a supply system for the SCR catalyst, applied to a wide range of diesel engines, from Light Duty (LD) vehicles to Off-Road (OR) applications. For this kind of applications the development has taken into account requirements in terms of performance, layout and cost, unlike the Heavy Duty (HD) vehicle, where the SCR is employed for many years with less constraints. The development phase has been characterized by a 0-D model simulation activity to define the system performances and the main management strategies, and 1-D and 3-D model simulation activities for the hydraulic design.
De Cesare, Matteo, Osbat, Giovanni, Sgatti, Stefano, Battistoni, Michele
Characterization of a New Advanced Diesel Oxidation Catalyst with Low Temperature NO x Storage Capability for LD Diesel2012-01-03734/16/2012
Currently, two consolidated aftertreatment technologies are available for the reduction of NOx emissions from diesel engines: Urea SCR (Selective Catalytic Reduction) systems and LNT (Lean NOx Trap) systems. Urea SCR technology, which has been widely used for many years at stationary sources, is becoming nowadays an attractive alternative also for light-duty diesel applications. However, SCR systems are much more effective in NOx reduction efficiency at high load operating conditions than light load condition, characterized by lower exhaust gas temperatures. One possible solution to improve the low temperature behavior, is the use of newly developed Advanced Diesel Oxidation Catalysts (A-DOC) which are capable to store NOx at low exhaust temperatures (typical of urban driving conditions) when SCR efficiency is low, and to release the stored NOx at higher temperatures (i.e., during extra-urban driving conditions) where the urea injected is effectively forming ammonia for the subsequent NOx conversion. Experimental tests were therefore carried out in order to assess the performance of an A-DOC when exposed at the emissions coming from a modern Euro 5, 2.0 L displacement turbocharged Common Rail DI diesel engine for a typical European passenger car: the engine features a DOC and a DPF in close-coupled position, hosted into an on-purpose-designed dismountable canning, thus allowing an easy switch between different components. The characterization of these newer DOC formulations was performed over NEDC cycles. Moreover, the catalysts were tested both in fresh and hydrothermally aged conditions in order to have a better understanding relative to robustness and durability of these newer catalysts. NOx storage capability, which was found to be impressively high for a fresh A-DOC, significantly decreased after aging, thus leading to a final NOx cumulated emissions figure which equals the engine-out value for the aged A-DOC. Nevertheless, since most of the NOx released from the A-DOC occurs during the EUDC segment, when a downstream SCR would likely have reached appreciable NOx reduction efficiencies, even an aged A-DOC could provide significant benefits in terms of NOx emissions reduction. However, the analysis of the NO/NO₂ share downstream of the DPF, which is of crucial importance for SCR efficiency at low temperature, revealed that the overall conversion efficiency for NO over NEDC was negative, while on the contrary the conversion efficiency for NO₂ was remarkably high. As a result, the NO₂/NOx ratio downstream of the DPF (i.e., at the inlet of a downstream SCR) remained significantly low during the whole EUDC segment, thus hindering the achievement of high NOx conversion efficiencies and the full exploitation of a synergetic combination of the A-DOC with a downstream SCR.
Millo, Federico, Vezza, Davide
Simulation of Catalytic Oxidation and Selective Catalytic NOx Reduction in Lean-Exhaust Hybrid Vehicles2012-01-13044/16/2012
We utilize physically-based models for diesel exhaust catalytic oxidation and urea-based selective catalytic NOx reduction to study their impact on drive cycle performance of hypothetical light-duty diesel-powered hybrid and plug-in hybrid vehicles (HEVs and PHEVs). The models have been implemented as highly flexible SIMULINK block modules that can be used to study multiple engine-aftertreatment system configurations. The parameters of the NOx reduction model have been adjusted to reflect the characteristics of commercially available Cu-zeolite catalysts, which are of widespread current interest. We demonstrate application of these models using the Powertrain System Analysis Toolkit (PSAT) software for vehicle simulations, along with a previously published methodology that accounts for emissions and temperature transients in the engine exhaust. Our results illustrate that the DOC-SCR combination can reduce CO, HC and NOx emissions without creating a significant direct fuel penalty, but there is also an increase in the possibility of ammonia slip. Also, the addition of an upstream DOC increases aftertreatment thermal inertia, delaying light-off of the SCR catalyst. We find that the emissions reduction efficiency of the DOC-SCR combination is better for our simulated HEV compared to our simulated PHEV.
Gao, Zhiming, Daw, C. Stuart, Chakravarthy, V. Kalyana
Development of a Numerical Model to Predict the Impact of Phosphorus on Flow through Aftertreatment Components2012-01-12994/16/2012
A predictive numerical model was developed to determine the impact of phosphorus exposure on the performance of flow through aftertreatment components such as Diesel Oxidation Catalysts (DOC) or Selective Catalytic Reduction (SCR) catalysts. The model is able to successfully determine the distribution of the phosphorus over the catalyst as a function of the aging history (temperature, flow rates, oil consumption rate, phosphorus content of the oil) as well as the component properties (diameter, length, cell density, wall thickness). The model then incorporates this information regarding the distribution of phosphorus over the catalyst surface to determine the impact of the phosphorus exposure on the overall catalytic activity. The model results were successfully validated using accelerated bench aging tests for the oxidation of hydrocarbons over DOC's and NH₃ oxidation and NOx reduction over SCR catalysts. The modeling approach and methodology should, however, be readily extendable to wall flow aftertreatment components such as Diesel Particulate Filters (DPF) as well as other flow through components such as Lean NOx Traps (LNT's) that were not included in this study.
Chavannavar, Praveen
Application of Artificial Neural Networks to Aftertreatment Thermal Modeling2012-01-13024/16/2012
Accurate estimation of catalyst bed temperatures is very crucial for effective control and diagnostics of aftertreatment systems. The architecture of most aftertreatment systems contains temperature sensors for measuring the exhaust gas temperatures at the inlet and outlet of the aftertreatment systems. However, the temperature that correctly reflects the temperature of the chemical reactions taking place on the catalyst surface is the catalyst bed temperature. From the Arrhenius relationship which governs the chemical reaction kinetics occurring in different aftertreatment systems, the rate of chemical reaction is very sensitive to the reaction temperature. Considerable changes in tailpipe emissions can result from small changes in the reaction temperature and robust emissions control systems should be able to compensate for these changes in reaction temperature to achieve the desired tailpipe emissions. This paper presents an artificial neural network based model for estimating the catalyst bed temperature in aftertreatment systems. The artificial neural network was used to model the functional relationship of the catalyst bed temperature at different axial locations as a function of the exhaust gas mass flow rate, catalyst inlet exhaust gas temperature, catalyst outlet exhaust gas temperature, ambient temperature, and rate of heat generation from chemical reactions. A physics based one-dimensional thermal model for flow through aftertreatment systems was also developed and used to motivate the structure of the neural network model. Temperature measurements from diesel oxidation catalysts of different sizes during engine steady state and throttle snap experiments were then used to generate training samples for calibrating both models. The physics based one-dimensional thermal model and artificial neural network based model were then evaluated with data from transient experiments. When compared with the reduced order thermal model, the results show that the artificial neural network was able to achieve better accuracies.
Chi, John Nji
Newly Developed Cordierite Honeycomb Substrate for SCR Coating Realizing System Compactness and Low Backpressure2012-01-10794/16/2012
Ammonia Selective Catalytic Reduction (SCR) and Lean NOx Trap (LNT) systems are key technologies to reduce NOx emission for diesel on-highway vehicles to meet worldwide tighter emission regulations. In addition DeNOx catalysts have already been applied to several commercial off-road applications. Adding the DeNOx catalyst to existing Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) emission control system requires additional space and will result in an increase of emission system back pressure. Therefore it is necessary to address optimizing the DeNOx catalyst in regards to back pressure and downsizing. Recently, extruded zeolite for DeNOx application has been considered. This technology improves NOx conversion at low temperature due to the high catalyst amount. However, this technology has concerned about strength and robustness, because the honeycomb body is composed of catalyst. A zeolite catalyst supported by a ceramic honeycomb structure resolves the strength and robustness issues. Also the honeycomb structure offers higher geometric surface area (GSA), a key characteristic for higher NOx conversion. Cordierite substrates with a honeycomb structure are a historically proven technology used for a variety of applications (gasoline, diesel, LDV, HDV, Non-Road) over the past 30 years. Cordierite substrates have been used widely for three-way catalyst (TWC) and DOC as well as ammonia SCR and LNT for several decades. However, today's DeNOx catalyst technologies require higher catalyst loading to ensure very high conversion efficiencies at lower temperature. Conventional cordierite substrate has not been optimized for high catalyst loadings for DeNOx catalysts applications. By modifying cordierite substrate material properties for high catalyst loadings, lower pressure drop and retention of high NOx conversion efficiency can be offered. In this investigation, the performances of newly developed cordierite substrates with material properties adjusted to address high catalyst loadings and in various geometrical configurations were compared to conventional substrate technology. The performance evaluation includes NOx conversion, pressure drop performance, as well as durability and material strength evaluation. The paper will discuss the opportunities this newly developed material provides in regards to compactness and low pressure drop while maintaining high NOx conversion efficiency.
Hirose, Shogo, Miyairi, Yukio, Katsube, Frank, Yuuki, Kazuya, Sakamoto, Hirofumi, Vogt, Claus, Fujii, Shuji
Controlling Particulate Matter Emissions in Vehicles Using Different Strategies under the Heavy-Duty Test Cycle2012-01-08854/16/2012
Since 1997 in Belgium, the market share of vehicles equipped with diesel engine has grown up from 50% to nearly 80%. Most of the drivers are using diesel cars for private or company purposes and gasoline powered engine vehicles sales dropped dramatically since then. This evolution is clearly a game-changer regarding the type of regulated emissions we can find as dominant. Tests and analysis for this work focused on diesel passenger cars and one of the main drivers for that was the great demand of new cars fitted with exhaust aftertreatment devices (DPF, DOC, LBC etc.). In this paper the performance of soot filters were measured and presented, based not on the NEDC but on the heavy duty 13-Mode test cycle which emphasize mainly at low-speed driving conditions, such as all passenger cars are running currently, and is also characterized by low average engine loads and low exhaust temperatures. Two modern test cars were used and tested under the same operational conditions on a chassis dynamometer. All tests were conducted at KdG University College in Antwerp. Exhaust gas emissions generated from both test cars were measured and analyzed and a comparison was made. The first car was a Peugeot 807 HDi FAP 2002 year of construction, fitted with a factory installed soot filter and the second one was a Volkswagen Golf TDI 2003 year of construction without particle trap. All regulated emissions were controlled as well as lambda values and oxygen content in the exhaust fumes. Analysis of the results showed that the Volkswagen car even though was not equipped with any particle trap was able to emit fewer particles than the Peugeot in some test points. During operational conditions and at the same engine torque results, it was found that having the particle trap equipped, at high loads, specifically, at points 10 and 12 of the 13-Mode test; the Peugeot had worse results than the VW Golf. This was linked to the increased fuel consumption originated by the increasing backpressure caused by the particle trap as well as exhaust after-treatment strategy. All the soot content measurements were made using an AVL 415 Smoke Meter, and using conventional diesel fuel, accordingly to the norm ISO 10054.
Oliveira, Luis Miguel, Savvidis, Dimitrios, Pecqueur Sr, Mark
Designing quiet off-highway equipment12OFHD0202_022/2/2012
OEMs and suppliers are using new materials and innovative designs to reduce NVH for both vehicle operators and the environment. Off-highway vehicles can generate a lot of noise. Many improvements are being made to engines, structures, and systems related to NVH. Whether in smaller vehicles working in urban areas and/or enclosed spaces, or in larger vehicles, quieter systems will eliminate the need for hearing protection and cut down on fatigue caused by long exposure to high noise or vibration levels.
Sniderman, Debbie
Meeting Nonroad Final Tier 4 Emissions on a 4045 John Deere Engine Using A Fuel Reformer and LNT System with An Optional SCR Showing Transparent Vehicle Operation, Vehicle Packaging and Compliance to End-of-Life Emissions2011-01-22069/13/2011
The nonroad Final Tier 4 US EPA emission standards require 88% reduction in NOx emission from the Interim Tier 4 standards. It is necessary to utilize aftertreatment technologies to achieve the required NOx reduction. The development of a fuel reformer, lean NOx trap (LNT) and optional selective catalytic reactor (SCR) on a John Deere 4045 nonroad engine is described in this paper. The paper discusses aftertreatment system performance, catalyst formulations and system controls of a fuel vaporizer, fuel reformer, LNT and SCR system designed to meet the nonroad Final Tier 4 emission standards. The 4045 John Deere engine was calibrated and integrated with the aftertreatment system. The system performance was characterized in an engine dynamometer performance test cell, durability test cell and on a vehicle. The catalyst performance was evaluated using aged catalysts and a detailed description of the LNT, DPF and SCR catalysts is provided. Test results show that the system performance met Final Tier 4 emission standards under a range of test conditions including limited vehicle operation. System performance was characterized under the nonroad transient cycle (NRTC), ramped eight-mode cycle, steady state modal points and not-to-exceed regulations. LNT regeneration, LNT desulfation and DPF regeneration were demonstrated in these test cycles while maintaining repeatable and consistent aftertreatment temperature control. The LNT system regeneration fuel consumption ranged between 1.4% to 3.1%. The system consistently demonstrated 85% NOx reduction in a performance and durability test cell, and on a vehicle. The downstream SCR catalyst can be removed as an option for tighter vehicle packages while still meeting Final Tier 4 emission standards.
McCarthy Jr, James, Yue, Yong, Mahakul, Budhadeb, Gui, Xinqun, Yang, Hanlong, Ngan, Evan, Price, Kenneth
Final Tier 4 Emission Solution Using An Aftertreatment System With A Fuel Reformer, LNT, DPF And Optional SCR2011-01-21979/13/2011
Diesel exhaust aftertreatment systems are required for meeting Final Tier 4 emission regulations. This paper addresses an aftertreatment system designed to meet the Final Tier 4 emission standards for nonroad vehicle markets. The aftertreatment system consists of a fuel dosing system, mixing elements, fuel vaporizer, fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF), and an optional selective catalytic reduction (SCR) catalyst. Aftertreatment system performance, both with and without the SCR, was characterized in an engine dynamometer test cell, using a 4.5 liter, pre-production diesel engine. The engine out NOx nominally ranged between 1.6 and 2.0 g/kW-hr while all operating modes ranged between 1.2 and 2.8 g/kW-hr. The engine out particulate matter was calibrated to approximately 0.1 g/kW-hr for various power ratings. Three engine power ratings of 104 kW, 85 kW and 78 kW were evaluated. Test results on aged catalysts show that the system performance met Final Tier 4 emission standards having NOx levels below 0.4 g/kW-hr under a range of test conditions that were reflective of actual vehicle operation. Aftertreatment performance was characterized under multiple testing conditions including the nonroad transient cycle (NRTC), ramped 8-mode cycle and a variety of steady state operating points to ensure all not-to-exceed (NTE) regulations were met. LNT regeneration, LNT desulfation and DPF regeneration were demonstrated in these test cycles while maintaining repeatable and consistent aftertreatment temperature control. Final Tier 4 emission standards were met with low fuel usages for LNT regeneration ranging between 1.4 and 3.1%. The aftertreatment system reduced NOx by 89% on the NRTC and 87% on the ramped 8-mode cycle. Likewise, a system without the SCR catalyst yielded similar results of 88% NOx reduction on the NRTC and 86% on the ramped 8-mode cycle. Both system configurations met Final Tier 4 emission levels.
Ngan, Evan, Wetzel, Philip, McCarthy JR, James, Yue, Yong, Mahakul, Budhadeb
De-NOx Characteristics of a Combined System of LNT and SCR according to Space Velocity2011-01-20888/30/2011
The purpose of this paper is to investigate the adsorption and desorption characteristics of only LNT and SCR catalysts with respect to SV (Space Velocity) and the de-NOx performance of a combined system of LNT and SCR according to the SV. The adsorption time to reach NOx concentration of 500 ppm at SV = 14,000 1/h of the LNT catalyst was about 1,000 sec. The physically and chemically absorbed NH₃ on the SCR catalyst desorbed in same concentration though various SVs. The NOx conversion of the LNT decreased with SV increased in range of 350° or lower temperature, the formation quantity of NH₃ increased as SV increased in the lower temperature range. The NOx conversion of the SCR with SV = 14,000 1/h showed 95% at 320°, the effect of SV on the NOx conversion was not so much. The NOx conversion of the combined system of LNT and SCR with fresh catalysts appeared maximum value of 70% and hydrothermal aging at 900° decreased about to 25% below range of 300°. And the hydrothermally aged catalysts showed trends of the reduction of NOx conversion and the increase of NH₃ slip due to the reduction of residence time according to SV increase.
Seo, Choong-Kil, Kim, Hwanam, Choi, Byungchul
Impact of Biodiesel Impurities on the Performance and Durability of DOC, DPF and SCR Technologies2011-01-11364/12/2011
It is estimated that operating continuously on a B20 fuel containing the current allowable ASTM specification limits for metal impurities in biodiesel could result in a doubling of ash exposure relative to lube-oil-derived ash. The purpose of this study was to determine if a fuel containing metals at the ASTM limits could cause adverse impacts on the performance and durability of diesel emission control systems. An accelerated durability test method was developed to determine the potential impact of these biodiesel impurities. The test program included engine testing with multiple DPF substrate types as well as DOC and SCR catalysts. The results showed no significant degradation in the thermo-mechanical properties of cordierite, aluminum titanate, or silicon carbide DPFs after exposure to 150,000 mile equivalent biodiesel ash and thermal aging. However, exposure of a cordierite DPF to 435,000 mile equivalent aging resulted in a 69% decrease in the thermal shock resistance parameter. It is estimated that the additional ash from 150,000 miles of biodiesel use would also result in a moderate increases in exhaust backpressure for a DPF. A decrease in DOC activity was seen after exposure to 150,000 mile equivalent aging, resulting in higher HC slip and a reduction in NO₂ formation. The metal-zeolite SCR catalyst experienced a slight loss in activity after exposure to 435,000 mile equivalent aging. This catalyst, placed downstream of the DPF, showed a 5% reduction in overall NOx conversion activity over the HDDT test cycle.
Williams, Aaron, McCormick, Robert, Luecke, Jon, Brezny, Rasto, Geisselmann, Andreas, Voss, Kenneth, Hallstrom, Kevin, Leustek, Matthew, Parsons, Jared, Abi-Akar, Hind
The Study of NOx Reduction Using Plasma-assisted SCR System for a Heavy Duty Diesel Engine2011-01-03104/12/2011
To reduce NOx emissions from a heavy-duty engine at low exhaust temperature conditions, the plasma-assisted SCR (Selective Catalytic Reduction) system was evaluated. The plasma-assisted SCR system is mainly composed of an ammonia gas supply system and a plasma reactor including a pellet type SCR catalyst. The preliminary test with simulated gases of diesel exhaust showed an improvement in the NOx reduction performance by means of the plasma-assisted SCR system, even below 150°C conditions. Furthermore, NOx reduction ratio was improved up to 77% at 110°C with increase in the catalyst volume. Also NOx emissions from a heavy-duty diesel engine over the transient test mode in Japan (JE05) were reduced by the plasma-assisted SCR system. However, unregulated emissions, e.g., aldehydes, were increased with the plasma environment. This paper reports the advantages and disadvantages of the plasma-assisted SCR system for a heavy-duty diesel engine.
Sato, Shinya, Kawada, Yoshihiro, Sato, Satoshi, Hosoya, Mitsuru, Mizuno, Akira
Lean Gasoline Engine Reductant Chemistry During Lean NOx Trap Regeneration2010-01-226710/25/2010
Lean NOx Trap (LNT) catalysts can effectively reduce NOx from lean engine exhaust. Significant research for LNTs in diesel engine applications has been performed and has led to commercialization of the technology. For lean gasoline engine applications, advanced direct injection engines have led to a renewed interest in the potential for lean gasoline vehicles and, thereby, a renewed demand for lean NOx control. To understand the gasoline-based reductant chemistry during regeneration, a BMW lean gasoline vehicle has been studied on a chassis dynamometer. Exhaust samples were collected and analyzed for key reductant species such as H₂, CO, NH₃, and hydrocarbons during transient drive cycles. The relation of the reductant species to LNT performance will be discussed. Furthermore, the challenges of NOx storage in the lean gasoline application are reviewed.
Parks, James E., Prikhodko, Vitaly, Partridge, William, Choi, Jae-Soon, Norman, Kevin, Huff, Shean, Chambon, Paul
Review of Diesel Emissions and Control2010-01-03014/12/2010
This review summarizes the latest developments in diesel emissions regarding regulations, engines, NOx (nitrogen oxides) control, particulate matter (PM) reductions, and hydrocarbon (HC) and CO oxidation. Regulations are advancing with proposals for PN (particle number) regulations that require diesel particulate filters (DPFs) for Euro VI in 2013-14, and SULEV (super ultra low emission vehicle) fleet average light-duty (LD) emissions likely to be proposed in California for ~2017. CO₂ regulations will also impact diesel engines and emissions, probably long into the future. Engine technology is addressing these needs. Heavy-duty (HD) research engines show 90% lower NOx at the same PM or fuel consumption levels as a reference 2007 production engine. Work is starting on HD gasoline engines with promising results. In light duty (LD), engine downsizing is progressing and deNOx is emerging as a fuel savings strategy. Much has recently been reported on optimized selective catalytic reduction (SCR) systems. The SCR catalyst can be placed before, after, or on the DPF. Work is progressing on non-urea ammonia systems, mixed zeolite catalysts, and on fundamental understanding on issues like ammonia storage, sulfur impacts, and reaction mechanisms. Developments on HC-based deNOx, like lean NOx traps (LNTs), result in a better understanding of durability, reduction in desulfation temperatures, and the use of LNT+SCR systems, wherein the LNT is calibrated to generate ammonia for use in a downstream SCR. PM control is very effective. US2007 HD engines are very clean, with the DPF systems delivering PM, HC, and CO emissions at levels lower than 10% of the regulation. DPF regeneration advances are reported in strategy, modeling PM loading, and catalyst utilization. The effect of catalyst coatings on PN emissions, and behavior of captured ash is becoming better understood. NO₂-based regeneration of soot is very critical for proper functioning of partial filters. Biodiesel effects on DPF functions are becoming clearer. Finally, diesel oxidation catalysts (DOCs) are being developed for use with premixed combustion engine strategies that function better at low temperatures, low oxygen levels, and at high HC+CO levels. The problem of platinum (Pt) migration to SCR catalysts from DOCs exposed to high temperatures for long times (850°C, 16 hours) is alleviated somewhat by using palladium (Pd) to replace some of the platinum.
Johnson, Timothy V.
Passive Ammonia SCR System for Lean-burn SIDI Engines2010-01-03664/12/2010
Lean-burn Spark Ignition Direct Injection (SIDI) engines offer potential fuel economy savings, however, lack of cost-effective lean NOx aftertreatment systems has hindered its broad application. Lean NO Trap (LNT) and Urea Selective Catalytic Reduction (SCR) technologies have been widely investigated as possible solutions, but they both have considerable drawbacks. LNT catalysts suffer from high Platinum Group Metals (PGM) cost, poor thermal durability, sulfur poisoning and active SO regeneration requirements. Urea SCR systems require a secondary fluid tank with an injection system, resulting in added system cost and complexity. Other concerns for urea SCR include potential freezing of the urea solution and the need for customers to periodically fill the urea reservoir. In this paper we report a low-cost, high efficiency concept that has the potential to be a key enabler for lean-burn gasoline engines. The aftertreatment system includes a close-coupled three-way catalytic converter (TWC) and one or more underfloor SCR catalysts. NH₃ is formed on the TWC during short periods of rich engine operations and the generated NH₃ is then stored on the underfloor SCR catalysts. During the subsequent lean operations, the NO that breaks through the TWC converter is converted by the NH₃ stored on the SCR catalysts. Test results during the New European Driving Cycles (NEDC) showed that very high (≻85%) lean NO conversion efficiencies were achieved with aged converters. The potential and remaining issues of this new concept will be discussed. HC emission reduction is challenging due to the low exhaust temperatures. Further improvements in SCR catalyst technologies are required for high speed (≥100 km/h) lean operations. In summary, passive NH₃ SCR has been demonstrated as an efficient and low cost lean NO aftertreatment technology for stratified gasoline engines.
Li, Wei, Perry, Kevin L., Narayanaswamy, Kushal, Kim, Chang Hwan, Najt, Paul
Items per page:
1 – 50 of 101