Browse Topic: Lean NOx traps
Lean NOx trap is a dedicated DeNOx catalyst for lean hybrid gasoline engines. Noble metals (usually platinum group metals) play the role of catalytic sites for NOx oxidation and reduction, which have significant impact of the performance of LNT. This work focuses on the influence of noble metal catalysts on self-inhibition effect from the view of competitive adsorption between NO and CO, and investigates the influence of CO self-inhibition effect on the main by-product of LNT: N2O formation. Adsorption configurations for NO, CO and N2O on noble metal clusters supported by γ-Al2O3(100) are confirmed. For detailed investigation, electron structures are analyzed by investigating Bader charge, DOS (density of state), charge density differences and COHP (crystal orbital Hamilton population) of selected configurations.The results show that CO self-inhibition effect is caused by competitive adsorption between CO and NO. The essence of competitive adsorption between CO and NO is that adsorption process of CO and NO on catalytic sites is similar. Excessive adsorption of CO on the catalytic site occupies the catalytic site and limits the NO adsorption and subsequent processes, making NO conversion efficiency decrease. Competitive adsorption between CO and NO will limit NO adsorption and dissociation, thus limiting N2O formation. Meanwhile, stronger adsorption of N2O on catalytic sites will make N2O desorption difficult.
Even though the 3-way catalyst chemistry has been studied extensively in the literature, some performance aspects of practical relevance have not been fully explained. It is believed that the Oxygen Storage Capacity function of 3-way catalytic components dominates the behavior during stoichiometry transitions from lean to rich mode and vice versa whereas a number of mathematical models have been proposed to describe the dynamics of pollutant conversion. Previous studies have suggested a strong impact of Sulfur on the pollutant conversion after a lean to rich transition, which has not been adequately explained and modelled. Lean to rich transitions are highly relevant to catalyst ‘purging’ needed after exposure to high O2 levels (e.g. after fuel cut-offs). This work presents engine test measurements with an engine-aged catalyst that highlight the negative impact of Sulfur on pollutant conversion after a lean to rich transition. Sulfur appears to impact not only the available Oxygen to treat the excess reductants but also the water-gas shift and the steam reforming pathways that are desired to minimize CO and HC slip converting them to H2. We speculate that the above H2 production pathways are linked to Oxygen Storage dynamics due to the reversible (equilibrium controlled) nature of Oxygen Storage. The proposed mechanism is based on our earlier work on Sulfation of OSC-containing Lean NOx traps where we identified the role of SO2 storage and release at moderate/high temperature leading to reversible sulfation of the active sites in rich mode. An initial modeling attempt of the above complex interactions seems to confirm the main elements of the proposed mechanism predicting the main behavioral trends of pollutant conversion at two different temperatures. This opens the way to develop predictive models to optimize lambda controls addressing the zero-impact emission challenges.
For the regeneration of the Lean NOx Trap (LNT) a rich air-to-fuel ratio must be generated. This operation is very critical and has low combustion stability, especially in low load operation. A certain minimum engine load is always required for the regeneration phase. In the Real Driving Emissions this minimum engine load can be undercut over a long period of time. Hence, a reliable regeneration phase is not possible. The aim of these investigations is to extend the engine map range in which regeneration is possible towards lower loads. This is done by means of a variable valve train with second exhaust valve lift, which increases the internal residual gas amount. This in turns increases the temperature at start of combustion in the cylinder. Especially at low load and low combustion stability this leads to a stabilization of the combustion process. This advantage in combustion stability can be used for a reduction of the minimum engine load. The approach of this work consists of investigations on the engine test bench and accompanying simulations. The combustion process is thermodynamically examined and evaluated on the engine test bench using pressure trace and gas exchange analysis, including a residual gas model.
The ever-stringent emission regulations are major challenges for the diesel fueled engines in automotive industry. The applications of advanced after-treatment technologies as well as alternative fuels [1] are considered as promising methodology to reduce exhaust emission from compression ignition (CI) engines. Using dimethyl ether (DME) as an alternative fuel has been extensively studied by many researchers and automotive manufactures since DME has demonstrated enormous potential in terms of emission reduction, such as low CO emission, and soot and sulfur free. However, the effect of employing DME in a lean NOX trap (LNT) based after-treatment system has not been fully addressed yet. In this work, investigations of the long breathing LNT system using DME as a reductant were performed on a heated after-treatment flow bench with simulated engine exhaust condition. The scope of the study covers the regeneration effectiveness of NOX on the LNT after-treatment system, the formation of the by-products, including ammonia (NH3), nitrous oxide(N2O), methane (CH4). These by-products were measured and compared with the results when using other types of reductants, such as diesel, ethanol, n-butanol, under the same LNT test conditions. The test results reveal the constantly high regeneration effectiveness of DME as a reductant during the LNT regeneration process under different injection quantities. A lower amount of N2O and NH3, coming along with a higher amount of CH4, are generated when using DME as a reductant, as compared to that of using diesel and n-butanol as reductants under the same conditions.
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.
A supervisory Model Predictive Control (MPC) approach is developed for an air path system for multi-mode operation in a diesel engine. MPC is a control method based on a predictive dynamic model of system and determines actuator control positions through the optimization of various factors such as tracking performances of target setpoints, moving speed of actuators, limits, etc. Previously, linear MPC has been successfully applied on the air path control problem of a diesel engine, however, most of these applications were developed for a single operation mode which has only one set of control target setpoint values. In reality, a single operation mode cannot cover all requirements of current diesel engines and this complicates practical implementations of linear MPC. The high priority targets for the development of diesel engines are low emissions, high thermal efficiency and robustness. These objectives require multi-mode operations such as a HP EGR (High pressure exhaust gas recirculation) mode in cold coolant condition, a Double EGR mode for sufficient EGR rates, a Diesel Particulate Filter (DPF) regeneration mode for the heat-up of exhaust gas temperature and a rich mode of exhaust gas for Lean NOx Trap (LNT) regeneration. Each engine operation mode requires different target setpoints from the air path, such as air mass flow rate and oxygen concentration. In the multi-mode operation, simple linearization based MPC is limited in the practical application because a linearization point changes depending on target setpoints of each operation mode. This means that a linear model for a specific operation mode is not valid in other operation modes, which have different target setpoints. Moreover, the modern diesel air path system is highly nonlinear and would require a significant number of linear models to adequately represent the entire behavior not only at all operation points of engine speed and load, but also at the various operation modes. In this study, a new scheme is proposed and tested on a diesel engine utilizing combined benefits of a supervisory MPC and component level nonlinear compensators. The developed nonlinear compensators are based on dynamic real-time inversions of individual component models. The control scheme comprises of three parts: a supervisory MPC as the coordination of target setpoints in high-level to achieve the objectives, a component level control of nonlinear compensator, state observation either by virtual sensor or by Electronic Control Unit (ECU) sensor. The test results from an engine test bench and a chassis dynamometer demonstrates that the proposed method works well in multi-mode operation and can be applied with the significant benefit that no mode specific control strategies and calibration are needed. A valuable benefit of this approach can be seen in the calibration effort, particularly during development when the setpoints are not necessarily fixed.
The Diesel Particulate NOx Reduction (DPNR) system is used for simultaneous reduction of PM and NOx in diesel engine. DPF is used to trap particulate matter in diesel engines. NOx absorber technology removes NOx in a lean (i.e. oxygen rich) exhaust environment for both diesel and gasoline lean-burn GDI engines. The NOx storage and reduction catalyst is uniformly coated on the wall surface and in the fine pores of a highly porous filter substrate. Combination of these two components in the DPNR results in a compact size of the system. The base diesel engine model validated with pressure crank angle diagram and performance parameters such as Indicated mean effective pressure. This base engine’s exhaust emission is given as an input to the DPNR system. The surface reaction is connected to the DPF through chemcon template. The surface reaction is NOx storage and reduction chemical kinetics like Lean NOx Trap. The modelling of DPNR and Base engine is done using GT-SUITE. This paper describes about the 1D simulation of DPNR system with base diesel engine model and the percentage reduction of PM and NOx from the base model.
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.
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.
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.
Improved Lean NOx Trap (LNT) catalysts with enhanced NH3 generation feature were developed for the small diesel engine. The next generation LNT system needs to perform good NOx conversions over the wide temperature range including below 200°C for urban driving and above 400°C for motorway of real road driving. However, the extended use of BaO, a component of LNT known to be very effective for high temperature NOx storage, results in the decrease of low temperature NOx conversion due to the degradation of NO oxidation associating with sulfur over time. The improvement of the low-temperature LNT performance is a key requirement for the real driving emission control as the best operation temperature for urea-SCR is above ~250°C. In this study, our next generation LNT with new washcoat architecture has demonstrated improved NOx removal efficiencies under the wider operation temperature window than the current production technology. The new LNT technology also offered an enhanced on-board NH3 generation from the engine out and stored NOx during the fuel-rich operation while preserving its NOx reduction activity by the implement of zone and layered architecture in the LNT washcoat. In addition, platinum group metal (PGM), oxygen storage capacity (OSC) and BaO content have been optimized for each zone and layer. The multi-functioning LNT catalyst then evaluated using both simulated gas bench and engine dyno tests. The newly developed LNT with enhanced NOx reduction as well as NH3 production performance will enable the future diesel aftertreatment systems to meet the real world driving tailpipe emission requirement.
Despite the trend in increased prosperity, the Indian automotive market, which is traditionally dominated by highly cost-oriented producion, is very sensitive to the price of fuels and vehicles. Due to these very specific market demands, the U-LCV (ultra-light commercial vehicle) segment with single cylinder natural aspirated Diesel engines (typical sub 650 cc displacement) is gaining immense popularity in the recent years. By moving to 2016, with the announcement of leapfrogging directly to Bharat Stage VI (BS VI) emission legislation in India, and in addition to the mandatory application of Diesel particle filters (DPF), there will be a need to implement effective NOx aftertreament systems. Due to the very low power-to-weight ratio of these particular applications, the engine operation takes place under full load conditions in a significant portion of the test cycle. These lead to further challenges in terms of high engine-out NOx emissions and non-optimum temperature window for efficient operation of NOx aftertreatment devices. In the state-of-the-art calibration processes, the aftertreatment system is considered separately from the calibration of the thermodynamics. This conventional approach makes it more challenging to achieve a simultaneous optimization of the fuel consumption and the tailpipe emissions under transient operating conditions. To meet this goal, the SimEx powertrain simulation tool from FEV enables a simultaneous optimization of the multiple sub-systems considering engine thermodynamics, controls, transmission system, gear shifting strategy and exhaust gas aftertreatment. In the 1st phase of the research study presented here, the base engine was optimized in terms of friction reduction and cylinder volume right-sizing to enable sufficient EGR rates even at full load to achieve lower engine out NOx without compromising the fuel economy and performance. In the 2nd phase of the study, different configurations of NOx aftertreatment concepts were analysed. The results indicate that an improved engine design with single stage LNT (lean NOx trap) system i.e. “LNT + cDPF” can bring the tailpipe NOx into the BS VI window, but without sufficient engineering margins. However, a two stage LNT i.e. “LNT + cDPF + LNT” due to its improved behavior also ensures sufficient engineering margins. Finally, the BS VI capability of all the engine concepts was also investigated with a SCR coated DPF (SDPF) based system, which showed lowest tailpipe emissions due to its improved conversion behavior in a wide temperature window. A final selection of the aftertreament strategy will depend significantly on the application specific boundary conditions (i.e. base engine technology, performance, robustness, costs etc.). Overall, this integrated simulation approach supports efficient frontloading strategies and allows the cumulative optimization of the total system configuration meeting the stringent tailpipe legislation and fuel economy targets with the lowest total cost of ownership.
There are numerous off-road diesel engine applications. In some applications there is more focus on metrics such as initial cost, packaging and transient response and less emphasis on fuel economy. In this paper a combustion concept is presented that may be well suited to these applications. The novel combustion concept operates in two distinct operation modes: lean operation at light engine loads and stoichiometric operation at intermediate and high engine loads. One advantage to the two mode approach is the ability to simplify the aftertreatment and reduce cost. The simplified aftertreatment system utilizes a non-catalyzed diesel particulate filter (DPF) and a relatively small lean NOx trap (LNT). Under stoichiometric operation the LNT has the ability to act as a three way catalyst (TWC) for excellent control of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). The two-mode diesel combustion concept was implemented on a 6.8L medium duty diesel engine and several iterations of the combustion system were evaluated for smoke response and combustion efficiency. The engine was then evaluated over the Non Road Transient Cycle (NRTC) to evaluate performance, emissions and fuel consumption. Results show that this novel combustion concept can meet the Tier 4 final emissions regulations without the use of selective catalytic reduction (SCR).
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.
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.
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.
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.
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).
This review paper summarizes major developments in vehicular emissions regulations and technologies from 2014. The paper starts with the key regulatory advancements in the field, including newly proposed Non-Road Mobile Machinery regulations for 2019-20 in Europe, and the continuing developments towards real driving emissions (RDE) standards. An expert panel in India proposed a roadmap through 2025 for clean fuels and tailpipe regulations. LD (light duty) and HD (heavy-duty) engine technology continues showing marked improvements in engine efficiency. Key developments are summarized for gasoline and diesel engines to meet both the emerging NOx and GHG regulations. HD engines are demonstrating more than 50% brake thermal efficiency using methods that can reasonably be commercialized. Next, NOx control technologies are summarized, including SCR (selective catalytic reduction), lean NOx traps, and combination systems. Emphasis is on durability and control. Diesel PM (particulate matter) reduction findings are evolving around the behavior of the soot cake and PM sensors. Gasoline particulates are further described and gasoline particulate filter regeneration is now better understood. Oxidation catalysts mainly involve developments towards stubborn problems, like sulfur tolerance, low-temperature performance with exhaust with high hydrocarbon and CO, and methane oxidation. Finally, the paper discusses some key developments in gasoline gaseous emission control, focusing on meeting new regulatory requirements in the US, durability, and on lean burn gasoline emissions control.
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.
The paper examines how the issue of lengthy development times can be mitigated by adopting a multivariable physics based control method for the development and deployment of complex engine control algorithms required for modern diesel engines equipped with Lean NOx Trap aftertreatment technology. The proposed approach facilitates manufacturers to consider lower cost powertrain configurations for selected markets while maintaining higher performance configurations for other markets. The contribution includes on-engine results from joint work between General Motors and Honeywell. The Honeywell OnRAMP Design Suite which applies model predictive control techniques was used for model identification, control design (using model predictive control) and its calibration. With no prior work on the engine this process of calibrating an engine model and achieving transient drive cycle control on the engine required ten days in the test cell and five days of offline work using the OnRAMP software.
Driven by the desire to implement low-cost, high-efficiency NOx aftertreatment systems, such as Three Way Catalysts (TWC) or Lean NOx Traps (LNT), a novel 6-Stroke engine cycle was explored to determine the feasibility of implementing such a cycle on a compression ignition engine while continuing to deliver fuel efficiency. Fundamental questions regarding the abilities and trade-offs of a 6-stroke engine cycle were investigated for near-stoichiometric and lean operation. Experiments were performed on a single-cylinder 15-liter (equivalent) research engine equipped with flexible valvetrain and fuel injection systems to allow direct comparison between 4-stroke and 6-stroke performance across multiple hardware configurations. 1-D engine simulations with predictive combustion models were used to support, iterate on, and explore the 6-stroke operation in conjunction with the experiments. Output from the experiments and simulations were then used to perform Availability and Energy balances for a thermodynamic comparison of the two cycles. Compared to 4-stroke cycle operation, the 6-stroke cycle exhibited lower PM emissions at stoichiometric operation, while higher NOx/PM emissions were observed under some lean conditions. The ratio of fuel burned in the first combustion event to the second event had a strong impact on performance, heat loss, and emissions. For some 6-stroke strategies engine breathing and airflow management were found to be challenging, and beneficial for other strategies. The thermodynamic analysis showed that under similar boundary conditions, the 6-stroke and 4-stroke engine cycles could attain very similar brake efficiencies, though the detailed availability balance breakdown could differ substantially.
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.
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.
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.
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.
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.
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.
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