Browse Topic: Selective catalytic reduction (SCR)

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Simulation of Aftertreatment Thermal Management Strategies for Low-Load Operation2020-01-03594/14/2020
The low-NOx regulation for heavy duty trucks proposed by California’s Air Resources Board (CARB) will present a significant challenge to truck, engine and aftertreatment system manufacturers. This regulation will include a new test cycle representative of low-load operation. With low-load cycles, NOx conversion by the SCR (selective catalytic reduction) system is limited primarily by the exhaust temperature; thus, thermal management will dominate development. Simulation can be used to examine different thermal management strategies, and to define high-level requirements for new components. In this study, modeling was used to investigate SCR performance on two different low-load cycles, including the one selected by CARB for the low-NOx regulation. First, the “thermal deficit” of the cycle was quantified using a constant heat input. Next, direct heating of the exhaust with a fuel mini-burner or an electric heater, using realistic controls, was simulated to determine their capability to overcome the thermal deficit. For comparison, the performance of a dual-injection SCR system on these cycles was also modeled.
Harris, Thomas
Numerical Optimization of a SCR System Based on the Injection of Pure Gaseous Ammonia for the NOx Reduction in Light-Duty Diesel Engines2020-01-03564/14/2020
Selective Catalytic Reduction (SCR) systems are nowadays widely applied for the reduction of NOx emitted from Diesel engines. The typical process is based on the injection of aqueous urea in the exhaust gases before the SCR catalyst, which determines the production of the ammonia needed for the catalytic reduction of NOx. However, this technology is affected by two main limitations: a) the evaporation of the urea water solution (UWS) requires a sufficiently high temperature of the exhaust gases and b) the formation of solid deposits during the UWS evaporation is a frequent phenomenon which compromise the correct operation of the system. In this context, to overcome these issues, a technology based on the injection of gaseous ammonia has been recently proposed: in this case, ammonia is stored at the solid state in a cartridge containing a Strontium Chloride salt and it is desorbed by means of electrical heating. In this work, an after-treatment system based on the injection of gaseous ammonia in the SCR system is considered. Numerical 1D and 3D CFD simulations are applied in order to optimize the NOx reduction process. In particular, CFD methodology is applied to study in details the process of injection of the gaseous ammonia in the main exhaust gas stream and the effectiveness of the mixing process. Different geometrical layouts are compared to evaluate their performances in terms of uniformity of the NH3 distribution across the inlet section of the catalyst and pressure drop introduced in the exhaust line. Moreover, a 1D simulation tool is applied to evaluate the performances of the entire exhaust after-treatment system. The 1D model is calibrated on the basis of the information coming from detailed CFD simulations, in particular for what concerns the modeling of the effects of the different mixer geometries in terms on NH3 distribution. In this case, a simplified 3D catalyst is simulated, to take into account the maldistribution of ammonia at the inlet cross section and to evaluate its impact on the global deNOx performance of the system for different dosing strategies and for different levels of the ammonia maldistribution.
Della Torre, Augusto, Montenegro, Gianluca, Onorati, Angelo, Cerri, Tarcisio, Tronconi, Enrico, Nova, Isabella
Design, Development and Analysis of Mullite Catalytic Converter for CI Engines2019-28-001710/11/2019
Emissions of Hydrocarbon (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx) are the largest concerns for fossil fuel driven automotive vehicles. Catalytic converter is an important component in the selective catalytic reduction process. It oxidizes harmful CO and HC emission to CO2 and H2O in the exhaust system and thus the emission is controlled. Different kinds of problems are associated with noble metal based catalytic converter. A catalytic converter with a new catalyst for compression ignition engine is considered in this study. The catalytic converter is designed and developed with a new catalyst. Due to better durable characteristics and poison resistant nature, non-noble metal based material limestone (mullite) is selected as a catalyst for catalytic convertor and the emission characteristics are studied on four stroke single cylinder CI engine by using mullite based catalytic converter. The results are compared without catalytic converter in the same engine. In the design stage, the back pressure analysis is performed on perforated mullite plate with ANSYS software. After arriving satisfactory results, the design is taken for development. The developed catalytic converter is tested on a single cylinder DI diesel engine coupled with dynamometer under variable engine running conditions. Though not a noble metal, limestone works as a catalyst for reduction of HC, CO and NOx emissions. It is therefore concluded that a simple low-cost limestone based catalytic converter can be thought as an alternative for expensive noble metal based converters.
Pandiaraj, Selvakumar, Subbaiyan, Dhamotharan, Ayyasamy, Tamilvanan, Nagarajan, Sathishkumar
Analysis of TWC Characteristics in a Euro6 Gasoline Light Duty Vehicle2019-24-01629/9/2019
A Euro6 gasoline light duty vehicle has been tested at the engine dynamometer and the emissions have been analyzed upstream and downstream the Three-Way-Catalyst (TWC) during a WLTC cycle. Catalyst simulations have been used for assessing the processes inside the catalytic converter using a reaction scheme based on 19 brutto reactions (direct oxidation and reduction, selective catalytic reductions with CO, C3H6 and H2, steam reforming, water-gas shift and bulk ceria as well as surface ceria reactions). The reactions have been parameterized in order to best approximate the measurements. Based on the reactions taken into account, the real vehicle emissions can be predicted with good accuracy. The simulations show that the cycle emissions comprise mainly the cold start contribution as well as discrete emission break-through events during transients. During cold start no reactions are evident in the catalyst before the temperature of the gas entering the catalyst reaches 270°C. Following the light-off, prevailing reactions are direct oxidation as well as surface ceria reactions for CO and THC. NO reduction during cold start is due to reaction with CO as well as due to surface ceria. During warm engine operation, CO break-throughs during transients are mainly due to lack of oxygen following short periods where the engine lambda drops below one and most of surface and bulk CeO2 has reacted to surface and bulk Ce2O3. Moreover in such incidents ceria is reacting with THC forming additional CO. THC break-throughs during transients are mostly simultaneous with CO peaks and are also due to lack of oxygen and depleted CeO2. NO transient break-throughs occur when engine-out NO sharply increases, and the reactions with CO and ceria are not sufficient. Further analysis focused in highlighting the effects of variations of Lambda and precious metal content on reaction emissions and mechanisms.
Papetti, Viola, Dimopoulos Eggenschwiler, Panayotis, Emmanouil, Vasiliki, Koltsakis, Grigorios
Deposit Reduction in SCR Aftertreatment Systems by Addition of Ti-Based Coordination Complex to UWS2019-01-03134/2/2019
Formation of urea-derived deposits in selective catalytic reduction (SCR) aftertreatment systems continues to be problematic at temperatures at and below 215 °C. Several consequences of deposit formation include: NOx and NH3 slip, exhaust flow maldistribution, increased engine backpressure, and corrosion of aftertreatment components. Numerous methods have been developed to reduce deposit formation, but to date, there has been no solution for continuous low-temperature dosing of Urea-Water Solution (UWS). This manuscript presents a novel methodology for reducing low-temperature deposit formation in SCR aftertreatment systems. The methodology described herein involves incorporation and dissolution of an HNCO hydrolysis catalyst directly into the UWS. HNCO is a transient species formed by the thermolysis of urea upon injection of UWS into the aftertreatment system. Ideally HNCO undergoes hydrolysis to form NH3 and CO2, but under certain conditions HNCO may polymerize or react with other constituents in the exhaust. Reaction of HNCO with species other than water generally results in the formation of deposits in the aftertreatment system. Addition of an HNCO hydrolysis catalyst directly into the UWS provides maximum contact between catalyst and substrate, thereby improving deposit reduction efficacy. This method of reducing deposits has been shown to reduce deposits by 89% at a 215 °C operating condition.
Hartley, Ryan, Henry, Cary, Eakle, Scott, Tonzetich, Zachary
Study on Improvement of NOx Reduction Performance at Low Temperature Using Urea Reforming Technology in Urea SCR System2019-01-03174/2/2019
To reduce NOx and PM emissions in exhaust gas, after-treatment systems for low NOx emissions are being developed in combination with improvements of engine combustion. In recent years, the exhaust gas temperature has been dropping because of enhanced low-fuel consumption of the engine. Therefore, it is urgent to develop NOx reduction technologies that work at a low temperature under 200degC. Since NOx is reduced by reacting with ammonia supplied to the SCR catalyst, it is necessary to make the urea solution decompose into ammonia using the heat of the exhaust gas to supply sufficient ammonia to the SCR catalyst. However, both the decomposition reaction and hydrolysis reaction of the urea have insufficient exhaust heat, thus making it difficult for urea to decompose and hydrolyze to ammonia at a low temperature. To solve this problem, it focuses on forcibly decomposing the urea solution without depending on the exhaust gas temperature. We selected a urea reforming method in which the urea is directly heated using the glow plug as the heat source. In this study, we have considered further improvement of the NOx reduction performance at a low temperature with a view to improving the ammonia generation efficiency by urea reforming.
Okada, Yuichi, Hirabayashi, Hiroshi, Sato, Shinya, Inoue, Hiroshi
Low Pressure-Driven Injection Characterization for SCR Applications2019-01-09944/2/2019
Aqueous Urea is a non-toxic and stable ammonia carrier and its injection and mixing represent the basis for the most common de-NOx technology for mobile applications. The reactant feed preparation process is defined by evaporation, thermolysis and hydrolysis of the liquid mixture upstream the Selective Catalytic Reduction reactor, and it is strongly dependent on the interaction between spray and gaseous flow. Low-pressure driven injectors are the common industrial standard for these applications, and their behavior in almost-ambient pressure cross flows is significantly different from any in-cylinder application. For this reason, two substantially different injectors in terms of geometry and design are experimentally studied, characterizing drop sizes and velocities through Phase Doppler Anemometry (PDA) and liquid mass spatial distribution through Shadow Imaging (SI). The measurements involve the analysis of the spray in quiescent air conditions, gathering information at the closest to the nozzle reliable location. Distilled water and Urea Water Solution are characterized, clearly showing that the spray evolution is only slightly affected by the mixture composition. These experimental findings act as the basis for the construction of a numerical description of liquid injection within the Lagrangian tracking framework inside 3D finite volume CFD simulations. A robust injection model is defined, pointing out the singularities of the system and identifying the most critical aspects. The proposed model is built on the direct definition of a droplet diameter distribution, putting particular attention in the droplet-to-parcel ratio definition. One of the two injectors is taken as the input and the other one, which shows a considerable different design and spray pattern is used as a test for the modeling approach. The simulation setup is then assessed in cross-flow conditions and validated on data gathered in a synthetic exhaust gas test bench, where the injectors are installed in an optically accessible chamber, allowing PDA and SI measurements over a wide range of thermal and kinematic cross flow conditions, representative of typical Diesel after-treatment systems. Good agreement with the experimental data is obtained, highlighting how the definition of the initial spray droplet kinematic properties is the key feature in the correct description of a spray for SCR applications, regardless of the Urea mass fraction in the mixture. The evolution of the liquid plume inside a realistic after-treatment channel size geometry shows that most of the momentum of the spray is carried by the largest droplets, which are the ones to be correctly described to address important issues in the Urea Water Solution dosing; these are responsible for the excessive wall impingement and subsequent formation of solid deposits. Specific care is applied in the definition of a reasonable CFD framework, determining mesh sizes and sub-model setups able to fulfill affordable computational costs, according to the current industrial standards.
Nocivelli, Lorenzo, Montenegro, Gianluca, Dimopoulos Eggenschwiler, Panayotis
Experimental and Computational Study of DOC on CSF for Heavy Duty Diesel Applications2019-01-05864/2/2019
For diesel exhaust aftertreatment applications with space limitations, as well as to move the selective catalytic reduction system (SCR) to a warmer location closer to the engine, DOC on CSF technology can be used. This technology combines the diesel oxidation catalyst (DOC) and catalyzed soot filter (CSF) functionalities in one component, thereby enabling volume reduction. DOC on CSF maintains the abatement of hydrocarbon (HC), carbon monoxide (CO), and particulate matter (PM), and the oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) for passive soot oxidation and fast SCR reaction of NOx on a downstream SCR catalyst. In this study, the performance of DOC on CSF was compared to a DOC + bare diesel particulate filter (DPF) and a DOC + CSF system, to understand the performance benefits and challenges. All the components were optimized individually for their respective functions. The DOC on CSF was optimized for NO oxidation and passive soot oxidation performance. Experimental data and simulations were used to understand the underlying mechanisms in the DOC on CSF technology. Steady state HC oxidation under active regeneration conditions showed a benefit for DOC on CSF compared to the DOC + DPF system. The soot oxidation characteristics of the DOC on CSF were evaluated in comparison to a DPF or CSF downstream of a DOC under passive and active soot oxidation conditions. In addition, the contribution of NO2 generated within the filter on the soot oxidation was assessed. The passive soot oxidation characteristics of a DOC on CSF were found to be similar, or better, compared to DOC + DPF and DOC + CSF under certain conditions. The active regeneration efficiency was lower for the DOC on CSF due to the gradual increase in temperature along the length of the part during fuel injection. This work demonstrates the differences between the DOC on CSF and DOC + bare/coated DPF systems, thus enabling a better understanding of the performance of DOC on CSF to current applications.
Sethuraman, Sharan, Sitamraju, Siddarth, Lopez-De Jesus, Yaritza M, Markatou, Penelope
Modeling of Close-Coupled SCR Concepts to Meet Future Cold Start Requirements for Heavy-Duty Engines2019-01-09844/2/2019
The low-NOx standard for heavy-duty trucks proposed by the California Air Resources Board will require rapid warm-up of the aftertreatment system (ATS). Several different aftertreatment architectures and technologies, all based on selective catalytic reduction (SCR), are being considered to meet this need. One of these architectures, the close-coupled SCR (ccSCR), was evaluated in this study using two different physics-based, 1D models; the simulations focused on the first 300 seconds of the cold-start Federal Test Procedure (FTP). The first model, describing a real, EuroVI-compliant engine equipped with series turbochargers, was used to evaluate a ccSCR located either i) immediately downstream of the low-pressure turbine, ii) in between the two turbines, or iii) in a by-pass around the high pressure turbine. These simulations indicate that the location downstream of the low-pressure turbine offers nearly the best NOx conversion, and that the optimal volume of the ccSCR in this location is 25% of a conventional SCR catalyst. The second model describes a conventional heavy-duty aftertreatment system, to which a ccSCR was added. This model was used to examine the performance of the ccSCR in the context of the full ATS. Optimization of the diesel oxidation catalyst (DOC) and SCR catalyst designs in this system was considered, as well as the use of an NH3 storage-based control strategy for DEF dosing to the SCR catalysts.
Harris, Thomas Miller, Mc Pherson, Kristoffer, Rezaei, Reza, Kovacs, David, Rauch, Hendrik, Huang, Yinyan
Review of Vehicle Engine Efficiency and Emissions2019-01-03144/2/2019
This review paper covers major regulatory and technology developments in 2018 pertinent to tailpipe emissions of greenhouse gases and criteria pollutants. Europe has proposed ambitious reductions in CO2 limits for both light- and heavy-duty sectors. The challenge is compounded with changing measurement norms and a significant shift away from fuel efficient diesels in the light-duty (LD) space. Both incremental and step changes are being made to advance internal combustion. New studies show that in-use NOx emissions from diesels can be much lower than required by the Euro 6 regulation. Discussions have already started on Euro 7 regulations, and the leading regulatory concepts and proposed technical solutions are provided. In the heavy-duty (HD) sector, the progress is outlined in improving engine and vehicle fuel efficiency through the US Department of Energy’s (DOE’s) SuperTruck II program and other representative studies. Common approaches among the participants include hybridization, waste heat recovery, and both open- and closed cycle incremental improvements. Emissions control focus is on evaluating pathways to achieve California’s contemplated low-NOx standards, recently also supported by the US EPA through the Cleaner Trucks Initiative. The challenge is to reduce cold start and low load emissions, requiring innovative engine and after-treatment system solutions. Leading concepts include close-coupled SCR (selective catalytic reduction), use of passive NOx adsorbers, integration of SCR (selective catalytic reduction) on DPFs (diesel particulate filters), low temperature urea or ammonia injection, dual SCR, and active and passive thermal management to raise exhaust temperatures. Work is also underway on a new low load certification cycle. Continued advancement is made on after-treatment components. Aged three-way catalysts (TWCs) and diesel oxidation catalysts (DOCs) are nearing 90% conversion at 150 °C. SCR catalysts continue to improve both their low temperature conversion as well as high temperature durability. Particulate regulations in Europe, China and India are leading to widespread adoption of gasoline particulate filters (GPFs). Lean burn gasoline engines can offer significant fuel economy benefits. NOx control is a challenge, and passive SCR systems and new catalysts are proposed.
Joshi, Ameya
Optimization of a Diesel Engine with Variable Exhaust Valve Phasing for Fast SCR System Warm-Up2019-01-05844/2/2019
Early exhaust valve opening (eEVO) increases the exhaust gas temperature by faster termination of the power stroke and is considered as a potential warm up strategy for diesel engines aftertreatment thermal management. In this study, first, it is shown that when eEVO is applied, the engine main variables such as the boost pressure, exhaust gas recirculation (EGR) and injection (timing and quantity) must be re-calibrated to develop the required torque, avoid exceeding the exhaust temperature limits and keep the air fuel ratio sufficiently high. Then, a two-step procedure is presented to optimize the engine operation after the eEVO system is introduced, using a validated diesel engine model. In the first step, the engine variables are optimized at a constant eEVO shift. In the second step, optimal eEVO trajectories are calculated using Dynamic Programming (DP) for a transient test cycle. The optimized results indicate that with early EVO, the boost pressure should be increased to provide enough cylinder air charge and to maintain the engine torque. External EGR can be reduced due to increased internal EGR while maintaining the same engine out NOx. An optimal zone to maximize temperature benefit with least impact to BSFC has been observed. The study also shows some of the penalties related to eEVO including increased flow pulsation at the air flow sensor location. Finally, with optimal eEVO, a 6.5% - 11% reduction is observed in the light-off time of the selective catalytic reduction (SCR) catalyst and 45% reduction in tailpipe NOx compared to the baseline operation without eEVO.
Srinivas, Pavan Kumar, Salehi, Rasoul
Accelerating Accurate Urea/SCR Film Temperature Simulations to Time-Scales Needed for Urea Deposit Predictions2019-01-09824/2/2019
Urea water solution-based Selective Catalytic Reduction (SCR) of NOx emissions from vehicular diesel engines is now widely used world-wide to meet strict health and environmental protection regulations. While urea-based SCR is proven effective, urea-derived deposits often form near injectors, on mixers and pipes, and on the SCR catalyst face. Further understanding of these deposit-formation processes is needed to design aftertreatment system hardware and control systems capable of avoiding severe urea-derived deposits. Computational Fluid Dynamics (CFD) is widely used in SCR aftertreatment design. Film formation, movement, solid wall cooling and deposit initiation/growth time-scales are in the range of minutes to hours, but traditional CFD simulations take too long to reach these time-scales. Here, we propose and demonstrate the frozen flow approach for pulsed sprays and conjugate heat transfer to reduce computation time while maintaining accuracy of key physics. The motivation and assumptions of frozen flow are discussed and the experiments of Birkhold et al. are simulated for validation. Simulations up to 200 seconds are completed in several days computation time, including every injection event and continuous thermal modeling of the solid. These simulations resolve the time history of solid cooling accurately, without scaling any physical properties.
Maciejewski, Daniel, Sukheswalla, Parvez, Wang, Chu, Drennan, Scott A., Chai, Xiaochuan
Identification of Film Breakup for a Liquid Urea-Water-Solution and Application to CFD2019-01-09834/2/2019
The reduction of NOx-emissions from diesel engines is crucial for the fulfilment of environmental standards. Selective catalytic reduction (SCR) is an effective way to achieve very low tailpipe NOx-emission levels. For an efficient after treatment system, a homogeneous distribution of gaseous ammonia across the catalytic surface is essential. Therefore, a detailed understanding of the impingement of the injected urea water solution (UWS), its evaporation and transformation to gaseous ammonia is of vital importance. Due to the complex physics of the impingement process, the simulation of SCR systems with computational fluid dynamics (CFD) relies upon empirical models known as impingement maps. In the current study a droplet chain generator was used to investigate single droplet impingement of UWS. The impingement events were filmed with a high speed camera and then analysed with respect to impingement velocity and droplet diameter as well as droplet Weber-number. Together with the recorded surface temperature of the impingement target, an impingement map was drawn. In contrast to previous investigations, these experiments were mainly carried out in the range of the critical temperature that separates impingement regimes that result in wall wetting and regimes with thermal rebound or break-up. The results revealed a temperature range that is relevant for SCR applications where instead of pure film formation and evaporation an immediate boiling of the film followed by thermal breakup was observed. Consequently, in comparison to the often used Bai-Gosman- or Bai-Onera-impingement-diagram, a significant amount of secondary droplets is created instead of all mass being transferred to liquid film. Although this film boiling has been described for water in literature before, to the best of our knowledge, it has never been implemented into CFD and applied to a complete SCR system. With the implementation of the observed behaviour by specifying a certain fraction of droplets to rebound from the surface in the specific regions of the impingement map, a significant improvement of the simulation results could be demonstrated.
Quissek, Max, Lauer, Thomas, García-Afonso, Oscar, Fowles, Stewart
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
Towards Quantitative Prediction of Urea Thermo-Hydrolysis and Deposits Formation in Exhaust Selective Catalytic Reduction (SCR) Systems2019-01-09924/2/2019
In order to assist in fast design cycle of Diesel engines selective catalytic reduction (SCR) exhaust systems, significant endeavor is currently being made to improve numerical simulation accuracy of urea thermo-hydrolysis. In this article, the achievements of a recently developed urea semi-detailed decomposition chemical scheme are assessed using three available databases from the literature. First, evaporation and thermo-hydrolysis of urea-water solution (UWS) single-droplets hanged on a thin thermocouple ring (127 μm) as well as on a thick quartz (275 μm), have been simulated at ambient temperature conditions ranging from 473K to 773K. It has been shown that the numerical results, in terms of evaporation rate and urea gasification, as well as droplet temperature history are very close to the experiments if the heat flux coming from the droplet support is properly accounted for. Indeed, an additional conduction flux has proved to be necessary in the evaporation model in order to account for the droplet heating coming from the support (i.e. thermocouple ring or quartz bead). This additional heat conduction flux has shown more critical for droplets suspended on a thick quartz. It is also argued that our detailed kinetic mechanism is able to ensure accurate thermal decompositions as long as the temperature inside the droplet is still nearly uniform. This assumption is shown to be true at low temperature and so, at low evaporation and thermo-hydrolysis rates. However, for high gas temperature, bubble nucleation near the support surface induces non-uniform temperature distribution.. This process makes accurate simulation of thermal decomposition extremely dependent on the local temperature inside such large suspended droplets. These results are also relevant and underline the modelling difficulties that we must tackle when it comes to studying the evaporation, boiling and thermolysis of liquid films and deposits on the exhaust walls. Next verification of the models has been carried out using UWS sprays injected in 6-m long pipe under typical Diesel engine exhaust manifold conditions. In this case, good agreement with experiments in terms of urea to ammonia (NH3) conversion efficiencies has been obtained under different temperatures and residence times. In addition, it proved that by-products (like solid biuret, Cyanuric acid and even ammelide) can be formed in the spray parcels upon water evaporation is completed during their travel to the exhaust catalyst inlet. These solid by-product particles may clog the catalyst inlet section.
Habchi, Chaouki, Quan, Shaoping, Drennan, Scott, Bohbot, Julien
Influence of the Backpressure on Urea Sprays Generated by an Air-Blast Atomizer for Large-Scale SCR-Applications2019-01-00461/15/2019
In 2016, the latest step of emission standards for marine ships came into operation. As the emission limit for nitric oxides has decreased to approximately 25% of the former values, selective catalytic reduction (SCR) will play an important role to fulfil those limits. SCR is an established method in the field of trucks and heavy diesel cars, but applying it to ships requires further research and development. The demands on ship engines are different, not only due to the large scales but also because the engineering process is strongly based on numerical simulations. To allow the validation of simulations at well-defined conditions and to investigate the fundamental processes, e.g. of the injection of urea solution for marine applications, a high pressure hot gas test rig was built up at the ITV. The current work focuses on the injection of urea solution by an air-blast atomizer. The spray breakup is the initial part of the urea decomposition, which is why reliable validation data is needed for modelling and simulating the respective spray and chemical processes. Therefore, the role of the atomization air flow rate in combination with different hot gas pressures was studied. The pressure influence is of particular interest, due to the possibility to install an SCR-system upstream the turbocharger of a marine engine. High speed shadowgraphy was applied to investigate the primary breakup of the urea spray. The breakup phenomena are discussed and combined with droplet spectra, which were measured by phase-Doppler anemometry (PDA). Apart from obtaining validation data, the study gives answers to the guiding question how to obtain acceptably fine sprays by using minimal atomization air under various circumstances.
Höltermann, Markus, Wichmar, Jan, Dinkelacker, Friedrich
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
NOx-Conversion Comparison of a SCR-Catalyst Using a Novel Biomimetic Effervescent Injector on a Heavy-Duty Engine2019-01-00471/15/2019
NOx pollution from diesel engines has been stated as causing over 10 000 pre-mature deaths annually and predictions are showing that this level will increase [1]. In order to decrease this growing global problem, exhaust after-treatment systems for diesel engines have to be improved, this is especially so for vehicles carrying freight as their use of diesel engines is expected to carry on into the future [2]. The most common way to reduce diesel engine NOx out emissions is to use SCR. SCR operates by injecting aqueous Urea solution, 32.5% by volume (AUS-32), that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water. Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths. The mixer plates create extra exhaust back pressure and cool the exhaust gases, which decreases engine and catalyst efficiency, resulting in overall poor NOx conversion (<40%) and higher CO2 production under real life drive cycle conditions. To achieve future emission legislation targets, SCR efficiency has to be improved, especially under low catalyst temperature conditions. It should also be noted that Ammonia slip has to be avoided as it is now legislated against [3]. In this study a novel biomimetic effervescent aqueous urea injector, its design inspired by the natural spray phenomenon of the Bombardier Beetle, is used to compare against a market-leading aqueous urea doser in comparable exhaust conditions with and without aggressive mixer plates being installed. The novel biomimetic effervescent injector operates by increasing the temperature of the Urea solution inside a constant volume chamber to its saturated vapour pressure. At the required time of injection an electromagnetically controlled outlet valve opens exposing the now superheated fluid to lower pressure conditions, this results in a hot, effervescent spray being ejected which rapidly breaks up into very fine droplets (<20um) projected at high velocity (60m/s) into the exhaust stream targeted at the face of the SCR catalyst. The novel biomimetic effervescent injector shows great potential with a significant higher NOx conversion rate and lower ammonia slip compared to the market-leading doser on a heavy-duty engine.
Larsson, Peter, Ravenhill, Paul, Tunestal, Per
Study on the Prevention of Face-Plugging of Diesel Oxidation Catalyst (DOC)2018-32-006910/30/2018
In order to meet the reinforcement of worldwide environmental regulations, latest diesel engines for industrial machinery are required to reduce the emission of harmful gases such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx), and particulate matter (PM). For this reason, some of the diesel engines are equipped with exhaust gas treatment devices such as diesel particulate filter (DPF), diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) catalyst. However, applications of such industrial diesel engines bring about excessive back pressure increase and deterioration in the performance of the catalysts when continuous operation is performed at low load conditions: soot accumulates on the inlet faces of DOC and DPF, causing face plugging issues. To resolve this issue, it is necessary for the system to be equipped with certain additional devices to raise an exhaust gas temperature to a high level enough to burn out the soot [1]. In this research, in order to solve the face plugging at the inlet of DOC without using such an additional equipment, we studied the cause of the face plugging of DOC. First, in order to estimate the cause of face plugging, we grasped the engine operating conditions leading to the face plugging and analyzed the soot/coke deposits accumulating on the inlet face of DOC under specific conditions. Next, in order to identify the origin of the face plugging causative deposits, we performed a component analysis of an engine exhaust gas and also conducted catalytic reaction experiments using a model exhaust gas. Then, verification experiments using an engine were carried out. As a result, we found that the production of less combustible HC by incomplete catalytic oxidation is one of the factors of the plugging problem of DOC.
Nakano, Kota, Okano, Hiroaki, Inoue, Katsushi, Obuchi, Akira
NH 3 Sensor Measurements in Different Engine Applications2018-01-18149/10/2018
In this study the exhaust gas ammonia (NH3) concentrations from different exhaust sources were measured with an ammonia sensor. The aim of the study was to verify whether an NH3 sensor has the potential to be used for monitoring and control purposes for SCR systems. Measurements were performed in laboratory and field conditions and comparison was made between Fourier Transform Infrared (FTIR) and Laser Diode Spectrometer (LDS) measurement techniques. With heavy-duty vehicles, a comparison between an LDS, FTIR and NH3 sensor was performed on a heavy-duty chassis dynamometer. Measurements were performed at steady speeds using a World Harmonized Vehicle Cycle (WHVC) and Braunschweig test cycles. The urea injection rate for the SCR system was varied to generate different ammonia levels in the exhaust gas. NH3 measurements with FTIR and NH3 sensor were performed on large cruise ships using heavy fuel oil (HFO) and marine gas oil (MGO) as fuels. Also, long-term trials on two cruise ships were conducted using heavy fuel oil and low sulphur (S < 0.1%) residual fuel. The results indicate that the NH3 sensor has the potential for being used in different applications for monitoring and controlling the SCR system. Measurement results with the sensor were in good correlation with LDS and FTIR techniques and, in dynamic measurements, the sensor response was very fast.
Murtonen, Timo, Vesala, Hannu, Koponen, Paivi, Pettinen, Rasmus, Kajolinna, Tuula, Antson, Olli
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
Development of Model Predictive Control Strategy of SCR System for Heavy-Duty Diesel Engines with a One-State Control-Oriented SCR Model2018-01-17639/10/2018
Urea-based selective catalytic reduction (SCR) of nitric oxides (NOx) is a key technology for heavy-duty diesel engines to achieve the increasingly stringent NOx emission standards. The aqueous urea injection control is critical for urea-SCR systems in order to achieve high NOx conversion efficiency while restricting the tailpipe ammonia (NH3) slip. For Euro VI emission regulation, an advanced control strategy is essential for SCR systems since its NOx emission limits are tighter and test procedure are more stringent compared to Euro IV and Euro V. The complex chemical kinetics of the SCR process has motivated model-based control design approaches. However, the model is too complex to allow real-time implementation. Therefore, it is very important to have a reduced order model for SCR control system. Based on a continuous stirred tank reactor (CSTR) and mass conservation law, a one-State control-oriented SCR model was developed and validated to estimate the downstream NOx emission, NH3 slip, and NH3 storage of the SCR catalyst. A model predictive control (MPC) coupled to the control-oriented SCR model was established to control the urea injection rate and maintain the NH3 storage at a required level. The control-oriented SCR model can capture the main dynamics of the steady state condition as well as the transient condition very well, and the NOx emissions, NH3 storage, and NH3 slip can be well predicted. With the MPC, the simulation results showed that the NH3 storage in the SCR catalyst could be well controlled, the NOx emission in the world harmonized transient cycle (WHTC) after the SCR system of a heavy-duty diesel engine with raw NOx emission at 8.66 g/kW·h was reduced to about 0.37 g/kW·h, and the averaged NOx conversion efficiency was up to 96%, while the averaged NH3 slip in the cycle was kept below 10 ppm, which met the requirements of the Euro VI emission regulation.
Wang, Guoyang, Ali, Hafiz Liaqat, Zhang, Jun, Qi, Jinzhu, Liu, Yang, Liu, Shiyu, Cai, Kaiyuan, Shuai, Shi-Jin, Wang, Zhiming
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
Real Driving NO x Emissions from Euro VI Diesel Buses2018-01-18159/10/2018
Since 2013, Euro VI heavy-duty on-road vehicles have been on the market in the Europe. Regulated exhaust emissions, including nitrogen oxides and particulate matter, have been cut down to a very low level, independent of fuel (diesel or natural gas). Multiple research papers have shown that the regulated emissions from the Euro VI and US 2010 heavy-duty on-road vehicles tested on chassis dynamometers really deliver emission levels which correspond the type approval requirements, independent of the test cycle used. In-service conformity (ISC), which is included in the Euro VI legislation, requires heavy-duty on-road engine manufacturers to test and prove their engines to comply with the emission legislation during the engine in-use period. The measurements are carried out in the field using PEMS (Portable Emission Measurement System) equipment. This kind of testing, depicting real-world emissions is the final stage to confirm low real-life emissions. Although there is evidence that the exhaust aftertreatment systems of Euro VI heavy-duty on-road engines work well on an average, there is only a limited data of city buses covering their functionality over longer operation periods, especially not at lower ambient temperatures. Especially reduction of nitrogen oxides in the SCR-system (Selective Catalytic Reduction) is sensitive to SCR catalyst operation temperature, and also to impurities transferred from engine oil or fuel. This paper present results of a unique combination of chassis dynamometer measurements, on-road PEMS measurements and continuous NOx-emission monitoring during operation in winter condition from four Euro VI diesel city buses operating in the Helsinki metropolitan area. Based on the research done, four Euro VI city buses monitored and measured during the project showed decreased NOx conversion rate and increased tailpipe NOx emissions when operating in ambient temperatures below 0 °C. Especially in ambient temperatures below −10 °C, the continuous monitoring showed dramatically increased tailpipe NOx concentrations.
Söderena, Petri, Nylund, Nils-Olof, Pettinen, Rasmus, Mäkinen, Reijo
Polycyclic Aromatic Hydrocarbons in Diesel Engine Exhaust Both with and without Aftertreatment2018-01-18129/10/2018
Since the conception of the internal combustion engine, smoky and ill-smelling exhaust was prevalent. Over the last century, significant improvements have been made in improving combustion and in treating the exhaust to reduce these effects. One group of compounds typically found in exhaust, polycyclic aromatic hydrocarbons (PAH), usually occurs at very low concentrations in diesel engine exhaust. Some of these compounds are considered carcinogenic, and most are considered hazardous air pollutants (HAP). Many methods have been developed for sampling, handling, and analyzing PAH. For this study, an improved method for dilute exhaust sampling was selected for sampling the PAH in diesel engine exhaust. This sampling method was used during transient engine operation both with and without aftertreatment to show the effect of aftertreatment. A total of 23 different PAH were measured using a 2012 medium-duty diesel engine equipped with a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst in series. The PAH were then analyzed by gas chromatography/mass (GC/MS) spectrometry to determine the individual concentrations for engine-out (without aftertreatment) and aftertreatment-out emissions. Concentrations for the engine-out PAH were significantly higher than when the aftertreatment was present. PAH in the exhaust were then compared to the PAH in the fuel.
Fanick, E. Robert, Kroll, Svitlana
Kinetic Measurements of HNCO Hydrolysis over SCR Catalyst2018-01-17649/10/2018
To meet the strict emission regulations for diesel engines, an advanced processing device such as a Urea-SCR (selective catalytic reduction) system is used to reduce NOx emissions. The Real Driving Emissions (RDE) test, which is implemented in the European Union, will expand the range of conditions under which the engine has to operate [1], which will lead to the construction of a Urea-SCR system capable of reducing NOx emissions at lower and higher temperature conditions, and at higher space velocity conditions than existing systems. Simulations are useful in improving the performance of the urea-SCR system. However, it is necessary to construct a reliable NOx reduction model to use for system design, which covers the expanded engine operation conditions. In the urea-SCR system, the mechanism of ammonia (NH3) formation from injected aqueous urea solution is not clear. Thus, it is important to clarify this mechanism to improve the NOx reduction model. In particular, the investigation of the hydrolysis of isocyanic acid (HNCO), which is formed as an intermediate product in the process of NH3 formation from urea-water solution, is required. Although previous studies have reported the rate constant of HNCO hydrolysis, these were obtained from indirect rather than direct measurements of HNCO. In this study, the reaction rate of HNCO hydrolysis over Cu-ZSM5 catalyst was measured by generating high-purity HNCO and conducting high-precision HNCO measurements. The reaction rate of HNCO hydrolysis is used in the simulation of the urea-SCR system in order to construct a reliable NOx reduction model for system design.
Matsuoka, Masahiro, Kitamura, Takaaki, Obuchi, Akira, Tsuchida, Jun, Tanaka, Kotaro, Konno, Mitsuru
Effects of Hot and Cooled EGR for HC Reduction in a Dual-Fuel Premixed Charge Compression Ignition Engine2018-01-17309/10/2018
Most internal combustion engine makers have adopted after-treatment systems, such as selective catalytic reduction (SCR), diesel particulate filter (DPF), and diesel oxidation catalyst (DOC), to meet emission regulations. However, as the emission regulations become stricter, the size of the after-treatment systems become larger. This aggravates the price competitiveness of engine systems and causes fuel efficiency to deteriorate due to the increased exhaust pressure. Dual-fuel premixed charge compression ignition (DF-PCCI) combustion, which is one of the advanced combustion technologies, makes it possible to reduce nitrogen oxides (NOx) and particulate matter (PM) during the combustion process, while keeping the combustion phase controllability as a conventional diesel combustion (CDC). However, DF-PCCI combustion produces high amounts of hydrocarbon (HC) and carbon monoxide (CO) emissions due to the bulk quenching phenomenon under low load conditions as a huddle of commercialization. In this study, the effects of exhaust gas recirculation (EGR) rate and EGR temperature were investigated to overcome the bulk quenching phenomenon under low load conditions in the DF-PCCI combustion. Natural gas (NG) and diesel were selected for low reactivity fuel (LRF) and high reactivity fuel (HRF) respectively. As experimental results, adopting the high temperature EGR could reduce the HC emission, and improve combustion efficiency (ηc) and fuel conversion efficiency (ηf), while maintaining the NOx and PM emissions under the EU-VI emission regulations. The results suggest that controlling the global equivalence ratio (∅global) and increasing the initial charge temperature by hot-EGR are quite effective way to mitigate the bulk quenching phenomenon and incomplete combustion under low load conditions in the DF-PCCI combustion.
Shim, Eui joon, Park, Hyunwook, Bae, Choongsik
Effects of Soot Deposition on NOx Purification Reaction and Mass Transfer in a SCR/DPF Catalyst2018-01-17079/10/2018
Experimental studies were carried out to investigate the effect of soot deposition on NOx purification phenomena in an ammonia selective catalytic reduction coated diesel particulate filter (SCR/DPF) catalyst. To study soot deposition effects on the chemical reactions and mass transfer, two types of testing device were used. A synthetic gas bench enabling tests to be conducted with temperature and flow rate ranges relevant to real driving conditions was used to investigate the soot influence on reduction of NOx to N2 (DeNOx). A micro-reactor that removed the effect of soot deposition on mass transfer in the catalyst layer was used to analyze chemical reactions on a soot surface and their interaction with the SCR catalyst. A filter test brick of a Cu-zeolite SCR/DPF catalyst and a powder catalyst were used for the synthetic gas bench and micro-reactor tests, respectively. Engine soot was sampled in all the tests. The synthetic gas bench results showed that soot deposition had a negative impact on NOx conversion performance. The micro-reactor results showed that NOx purification reactions took place simultaneously with side reactions, e.g., NH3 oxidation and NO2 related reactions, even when no SCR catalyst was present. Reactions on the soot surface decreased the NOx purification performance of the SCR catalyst. The influence of soot deposition on the reactivity of side reactions in the filter test brick showed the opposite effect to the powder catalyst: the former effect was intensified as the flow rate was increased. It was concluded that both the effect of reaction on the soot surface and the influence on mass transfer of soot deposition must be considered to describe the internal phenomena of NOx purification in a SCR/DPF catalyst.
Tsukamoto, Yoshihisa, Utaki, Shun, Zhang, Wencong, Fukuma, Takao, Kusaka, Jin
Design Optimization of Urea Injectors and Mixers in a Compact SCR System2018-28-00257/9/2018
Abstract Stringent emission norms require the implementation of an effective after treatment technology like Selective Catalytic Reduction (SCR). The SCR system converts NOx from exhaust gases into harmless N2. The efficiency of the system lies on two main regions. First, is the full conversion of urea to NH3 and proper uniformity of NH3 over the exhaust gases and next, is complete reaction over the catalyst bed which produces maximum NOx conversion efficiency. The NOx conversion efficiency is variable, not constant, and is dependent on many parameters, including temperature, exhaust mass flow, NOx concentration, NO2:NO ratio and SCR catalyst formulation. This paper deals with few concepts to improve the NH3 uniformity at the upstream of the catalyst. CFD simulation helps in developing and diagnosing the urea water injection systems. Mixers enable fast urea water droplet breakup and mixing with the exhaust gases. The performance of mixers varies regarding blade profiles and blade area. Augmented turbulence improves the mixing process. The design and position of urea injectors facilitate the NH3 uniformity at the SCR inlet. There exists a trade-off between the risk of clogging and pressure drop due to injector and mixer. An investigation is carried out to study the effect of various types of mixer designs along with injection position and their impact on NH3 conversion ratio.
V, Praveena, Jesu Martin, Leenus
Continuous Particulate Filter State of Health Monitoring Using Radio Frequency Sensing2018-01-12604/3/2018
Reliable means for on-board detection of particulate filter failures or malfunctions are needed to meet diagnostics (OBD) requirements. Detecting these failures, which result in tailpipe particulate matter (PM) emissions exceeding the OBD limit, over all operating conditions is challenging. Current approaches employ differential pressure sensors and downstream PM sensors, in combination with particulate filter and engine-out soot models. These conventional monitors typically operate over narrowly-defined time windows and do not provide a direct measure of the filter’s state of health. In contrast, radio frequency (RF) sensors, which transmit a wireless signal through the filter substrate provide a direct means for interrogating the condition of the filter itself. This study investigated the use of RF sensors for the continuous measurement of filter trapping efficiency, which was compared to downstream measurements with an AVL Microsoot Sensor, and a PM sampling probe simulating the geometry and installation configuration of a conventional PM sensor. The study included several particulate filter failure modes, both above and below the OBD threshold. The results confirmed the use of RF sensors to provide a direct and continuous measure of the particulate filter’s state of health over a range of typical in-use operating conditions, thereby significantly increasing the time window over which filter failures may be detected.
Sappok, Alexander, Ragaller, Paul, Herman, Andrew, Bromberg, Leslie, Prikhodko, Vitaly, Parks, James, Storey, John
Solid Particle Number and Ash Emissions from Heavy-Duty Natural Gas and Diesel w/SCRF Engines2018-01-03624/3/2018
Solid and metallic ash particle number (PN) and particulate matter (PM) mass emission measurements were performed on a heavy-duty (HD) on-highway diesel engine and a compressed natural gas (CNG) engine. Measurements were conducted under transient engine operation that included the FTP, WHTC and RMC. Both engines were calibrated to meet CARB ultra low NOX emission target of 0.02 g/hp-hr, a 90% reduction from current emissions limit. The HD diesel engine final exhaust configuration included a number of aftertreatement sub-systems in addition to a selective catalytic reduction filter (SCRF). The stoichiometric CNG engine final configuration included a closed coupled Three Way Catalyst (ccTWC) and an under floor TWC (ufTWC). The aftertreatment systems for both engines were aged for a full useful life (FUL) of 435,000 miles, prior to emissions testing. PM mass emissions from both engines were comparable and well below the US EPA emissions standard. However, the CNG engine emitted a substantially higher number of solid particles, larger and smaller than 25 nm in diameter, compared to the number of particles emitted from the HD diesel engine for each of the three transient cycles tested. The CNG engine metallic ash particle number emission was also much higher than that of the diesel. The stringent solid particle number regulation in the EU and China will address the CNG particle number emission problem. However, in the USA there is no such regulation to specifically address particle number emissions, which is a short coming. Ultrafine PN emissions from engines is a health concern. Reducing solid particle number emissions from old and new CNG engines to a level comparable to that of a diesel with DPF is an important task that needs to be addressed by policy makers around the globe.
Khalek, Imad A., Badshah, Huzeifa, Premnath, Vinay, Brezny, Rasto
Impact of SCR Activity on Soot Regeneration and the Converse Effects of Soot Regeneration on SCR Activity on a Vanadia-SCRF®2018-01-09624/3/2018
The influence of SCR (selective catalytic reduction) activity on soot regeneration was investigated using engine test measurements with and without urea dosing on a vanadia-SCRF®1, also known as a vanadia SCR coated diesel particulate filter (V.SCR-DPF). The extent and rate of passive soot regeneration is significantly reduced in the presence of SCR activity especially at high temperatures (>250 °C). The reduction in soot regeneration is because some of the NO2, which would otherwise react with the soot, is consumed by SCR reactions and consequently the rate of soot regeneration is lower when urea is dosed. The converse effects of soot oxidation on SCR activity were studied separately by analysing steady-state light-off engine measurements with different initial soot loadings on the V.SCR-DPF. The measurements show an increase in NOX conversion with increasing soot loading. This is because the reaction of soot with NO2 results in NO2/NOX ratio becoming closer to the optimal value for SCR activity of 0.5. This observation for these particular engine tests is because the V.SCR-DPF inlet NO2/NOX ratio was greater than 0.5. At low temperatures (<250 °C), NO2 conversion decreases with increasing temperature, which was attributed to the decrease in the net rate of ammonium nitrate formation with increasing temperature in this temperature range, which in turn results in a decrease in NO2 consumption. The impact of ammonium nitrate formation on NO2 conversion was also observed to be correlated to soot loading at these low temperatures. Numerical modelling was also utilised to gain further insights into the influence of soot regeneration on SCR activity and the converse effects of SCR activity on soot regeneration on a V.SCR-DPF. The model captures qualitatively and quantitatively the decrease in soot regeneration rate as a result of NO2 competition between passive soot oxidation and SCR reactions. The model also fairly predicts the enhanced SCR activity for the soot loaded V.SCR-DPF due to alteration of NO2/NOx ratio by passive soot oxidation.
Chigada, Peter I., Ahmadinejad, Mehrdad, Newman, Andrew D., Ng, Alfred Iam Pou, Torbati, Reza, Watling, Timothy C.
Exploring the NOx Reduction Potential of Miller Cycle and EGR on a HD Diesel Engine Operating at Full Load2018-01-02434/3/2018
The reduction in nitrogen oxides (NOx) emissions from heavy-duty diesel engines requires the development of more advanced combustion and control technologies to minimize the total cost of ownership (TCO), which includes both the diesel fuel consumption and the aqueous urea solution used in the selective catalytic reduction (SCR) aftertreatment system. This drives an increased need for highly efficient and clean internal combustion engines. One promising combustion strategy that can curb NOx emissions with a low fuel consumption penalty is to simultaneously reduce the in-cylinder gas temperature and pressure. This can be achieved with Miller cycle and by lowering the in-cylinder oxygen concentration via exhaust gas recirculation (EGR). The combination of Miller cycle and EGR can enable a low TCO by minimizing both the diesel fuel and urea consumptions. In this work, Miller cycle with late intake valve closing (IVC) and EGR technology were investigated on a single cylinder common rail heavy-duty diesel engine at high load operation of 24 bar net indicated mean effective pressure. The experiments were performed with a constant intake manifold pressure of 3 bar while optimizing the start of diesel injection to keep the peak in-cylinder pressure limit of 180 bar. The aqueous urea solution consumption in the SCR aftertreatment system was estimated to evaluate the effectiveness of the strategies in terms of TCO. The calculation was based on the engine-out NOx emissions and the Euro VI NOx limit. The results revealed that the use of the Miller cycle without EGR reduced NOx emissions by 35% and the net indicated efficiency by 4% when compared to the case with the baseline IVC at −178 crank angle degrees (CAD) after top dead center (ATDC). The introduction of 8%EGR decreased the levels of NOx by 54% while maintaining similar net indicated efficiency at the baseline IVC. The combination of Miller cycle with an IVC at −127 CAD ATDC and an EGR rate of 8% achieved the best trade-off between NOx and ISFC, decreasing the NOx levels by 57% and the fuel consumption by 1.6% compared to the baseline case. Soot emissions were maintained below the Euro VI limit of 0.01 g/kW h. Carbon monoxide emissions were maintained at low levels except for the combination of an IVC at −114 and an EGR rate of 8%. Unburned hydrocarbon emissions were slightly decreased with EGR and late IVCs likely due to relatively longer ignition delays and higher exhaust gas temperature. Overall, the analysis showed that the combination of Miller cycle with an IVC at −127 CAD ATDC and 8%EGR achieved the lowest total fluid consumption despite the reduction in net indicated thermal efficiency.
Guan, Wei, Pedrozo, Vinícius, Zhao, Hua, Ban, Zhibo, Lin, Tiejian
1D Engine Simulation Approach for Optimizing Engine and Exhaust Aftertreatment Thermal Management for Passenger Car Diesel Engines by Means of Variable Valve Train (VVT) Applications2018-01-01634/3/2018
Using a holistic 1D engine simulation approach for the modelling of full-transient engine operation, allows analyzing future engine concepts, including its exhaust gas aftertreatment technology, early in the development process. Thus, this approach enables the investigation of both important fields - the thermodynamic engine process and the aftertreatment system, together with their interaction in a single simulation environment. Regarding the aftertreatment system, the kinetic reaction behavior of state-of-the-art and advanced components, such as Diesel Oxidation Catalysts (DOC) or Selective Catalytic Reduction Soot Filters (SCRF), is being modelled. Furthermore, the authors present the use of the 1D engine and exhaust gas aftertreatment model on use cases of variable valve train (VVT) applications on passenger car (PC) diesel engines. The VVT applications consider a wide range of variables such as exhaust cam phasing, late intake valve opening, Miller, 2nd exhaust event and cylinder deactivation. The model has been validated with the results of experimental investigations to do this in a first step. Secondly, the VVT applications are implemented to the model to analyze their heating potential according to an efficient engine and exhaust gas thermal management. Various heating strategies have been investigated for a full-size vehicle within extended engine speed and load ranges which are relevant for the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) and even more for the determination of Real Driving Emissions (RDE). The results are compared to a conventional heating measure to demonstrate the potential in terms of a faster aftertreatment light-off with increased conversion efficiencies and benefits in CO2 emissions. As conclusion out of the investigations it can be seen, that a cylinder deactivation or a second exhaust event could provide up to 5-10% CO2 reduction under RDE conditions that comply with the EU6d legislation limit.
Deppenkemper, Kai, Özyalcin, Can, Ehrly, Markus, Schoenen, Markus, Bergmann, Dirk, Pischinger, Stefan
Urea Deposit Predictions on a Practical Mid/Heavy Duty Vehicle After-Treatment System2018-01-09604/3/2018
Urea/SCR systems have been proven effective at reducing NOx over a wide range of operating conditions on mid/heavy duty diesel vehicles. However, design changes due to reduction in the size of modern compact Urea/SCR systems and lower exhaust temperature have increased the possibility of urea deposit formation. Urea deposits are formed when urea in films and droplets undergoes undesirable secondary reactions and generate by-products such as ammelide, biuret and cyanuric Acid (CYA). Ammelide and CYA are difficult to decompose which lead to the formation of solid deposits on the surface. This phenomenon degrades the performance of the after treatment system by decreasing overall mixing efficiency, lowering de-NOx efficiency and increasing pressure drop. Therefore, mitigating urea deposits is a primary design goal of modern diesel after-treatment systems. The purpose of current study is to introduce the Computational Fluid Dynamics (CFD) approach to predict urea deposit formation in the Isuzu exhaust system using detailed urea decomposition mechanism. Conjugate Heat Transfer (CHT) is used along with the advanced splashing and film evaporation models to correctly predict the film temperature. Detailed decomposition mechanism approach with a modified multi component evaporation model was used to capture the urea deposit production process. The results were compared against engine dyno test data for mass accumulation prediction and gas-chromatograph (GC) - QTOFMS results for urea deposit chemical component prediction.
Sun, Yong, Sharma, Saurabh, Vernham, Bruce, Shibata, Keiko, Drennan, Scott
Effects of NO X Storage Component on Ammonia Formation in TWC for Passive SCR NO X Control in Lean Gasoline Engines2018-01-09464/3/2018
A prototype three-way catalyst (TWC) with NOX storage component was evaluated for ammonia (NH3) generation on a 2.0-liter BMW lean burn gasoline direct injection engine as a component in a passive ammonia selective catalytic reduction (SCR) system. The passive NH3 SCR system is a potential approach for controlling nitrogen oxides (NOX) emissions from lean burn gasoline engines. In this system, NH3 is generated over a close-coupled TWC during periodic slightly-rich engine operation and subsequently stored on an underfloor SCR catalyst. Upon switching to lean, NOX passes through the TWC and is reduced by the stored NH3 on the SCR catalyst. Adding a NOX storage component to a TWC provides two benefits in the context of a passive SCR system: (1) enabling longer lean operation by storing NOX upstream and preserving NH3 inventory on the downstream SCR catalyst; and (2) increasing the quantity and rate of NH3 production during rich operation. Since the fuel penalty associated with passive SCR NOX control depends on the fraction of time that the engine is running rich rather than lean, both benefits (longer lean times and shorter rich times achieved via improved NH3 production) will decrease the passive SCR fuel penalty. However, these benefits are primarily realized at low to moderate temperatures (300-500 °C), where the NOX storage component is able to store NOX, with little to no benefit at higher temperatures (>500 °C), where NOX storage is no longer effective. This study discusses engine parameters and control strategies affecting the NH3 generation over a TWC with NOX storage component.1
Prikhodko, Vitaly, Pihl, Josh, Toops, Todd, Parks, James
Experimental Investigation of Novel Ammonia Mixer Designs for SCR Systems2018-01-03434/3/2018
Meeting Euro 6d NOx emission regulations lower than 80 mg/km for light duty diesel (60 mg/km gasoline) vehicles remains a challenge, especially during cold-start tests at which the selective catalyst reduction (SCR) system does not work because of low exhaust gas temperatures (light-off temperature around 200 °C). While several exhaust aftertreatment system (EATS) designs are suggested in literature, solutions with gaseous ammonia injections seem to be an efficient and cost-effective way to enhance the NOx abatement at low temperature. Compared to standard SCR systems using urea water solution (UWS) injection, gaseous NH3 systems allow an earlier injection, prevent deposit formation and increase the NH3 content density. However non-uniform ammonia mixture distribution upstream of the SCR catalyst remains an issue. These exhaust gas/ NH3 inhomogeneities lead to a non-optimal NOx reduction performance, resulting in higher than expected NOx emissions and/or ammonia slip. Thus, efficient mixers upstream of the SCR are crucial for the overall EATS performance. In the experimental study reported in this article, planar laser induced fluorescence (PLIF) is used to quantify mixing performance of four novel CFD optimized static mixers in an optically accessible flow bench. The variation of boundary conditions and the change of exhaust line configurations (e.g. w/wo DOC upstream, w/wo DPF downstream) show a major effect on the mixing process and subsequently the homogeneity of the ammonia-exhaust gas mixture (for example: drop in uniformity index from UI = 0.95 to UI = 0.60 for a blade mixer design). This points out the need to purposefully design and optimize static mixers for a specific exhaust line configuration.
Schiffmann, Philipp, Lecompte, Matthieu, Laget, Olivier
Improvement in Selective Catalytic Reduction Model Accuracy for Predicting NO x Conversion at High Temperature2018-01-03464/3/2018
As a result of WNTE regulations and the introduction of close-coupled aftertreatment systems, exhaust purification at high temperatures in commercial vehicles has become increasingly important in recent years. In this report, we improve the prediction accuracy for NOx conversion at high temperatures in the kinetic model of conventional Cu-selective catalytic reduction (Cu-SCR). Reaction rate analysis indicated that the rate of NH3 oxidation was extremely low compared to the rate of standard SCR. We found that NOx concentration-dependent NH3 oxidations (termed NOx-assisted NH3 oxidations) were key to the rate of NH3 oxidation. The output of the improved Cu-SCR kinetic model was in agreed with experimental results obtained from the synthetic gas bench and engine dynamometer bench. We analyzed the contribution of each reaction to NH3 consumption during Cu-SCR. Under NH3 + NO + O2, standard SCR was dominant at low temperature. At high temperatures, the rate of NO-assisted NH3 oxidation increased, and this reaction competed with standard SCR. Under NH3 + NO + NO2 + O2, fast SCR, NH4NO3 formation, and standard SCR were the dominant reactions at low temperature. With increasing temperature, NO2-assisted NH3 oxidation competed with the other reactions, resulting in a decreased NOx conversion.
Oka, Kohei, Ohori, Teppei, Itagaki, Yutaka, Osumi, Kazuo, Ishikawa, Naoya, Dobashi, Yuuki, Wako, Eiji
Sustained Low Temperature NOx Reduction2018-01-03414/3/2018
Sustained NOx reduction at low temperatures, especially in the 150-200 °C range, shares some similarities with the more commonly discussed cold-start challenge, however, poses a number of additional and distinct technical problems. In this project, we set a bold target of achieving and maintaining 90% NOx conversion at the SCR catalyst inlet temperature of 150 °C. This project is intended to push the boundaries of the existing technologies, while staying within the realm of realistic future practical implementation. In order to meet the resulting challenges at the levels of catalyst fundamentals, system components, and system integration, Cummins has partnered with the DOE, Johnson Matthey, and Pacific Northwest National Lab and initiated the Sustained Low-Temperature NOx Reduction program at the beginning of 2015 and completed in 2017. Through this collaboration, we are exploring catalyst formulations and catalyst architectures with enhanced catalytic activity at 150 °C; opportunities to approach the desirable ratio of NO and NO2 in the SCR feed gas; options for robust low-temperature reductant delivery; and the requirements for the overall system integration. This paper will provide information on the approach used and share results of an on-engine performance demonstration on the path towards a commercially viable solution.
Zha, Yuhui, Cunningham, Michael, Tang, Yadan, Srinivasan, Anand, Luo, Jinyong, Heichelbech, John, Lakkireddy, Venkata, Yezerets, Aleksey, Ruffin, Sade, Wei, Zhehao, Fedeyko, Joseph, Sukumar, Balaji, Hess, Howard, Gao, Feng, Szanyi, Janos, wang, Yong
Eaton goes internal with its next-generation EGR solution18AUTP08_051/1/2018
Eaton's Internal Exhaust Gas Recirculation (iEGR) solution production-debuts in the 2020MY as a next-generation technology providing near-instantaneous heating of the selective catalytic reduction system to reduce diesel exhaust emissions. “The iEGR technology is controlled by an electro-mechanical actuator, so operation can occur in cold conditions,” Nicola Andrisani, Eaton's Engineering Manager of the Valvetrain Advanced Engineering Vehicle Group based in Torino, Italy, said in an Automotive Engineering interview.
Buchholz, Kami
In-Situ Exhaust Visualization of Near-Nozzle Urea-Based Deposits Formation in an Underfloor SCR Injection Location2017-01-237610/8/2017
Selective Catalytic Reduction (SCR) diesel exhaust aftertreatment systems are virtually indispensable to meet NOx emissions limits worldwide. These systems generate the NH3 reductant by injecting aqueous urea solution (AUS-32/AdBlue®/DEF) into the exhaust for the SCR NOx reduction reactions. Understanding the AUS-32 injector spray performance is critical to proper optimization of the SCR system. Specifically, better knowledge is required of the formation of near-nozzle deposits that have been observed on existing underfloor SCR systems. The current work presents in-situ time lapse imaging of an underfloor mounted AUS-32 exhaust-mounted urea dosing unit. The operating conditions under examination are representative of low-load low speed urban driving interspersed with high temperature exposures typical of periodic DPF regeneration. Analysis is provided of various phenomena leading to the creation of urea-based thermal decomposition products and their deposition on the near-nozzle injector surfaces. Further imaging during the high temperature exposure reveals the subsequent polymerization of liquid films generated during the lower temperature operation. Burnoff of solid urea buildup is also observed during the high temperature events. The present test campaign provides new insights on the various mechanisms leading to the near-nozzle deposits, including indications of urea vapor transport back to the dosing unit injection point.
Van Vuuren, Nic, Armitage, Phil
The Application of Solid Selective Catalytic Reduction on Heavy-Duty Diesel Engine2017-01-236410/8/2017
Urea SCR technology is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea SCR process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and reduces NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12°C. For preventing deposits formation, aqueous urea solution is hardly injected into exhaust gas stream at temperature below 200°C. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for control NOx emissions from heavy duty diesel engines. The solid SCR technology, using a solid metal ammine complex to store ammonia, can overcome the issues of urea SCR by dosing gaseous ammonia directly to the exhaust gas steam. In this paper, the applications of solid SCR for a CN-5 heavy duty diesel engine and a CN-4 heavy duty diesel vehicle was discussed based on engine bench tests and portable emission measurement system tests, a comparison study on NOx emission was performed with urea SCR during real world driving conditions. The results showed that the solid SCR technology could promote the deNOx performances more efficiently than urea SCR technology at low temperature conditions.
Li, Jiaqiang, Ge, Yunshan, He, Chao, Tan, Jianwei, Peng, Zihang, Li, Zidi, Chen, Wei, Wang, Shijie
Performance Improvement of Regulator Rectifier for 2-Wheeler Engine with Respect to Upcoming Stringent Regulations in Emerging Market2017-01-242510/8/2017
On two wheelers, magneto/alternator generates either single/three phase AC power and Regulator Rectifier Unit (RRU) does regulated rectification to charge the battery. In order to face the requirements of 2-wheeler engine with respect to upcoming stringent regulations like electronic fuel injection (EFI), anti-lock braking system (ABS), automatic headlamp on (AHO) in emerging markets like India; vehicles demand more electrical power from batteries. This demands higher power from alternator and consequently from RRU. Requirement of higher output power presents challenges on regulator rectifier unit in terms of size, power dissipation management and reliability. In this paper, improved performance of MOSFET based RRU is discussed in comparison to Silicon Controlled Rectifier (SCR) based RRU. The motivation/benefits of MOSFET based design is described along with the thermal behavior and temperature coefficient performance of RRU with test results. The second topic discussed is how the MOSFET based RRU helps to improve performance by respecting form factor and total power dissipation compared to SCR based design.
Verma, Ramit, R Ugale, Ramdas
Development of Model Based Closed Loop Control Strategy of SCR System for Heavy-Duty Diesel Engines2017-01-238310/8/2017
Urea selective catalytic reduction (SCR) is a key technology for heavy-duty diesel engines to meet the increasingly stringent nitric oxides (NOx) emission limits of regulations. The urea water solution injection control is critical for urea SCR systems to achieve high NOx conversion efficiency while keeping the ammonia (NH3) slip at a required level. In general, an open loop control strategy is sufficient for SCR systems to satisfy Euro IV and Euro V NOx emission limits. However, for Euro VI emission regulation, advanced control strategy is essential for SCR systems due to its more tightened NOx emission limit and more severe test procedure compared to Euro IV and Euro V. This work proposed an approach to achieve model based closed loop control for SCR systems to meet the Euro VI NOx emission limits. A chemical kinetic model of the SCR catalyst was established and validated to estimate the ammonia storage in the SCR catalyst. Based on the model, a PI controller was designed to control the ammonia storage in the SCR catalyst at the level close to the saturated condition to maximize the NOx conversion efficiency without exceeding the NH3 slip limit. Both simulation results and engine bench test results demonstrated good effects of the control strategy. With the effects of the control strategy, the ammonia storage in the SCR catalyst can be well controlled, the NOx emission in the world harmonized transient cycle (WHTC) after the SCR system of a heavy-duty diesel engine with raw NOx emission at 8.13 g/kW·h can be reduced to about 0.3 g/kW·h, and the averaged NOx conversion efficiency was higher than 96%, while the averaged NH3 slip in the cycle kept below 10 ppm, which has met the NOx emission requirements of the Euro VI emission regulation.
Wang, Guoyang, Zhang, Jun, Yang, Bo, Li, Chuandong, Shuai, Shi-Jin, Yin, Shi, Jian, Meng
Dilute Measurement of Semi-Volatile Organic Compounds (SVOC) from a Heavy-Duty Diesel Engine2017-01-239310/8/2017
Semi-volatile organic compounds (SVOC) are a group of compounds in engine exhaust that either form during combustion or are part of the fuel and lubricating oil. Since these compounds occur at very low concentrations in diesel engine exhaust, the methods for sampling, handling, and analyzing these compounds are critical to obtaining good results. An improved dilute exhaust sampling method was used for sampling and analyzing SVOC in engine exhaust, and this method was performed during transient engine operation. A total of 22 different SVOC were measured using a 2012 medium-duty diesel engine. This engine was equipped with a stock diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst in series. Exhaust concentrations for SVOC were compared both with and without exhaust aftertreatment. Concentrations for the engine-out SVOC were significantly higher than with the aftertreatment present. Distribution of the SVOC between semi-volatile- and particulate-phase depended on the number of aromatic rings, the molecular weight, and the volatility of the compounds detected.
Fanick, E. Robert, Kroll, Svitlana
The Benefits of Diesel Exhaust Fluid (DEF) Additivation on Urea-Derived Deposits Formation in a Close-Coupled Diesel SCR on Filter Exhaust Line2017-01-237010/8/2017
Diesel Exhaust Fluid (DEF) like Adblue® is a urea/water solution injected upstream from the SCR catalyst. Urea decomposes into ammonia (NH3) which acts as reducing agent in the de-NOx reaction process. However, incomplete decomposition of urea can lead to unwanted deposits formation, thereby resulting into backpressure increase, loss of NOx reduction efficiency, and durability issues. The phenomenon is aggravated at low temperatures and can lead to restriction or stop of DEF injection below certain exhaust temperatures. This paper focuses on the influence of the additivation of DEF on deposits formation in a passenger car close-coupled SCR on filter Diesel exhaust line installed in a laboratory flow bench test. The behavior of two different additivated DEF was compared to Adblue® in terms of deposits formation on the mixer and SCRF canning at different temperatures comprised between 240°C and 165°C, and different air flows. The influence of the DEF additivation on the cooling effect of the fluid and the surface temperature of the exhaust line downstream from the injector were also investigated.
Lecompte, Matthieu, Obiols, Jerome, Cherel, Jerome, Raux, Stephane
Kinetic Modeling Study of NOx Conversion Based on Physicochemical Characteristics of Hydrothermally Aged SCR/DPF Catalyst2017-01-238610/8/2017
Diesel engines have better fuel economy over comparable gasoline engines and are useful for the reduction of CO2 emissions. However, to meet stringent emission standards, the technology for reducing NOx and particulate matter (PM) in diesel engine exhaust needs to be improved. A conventional selective catalytic reduction (SCR) system consists of a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and urea-SCR catalyst. Recently, more stringent regulations have led to the development of SCR systems with a larger volume and increased the cost of such systems. In order to solve these problems, an SCR catalyst-coated DPF (SCR/DPF) is proposed. An SCR/DPF system has lower volume and cost compared to the conventional SCR system. The SCR/DPF catalyst has two functions: combustion of PM and reduction of NOx emissions. As PM is removed from the DPF at high temperatures (>650°C), the SCR/DPF system is exposed to higher temperatures as compared with those in the conventional SCR system. In this study, we investigated the NOx reduction performance and the properties of a hydrothermally aged SCR/DPF catalyst. Using these data, a model that can predict the NOx conversion of the hydrothermally aged SCR/DPF catalyst was constructed. A commercial copper-exchanged zeolite catalyst, Cu-ZSM-5, was used and aged in synthetic air with 10% water over the temperature range 650-750 °C. The effects of hydrothermal aging on the catalysts were investigated using a synthetic gas bench, and a detailed analysis of the structure of the hydrothermally aged catalyst was performed. Using the experimental data, we succeeded in constructing a hydrothermally aged SCR/DPF model for predicting the NOx conversion based on changes in the physicochemical characteristics of the catalysts with changes in the hydrothermal aging conditions. This work is the first step toward bridging the gap between a lab-simulated performance model and the global reactivity observed under real-world conditions.
Ohya, Naoki, Hiyama, Kohei, Tanaka, Kotaro, Konno, Mitsuru, Tomita, Atsuko, Miki, Takeshi, Tai, Yutaka
Prediction of Spray Behavior in Injected by Urea SCR Injector and the Reaction Products2017-01-237510/8/2017
In the urea SCR system, urea solution is injected by injector installed in the front stage of the SCR catalyst, and NOx can be purified on the SCR catalyst by using NH3 generated by the chemical reaction of urea. NH3 is produced by thermolysis of urea and hydrolysis of isocyanic acid after evaporation of water in the urea solution. But, biuret and cyanuric acid which may cause deposit are sometimes generated by the chemical reactions without generating NH3. Spray behavior and chemical reaction of urea solution injected into the tail-pipe are complicated. The purpose of this study is to reveal the spray behavior and NH3 generation process in the tail-pipe, and to construct the model capable of predicting those accurately. In this report, the impingement spray behavior is clarified by scattered light method in high temperature flow field. Liquid film adhering to the wall and deposit generated after evaporation of water from the liquid film are photographed by the digital camera. NH3 concentration is measured at 13 points of the cross section of the tail-pipe by FTIR, and NH3 concentration distribution is calculated. From the experiment, the influences of gas temperature on droplets scattering after wall impingement and impingement conditions on NH3 concentration distribution are clarified. It is suggested that the deposit after evaporation of liquid film may be an intermediate product such as biuret or cyanuric acid. Also, by comparing and verifying the results of calculation using CFD software FIRE v2014.2 and the experimental results, the phenomenon influencing the prediction accuracy of the NH3 concentration distribution is clarified. Factors influencing the prediction accuracy of calculation are atomization characteristics after wall impingement for NH3 concentration, gas flow in the tail-pipe for NH3 concentration distribution and liquid film generation due to the decrease of the plate temperature for NH3 generation process.
Niwa, Akihiro, Sakatani, Shogo, Matsumura, Eriko, Kitamura, Takaaki
Estimation of Fuel Economy and Emissions for Heavy-Duty Diesel Plug-In Hybrid Vehicle with Electrical Heating Catalyst System2017-01-220710/8/2017
Next-generation vehicles which include the Electric Vehicles, the Hybrid Electric Vehicles and the Plug-in Hybrid Electric Vehicles are researched and expected to reduce carbon dioxide (CO2) emission in the future. In order to reduce the emissions of the heavy-duty diesel plug-in hybrid electric vehicles (PHEV), it is necessary to provide the high exhaust-gas temperature and to keep the exhaust-gas aftertreatment system effective. The engine starting condition of the PHEV is cold, and the engine start and stop is repeated. And, the engine load of the PHEV is assisted by the electric motor. Therefore, the exhaust-gas aftertreatment system of the PHEV is not able to get the enough high exhaust-gas temperature. And, the warm-up of the exhaust-gas aftertreatment system for the PHEV is spent the long time. So, it is worried about a bad effect on the emission characteristics of the PHEV. In this study, we focused on the Electrical Heating Catalyst (EHC) system, which is one of the next generation electrical technologies. This test PHEV was equipped with an EHC. The fuel economy and emission characteristics of this test PHEV were estimated using the extended-HILS, which is combined the real engine with the PHEV model of the HILS (Hardware-In-the-Loop-Simulator). This result is that an EHC showed good performance at the engine low speed and low torque range. And, NOx emission was reduced when the tailpipe layout was setup in order of the urea solution injector, an EHC and the Selective Catalytic Reduction (SCR) catalyst. NOx and CO2 emission of this test PHEV which was equipped with an EHC was good, compared with the heavy-duty diesel engine vehicle, the heavy-duty diesel hybrid electric vehicle and the PHEV which was not equipped with an EHC.
Okui, Nobunori
Simulation Research of the Structural Downsizing of SCR Reactor2017-01-238710/8/2017
Currently, selective catalytic reduction (SCR) is one of the main after-treatment systems to control diesel engine NOx emission. But the SCR system is bulky, considering the limited installation space. Therefore, the design of SCR system with the compact structure and reliable performance is one of the essential topics. In this study, the structure parameters, such as catalyst cross-sectional area, catalyst length, substrate wall thickness, coating thickness, channels per square inch (CPSI) of substrate, are taken into consideration to study their effects on the SCR performance and narrow the scope of various structural parameters for the following optimization study. Then, the structural parameters of the SCR reactor are optimized by considering the coupling relationship among these structural parameters by using the Response Surface Methodology (RSM) at high load of diesel engine. The numbers of structural parameters are finally optimized as follows: cross-sectional area is 59612 mm2; length is 190 mm; CPSI is 350; coating thickness is 0.01 mm; substrate wall thickness is 0.21 mm. At the same time, NOx conversion rate is 94%; catalyst pressure drop is 733.9 Pa. Compared with the original, catalyst volume is reduced by 31.3%. Optimized structure parameters are validated. The differences between the predicted values and the simulated values of NOx conversion rate and pressure drop are within acceptable limits.
Wu, Yonge, Liang, Xingyu, Shu, Ge-Qun, Shen, Boxi, Wang, Yuesen, Liu, Xikai, Li, Zhijun
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