Urea Injection Research Articles

Application of Model-Based Controller on a Heavy-Duty Dual Selective Catalytic Reduction Aftertreatment

<div>Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NO<sub>x</sub>) and carbon dioxide (CO<sub>2</sub>) regulations. This article focuses on the development and calibration of a model-based controller (MBC) for an advanced diesel AT system. The MBC was first applied to a standard AT system including a diesel particulate filter (DPF) and selective catalytic reduction (SCR) catalyst. Next, a light-off SCR (LO-SCR) was added upstream of the standard AT system. The MBC was optimized for both catalysts for a production engine where the diesel exhaust fluid (DEF) was unheated for both SCRs. This research shows that the tailpipe (TP) NO<sub>x</sub> could be reduced by using MBC on both catalysts. The net result was increased NO<sub>x</sub> conversion efficiency by one percentage point on both the LO-SCR and the primary SCR. The CO<sub>2</sub> emissions were slightly reduced, but this effect was not significant. Finally, the MBC was used with a final setup representative of future AT systems which included standard insulation on the catalysts and optimal DEF dosing controls. This final configuration resulted in an improved NO<sub>x</sub> and CO<sub>2</sub> such that the composite Federal Test Procedure (FTP) NO<sub>x</sub> was 0.060 g/hp-hr and the composite FTP CO<sub>2</sub> was 508.5 g/hp-hr. The article details this cycle along with the low-load cycle (LLC) and beverage cycle. More technologies are required to meet the future California Air Resources Board (CARB) 2027 standard, which will be shown in future work.</div>

Optimization of the Urea SCR injector based on entropy generation minimization and entransy dissipation extremum

A urea injection model with a mixer was established, and the of the urea-water-solution (UWS) heat transfer behavior in the pipeline was studied using the ML-CFD method, The influence of the urea injector parameters on NH3 concentration and uniformity was analyzed through parameter analysis. To improve the quality of NH3 produced by the UWS, according to the heat transfer efficiency of UWS in the pipeline, the parameters of the urea injector were optimized with the mutil-objectives of entropy generation minimization (EGM) and entransy dissipation extremum (EDE) respectively. The corresponding Pareto front was obtained, and the CFD model was established to compare the application of the two heat transfer indicators in engineering practice. The results show that both the EGM and the EDE methods can effectively optimize the heat transfer of UWS in the flow field, but the EDE method is better than EDG. The uniformity is 0.724% higher, and the NH3 concentration is 6.411% higher. This provides technical support for enhancing the UWS heat transfer.

Nitrogen Oxides and Ammonia Removal Analysis Based on Three-Dimensional Ammonia-Diesel Dual Fuel Engine Coupled with One-Dimensional SCR Model

Ammonia, as an alternative fuel for internal combustion engines, can achieve nearly zero carbon emissions. Although the development of the pure ammonia engine is limited by its poor combustion characteristics, ammonia–hydrocarbon mixed combustion can effectively improve the combustion of ammonia fuel. With the increase in the ammonia fuel proportion in the fuel mixture, a large number of nitrogen oxides (NOX) and unburned ammonia may be discharged, which have a poor impact on the environment. In this study, the performance of selective catalytic reduction (SCR) aftertreatment technology in reducing NOX and ammonia emissions from ammonia–diesel dual-fuel engines was investigated using simulation. A good cross-dimensional model was established under the coupling effect, though the effect of a single-dimensional model could not be presented. The results show that when the exhaust gas in the engine cylinder is directly introduced into the SCR without additional reducing agents such as urea, unburned ammonia flowing into SCR model is in excess, and there will be only ammonia at the outlet; however, if the unburned ammonia fed into the SCR model is insufficient to reduce NO, the ammonia concentration at the outlet will be 0. NOX can be 100% effectively reduced to N2 under most engine conditions; thus, unburned ammonia in exhaust plays a role in reducing NOX emissions from ammonia–diesel dual-fuel engines. However, when the concentration of unburned ammonia in the exhaust gas of an ammonia–diesel dual-fuel engine is large, its ammonia emissions are still high even after the SCR. In addition, the concentrations of N2O after SCR do not decrease, but increase by 50.64 in some conditions, the main reason for which is that by the action of the SCR catalyst, NO2 is partially converted into N2O, resulting in an increase in its concentration at the SCR outlet. Adding excessive air or oxygen into the SCR aftertreatment model can not only significantly reduce the ammonia concentration at the outlet of the model without affecting the NOX conversion efficiency of SCR, but inhibit N2O production to some extent at the outlet, thus reducing the unburned ammonia and NOX emissions in the tail gas of ammonia–diesel dual-fuel engines at the same time without the urea injection. Therefore, this study can provide theoretical guidance for the design of ammonia and its mixed-fuel engine aftertreatment device, and provide technical support for reducing NOX emissions of ammonia and its mixed fuel engines.

Influence of Urea Uneven Injection on the Performances of a Diesel Engine

The influence of heterogeneous flow injection of urea at different velocities and temperatures on NOx conversion efficiency, ammonia storage and ammonia leakage is investigated experimentally. A diesel engine employing a selective catalytic reduction (SCR) technology is considered. It is found that for a fixed injection velocity, the degree of ammonia leakage changes depending on the temperature. The higher the temperature, the faster the catalytic reduction reaction and the smaller the degree of ammonia leakage. The temperature has a great influence on the catalytic reduction reaction rate. At an injection velocity of 10000/h, the average reaction rate at 420 C is 12 times higher than that at 180 C. The injection velocity has a weak influence on the reaction rate. When the injection velocity changes from 10000/h to 40000/h at the same temperature, the average reaction rate does not change appreciably. However, increasing the space velocity can accelerate the leakage of ammonia, thereby mitigating the benefits associated with the NOx conversion.

Ammonia Slip Estimation Based on Ammonia Slip Catalyst Control-Oriented Modeling and On-Board Diagnostics NOX Sensor Cross-Sensitivity Analysis

Abstract The incoming emission regulations for internal combustion engines are gradually introducing new pollutant species, which require greater complexity of the aftertreatment systems concerning layout, control, and diagnostics. This is the case of ammonia, which is injected into the exhaust gas through urea injections for NOx abatement in selective catalytic reduction (SCR) systems and can also be generated in three-way catalysts. However, ammonia slip requires its oxidation on a dedicated ammonia slip catalyst (ASC). The set composed of the urea injection system, SCR, and ASC requires control tools to ensure high NOx conversion efficiency and compliant ammonia slip under real driving conditions. These tasks are based on the use of NOx sensors ZrO2 pumping cell-based, which has the disadvantage of high cross-sensitivity to ammonia that can affect the measurement of NOx and compromise the SCR-ASC control strategies. The present work proposes a methodology to predict ammonia and NOx tailpipe emissions. For this purpose, a control-oriented ASC model was developed to use its ammonia slip prediction to determine the cross-sensitivity correction of the tailpipe NOx sensor. The model is based on a simplified solution of the transport equations of the species involved in the ASC reaction mechanism. The model was calibrated using steady- and quasi-steady-state tests performed in a Euro 6c engine. Finally, the performance of the proposed methodology to predict NOx and ammonia emissions was evaluated against experimental data corresponding to worldwide harmonized light vehicles test cycles (WLTC) applying different urea dosing strategies.

Experimental investigation of the high-pressure SCR reactor impact on a marine two-stroke diesel engine

The high-pressure selective catalytic reduction (HP-SCR) system arranged before the turbine is more suitable for high-power marine low-speed engines to reduce NOx emission. However, the HP-SCR reactor will cause an increase in engine exhaust back pressure, affecting its performance and brake-specific fuel consumption (BSFC). The 10WM marine low-speed two-stroke diesel engine and its HP-SCR system are taken as the research object in this paper. The engine performance and emissions in International Maritime Organization (IMO) Tier II and Tier III modes are tested by bench experiments. The effects of the HP-SCR reactor on engine performance parameters, emission characteristics, and pulse effect in exhaust pipe are obtained. The research showed that when the HP-SCR reactor is used, the BSFC of the engine will slightly increase, but the maximum will not exceed 1 g/kWh. The weighted specific emission of NOx is 2.09 g/kWh, which can meet Tier III emission regulations. In addition, under the Tier II mode, the engine exhaust pipe has a noticeable pulse effect. The exhaust gas temperature before the turbine is about 30 °C higher than that after the cylinder. However, under Tier III mode, the pulse effect in the exhaust pipe disappears completely. In addition to the fact that the HP-SCR reactor weakens the linear velocity of exhaust gas, the main reason is that the urea injection unit reduces exhaust gas temperature by 36 ∼ 47 °C.

A novel high-selectivity mixed potential ammonia gas sensor based on FeCr2O4 sensing electrode

• Sensing material FeCr 2 O 4 was prepared using the polymer precursor method for fabricating sensing electrodes of mixed potential type NH 3 sensors based on yttria-stabilized zirconia (YSZ). • Sensing performance of the NH 3 sensors was strongly affected by sensing electrode thickness and operating temperature. • The sensor attached by FeCr 2 O 4 sensing electrode with a thickness of 98.95 μm demonstrated the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. And the mixed potential has a linear relationship with the logarithm of NH 3 concentration. • The FeCr 2 O 4 /YSZ/Ag sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. • According to the mixed potential mechanism, the sensitivity of the sensor was determined by the anodic reaction of NH 3 , the cathodic reaction of O 2 , as well as the non-electrochemical gas–solid heterogeneous catalytic reaction of NH 3 . Ammonia detection is of great significance for feedback control of urea injection in SCR system. In this paper, FeCr 2 O 4 sensing materials were prepared using the polymer precursor method used as the sensing electrode of mixed potential NH 3 sensors based on yttria-stabilized zirconia. The composition and structure of sensing electrodes were characterized using XRD and SEM. The effects of sensing electrode thickness and operating temperature on sensing performance were investigated. These related phenomena were ascribed to the adsorption and reactivity of NH 3 , as well as the competition between electrochemical catalytic reactions and gas–solid heterogeneous catalytic reactions. It was found that the sensor coated by FeCr 2 O 4 sensing materials with a thickness of 98.95 μm exhibited the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. Furthermore, the sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. Moreover, the sensing mechanism of the mixed potential sensor was discussed.

Meeting future NOX emission regulations by adding an electrically heated mixer

New regulations by the California Air Resources Board (CARB) demand a stringent 0.02 g/hp-hr tailpipe NOx limit by the year 2027, requiring Selective Catalytic Reduction (SCR) catalysts to provide high NOx conversions even at low (below 200°C) exhaust temperatures. This work describes utilizing an Electrically Heated Mixer System (EHM system) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) catalyst followed by a conventional aftertreatment (AT) system containing DOC, DPF, and SCR, enabling high NOx conversions meeting CARB’s NOx emission target. The AT catalysts were hydrothermally aged to Full Useful Life. Conventional unheated Diesel Exhaust Fluid (DEF) was injected upstream of both the LO-SCR and primary downstream SCR. The EHM system allowed for DEF to be injected as low as 130°C upstream of the LO-SCR, whereas, in previous studies, unheated DEF was injected at 180°C or dosed at 130°C with heated DEF. The combination of unheated DEF, EHM system, LO-SCR, and downstream SCR enabled the needed increase in NOx efficiency in low exhaust temperatures, which was observed in drive cycles such as in cold-FTP, LLC, and World Harmonized Transient Cycle (WHTC). There were several-fold reductions in tailpipe NOx using this configuration compared to its baseline: 3.3-fold reduction in FTP, 22-fold in Low Load Cycle (LLC), 38-fold in Beverage Cycle, 8-fold in “Stay Hot” Cycle, and 10-fold in WHTC. Finally, it is shown that the EHM system can heat the exhaust gas, such as during a cold start, without needing additional heating hardware integrated into the system. These results were observed without performing changes in the engine base calibration.

Experimental study on the performance and diagnosis of hydrothermally aged selective catalytic reduction over a copper-based catalyst

The conversion of nitrogen oxides (NOx) by hydrothermally aged copper (Cu)–based selective catalytic reduction (SCR) is an irreversible phenomenon. Tail exhaust NOx emission control and on-board diagnostics (OBD) monitoring are difficult with hydrothermally aged Cu–based SCR because the on-board NOx sensor has cross sensitivity to NH3 in the exhaust. In this study, the performance and diagnosis of hydrothermally aged SCR under real engine exhaust were studied. The influence of hydrothermally aged SCR on NH3 storage, tail exhaust NOx, urea injection, and OBD diagnosis were quantitatively analyzed under the World Harmonized Transient Cycle (WHTC). The results show that hydrothermally aged SCR had a great influence on the NH3 storage capacity. In terms of SCR conversion efficiency and OBD detection, compared with fresh SCR, hydrothermally aged SCR was more sensitive to space velocity than to temperature. Under different OBD monitored release conditions, the NOx conversion efficiency was greatly different; hence, the occurrence of a false diagnosis can be avoided through the selection of appropriate release conditions. These research results provide a reference for SCR size design, NOx control, and diagnostic strategies.

Meeting future NOX emissions using an electric heater in an advanced aftertreatment system

Engine and aftertreatment solutions are being identified to meet the upcoming ultra-low NOx regulations on heavy duty vehicles as published by the California Air Resources Board (CARB) and proposed by the United States Environmental Protection Agency (US EPA) for the year 2027 and beyond. These standards will require changes to current conventional aftertreatment systems for dealing with low exhaust temperature scenarios. One approach to meeting this challenge is to supply additional heat from the engine; however, this comes with a fuel penalty which is not attractive and encourages other options. Another method is to supply external generated heat directly to the aftertreatment system. The following work focuses on the later approach by maintaining the production engine calibration and coupling this with an Electric Heater (EH) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) followed by a primary aftertreatment system containing a downstream Selective Catalytic Reduction (SCR). External heat is supplied to the aftertreatment system using an EH to reduce the Tailpipe (TP) NOx emissions with minimal fuel penalty. Two configurations have been implemented, the first is a Close Coupled (CC) LO-SCR configuration and the second is an Underfloor (UF) LO-SCR configuration. The CC LO-SCR configuration shows the best outcome as it is closer to the engine, helping it achieve the required temperature with lower EH power while the UF LO-SCR configurations addresses the real-world packaging options for the LO-SCR. This work shows that a 7 kW EH upstream of a LO-SCR, in the absence of heated Diesel Exhaust Fluid (DEF), followed by a primary aftertreatment system met the 2027 NOx regulatory limit. It also shows that the sub-6-inch diameter EH with negligible pressure drop can be easily packaged into the future aftertreatment system.

Towards tailpipe sub-23 nm solid particle number measurements for heavy-duty vehicles regulations

A heavy-duty engine is type-approved in engine dynamometers, while its in-service conformity is controlled on the road. In the first case, laboratory particle number systems (LABS) sample from a full dilution tunnel or a proportional partial flow dilution system (PFDS). In the second case portable emissions measurements systems (PEMS) measure directly from the tailpipe. Permitting in the regulation LABS sampling directly from the tailpipe would simplify testing and would improve their comparability with PEMS. In this study PEMS and LABS, both sampling from the tailpipe and measuring solid particles >10 nm, were compared with references systems (i.e. LABS from PFDS). One compressed natural gas (CNG) engine, and three diesel engines, all Euro VI step E, with or without urea injection, and with or without crankcase ventilation connected to the tailpipe, challenged the systems with different emission levels and particle sizes and properties. The results showed that the differences of the LABS to the references were in most cases within ±25%, with a few exceptions. The PEMS were within ±50%. There was no or small effect on the differences from engine technology, urea injection or crankcase ventilation. The inclusion of sub-23 nm particles increased 100% to 250% the particle number emissions. The urea injection increased the >10 nm emissions 300–600% (2–5 × 1010 p/kWh). Connecting the crankcase ventilation to the tailpipe further increased the >10 nm particle number emissions 340–560% (1.4–2.5 × 1011 p/kWh), bringing the >10 nm levels of the engines to approximately half of the current particle number limit, applicable to particles >23 nm.

Investigation of ammonia homogenization and NOx reduction quantity by remodeling urea injector shapes in heavy-duty diesel engines

Gaseous NOx emission is very hazardous for human health and heavy-duty diesel engines contribute 40% of these global highway emissions. Among technologies for reducing emissions, DPF and SCR are most common, and are used in many automotive industries. The honeycomb-shaped catalyst and ammonia gas utilized in these methods can reduce NOx emissions by more than 90%. However, improvement of NOx emission reduction emission is needed. This study investigates two model injectors to optimize spray distribution for improve the NOx conversion quality in the diesel engine, especially a heavy-duty diesel engine, because these engines produce a huge amount of NOx concentration compared to another engines. These investigations also identified the amount of ammonia gas on the catalyst surface by utilizing 19 gas sensors. Comparison between the experiment and simulation shows the ammonia and NOx quantities from the two injector models and elucidates the temperature results for vaporization and saturation quantity, ammonia homogenization distribution, and NOx conversion in the system.

Comparative estimation of nitrogen in urea and its derivative products using TKN, CHNS and hand-held refractometer

In this paper, a comparative analysis between the hand-held refractometer and other methods (TKN and CHNS) was accomplished for the estimation of nitrogen percentage (N%) in urea, nano urea fertilizer, and diesel exhaust fluid (DEF) solution. In order to compare the performance of all methods/devices, the detection of N% in different concentrations of urea, nano urea, and DEF were evaluated in terms of their linearity. The most important finding of this study was that the refractometer-based device revealed a good linear coefficient up to 40% urea solution (R2 = 0.99918) among other approaches, which means the estimation of N% is more close to the theoretical value. Moreover, the refractometer has detected the urea, nano urea, and DEF samples within 3 s which were quite fast as compared to other tested methods and no requirement of any chemicals during the sample preparation and analyses. Thus, the finding of this study suggests that a hand-held urea refractometer-based portable device can be used for onsite N% determination by the fertilizer and DEF manufacturing industries and their customers due to its low cost, low power requirement, reliable estimation, rapid N% detection, and its environmental suitability.

Fat Stem Cells Combined with Complement C3 Inhibits the Progress of Type 2 Diabetes in Rats

This study assessed the effect of fat stem cells combined with complement C3 on Wnt/β-catenin pathway in type 2 diabetic rats. 30 male rats were randomly and equally divided into group of type 2 diabetes (intraperitoneal injection of urea with cephalosporins at a dose of 30 mg/kg and fed with high sugar and fat), type 2 diabetes+adipose stem cells+C3 group (after adipose stem cells+C3 group) and control group. Rats in adipose stem cells+C3 group received administration of stem cells and C3. The model of type 2 diabetic rats was successfully constructed. The blood glucose of type 2 diabetic rats and fat stem cell+C3 group was significantly higher than 11.1 mmol/L. Adipocyte was induced to be differentiated into islet cells depending on insulin secretion and glucose concentration. The combination of complement C3 improved the glucose sensitivity in type 2 diabetic rats. Compared with diabetic group, β-catenin and TCF in fat stem cell+C3 group were significantly decreased (P < 0.05). In conclusion, fat stem cells combined with complement C3 inhibit the disease progression in type 2 diabetic rats possibly by inhibiting the activation of Wnt/β-catenin signaling pathway.

Diesel exhaust fluid market worth $50.0 bn by 2027

Diesel exhaust fluid market worth $50.0 bn by 2027

3-D Numerical Study of Effect of Urea Injector Location and Intake Cone Geometry on SCR Performance

In response to current strict laws aiming to reduce motor vehicle emissions, more and more research projects are being carried out in order to enhance the flow of automotive catalysts. There have been substantial efforts to further refine the SCR technology (selective catalytic reduction) for diesel-powered vehicles. Furthermore, only a little distance from the catalytic input between the exhaust system is available for a mobile SCR system. This therefore leads to an insufficient urea residence period, and evaporation and thermolysis at the catalyst entry cannot therefore be completed. This can lead to substantial secondary ammonia and isocyanic acid emissions. Therefore, fast thermolysis, effective ammonia blend with exhaust gas and reduction of ammonia slip are crucial factors for the deployment of SCR technology on cars. The Computational Fluid Dynamics (CFD) approach is used for optimizing the exhaust gas flow inside the existing catalyst by changing intake cone designs which is intended to be used on Euro VI/Bharat Stage-VI emissions legislation compliant heavy-duty diesel engines in India. This study is divided in to two parts. The first part of the study deals with finding the optimized ammonia injector location, and in the second part, the proposed inlet cone design’s flow velocity uniformity index is estimated and compared with that of the existing SCR catalyst model.

Experimental investigation of urea injection strategy for close-coupled SCR aftertreatment system to meet ultra-low NO emission regulation

• The tailpipe NOx and PM emission satisfy CARB ultra-low emission regulation under FTP cycle. • The effect of temperature and space velocity on NO x conversion is investigated. • A high NO x conversion efficiency is observed on ccSCR with air-assisted urea nozzle. • A zonal control strategy for dual urea injection is adopted to reduce tailpipe NOx emission. • The supplemental urea injection strategy is effective to reduce tailpipe NOx emission. Worldwide automotive emission regulations for heavy-duty diesel engines are increasingly stringent, especially for nitrogen oxide (NO x ) and particulate matter (PM). The development of high-efficiency aftertreatment technologies and the optimization of the urea injection strategies are key factors for the diesel engines to meet the future regulations. In this paper, the effects of temperature and space velocity on close coupled selective catalyst reduction (ccSCR) and SCR are investigated firstly. The highest NO x conversion efficiency of ccSCR and main SCR is observed at 350 °C, and an increase of space velocity leads to a more significant decrease on NO x conversion efficiency of ccSCR than that of SCR. Then three phases of urea injection state for both nozzles are determined according to the catalyst inlet temperature in the Federal Test Procedure (FTP) cycle. Urea injection strategy is optimized by urea injection ratio calibration and urea injection strategy updating based on the characteristic of three phases, as well as NH 3 sensor feedback. Finally, the composite tailpipe NO x emission under FTP cycle is reduced below 0.027 g/kW·h, satisfying California air resources board (CARB) ultra-low NO x emission regulation with a penalty of slight increase in CO 2 emissions. However, adopting a high reactivity gasoline can improve the efficiency while maintaining the low level of NO x emissions.

Experimental and Numerical Analysis of an Innovative Mixer Geometry for Urea Injection in SCR Applications

Selective catalytic reduction (SCR), based on the injection of urea-water-solution (UWS), is one of the prevailing and more effective approaches to reduce NOx emissions in diesel engines. To improve the performance and durability of the system, it is crucial to develop reliable simulation tools able to correctly describe not only the urea conversion into ammonia and the mixing with exhaust gases but also the possible formation of solid deposits along with the engine’s exhaust line.In the present paper, two different exhaust systems for off-road applications are analyzed, both of them consisting of a diesel oxidation catalyst (DOC) followed by a diesel particulate filter (DPF), a UWS injection and a mixing device, and an SCR catalyst. Two alternative UWS mixing subsystems are evaluated, including a newly developed design. A 3D-CFD numerical analysis is carried out to assess the performance of both systems in terms of pressure drop, UWS spray, and liquid film development, in addition to flow velocities and species concentration uniformities at SCR catalyst inlet. A detailed analysis of droplet impingement on walls and liquid film development is enabled, thanks to a conjugate heat transfer (CHT) approach. Moreover, a deposit risk index is used to identify the areas of the systems where urea deposit formation is expected.Eventually, numerical results are compared with experiments on one operating condition chosen as the most challenging in terms of exhaust temperature and flow rate, both in terms of systems NOx conversion efficiency and deposit formation, showing a satisfactory agreement, thus paving the way to use the proposed synergetic numerical and experimental approach to further optimize the design and the system’s performance.

A study on effect of engine operating parameters on NOx emissions and exhaust temperatures of a heavy-duty diesel engine during idling

Though NOx emissions from on-road heavy duty vehicles (HDVs) have reduced drastically over the past three decades, upcoming North American regulations may call for further reductions. Lowering NOx emissions below current levels is challenging, especially at lower operating loads such as idling and/or colder climates when the exhaust gas temperature is insufficient for high NOx conversion in the HDV’s exhaust after treatment (EAT) system. This paper investigates the impact of various engine operating parameters on the three-way trade-off between NOx emissions, exhaust temperature, and fuel consumption using a single-cylinder, heavy-duty diesel engine outfitted with a conventional EAT system and diesel exhaust fluid (DEF) injection. The engine parameters investigated include exhaust gas recirculation (EGR) ratio, intake pressure, intake temperature, injection pressure, multiple injections, and engine fluid temperatures. In order to simulate cold climate operation, the baseline intake air, coolant, and lubricating oil temperatures are maintained at 10°C, 40°C, and 50°C, respectively. Results show that using a moderate level of EGR has the dual benefit of reducing the engine-out NOx and increasing the intake charge temperature. Increasing the intake or injection pressure does not result in significant benefit in improving the three-way trade-off. However, using double injection with the second injection at the start of the expansion stroke can help reduce NOx emissions and increase exhaust temperature with marginal impact on fuel efficiency. Based on the parametric study, three particular engine operating conditions are chosen for further investigation with the EAT online. At an identical DEF dosing rate, the rates of NOx reduction in the SCR are similar for the three conditions (∼96%), and the lowest tail-pipe NOx observed for this study is 0.032 g/kWh.

Spray strategy and mixer optimization in Urea-SCR system based on frozen flow modeling

An integrated after-treatment device model was established by Converge and the experiments were conducted on rapid urea deposits platform under low and medium load conditions. The model was validated by back pressure of catalysts, mixer wall temperature and distribution of urea deposits. In order to reduce the computational costs, the urea injection strategy and mixer structure was optimized based on the frozen flow method. The effects of frozen flow method on the simulation errors and computational costs were evaluated by film mass, film distribution and cycle numbers. The results show that the simulation errors after frozen flow were larger under low load condition but lower under medium load condition. However, the frozen flow method could effectively reduce the cycle numbers under both low and medium load conditions, which was reduced by 9.05% and 17.77%. Furthermore, the cycle numbers were reduced by 31.23% in 5 times injection simulation. With the optimal scheme under low and medium load conditions, the urea deposition rate was reduced by 43.51% and 23.16%. The mass of NH3 was increased by 23.99% under medium load condition. The NH3 uniformity coefficient increased by 5.04% and 2.69%, and the mixer back pressure declined by 24.40% and 27.44%.