Urea-based Selective Catalytic Reduction Research Articles

A Simulation Study on Urea Maldistribution and Implications for NOx Reduction with a Multi-Channel Modelling Approach

Urea-based selective catalytic reduction (SCR) is highly efficient for NOx abatement within a diesel aftertreatment system. However, abnormally high NOx emissions in the aftertreatment system tailpipe during WHSC (World Harmonized Steady-State Cycle) evaluation have been observed due to insufficient urea decomposition or mixing, which cannot be predicted by the current uniform 1D (one-dimensional) modelling approach with different urea dosing ratios. As a result, a multi-channel model has been developed to investigate the effect of urea maldistribution on aftertreatment system performance, where the uniformity index (UI) is used as a characteristic parameter to describe urea mixing efficiency. It was found that NOx emissions at the tailpipe can be successfully described with the multi-channel model even with a relatively high UI (UI = 0.95). Additionally, an improved segment UI factor as a function of mass flow rate has also been applied for maldistribution description, wherein better correlation with the measured NOx emission can be obtained.

Ammonia coverage ratio control of a novel two-cell SCR-DeNOX system configuration based on IA-ISMC

To respond the China’s “14th Five-Year Plan” on the control of nitrogen oxides (NOX) emission, urea-based selective catalytic reduction (SCR) system has been widely applied to reduce the NOX emission from the diesel engine. NO2 is no longer a factor to be ignored while refining the SCR-DeNOX system model because of the ship diesel engine's long-term low temperature and oxygen-rich condition, which provides abundant conditions for the creation of NO2. Therefore, a refined eight-state two-cell SCR-DeNOX model is established in this paper. Meanwhile, the trade-off between NOX emission and tailpipe ammonia (NH3) slip is one of the major challenges which SCR-DeNOX system is facing. While meeting NOX emission standards, the requirement of limiting NH3 slip to prevent secondary pollution is becoming increasingly urgent, which needs a better structure or controller. Therefore, a two-cell SCR-DeNOX system with a by-pass valve in front of the NH3 injection is designed, integral sliding mode control based on inversion algorithm (IA_ISMC) is proposed for each cell. Based on the FTP-75 test cycle, there are three points of view are presented. Firstly, compared with the traditional six-state model, simulation results from the refined eight-state SCR-DeNOX model are closer to the experimental data. Secondly, the introduction of the by-pass structure has a mild impact on the NOX conversion efficiency, but can largely limit the NH3 slip. Finally, the controller based on IA_ISMC effectively improves the tracking performance of NH3 coverage ratio and reduces the cost of NH3 injection. To sum up, the refined two-cell SCR-DeNOX system with a by-pass valve based on IA_ISMC can enhance SCR performance and lower costs.

CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

Computational fluid dynamics (CFD) are an essential tool for the development of diesel engine aftertreatment systems using selective catalytic reduction (SCR) to reduce nitrous oxides (NOx). In urea-based SCR, liquid urea–water solution (UWS) is injected into the hot exhaust gas, where it transforms into gaseous ammonia. This ammonia serves as a reducing agent for NOx. CFD simulations are used to predict the ammonia distribution in the exhaust gas at the catalyst inlet. The goal is to achieve the highest possible uniformity to realize homogeneous NOx reduction across the catalyst cross section. The current work focuses on the interaction of UWS droplets with the hot walls of the exhaust system. This is a crucial part of the preparation of gaseous ammonia from the injected liquid UWS. Following experimental investigations, a new impingement model is described based on the superposition of four basic impingement behaviors, each featuring individual secondary droplet characteristics. The droplet–wall heat transfer, depending on surface temperature and impingement behavior, is also calculated using a newly parameterized model. Applying the presented approach, the cooling of a steel plate from intermittent spray impingement is simulated and compared to measurements. The second validation case is the distribution of ammonia at the catalyst inlet of an automotive SCR system. Both applications show good agreement and demonstrate the quality of the new model.

Experimental study on pollutant emission characteristics of diesel urea-based selective catalytic reduction system based on corrugated substrate

In this study, a corrugated substrate of diesel engines for urea-based selective catalytic reduction (urea-SCR) with V2O5-WO3/TiO2 (V-SCR) and Cu-based (Cu-SCR) catalysts is proposed and the effects of the ammonia-to-nitrogen ratio α on the NOx emission, NH3 slip, and N2O emission were experimentally investigated on a diesel engine test bench with the World Harmonized Transient Cycle (WHTC). The volume ratio of the catalyst to the engine capacity is 1.6. With the increase of α, the NOx reduction reaction of V-SCR performed better NOx emission characteristics than that of Cu-SCR. When α increased from 1.0 to 1.2, the NOx emission of V-SCR and Cu-SCR decreased from 0.44 to 0.26 g/kW·h and from 0.63 to 0.36 g/kW·h, respectively. However, the NH3 slip of Cu-SCR was less because of its absorption capacity of NH3. The NOx conversion efficiency β and N2 selectivity δ of V-SCR outperformed those of Cu-SCR. At α = 1.1, β and δ of V-SCR were 1.07% and 3.25% higher than those of Cu-SCR, respectively. The dynamic response of V-SCR to NH3 showed high competitiveness compared to Cu-SCR. It was concluded that, based on the corrugated substrate, the V-SCR showed better pollutant emission characteristics than did the Cu-SCR.

Simplified Modeling and Analysis of Surface Temperature Distribution in Electrically Heated Catalyst for Diesel Urea-SCR Systems

Impending emission regulations of diesel engines for construction machineries would regulate nitrogen oxide emissions strictly in cold operating conditions. The urea-based selective catalytic reduction (urea-SCR) system coupled with the electrically heated catalyst (EHC) has been considered as a potential measure to meet the strict emission regulations by promoting evaporation and thermal decomposition of urea–water solution in cold operating conditions. Analyzing the thermal conditions in the EHC is crucial for the optimized operation and control of EHC-based urea-SCR systems under various engine operating conditions. In the current study, we introduce a simple one-dimensional analysis scheme to characterize the surface temperature distribution in the EHC based on energy conservation and the theories of forced internal convection. Since the EHC has a complicated internal structure with fine flow cells inside it, a flow cell in the EHC is extracted for the one-dimensional heat transfer analysis. EHC operation parameters such as exhaust gas flow rate and supplied electric power to the EHC are scaled to be applied for the flow cell analysis. The adequacy of the analysis scheme is then validated by surface temperature measurement results at the EHC outlet. The validation results showed over 95% prediction accuracy of the 1D analysis scheme in the operating conditions of a heavy-duty diesel engine. Based on proven reliability, the effects of geometric and operation parameters on the surface temperature distribution in the EHC were analyzed and discussed using the analysis results.

A Green Analytical Methodology for Detecting Adulteration in Automotive Urea-SCR Products Using Microfluidic-Paper Analytical Devices

The application of urea-based selective catalytic reduction products (i.e., Urea-SCR) provides a reduction of NOx and, therefore, minimizes pollution emissions from vehicles fueled by diesel. Such products can be easily found in the market; however, they are often susceptible to adulteration, mainly in terms of the urea content and dilution with non-mineralized water. In this study, we propose a simple, low-cost, disposable, and straightforward paper-based microfluidic device for the quality-control of Urea-SCR products for the first time by quantifying urea and water hardness simultaneously via colorimetric reactions using a small volume of sample. 4-(dimethylamino)benzaldehyde and Eriochrome T were used as colorimetric indicators for urea and water hardness determination, respectively. Each reagent (1.5 µL) was combined with 6 µL of sample for analysis, contributing to an expressive reduction of waste generation. Digital images of the µPAD were obtained, and linear relations between color intensity and urea and Ca2+ and Mg2+ concentrations in the range of 0.2 to 1.0% and 0.1 to 3.5 mmol L−1 were obtained with a correlation coefficient higher than 0.99. Recovery experiments were employed to evaluate the accuracy of the methodology, revealing suitable values between 91.5 and 115%. Brazilian Urea-SCR samples were acquired from different distributors and submitted to the proposed procedure to evaluate its applicability. The application of microfluidic paper-based devices with colorimetric reactions enables the quality control of Urea-SCR products with high accuracy, portability, low consumption of reagents, and no generation of toxic residues; thereby contributing to the green analytical chemistry field.

Mathematical Modeling of Urea Reaction with Sulfuric Acid and Phosphoric Acid to Produce Ammonium Sulfate and Ammonium Dihydrogen Phosphate Respectively

Urea is the final product of protein metabolism in mammals and can be found in different biological fluids. Use of mammalian urine in agricultural production as organic fertilizer requires safe handling to avoid the formation of ammonia that will decrease the fertilizer value due to the loss of nitrogen. Safe handling is also required to minimize the decomposition of urea into condensed products such as biuret and cyanuric acid, which will also have a negative impact on the potential sustainable production of crops and sanitation technologies. The study of thermodynamics and reaction kinetics of urea stabilization plays a key role in understanding the conditions under which undesirable compounds and impurities in urea-based fertilizers and urea-based selective catalytic reduction systems are formed. For this reason, we studied the reaction of urea in acid media to achieve urea stabilization by modeling the reaction of urea with sulfuric acid and phosphoric acid, and estimating the reaction enthalpy and adiabatic heat difference for control of the heat released from the neutralization step using Ca(OH)2 or MgO for the safety of the process. Numerical and simulation analyses were performed by studying the effect of the surrounding temperature, the ratio of acid reagent to urea concentration, the rate of addition, and the reaction rate to estimate the required time to achieve an optimum value of urea conversion into ammonium dihydrogen phosphate or ammonium sulfate as potential technological opportunities for by-product valorization. Full conversion of urea was achieved in about 10 h for reaction rates in the order of 1 × 10−5s−1 when the ratio of H2SO4 to CH4N2O was 1.5. When increasing the ratio to 10, the time required for full conversion was considerably reduced to 3 h.

Nitrous oxide in diesel aftertreatment systems including DOC, DPF and urea‐SCR

The formation of Nitrous oxide (N2O) over urea-based selective catalytic reduction (SCR) systems was scrutinized using exhaust gases from a 3.4-liter non-road diesel engine. Four catalysts were used for the SCR systems; Cu-zeolite (Cu/Fe = 4), Fe-zeolite (Fe only), vanadia and mixed (vanadia and Cu-zeolite) one. For all SCR systems, the N2O concentration at the SCR inlet (before SCR) was below 1 ppm, except for the low-load and low-speed engine conditions, where it was below 3 ppm. However, at the SCR outlet, the N2O concentration had risen to nearly 20 ppm, except for a few conditions. That is, N2O increased more than a dozen times by passing through the SCR systems. The amount of N2O formed within the SCR systems depended on the SCR catalysts; the vanadia catalyst had the lowest amount of N2O, while the Fe-zeolite catalyst as well as the Cu-zeolite catalyst had the highest. In addition, the formation of N2O was strongly involved in the ratio of nitrogen dioxide (NO2) to nitrogen oxides (NOx) at the SCR inlet, which was coupled to SCR inlet temperatures. The higher ratio of NO2 to NOx led to higher N2O at the SCR outlet. It was found that the start of N2O formation corresponded to the moment when nitric oxide (NO) was close to 0 ppm as the ratio of an ammonia (NH3) in aqueous urea solution to NOx increased. In other words, NO depletion played a crucial role in the start of N2O formation when NO and NO2 were simultaneously consumed. Therefore, the difference in N2O formation among the four catalysts for the SCR systems depended on how quickly NO was depleted. Results from α values of intersections of N2O and NO (α@N₂O = NO) for Cu- and Fe-zeolite catalysts showed that α@N₂O = NO for the Fe-zeolite catalyst are much smaller than that for the Cu-zeolite catalyst, and this implies that the Fe-zeolite catalyst can start N2O formation earlier or have faster NO depletion than the Cu-zeolite catalyst.

Spraying and Mixing Characteristics of Urea in a Static Mixer Applied Marine SCR System

The most effective de-NOx technology in marine diesel applications is the urea-based selective catalytic reduction (SCR) system. The urea-SCR system works by injecting a urea solution into exhaust gas and converting this to NH3 and CO2. The injection, mixing, and NH3 conversion reaction behavior of the urea-water solution all have a decisive effect on the performance of the system. To improve de-NOx efficiency, it is important to provide enough time and distance for NH3 conversion and uniform distribution prior to the solution entering the catalyst. In this study, therefore, the characteristics of gas flow, NH3 conversion, and its distribution are investigated with a static mixer by means of numerical methods, providing a special advantage to ship manufacturing companies through the optimization of the urea-SCR system. The results show that the inclusion of the mixer induces strong turbulence and promotes the NH3 conversion reaction across a wider region compared to the case without the mixer. The mean temperature is 10 °C lower due to the activated endothermic urea-NH3 conversion reaction and the NH3 concentration is 80 PPM higher at 1D than those without the mixer. Moreover, the uniformity of NH3 distribution improved by 25% with the mixer, meaning that the de-NOx reaction can take place across all aspects of the catalyst thus maximizing performance. In other words, ship manufacturing companies have degrees of freedom in designing post-processing solutions for emissions by minimizing the use of the reduction agent or the size of the SCR system.

Decision tree analysis on the performance of zeolite-based SCR catalysts

Urea-based selective catalytic reduction (SCR) is a promising method for removing NOx emissions. In the urea-based SCR method, zeolite-based catalysts are popularly used owing to their applicability over a wide range of temperatures compared to other catalysts. However, they still have several drawbacks such as inferior performance at low temperatures and thermal instability. This has subsequently led to numerous studies and experiments on the development of superior catalysts. While substantial experimental data exist on zeolite-based catalysts, extracting useful information from the data with a simple literature search is difficult owing to not only the amount of data but also complex correlations between feature, including preparation variables such as doped-metal loading and operational variables such as reaction temperature. Recently, extracting insights from a large database has become possible by utilizing machine learning tools. Among them, the decision tree can extract insights on the synthesis of the catalysts as the results derived from the models are intuitive and easy to interpret, unlike those from conventional discriminant machine learning models. In this study, classification models are obtained by training decision tree models with literature data on zeolite-based urea SCR catalysts, particularly the Beta and ZSM-5 types, and several experimental heuristics are extracted from the derived models.

LPV Controller Design for Diesel Engine SCR Aftertreatment Systems Based on Quasi-LPV Models

This letter presents linear parameter-varying (LPV) controller design for the urea-based selective catalytic reduction (SCR) system in diesel engines to reduce nitrogen oxides (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> ) and ammonia (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) emissions. Although such LPV SCR controller design has been previously developed, this letter extends it in various ways. The extension includes the usage of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> slip sensor for feedback LPV control, the adoption of NOX and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> measurements downstream of the catalyst as gain-scheduling parameters, the simultaneous design of feedforward and feedback LPV controllers, and a robustness analysis of the LPV controllers. Quasi-LPV SCR models derived from an existing control-oriented nonlinear parameter-varying model are utilized in the LPV controller design. The LPV controller performance is demonstrated based on an SCR simulation utilizing experimentally obtained engine-out NOX, and exhaust gas temperatures and flow rates. It is shown that the LPV controller provides satisfactory emission performance, as well as robustness against sensor noise and model parameter uncertainty.

Impact of Choice of Spray Inputs on Simulations of Urea-Based Selective Catalytic Reduction Systems

Impact of Choice of Spray Inputs on Simulations of Urea-Based Selective Catalytic Reduction Systems

Insights on the morphology of air-assisted breakup of urea-water-solution sprays for varying surface tension

The efficacy of NOx reduction in diesel engines is mainly dependent on how uniformly urea-water solutions (UWS) are dispersed onto the catalyst surface of the Selective Catalytic Reduction (SCR) systems. The urea-based SCR systems also suffer drawbacks due to the formation of urea deposits onto the walls of after-treatment devices due to poor atomization characteristics of UWS. In this work, the impact of lowering the surface tension of UWS on the morphology of UWS sprays was explored using high-speed shadowgraph imaging techniques. The surface tension of UWS was lowered by adding surfactants; two surfactants viz., Sodium Dodecyl Sulfate (SDS) and Dodecyl-Dimethyl-Amine-oxide (DDA) were considered in this investigation. The surface tension of UWS was reduced to a maximum from 73.7 to 30.2 mN/m and 39.8 mN/m with the addition of DDA and SDS respectively at 75% of its respective Critical Micelle Concentration (CMC) in UWS. Even at a very low-pressure difference of 500 mbar of co-flowing air, the surfactant-added UWS tends to break-up relatively closer to the nozzle tip due to flapping-induced bag breakup, which improved its drop-size distribution. Under a relatively higher pressure difference of 2000 mbar of co-flow atomizing air, the liquid breakup was mostly due to surface stripping in surfactant-added UWS sprays that generated a large number of fine droplets. The image analyses of sprays were performed at far downstream locations from the nozzle to quantify the variations of their droplet-sizes caused by varying the surface tension of UWS. The surfactants added UWS sprays revealed a considerably narrower drop-size distribution by up to 43% compared to UWS sprays under high-pressure conditions, and this was due to a combination of flapping-induced bag breakup, surface stripping and secondary atomization of big droplets caused by reducing the surface tension of UWS. Reducing the surface tension of UWS has the potential to improve NOx reduction in SCR systems due to the reduction in droplet sizes of UWS sprays and also to reduce the formation of urea deposits.

On the influence of water on urea condensation reactions: a theoretical study

Abstract The influence of water molecules on the kinetics of urea condensation reactions was studied with high-level quantum chemical methods and statistical rate theory. The study focuses on the production of biuret, triuret, and cyanuric acid from urea because of their relevance as unwanted byproducts in the urea-based selective catalytic reduction (urea-SCR) exhaust after treatment of Diesel engines. In order to characterize the potential energy surfaces and molecular reaction pathways, calculations with explicitly-correlated coupled-cluster methods were performed. It turned out that the reactions proceed via pre-reactive complexes and the inclusion of one or two water molecules into the condensation mechanisms leads to a decrease of the energy barriers. This effect is particularly pronounced in the production of biuret. Due to the pre-reactive equilibria, the rates of the overall reactions can increase or decrease by incorporating water into the mechanism, depending on the temperature and water concentration. Under the conditions of urea-SCR, the studied reactions are too slow to contribute to the observed byproduct formation.

Urea Injection Control Based on Deep-Q Networks for SCR Aftertreatment Systems

The regulations on NOx emissions from diesel vehicles have been stringent in recent years. Various techniques such as lean NOx trap (LNT) and selective catalytic reduction (SCR) have been developed to lessen the NOx emissions. The urea-based SCR method, which utilizes NH3 as reducing agent to remove NOx, is widely used. Determining optimal amount of injected urea that keeps NOx at outlet below regulated NOx emission and also minimizes the amount of dosed urea is important. Model predictive control (MPC) is popularly used to determine the optimal amount of injected urea. However, applying MPC to real vehicle driving may be difficult because the on-line computation of MPC is too costly to be conducted in the engine control unit (ECU), the computation performance of which is significantly low at present. Therefore, reinforcement learning (RL) is considered as an alternative to on-line control method. In this paper, deep Q-networks (DQN), which is an off-policy RL with discrete action space and suitable to solve high dimensional problem, is applied to determine the amount of urea injection in the SCR system. The simulation of urea injection control with DQN has been conducted with respect to inlet NOx emissions of real driving data.

NOx abatement and N2O formation over urea-SCR systems with zeolite supported Fe and Cu catalysts in a nonroad diesel engine

NO and NO2 emissions over urea-based selective catalytic reduction (SCR) systems were investigated in a nonroad diesel engine. For catalysts of the SCR systems, two types of metal ion-exchanged zeolites were used; one is Fe, the other Cu. The Fe/zeolite was composed of Fe only, however, the Cu/zeolite consisted of Cu (80%) and Fe (20%). Nitrogen oxides (NOx) conversion efficiency of the Fe/ and Cu/zeolite catalysts remained greater than 80% in the temperature range of approximately 300 and 450 °C. The Cu/zeolite catalyst retained high efficiency above approximately 450 °C, however, the Fe/zeolite exhibited a drastic decrease resulting from the deterioration of NO conversion efficiency due to the ammonia storage capability of Fe/zeolite, which was inferior to that of Cu/zeolite. It was also found that NO was oxidized to NO2 in the diesel oxidation catalyst and diesel particulate filter, and NO2/NOx ratio at the SCR inlet consistently maintained thermodynamic equilibrium irrespective of the SCR catalyst. The ratio was higher than 50% between 200 and 410 °C. N2O emission that forms in SCR systems through side reactions during NOx reduction was also studied because N2O is a greenhouse gas with approximately 300 times greater global warming potential than carbon dioxide. The ratio of N2O at the SCR outlet to NOx at the SCR inlet for both catalysts was higher between 200 and 410 °C than at other temperatures, which implies that N2O formation is considerably involved in the NO2/NOx ratio. The Cu/zeolite catalyst in the urea-SCR system exhibited higher NO and NO2 conversion efficiencies while maintaining a lower amount of N2O formation compared to the Fe/zeolite catalyst.

Estimation of Ammonia Storage Nonuniformity for Urea-Based Selective Catalytic Reduction Systems

Ammonia storage nonuniformity has a significant impact on the emission reduction performance of urea-based selective catalytic reduction (SCR) systems. In this paper, a unique SCR platform with two catalysts in a parallel configuration was created for investigating the impact of ammonia storage nonuniformity on the emission reduction performance in a simulation environment. The established two-cell SCR platform allows users to independently control the ammonia-to-NOx ratio (ANR) for each catalyst using two independent urea solution injectors. Simulation results over US06 cycle demonstrate that, compared to the case without ammonia storage nonuniformity, the tailpipe NOx and ammonia emissions can be increased by 6.73% and 22.0%, respectively, due to the nonuniform ammonia storage in the case of an ANR nonuniformity index (NUI) at 0.2. Furthermore, an innovative model-based method was proposed for estimating the ammonia coverage ratio nonuniformity (i.e., ammonia storage nonuniformity if storage capacity is known) by utilizing a control-oriented SCR model and the tailpipe NOx and ammonia measurements at the confluence point. Simulation results proved the effectiveness of the proposed method in estimating the ammonia coverage ratio nonuniformity.

Experimental study of the selective catalytic reduction after-treatment for the exhaust emission of a diesel engine

In this experimental study, the after-treatment characteristics of urea-based selective catalytic reduction (urea-SCR) in a diesel engine was investigated at a low engine exhaust temperature (250 °C). This represented the idle state of diesel vehicles during road congestion. Detailed experimental work was performed on a heavy-duty diesel engine test bench under the World Harmonized Transient Cycle. The influence of the ammonia/nitrogen ratio was first investigated using vanadium-based SCR (V-SCR) catalyst. When the ammonia/nitrogen ratio was 1.0, the influences of space velocity on the after-treatment characteristics of two different configurations of V-SCR catalysts were investigated in terms of NOX emission, NH3 slip and NOX conversion efficiency. Small SV resulted in reduction of the NH3 slip and the coated-type catalyst indicated more NH3 slip than the extruded-type catalyst at equal catalyst dimensions. It was concluded that the extruded-type V-SCR catalyst showed better operating characteristics than did the coated-type V-SCR catalyst.

An NOx Sensor-Based Direct Algebraic Approach-Newton Observer for Urea Selective Catalytic Reduction System State Estimations

NOx sensor-based state estimations for urea-based selective catalytic reduction (SCR) systems have attracted much attention in the past several years because of their significant importance in achieving high NOx conversion efficiency and low ammonia slip at low operation cost. Most of the existing SCR state estimation techniques require sophisticated design processes and significant tuning efforts, which may prevent them from widespread applications to production urea-SCR systems. In addition, the existing SCR state observers may not be able to achieve fast and accurate estimations due to the corresponding slow estimation error dynamics. The purpose of this study was to design a straightforward and effective NOx sensor-based SCR state estimation algorithm for decoupling post-SCR NOx sensor signals (NOx concentration, ammonia concentration), and for estimating ammonia coverage ratio of the urea-SCR systems. A singular-perturbation-based approach was applied to attain the reduced-order SCR model by decoupling the fast NO and NH3 concentration dynamic models from the slow ammonia coverage ratio dynamics model. Based on the reduced-order model, a direct algebraic approach (DAA)-Newton observer was proposed for estimating ammonia coverage ratio. The achieved ammonia coverage ratio estimation was applied to estimate the post-SCR NOx and NH3 concentrations. Simulation verification results under US06 cycle proved the effectiveness of the proposed method in accurately estimating the aforementioned key SCR states. The proposed observer can potentially be popularly applied to the production SCR systems for the advanced SCR control systems and on-board diagnostics.

Experimental investigation on emission reduction in neem oil biodiesel using selective catalytic reduction and catalytic converter techniques.

In the present study, non-edible seed oil namely raw neem oil was converted into biodiesel using transesterification process. In the experimentation, two biodiesel blends were prepared namely B25 (25% neem oil methyl ester with 75% of diesel) and B50 (50% neem oil methyl ester with 50% diesel). Urea-based selective catalytic reduction (SCR) technique with catalytic converter (CC) was fixed in the exhaust tail pipe of the engine for the reduction of engine exhaust emissions. Initially, the engine was operated with diesel as a working fluid and followed by refilling of biodiesel blends B25 and B50 to obtain the baseline readings without SCR and CC. Then, the same procedure was repeated with SCR and CC technique for emission reduction measurement in diesel, B25 and B50 sample. The experimental results revealed that the B25 blend showed higher break thermal efficiency (BTE) and exhaust gas temperature (EGT) with lower break-specific fuel consumption (BSFC) than B50 blend at all loads. On comparing with biodiesel blends, diesel experiences increased BTE of 31.9% with reduced BSFC of 0.29kg/kWh at full load. A notable emission reduction was noticed for all test fuels in SCR and CC setup. At full load, B25 showed lower carbon monoxide (CO) of 0.09% volume, hydrocarbon (HC) of 24ppm, and smoke of 14 HSU and oxides of nitrogen (NOx) of 735ppm than diesel and B50 in SCR and CC setup. On the whole, the engine with SCR and CC setup showed better performance and emission characteristics than standard engine operation.