NOx Reduction System Research Articles

Design of Hydrogen Combustion Engine (Conceptual Brainstorming)

Hydrogen combustion engines present a promising pathway for cleaner transportation, leveraging existing internal combustion engine (ICE) technologies. The design of hydrogen-fueled ICEs requires significant modifications to conventional gasoline or diesel engines due to hydrogen’s distinct combustion properties. This research outlines the key design considerations for hydrogen combustion engines, including fuel storage and injection, combustion chamber modifications, ignition control, and exhaust treatment. The study also discusses recent advancements in engine efficiency, NOx reduction, and dual-fuel systems, along with the challenges of implementing hydrogen-based ICEs in commercial applications. Keywords: hydrogen, combustion, design, ICE, alternative fuels

Experimental and numerical study of Cu-SSZ-13 SCR system for NOx reduction and hydrothermal aging under diesel exhaust conditions

Selective catalytic reduction (SCR) is a crucial technique for mitigating nitrogen oxides emission of internal combustion engines. Compared with vanadium-based catalysts, copper-based molecular sieve catalysts exhibit superior low-temperature catalytic performance and anti-aging properties. The catalytic characteristics of Cu-SSZ-13 catalyst in both fresh and aged states are investigated through experimental and numerical simulations. The catalytic performance of Cu-SSZ-13 catalyst with 200 g/L coating is investigated under wide inlet temperatures (180 °C–450 °C) and ANR (ammonia to nitrogen ratio) (1–1.4) conditions via an engine emission test device. Further, the apparatus is adopted to evaluate performance at various aging temperatures (600 °C, 700 °C, and 800 °C). The aging factor is introduced based on experimental results to establish and correct the kinetic model for SCR aging state. The results illuminate that the increase of ANR fails to compensate for decline of catalytic efficiency under low-temperature conditions (150 °C).The generated quantity of isocyanate acid through the side reaction of urea hydrolysis increases proportionally with ANR. And it increased supply only resulted in a marginal 1 %–3 % improvement of catalytic efficiency. As SV decreases from 60,000 h−1 to 35,000 h−1, the catalyst efficiency increases from 22 % to 45 %, resulting in an elevation of reactant concentration and its gradient on the catalyst surface. This leads to accelerated reaction rates and enhanced diffusion effects. The catalytic efficiency can be significantly enhanced at low temperatures when NO2 fraction in NOx falls within the range of 10 %–25 %. The sensitivity of SCR reactions to aging varies at low temperatures (<250 °C) due to the distinct reaction sites on catalyst for different types of SCR reactions. The NO2 SCR reactions exhibit minimal susceptibility, while the rapid SCR reactions are significantly impeded. Moreover, it has been observed that the catalyst microstructure was completely deteriorated under hydrothermal aging test at 900 °C operating condition. In general, the low-temperature catalytic performance of Cu-SSZ-13 catalyst can be further optimized by pretreating inlet gas components and optimizing the catalyst structure.

Mitigation of Ship Emissions: Overview of Recent Trends

The urgency of reducing flue gas pollution in maritime transport makes it necessary to take a holistic view of its sustainability and environmental impacts. Among the approaches to reducing ship exhaust emissions, marinized gas scrubbers, given their ability to be retrofitted to existing ships, are a central element in the tradeoff against the use of expensive low-sulfur fuels. However, compounding this issue, the priority of reducing greenhouse gas (GHG) emissions in the coming decades poses new challenges to emissions compliance. The use of exhaust gas cleaning systems to remove SOX, NOX, and particulate matter (PM) emissions will be enhanced in the short to medium term by GHG reductions. In this study, the different types of scrubbers for seaborne operation and the potential risks associated with their secondary emissions will be critically reviewed. In addition, NOX reduction systems and recent efforts to reduce CO2 through on-board carbon capture systems or alternative fuel combustion will also be covered.

Numerical Research of Flue Gas Denitrification Using the SNCR Method in an OP 650 Boiler

The presence of Poland in the European Union obliges the domestic economy and the professional energy sector to improve the condition of the natural environment by reducing the emissions of harmful substances into the environment. One of the substances that have a negative impact on the environment is nitrogen oxides. The results of numerical calculations of flue gas denitrification using the SNCR method in an OP 650 boiler are presented in the paper. The method of verifying the combustion of the numerical model, in terms of measurement and calculations with a zero-dimensional model, is presented. Then, the results of numerical tests of flue gas denitrification using the SNCR method with the use of urea solution injection in a specific temperature window for various nozzle positions are presented. In this paper, three variants of the reagent’s injection into the furnace chamber were carried out, depending on the height of the position of the nozzle. It is shown in this paper that thanks to combined NOx reduction systems, it is possible to adjust the emission of nitrogen oxides to a level below 200 mg/m3n with an oxygen content of 6% in the dry flue gas, with relatively low investment costs.

Flow Analysis of PM/NOX Aftertreatment System for Emergency Generator

Emergency generators normally use diesel engines. The generators need to conduct weekly no-load operation inspections to ensure stable performance in emergency situations. In particular, the generators with large diesel engines mainly use rectangle-type filter substrates. To minimize hazardous emissions generated by generators, optimizing the reduction efficiency through computational fluid dynamics (CFD) analysis of flow characteristics of particulate matter (PM)/NOX reduction system is important. In this study, we analyzed internal flow by CFD, which is difficult to confirm by experimental method. The main factors in our numerical study are the changes of flow uniformity and back pressure. As a result, the flow distribution characteristics according to the cross-sectional shape are similar at high engine loads. Spraying urea in the reverse direction increases static pressure, greatly improving flow uniformity. Raising the selective catalyst reduction (SCR) diffuser angle to 30 degrees improves both back pressure and flow uniformity characteristics, and when the porosity increases, both flow uniformity and back pressure decrease.

Investigation of an ammonium carbamate–based SCR system for NOx reduction in diesel engines under transient conditions

The deNOx performance of a selective catalytic reduction (SCR) system using ammonium carbamate (AC) was investigated and compared with that of a urea water solution (UWS). The effects of the NH3/NOx (α) ratio, injection threshold temperature (Tinj), and a zero-dimensional ammonia adsorption-desorption model on NOx conversion efficiency were evaluated. World harmonized transient cycle (WHTC) and non-road transient cycle (NRTC) tests were conducted using a 3.9-L diesel engine over a Cu-zeolite catalyst. The NOx conversion efficiency of AC in the WHTC and NRTC was increased compared with that of UWS during the cold phase by 6.43% and 8.71%, respectively, and during the hot phase by 14.79% and 11.93%, respectively. Gaseous ammonia injection at a low Tinj can explain improved deNOx performance, as increasing Tinj leads to a decrease in NOx conversion efficiency. Increasing the α ratio effectively increases NOx conversion efficiency, but a high α ratio leads to ammonia slip. Ammonia injection using a model-based control increased cold-start deNOx performance. These promising results provide an alternative pathway to controlling NOx emissions from heavy-duty diesel engines.

Modeling and Optimization of Multi-functional Ammonia Slip Catalysts for Diesel Exhaust Aftertreatment

Ammonia slip catalysts (ASC) are used downstream of the NH3-selective catalytic NOx reduction (SCR) system, to minimize ammonia slip from transport sector SCR units. The ASC may consist of an SCR active layer for NOx control, a layer with oxidation functionality for ammonia conversion, or a combination thereof, either as individual layers or as a single mixed layer. Mathematical models of such systems involve flow and mass transfer in the monolithic channels as well as coupled reaction/diffusion processes in the catalytic layers. In this work, we develop a single-channel 1D-1D (pseudo 2D) steady-state tank-in-series mathematical model for monolithic ammonia slip catalysts with up to two layers. Kinetics of relevant reactions over the Cu-Beta zeolite and the Pt/TiO2 layer, including SCR, ammonia oxidation, and the formation of N2O, were derived based on an extensive flow reactor study. The model was validated based on experiments using four different small-scale ASC monoliths, showing good agreement between the model predictions and the experimental results. Comparison of ten ASC configurations for the oxidation of 200 ppm NH3 at 300 °C shows that configurations with a pure layer of NH3 oxidation catalyst generate undesirable high N2O and NOx levels. The best ASC configurations feature fast diffusion in the catalytic layers (a high effective diffusion coefficient), a thin top layer loading with some ammonia oxidation catalyst, and a mixed layer of ammonia oxidation catalyst and the SCR catalyst to limit the formation of N2O and NOx.

Experimental Investigation of SCR System for Nox Reduction Using Waste Urea Based Organic Fluid

Experimental Investigation of SCR System for Nox Reduction Using Waste Urea Based Organic Fluid

Numerical research on the SNCR method in a grate boiler equipped with the innovative FJBS system

Abstract The paper describes numerical simulations of processes occurring in the combustion chamber of a stoker boiler. The main topic of CFD analysis presented in this paper is the process of reducing nitrogen oxides emission using the patented Furnace Jet Boiler System (FJBS) in combination with the selective non-catalytic reduction (SNCR) method (FJBS+). The presented method is characterized by introducing a compressed urea-air mixture into the furnace. The reagent is injected through supersonic nozzles, the operating conditions of which are shown on a separate CFD model. The developed model enabled optimization of the existing NOx reduction system, especially in the case of a boiler operating at maximum load. The overall effect of the operation of FJBS + technology is a significant reduction of NOx emissions, by approximately 57%. The results achieved are comparable to those obtained from measurements. It was also confirmed that the operation of FJBS + has a positive effect on the equalization of temperature distribution in the furnace and the concentration of flue gas components. Finally, a sensitivity analysis on the basis of two parameters, specific heat of the fuel and thermal conductivity is presented.

Perovskite-Based Catalysts as Efficient, Durable, and Economical NOx Storage and Reduction Systems

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO2 conversion, NOx storage capacity, and NOx reduction efficiency is addressed. Furthermore, the NOx removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al2O3) in the absence and presence of SO2 and H2O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted.

Improving pre-turbine selective catalytic reduction systems in marine two-stroke diesel engines using hybrid turbocharging: A numerical study of selective catalytic reduction operation range and system fuel efficiency

In this article, a performance evaluation of a novel system solution combining a hybrid turbocharger and a pre-turbine selective catalytic NOx reduction system is carried out. Pre-turbine selective catalytic system are used with marine two-stroke diesel engines to comply with International Maritime Organization Tier III. The system solution focuses on expanding the selective catalytic reduction operation range which is limited by fuel sulphur content by increasing exhaust temperature at low engine loads. The extended operation range is to be achieved while minimizing any fuel consumption penalties. Increasing the operation range brings improvements to emission levels during manoeuvring operations which are often carried out close to populated areas. It also provides flexibility by enabling emission reduction during slow steaming operations in which mitigating fuel consumption penalties is paramount. In addition to system evaluation in still water conditions, furthermore evaluations have been carried out taking into consideration the effect of waves on the system performance. Investigating the effect of operating in waves bring additional insight that is relevant for predicting performance in operational conditions. Analysis of the system solution found that improvements in selective catalytic reduction operation range can be achieved while also improving fuel consumption. Fuel consumption is significantly improved in the high load range. Effect of realistic operation conditions where found to affect performance; however, significant effects are only found for harsh sea states in the load range below the design point.

Design and Development of a Low Cost SCR System for NOx Reduction in a Diesel Engine

After-treatment of exhaust gases are generally preferred to control engine emissions since engine hardware demands no significant modification. Selective Catalytic Reduction (SCR) is a promising after-treatment method for NOx reduction in Diesel engines. In the present work an exhaust gas treatment system, involving Urea injection and an activated carbon catalyst chamber were designed and fabricated, for NOx control, in a Diesel engine. Activated carbon catalyst, which can perform at low temperatures, was expected to make the system cost-effective. Experiments were conducted at 60 percentage and 80 percentage of the maximum engine load. Apart from Diesel, engine was also fuelled with Bio-Diesel developed from chicken slaughter waste. The results demonstrated the capability of developed SCR system in reducing NOx emissions. The Nitric Oxide (NO) emission was reduced by 47 percentage 29 percentage for Bio-Diesel and Diesel respectively, at a brake power of 3kW, without increasing HC emission and sacrificing efficiency. Significant reduction in NO was also obtained at 2kW.

Development of NOx reduction system utilizing artificial neural network (ANN) and genetic algorithm (GA)

Abstracts A submerged combustion vaporizer (SCV) is normally used at a liquefied natural gas (LNG) terminal to vaporize LNG and supply natural gas to domestic and industrial markets. In this study, a new methodology was developed to reduce NOx efficiently in the flue gas of the SCV. The experimental setting of the SCV was prepared, and the impact of various process variables (e.g., excess O2 concentration, temperature, pH of water, and H2O2 concentration) on NOx reduction was investigated. For this, a surrogate model was developed by using an artificial neural network (ANN) algorithm based on the experimental data. The contributions of the input variables on NOx removal were assessed using sensitivity analysis. A genetic algorithm (GA) was integrated with the model to optimize the variables to maximize the removal of NOx in the flue gas. Finally, the ANN-GA model was validated through experimental verification, performed under the identified optimum condition.

Rethinking NOx emission factors considering on-road driving with malfunctioning emission control systems: A case study of Korean Euro 4 light-duty diesel vehicles

This study aims to quantify the differences between the standard laboratory-based NOx emissions factor (EF) and on-road measurements, and to estimate how much NOx emissions exceed the current EF under typical Korean road traffic conditions. Four Euro 4 light-duty diesel vehicles (LDVs) manufactured in Korea were driven on a chassis dynamometer and on test routes that included urban and rural roads and a motorway. NOx emissions, average speed, and acceleration were measured and calculated for each 1 km trip. We focused in particular on the possibility of vehicle malfunctions causing increased NOx emissions, and compared NOx emissions before and after the repair of faulty exhaust gas recirculation (EGR) valves, which are a key NOx reduction system for LDVs. The current NOx EF for Euro 4 LDVs only estimates 27–31% of on their on-road NOx emissions, and low acceleration during the standard driving cycle is a part of the reason for this weak representativeness. Another is the lack of tools with which to monitor EGR valve degradation. Even with fully functioning EGR valve hardware, the capability of vehicles to control NOx emissions differ in laboratory and on-road conditions; it is weaker for the latter compared to the former because the software controls are different. The findings here provide insights for different regions where Euro 4 LDVs are still in use, depending on their age. For Korea and the EU, where the fleet is old, accurate assessments of the real risk of NOx emissions are beneficial in terms of increasing the effectiveness of control measures. In countries where the Euro 4 fleet is still young, comprehensive changes are recommended for the on-board diagnostic system and the subsequent maintenance of the hardware and software of EGR valve.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma

A novel NOx storage and reduction (NSR) system is developed for NOx removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NOx adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NOx into N2 under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO4/BaO/Al2O3 (SKMCBA), SrKMnCeO4/BaO/Al2O3 (SKMCeBA), and SrKCoNiO4/BaO/Al2O3 (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NOx trapped (214μmole NOx/gcatalyst) at 400°C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NOx adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NOx reduction. Result indicates that NOx conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18kV and frequency of 10kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H2), carbon monoxide (CO), and propene (C3H6) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NOx conversion is achieved with H2-NTP. This study demonstrates that reduction of NOx via NTP-assisted process is promising.

Ad hoc risk assessments by Front Office Food and Product Safety

This study aims to quantify the differences between the standard laboratory-based NOx emissions factor (EF) and on-road measurements, and to estimate how much NOx emissions exceed the current EF under typical Korean road traffic conditions. Four Euro 4 light-duty diesel vehicles (LDVs) manufactured in Korea were driven on a chassis dynamometer and on test routes that included urban and rural roads and a motorway. NOx emissions, average speed, and acceleration were measured and calculated for each 1 km trip. We focused in particular on the possibility of vehicle malfunctions causing increased NOx emissions, and compared NOx emissions before and after the repair of faulty exhaust gas recirculation (EGR) valves, which are a key NOx reduction system for LDVs. The current NOx EF for Euro 4 LDVs only estimates 27–31% of on their on-road NOx emissions, and low acceleration during the standard driving cycle is a part of the reason for this weak representativeness. Another is the lack of tools with which to monitor EGR valve degradation. Even with fully functioning EGR valve hardware, the capability of vehicles to control NOx emissions differ in laboratory and on-road conditions; it is weaker for the latter compared to the former because the software controls are different. The findings here provide insights for different regions where Euro 4 LDVs are still in use, depending on their age. For Korea and the EU, where the fleet is old, accurate assessments of the real risk of NOx emissions are beneficial in terms of increasing the effectiveness of control measures. In countries where the Euro 4 fleet is still young, comprehensive changes are recommended for the on-board diagnostic system and the subsequent maintenance of the hardware and software of EGR valve.

Installing LNG-fueled Gas Turbine Combined Cycle on Marine Vessels - Comparison with Diesel Engines Using Exhaust Gas Cleaning Systems

Gas turbine combined systems using natural gas as fuel can be used as ship propulsion systems, given their low NOx and zero SOx emission characteristics. In this paper, the authors examined their adaptability to ships by comparing them with diesel engines that meet both NOx and SOx emission requirements, from the viewpoints of their sizes and initial costs. Up until now, gas turbine combined systems have rarely been used for ships, and NOx and SOx reduction systems for diesel engines have not been widely utilized. For these reasons, every available information about these systems has been used to examine the case. The results found that gas turbine combined systems using natural gas as fuel required much less space than the diesel engines and that the initial cost of the gas turbine combined systems per unit power was somewhere between that of a diesel engine with NOx and SOx reduction systems and that of a diesel engine with a NOx reduction system using low sulfur fuel.

Removal of High Concentrations of the Anesthetic Gas Nitrous Oxide Using Nonthermal Plasma Combined With an Adsorbent

Nitrous oxide (N2O) is commonly used as an anesthetic gas in hospitals. It is a greenhouse gas and should therefore be removed to limit pollution. As nonthermal plasma has low electron density, it has been considered effective for the treatment of low concentrations of gas. Moreover, N2O is extremely stable in the troposphere, and is therefore difficult to decompose. In this study, a system to remove high concentrations of N2 O using nonthermal plasma along with an adsorbent was investigated. A surface discharge plasma reactor was employed to decompose N2O gas. This gas simulated the waste gas from the anesthetic equipment used in operating theatres. Because of its high concentration, the decomposition of N2O afforded the mononitrogen oxides, nitric oxide, and nitrogen dioxide (NOx = NO + NO2), respectively. The generated NOx was adsorbed by the adsorbent. As a result, an N2O decomposition efficiency of 66% was achieved with air-based 12.8% N2O at a flow rate of 1.1 L/min and a plasma reactor input power of 375 W. Furthermore, 0.4% NO and 1.0% NO2 were generated during N 2O decomposition. Both gases were removed by the adsorbent. It was confirmed by the previous studies that the adsorbed NOx was decomposed by N2 plasma. It was demonstrated that the removal of high concentration of N2O could be accomplished by using a system that combines nonthermal plasma with an adsorbent. In practice, much higher volumes of N2O can be removed, without NOx formation, in a setup that involves a series of plasma reactors with recirculation, followed by an NOx reduction system with N2 plasma.

Release of Ammonia Odor from AAFA (Ammonia Adsorbed Fly Ash) by Installation of NOx Reduction System

Release of Ammonia Odor from AAFA (Ammonia Adsorbed Fly Ash) by Installation of NOx Reduction System

Lean NOx reduction over Ag/alumina catalysts via ethanol-SCR using ethanol/gasoline blends

This study focuses on the activity for lean NOx reduction over sol-gel synthesized silver alumina (Ag/Al2O3) catalysts, with and without platinum doping, using ethanol (EtOH), EtOH/C3H6 and EtOH/gasoline blends as reducing agents. The effect of ethanol concentration, both by varying the hydrocarbon-to-NOx ratio and by alternating the gasoline concentration in the EtOH/gasoline mixture, is investigated. High activity for NOx reduction is demonstrated for powder catalysts for EtOH and EtOH/C3H6 as well as for monolith coated catalysts (EtOH and EtOH/gasoline). The results show that pure Ag/Al2O3 catalysts display higher NOx reduction and lower light-off temperature as compared to the platinum doped samples. The 4wt.% Ag/Al2O3 catalyst displays 100% reduction in the range 340–425°C, with up to 37% selectivity towards NH3. These results are also supported by DRIFTS (Diffuse reflection infrared Fourier transform spectroscopy) experiments. The high ammonia formation could, in combination with an NH3-SCR catalyst, be utilized to construct a NOx reduction system with lower fuel penalty cf. stand alone HC-SCR. In addition, it would result in an overall decrease in CO2 emissions.