Aftertreatment Technologies Research Articles

Significant NO2 Formation in Truck Exhaust Plumes and Its Association with Ambient O3: Evidence from Extensive Plume-Chasing Measurements.

Vehicle nitrogen oxides (NOx) significantly increase nitrogen dioxide (NO2) exposure in traffic-related environments. The NO2/NOx ratios are crucial for accurate NO2 modeling and are closely linked to public health concerns. In 2020, we used a mobile platform to follow test trucks (plume-chasing) that were installed with a portable emission measuring system (PEMS) on two restricted driving tracts. Six hundred eighteen exhaust plumes were collected through the PEMS-chasing measurements from seven trucks. The NOx emission factors (EFs), and the NO2/NOx ratios, were calculated at distinct stages (i.e., tailpipe and on-road). A significant reduction in NOx EFs (>64%) was observed with normal operating after-treatment devices, except for trucks equipped with diesel particulate filter (DPF). Disparities in tailpipe NO2/NOx ratios were also found, attributed to the after-treatment technologies. The NO2/NOx ratios measured from plume-chasing were significantly higher (3-4 times, p < 0.001) than the tailpipe measurements, providing field evidence of substantial NO2 formation in exhaust plumes. We developed a quantitative relationship between NO2/NOx ratios from tailpipe and plume-chasing measurements and demonstrated a robust correlation (R2 > 0.90). Since the NO2 formation in the exhaust plume is not explicitly accounted for in NO2 modeling, the quantitative relationship (O3-NO2/NOx) could improve the estimation of NO2 exposure when local emission inventory (tailpipe emissions) is available.

A review of chemical kinetic mechanisms and after-treatment of amino fuel combustion.

Ammonia is a highly promising carbon-neutral fuel. The use of ammonia as a fuel for internal combustion engines can reduce fossil energy consumption and greenhouse gas emissions. However, the high ignition energy required for ammonia and the slow flame propagation rate result in low combustion efficiency when ammonia is used directly in internal combustion engines. The combination of ammonia with highly reactive fuels improves combustion quality and increases efficiency. However, the combustion of these combined fuels generates particulate matter, CO, hydrocarbon, and significant amounts of NOx. Therefore, pollutant emissions must be reduced through after-treatment technologies. In this paper, a series of combustion and post-treatment challenges faced by amino fuel combustion in internal combustion engines are extensively discussed and the combustion reaction mechanisms of different amino fuels are also analyzed. The paper then reviews five key technologies applicable to the reprocessing of amino fuels, including selective catalytic reduction, selective catalytic reduction filter technology, electrochemical methods for NOx removal, direct catalytic decomposition of N2O, and ammonia sliding catalysts. An in-depth discussion of the catalytic materials and reaction mechanisms involved in these technologies is also provided in this paper. Finally, the paper summarizes the main technical challenges that must be addressed for the future application of amino fuels in internal combustion engines. These discussions can serve as an essential reference for developing and applying critical technologies for combustion control and pollutant treatment of amino fuels.

Unraveling Reactive Nitrogen Emissions in Heavy-Duty Diesel Vehicles across Evolving Standards and Cheating Tactics.

Reactive nitrogen (Nr) emissions significantly affect air quality and the nitrogen cycle in ecosystems. Heavy-duty diesel vehicles (HDDVs), as major sources of these emissions, exhibit complex emission characteristics because of the combined effects of different driving conditions and aftertreatment technologies. This study first investigated the emission factors (EFs) of Nr species, including NO, NO2, HONO, N2O, and NH3, from HDDVs under different emission standards (China IV/V/VI) and cheating strategies, with a particular focus on the impact of selective catalytic reduction (SCR) systems. Vehicles employing water injection cheating present NO, NO2, and HONO EFs that are consistent with the China III standards, significantly undermining the effectiveness of Nr emission control. The evolution of SCR technology in China IV, V, and VI standards has generally led to substantial reductions in NO, NO2, and HONO emissions, yet the integration of ammonia slip catalysts (ASC) systems in China VI vehicles presents new challenges. While ASCs have successfully reduced NH3 slip to an average of 17 ± 12 mg/km, they have also caused a 6-13-fold increase in N2O emissions compared with those of China IV and V vehicles, reaching levels of 205 ± 85 mg/km. Additionally, China VI vehicles exhibit a marked increase in the HONO/NOx ratio, which increases from 0.9% in China V to 4.6%. These increases are attributed to high-temperature oxidation of NH3 within the ASC catalyst, leading to undesirable byproducts. The temporal dynamics of Nr emissions under real-world driving conditions further reveal that the effectiveness of aftertreatment technologies and their selectivity toward byproducts vary depending on the driving mode. This variability underscores the need for further optimization of the SCR and ASC technologies to balance the control of all the reactive nitrogen species effectively.

Contribution of Aftertreatment Technologies to Alleviating SOA and Toxicity Generation from Typical Diesel Engine-Emitted I/SVOCs.

The removal capacity of aftertreatment technologies equipped on diesel exhaust in intermediate and semivolatile organic compounds (I/SVOCs) remains unclear. This study quantified the effect of typical aftertreatment technologies (China VI) on diesel engine-emitted I/SVOCs, related secondary organic aerosol (SOA), and toxic effects. The equipped aftertreatment devices could mitigate the emission factors (EFs) by 70.8 ± 3.4 to 82.5 ± 20.9% for I/SVOCs, 72.7 ± 18.6 to 77.5 ± 4.2% for SOA production, and 75.7 ± 9.3 to 82.4 ± 9.2% for toxic equivalent quantity (TEQ). Aftertreatment units are better for removing alkanes, benzenes, and ketones. The TEQ from the cold-start cycle is 1.3- to 5.7-fold higher than that from the hot-start cycle. In contrast, the EFs of ship-emitted I/SVOCs are 3.7- to 5.3-fold higher than those of diesel vehicles equipped with an aftertreatment system when burning the same fuel, leading to 2.1- to 3.0-fold higher SOA production and 3.1- to 6.7-fold TEQ. Implementation of control devices on marine diesel engines could reduce I/SVOC EFs, SOA production, and eye irritation TEQ of ships by 76.7 ± 12.2, 75.1 ± 12.2, and 79.1 ± 9.6%, respectively. These results indicate that it is vital to equip marine engines with aftertreatment technologies to improve air quality and protect human health.

Effect of fuel modification and after treatment techniques on emissions fuelled by diesel tyre oil blend

ABSTRACT Reusing used tires as fuel has the potential to reduce environmental harm and the quick depletion of fossil fuel resources. Fuel modifications and after-treatment techniques are the two main strategies for reducing emissions. The fuel has been blended with an antioxidant ingredient and after-treatment technology in an effort to lower the NO emission. Tire oil is produced from old tires by the pyrolysis method. Based on the test results, it looks like used tire oil could be a decent fossil fuel alternative. Fuel modification is done by adding the A-tocopherol acetate as an antioxidant additive of 300 ppm with an 80:20 diesel-to-tire oil blend powering a four-stroke, mono-barrel diesel engine. A notable reduction in NO emissions up to 15.3% was observed. A copper-based catalytic converter is used as an after-treatment technique in the exhaust of the antioxidant-doped blend, resulting in a 27.35% reduction in NO emissions. Oxidative analysis and gas chromatography-mass spectrometry were used to examine the tire oil and blend. The results showed that the pure blend had an oxidative stability of 17 hours. It was discovered by the GC-MS analysis that the blend is better suited for engine use than pure tire oil.

Biofuel blends and nano-additives: a sustainable approach to diesel engine performance and emissions improvement

Abstract The utilization of compression ignition (CI) diesel engines has seen a substantial increase in recent years owing to their numerous advantages. However, the widespread adoption of these engines has also significantly contributed to environmental pollution issues, with diesel engines being recognized as major global contributors to exhaust emissions-related pollution. To address this issue, comprehensive research has been carried out on both emissions from diesel exhaust pollutants and advanced after-treatment technologies for emission control. This study aims to evaluate the efficiency and emissions of diesel fuel mixed with various ratios of biofuel derived from Karanja seeds (B10, B15, and B20). Among the different blends examined, B20 demonstrated superior performance in terms of brake thermal efficiency (BTE) and brake-specific fuel consumption (BSFC), along with lower levels of hydrocarbon (HC) and carbon dioxide (CO2) emissions compared to pure diesel. Further, the impact of nanoadditives, specifically titanium dioxide (TiO2), at different concentrations (80 ppm, 100 ppm, and 120 ppm), on B20 blends was evaluated. The findings indicated that B20 blended with 100 ppm of TiO2 exhibited superior performance in terms of BTE, BSFC, and lower emissions of HC, CO2, nitrogen oxides (NOx), and carbon monoxide (CO). From the results, the BTE increases from 1% to 33%, illustrating enhanced thermal efficiency under similar conditions. The average BSFC across all loads and speeds in the table is approximately 0.89 kg kW−1h−1, while the average BTE stands at approximately 23.1%.

The Activation of Oxygen Species on the Pt/CeO2 Catalyst by H2 for NO Oxidation

The Pt/CeO2 catalyst has attracted significant attention due to its exceptional performance in NO oxidation. This study comprehensively examines the effects of calcination temperature and H2 pretreatment on the structure and activity of the Pt/CeO2 catalyst. Experimental findings indicate that the calcination temperature significantly affects the catalyst’s redox performance, thereby modulating its efficacy in NO oxidation reactions. H2 pretreatment facilitates the creation of oxygen vacancies on the catalyst, assisted by the reduction in PtOx to Pt, enhancing the formation of activated oxygen and thereby improving NO oxidation. This study offers valuable insights into the design and optimization of Pt/CeO2 catalysts for environmental applications, particularly in the development of exhaust gas after-treatment technologies.

Breakup dynamics in a pressure-swirl injector for urea-water solution applications: A computational study

The co-optimization of in-cylinder combustion and after-treatment technology has become a major aspect in engine design and development, with the goal of meeting the increasingly restrictive emission regulations in the transportation industry. Selective Catalytic Reduction is a robust technology to control the emission of NOx, and the injection of urea in water solution is the exhaust tailpipe is a key aspect of its operation. The proposed work uses high-fidelity Computational Fluid Dynamics to characterize the atomization dynamics of the liquid jet in relevant cross-flow conditions. The study focuses on a commercial low-pressure (9 bar) pressure-swirl injector which is characterized in its internal geometry through high-resolution X-ray micro-computational tomography. The internal two-phase flow has been modeled according to the volume-of-fluid approach in a large eddy simulation framework and validated against near-nozzle X-ray radiography measurement. Moreover, characterizing the breakup dynamics for the swirling hollow cone formation, and assessing the influence of the cross-flow in the breakup dynamics was completed. The results have been reported proposing Re-Oh maps and probability density functions of the spray kinematics. Higher cross-flow momentum generates an increase in the jet intact length and a reduction of the liquid droplet diameters. The axial momentum of the jet is affected by the cross-flow already in the near-nozzle region, determining a relevant deviation of the spray velocities. This work aims to inform the initialization of Eulerian-Lagrangian spray models through the assignment of droplet kinematics and static one-way coupling between volume-of-fluid results and Lagrangian spray parcels, to be used for system-size domain simulations.

Results on the Use of an Original Burner for Reducing the Three-Way Catalyst Light-Off Time

Individual road mobility comes with two major challenges: greenhouse gas emissions related to global warming and chemical pollution. For the pollution reduction in the spark ignition engine vehicle, the standard and reliable aftertreatment technology is the three-way catalytic converter (TWC). However, the TWC starts to convert once an optimal temperature, usually known as the light-off temperature, is reached. There are many methods to reduce the warm-up period of the TWC, among which is using a burner. The initial question underlying this study was to see if the use of a relatively straightforward extra-combustion device mounted upstream the TWC, without complex elements, was able to serve the purpose of reducing the light-off time. Consequently, an original burner was designed and investigated numerically via the CFD method and experimentally via measurements of the temperature evolution within a TWC, along with the emissions specific to the burner’s operation. The main findings of this study are: (1) the CFD-based examination is a good way to decide on how to achieve the so-called fit-for-purpose internal aerodynamics of the burner (i.e., to obtain a homogeneous mixture) and (2) to reach the light-off temperature, conventionally taken as 500 K, the burner was operated for 5.2 s, i.e., 3.6 g of gasoline injected, 2.7 g of CO2 and 1.351 g of CO, respectively, emitted. Moreover, this study identified measures for improving the burner’s design as well as an enhanced procedure for the burner’s operating control both aiming to produce a cleaner combustion during the TWC pre-heating.

Integrated catalytic systems for simultaneous NOx and PM reduction: a comprehensive evaluation of synergistic performance and combustion waste energy utilization.

The global transition towards sustainable automotive vehicles has driven the demand for energy-efficient internal combustion engines with advanced aftertreatment systems capable of reducing nitrogen oxides (NOx) and particulate matter (PM) emissions. This comprehensive review explores the latest advancements in aftertreatment technologies, focusing on the synergistic integration of in-cylinder combustion strategies, such as low-temperature combustion (LTC), with post-combustion purification systems. Selective catalytic reduction (SCR), lean NOx traps (LNT), and diesel particulate filters (DPF) are critically examined, highlighting novel catalyst formulations and system configurations that enhance low-temperature performance and durability. The review also investigates the potential of energy conversion and recovery techniques, including thermoelectric generators and organic Rankine cycles, to harness waste heat from the exhaust and improve overall system efficiency. By analyzing the complex interactions between engine operating parameters, combustion kinetics, and emission formation, this study provides valuable insights into the optimization of integrated LTC-aftertreatment systems. Furthermore, the review emphasizes the importance of considering real-world driving conditions and transient operation in the development and evaluation of these technologies. The findings presented in this article lay the foundation for future research efforts aimed at overcoming the limitations of current aftertreatment systems and achieving superior emission reduction performance in advanced combustion engines, ultimately contributing to the development of sustainable and efficient automotive technologies.

Differentiated impact of low-exhaust-emission vehicles on NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {2}$$\\end{document} and particle concentrations in the Paris region

Higher concentrations of air pollutants, such as nitrogen dioxide (NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {2}$$\\end{document}) and particulate matter (PM), are observed in streets compared to the urban background. These concentrations could be predominantly attributed to road traffic, which remains an important source despite relentless efforts. In this study, performed over the Paris area, the impacts of the evolution of the fleet composition on urban air quality down to the street scale is assessed with two scenarios assuming the introduction of very-low-emission vehicles. Exhaust emission factors for these vehicles are based on the improvement of engine and after-treatment technologies, leading to factors lower than those proposed for the European emission standard Euro 7. Using the year 2014 as the baseline, very-low-emission vehicles are introduced up to the year 2030 for the Paris region. NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {2}$$\\end{document} emissions are thus reduced by 68 % in streets, and concentrations by 53 %. However, PM concentration reduction is limited to 18 % in streets as non-exhaust emissions from tyre and brake wear and road abrasion are preponderant. PM emissions from non-exhaust sources represent 59 % of the total road-traffic emission of PM in 2014 and 89 % in 2030. Non-regulated pollutant concentrations are also reduced, by 42 % for black carbon and 30 % for organic matter. Considering only very-low-emission and electric vehicles in the fleet further reduce NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {2}$$\\end{document} emissions and concentrations by 99.5 % and 80 % respectively. PM concentrations are only reduced by 22 %. This study highlights the high reduction potential of NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {2}$$\\end{document} concentrations with very-low-emission and electric vehicles, because of reduction of exhaust emissions. However, difficulties remain to reduce PM concentrations in urban areas, with the large majority of PM traffic emissions coming from non-exhaust sources.

Study on the Evolution of Physicochemical Properties of Carbon Black at Different Regeneration Stages of Diesel Particulate Filters Regenerated by Non-Thermal Plasma

As a new type of aftertreatment technology, non-thermal plasma (NTP) can effectively decompose the particulate matter (PM) deposited in diesel particulate filters (DPFs). In this paper, a regeneration test of a DPF loaded with carbon black was carried out using an NTP injection system, and the changes of oxidative activity, elemental content, and occurrence state, microstructure and graphitization degree of carbon black were analyzed to reveal the evolution of the physicochemical properties of carbon black at different regeneration stages of the DPF regenerated by NTP. As the regeneration stage of the DPF advanced, Ti, Tmax, and Te of the carbon black at the bottom of the DPF decreased, which were higher than those at the regeneration interface. After the NTP reaction, the proportion of C element decreased to less than 80%, while the proportion of O element increased to more than 20%; C-O was converted to C=O and the relative content of C=O increased. The average microcrystalline length and average spacing decreased, while the average microcrystalline curvature increased. The ID1/IG (relative peak intensities) of carbon black samples decreased from 3.31 to 3.10, and the R3 (relative peak intensities, R3 = ID3/(IG + ID2 + ID3)) increased from 0.41 to 0.58. The content of carbon clusters had a great influence on the disorder of the microcrystalline structure, so the graphitization degree of carbon black decreased and the oxidation activity increased.

Deciphering the improvement in (H2-)C3H6-SCR performance of Ag/Al2O3 catalysts prepared from warm-water-treated alumina: A NMR-assisted identification of the Ag anchoring sites of the alumina support

Lean exhausts aftertreatment has been the subject of numerous investigations due to ever stringent regulations on pollutants emissions such as that of NOx. Among aftertreatment technologies, the selective catalytic reduction of NOx by the hydrocarbons (HC-SCR) has been studied intensively, in particular by using Ag/Al2O3 materials. The present work highlights that pretreatment of pristine Al2O3 in warm water prior to Ag deposition allows to prepare catalysts of significantly higher (H2-)C3H6-SCR performance compared to conventional Ag/Al2O3 catalysts. In addition, NOx-TPD-C3H6-SCR structure-activity correlations indicate that optimum composition of the Ag/Al2O3 catalysts can be improved by about 50% in terms of Ag content for the first time. Unprecedented in-depth NMR investigations allow for the identification of the alumina sites of importance in the anchoring of Ag. These sites are µ1-OH groups located near the (100)/(110)l edge and then near the (110)b/(100) edge of Al2O3 crystallites and bonded to octahedrally coordinated Al species.

Towards zero pollution vehicles by advanced fuels and exhaust aftertreatment technologies

Vehicular emissions deteriorate air quality in urban areas notably. The aim of this study was to conduct an in-depth characterization of gaseous and particle emissions, and their potential to form secondary aerosol emissions, of the cars meeting the most recent emission Euro 6d standards, and to investigate the impact of fuel as well as engine and aftertreatment technologies on pollutants at warm and cold ambient temperatures. Studied vehicles were a diesel car with a diesel particulate filter (DPF), two gasoline cars (with and without a gasoline particulate filter (GPF)), and a car using compressed natural gas (CNG). The impact of fuel aromatic content was examined for the diesel car and the gasoline car without the GPF. The results showed that the utilization of exhaust particulate filter was important both in diesel and gasoline cars. The gasoline car without the GPF emitted relatively high concentrations of particles compared to the other technologies but the implementation of the GPF decreased particle emissions, and the potential to form secondary aerosols in atmospheric processes. The diesel car equipped with the DPF emitted low particle number concentrations except during the DPF regeneration events. Aromatic-free gasoline and diesel fuel efficiently reduced exhaust particles. Since the renewal of vehicle fleet is a relatively slow process, changing the fuel composition can be seen as a faster way to affect traffic emissions.

Applications of Electric Heating Technology in Vehicle Exhaust Pollution Control

Motor vehicle exhaust is an important cause of atmospheric pollution. Nowadays, mainstream exhaust emission aftertreatment technologies, such as TWC, DOC, SCR, and DPF, usually require sufficient temperature to perform good purification or maintain normal working conditions. Compared with exhaust gas heating technologies such as engine enrichment and fuel injection, electric heating technology can quickly increase the temperature of exhaust gas aftertreatment devices without adverse effects on engine operating conditions. This article introduces the research and progress of electric heating technology combined with traditional aftertreatment devices on major types of vehicles, such as gasoline vehicles, diesel vehicles, motorcycles, and hybrid vehicles, to improve exhaust purification efficiency and its accompanying fuel consumption impact. In addition, the common structure and characteristics of electric heaters, as well as the current status and development trend of electric heating unit technologies such as electric heating power supply are introduced.

Numerical Study on Compact Design in Marine Urea-SCR Systems for Small Ship Applications

With increasingly stringent emissions legislation, such as that stipulated by the International Maritime Organization, for nitrogen oxide emission reduction in marine diesel engines, the imperative of curtailing nitrogen oxide emissions from marine diesel engines is intensifying. Consequently, the significance of aftertreatment technologies, including diesel particulate filters (DPFs) and selective catalytic reduction (SCR), is poised to grow substantially. In particular, a redesign is required to reduce the size of DPF and SCR systems for application in small ships. In this study, we varied the shape of the filters in DPF and SCR systems, aiming to achieve a distinct flow pattern and enable overall miniaturization. The performance metrics, including the nitric oxide (NO) reduction rate, NH3 slip rate, and pressure drop, of the redesigned models were compared with those of the conventional model. Computational fluid dynamics simulations were used to compare the performance of the redesigned model with that of the conventional model in terms of NO reduction and pressure drop. The redesigned system achieved a NO reduction rate of 6.9% below that of the conventional system, offering additional noteworthy benefits such as a 50% reduction in both pressure and overall length.

Comprehensive characterization of speciated volatile organic compounds (VOCs), gas-phase and particle-phase intermediate- and semi-volatile volatility organic compounds (I/S-VOCs) from Chinese diesel trucks

We established the comprehensive emission profiles of organic compounds for typical Chinese diesel trucks. The profiles cover the entire volatility range, including speciated volatile organic compounds (VOCs), intermediate-volatility organic compounds (IVOCs), and semi-volatile organic compounds (SVOCs). The VOCs and I/SVOCs were analyzed by one-dimensional gas chromatography quadrupole mass spectrometry (GC qMS) and two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-ToF-MS) separately. The impacts of starting mode and aftertreatment technology on the VOC, gaseous and particulate I/SVOC emissions, and the gas-particle partitioning were investigated. The emission factor (EF) of gas phase I/SVOCs was approximately 10 times higher than that of particle phase I/SVOCs and the chemical compositions and volatility distributions varied greatly. VOC, IVOC, and SVOC emissions significantly decreased when vehicles were equipped with advanced aftertreatment technologies. Diesel particulate filters (DPF) can remove >71 % VOC, 74 % gaseous, and 88 % particulate I/SVOCs, many of which are significant secondary organic aerosol (SOA) precursors. The chemical compositions and volatility distributions of the gaseous I/SVOCs and unburned diesel fuel were similar, revealing that diesel fuel is the main origin of the gaseous I/SVOCs. The I/SVOC emission profiles covering the whole volatility range, i.e., log10C* = −3 to 10 (C*: effective saturation concentration, μg m−3) were established.

Study on the nano-structure characteristics of particle before and after diesel oxidation catalyst for diesel engines

ABSTRACT Diesel Oxidation Catalyst (DOC) is the most important and advanced part of the after-treatment technology route. After the exhaust passes through DOC, CO, and HC will be significantly reduced, while particles are mainly captured by the Diesel Particulate Filter (DPF) device behind. In order to further investigate the effect of DOC on the nano-structure characteristics of diesel emission particles. The particles before and after DOC of 186FA diesel engine at 2700 r/min, 100% load, and 3600 r/min, 100% load are collected. The nano-structure characteristics of particles are investigated using field emission transmission electron microscopy (FETEM) combined with small angle X-ray scattering radiation technique (SAXS). Based on FETEM and SAXS analysis of particles, a nano-scale particle spatial structure model including particle size, pores, and visual boundary layer is proposed. The results show that the average radius, interface layer thickness, and fractal dimension of the particles are reduced after the DOC. In contrast, the specific surface area of the particles is increased after the DOC. At 3600 r/min 100% load, the average radius is reduced from 23.3 to 21.5 nm, accounting for 7.8%. Interface layer thickness is reduced from 13.3 to 12.9 nm. The specific surface area of the particles is increased from 0.146 to 0.166 m2/mm3. The research results provide a theoretical basis for the regeneration and oxidation of particles in DPF.

Characteristics of NOX and NH3 emissions from in-use heavy-duty diesel vehicles with various aftertreatment technologies in China

Some in-use China IV and China V heavy-duty diesel vehicles (HDDVs) with selective catalytic reduction (SCR) systems probably fail to mitigate nitrogen oxide (NOX) emissions as expected. Meanwhile, these SCR-equipped HDDVs might emit excessive ammonia (NH3). To better understand the NOX and NH3 emissions from typical HDDVs in China, seventeen in-use vehicles with various emission-control technologies were tested by using laboratory chassis dynamometers. The results indicated that individual NOX and NH3 emissions from HDDV fleets widely varied owing to differences in aftertreatment performance. China V and VI HDDVs with effectively functioning SCRs could substantially control their NOX emissions to be below the corresponding emission limits (i.e., 4.0 and 0.69 g/kWh for China V and China VI vehicles, respectively) but with a potential risk of high NH3 emissions caused by diesel exhaust fluid (DEF) overdosing. Furthermore, higher vehicle speed and payload resulted in lower NOX emissions and possibly higher NH3 emissions from HDDVs with effectively functioning SCRs, while higher NOX emissions from tampered- and non-SCR HDDVs. NOX emissions from China VI HDDVs were more sensitive to cold starts compared to China V and earlier vehicles, but there was no significant discrepancy in NH3 emissions between cold- and hot-start tests.

Strategies to Reduce Emissions from Diesel Engines under Cold Start Conditions: A Review

Reducing diesel engine emissions under cold start conditions has become much more valuable as environmental issues become more important. Regarding diesel engine emissions under cold start conditions, this review summarizes the emission mechanisms and specifically focuses on the research progress of four reduction strategies: biodiesel utilization, intake heating, injection optimization, and aftertreatment technologies. In general, adding biodiesel and Di-Ethyl-Ether (DEE) could provide the benefit of reducing emissions and maintaining engine performance. Intake heating and appropriate injection strategies could also effectively reduce emissions under cold start conditions. Unlike normal operating conditions, lean nitrogen oxide traps (LNT) or electrically heated catalysts (EHC) should be utilized in the aftertreatment of diesel engines to minimize emissions under cold start conditions. By offering the valuable information above, this review could be a helpful reference in reduction strategies for diesel engines under cold start conditions in both academia and industry.