Review of the state-of-the-art of exhaust particulate filter technology in internal combustion engines

Real biofuel and fossil-fuel soot combustion activities in active and passive regeneration of diesel/gasoline particulate filters under different O2/NOx concentrations

In this work, we aim to investigate and compare the combustion reactivities of real biofuel soot and fossil-fuel soot in the active and passive regeneration conditions of DPF and GPF through temperature-programmed oxidation (TPO). Higher reactivity of biofuel soot is achieved even under GPF conditions with extremely low oxygen concentration (~ 1%), which provides a great potential for low-temperature regeneration of GPF. Such a result is mainly attributed to the low graphitization and less surface C = C groups of biofuel soot. Unfortunately, the presence of high-content ashes (~ 47%) and P impurity in real biofuel soot hinder its combustion reactivity. TPO evidences that the O2/NOX-lacking conditions in GPF are key factors to impact the combustion of soot, especially fossil-fuel soot. This work provides some useful information for understanding real biofuel and fossil-fuel soot combustion in GPF and DPF regeneration and further improvement in filter regeneration process.

Mn and Co decorated biomorphic ceria fiber catalysts for soot and benzene total oxidation

Mn or Co supported CeO2 fiber catalysts were synthesized following a biotemplating route and evaluated in soot combustion and benzene total oxidation. The catalysts were characterized by SEM, EDX, N2 physisorption, FTIR-ATR, XRD, RAMAN and XPS. SEM results confirmed that the "twisted ribbon" morphology of the biotemplate was mostly maintained. XRD and Raman showed that Mn and Co cations partially insert into ceria lattice and also segregate at the surface of the fibers. XPS allowed to determine that both set of catalysts exhibit Ce3+ and Ce4+ species, in addition to adsorbed and lattice oxygen. Also, the average oxidation state (AOS) of surface Mn could be calculated. Compared to bare Fib Ce, the performances for both reactions were improved for the supported catalysts, except from the catalyst with lowest Mn content for soot combustion. The catalytic activity was discussed in terms of the physicochemical features of the supported catalysts.

Recent Advances on Metal Oxide Based Sensors for Environmental Gas Pollutants Detection

Optimizing materials and associated structures for detecting various environmental gas pollutant concentrations has been a major challenge in environmental sensing technology. Semiconducting metal oxides (SMOs) fabricated at the nanoscale are a class of sensor technology in which metallic species are functionalized with various dopants to modify their chemiresistivity and crystalline scaffolding properties. Studies focused on recent advances of gas sensors utilizing metal oxide nanostructures with a special emphasis on the structure-surface property relationships of some typical n-type and p-type SMOs for efficient gas detection are presented. Strategies to enhance the gas sensor performances are also discussed. These oxide material sensors have several advantages such as ease of handling, portability, and doped-based SMO sensing detection ability of environmental gas pollutants at low temperatures. SMO sensors have displayed excellent sensitivity, selectivity, and robustness. In addition, the hybrid SMO sensors showed exceptional selectivity to some CWAs when irradiated with visible light while also displaying high reversibility and humidity independence. Results showed that TiO2 surfaces can sense 50 ppm SO2 in the presence of UV light and under operating temperatures of 298-473 K. Hybrid SMO displayed excellent gas sensing response. For example, a CuO-ZnO nanoparticle network of a 4:1 vol.% CuO/ZnO ratio exhibited responses three times greater than pure CuO sensors and six times greater than pure ZnO sensors toward H2S. This review provides a critical discussion of modified gas pollutant sensing capabilities of metal oxide nanoparticles under ambient conditions, focusing on reported results during the past two decades on gas pollutants sensing.

Effect of catalyst diesel particulate filter aging and catalyst loadings on particulate emission characteristics from a diesel vehicle

In this study, the effect of new and used catalyzed diesel particulate filter (CDPF) with different catalyst loadings on the particulate emissions including the particle mass (PM), particle number (PN), particle size distribution (PSD) and geometric mean diameter (GMD) from a diesel vehicle were investigated based on a heavy chassis dynamometer. Results showed that more than 97.9% of the PN and 95.4% of the PM were reduced by the CDPF, and the reduction efficiency was enhanced by the catalyst loading. After using the CDPF, the PSD transformed from bimodal to trimodal with the peak shifting towards smaller particle size, more nucleation mode particles were reduced compared with accumulation mode ones, but the reduction effect on the accumulation mode particles was more significantly influenced by the catalyst loading. Notably, the CDPF increased the accumulation mode particles proportion, producing a larger GMD. For the used CDPF, its reduction effect on the particulate emissions enhanced, especially for the PM in accumulation mode. The PSD returned to bimodal, but the peak at accumulation mode began to be higher than that at nucleation mode, illustrating that more nucleation mode particles was removed. The aging of the CDPF resulted in greater effect on the PN-based PSD than that of PM-based PSD, but the effect of catalyst loading on the PN and PM emission factors was weakened. The used CDPF further increased the GMD, and the effect of catalyst loading on the GMD was strengthened, a higher catalyst loading led to a reduction in the GMD.

Ultra-low emission power generation utilizing chemically stabilized waste plastics pyrolysis oil in RCCI combustion concept

Emission standards in European Union, designed to reduce the environmental impact of power generation, present a significant challenge for fast-response distributed power generation systems based on internal combustion engines. Regulated emissions, such as NOx and particulate matter present a major concern due to their adverse number of environmental and health effects. Simultaneously, European Union strives towards sustainable management of plastic waste and seeks the ways for its upcycling and production of new fuels and chemicals. As an answer to the presented challenges, the present experimental study addresses the potential for use of chemically stabilized Waste Plastics Oil (WPO), a product of pyrolysis process of waste plastics in a Reactivity Controlled Compression Ignition (RCCI) combustion concept. To establish a reactivity-controlled combustion, the study uses a combination of methane (a model fuel for biomethane) and WPO to a) simultaneously reduce NOx and particulate matter emissions due to low local combustion temperatures and a high degree of charge homogenization and b) address waste and carbon footprint reduction challenges. Through experiments, influence of direct injection timing and energy shares of utilized fuels to in-cylinder thermodynamic parameters and engine emission response were evaluated in engine operating points at constant indicated mean effective pressure. Acquired results were deeply investigated and benchmarked against compression ignition (CI) and RCCI operation with conventional diesel fuel to determine potential for WPO utilization in an advanced low-temperature combustion concept. Results show that chemically stabilized WPO can be efficiently utilized in RCCI combustion concept without adaptation of injection parameters and that with suitable control parameters, ultra-low emissions of NOx and PM can be achieved with utilized fuels. For diesel/methane mix, NOx and PM emissions were reduced compared to conventional CI operation for 82.0% and 93.2%, respectively, whereas for WPO/methane mix, NOx and PM emissions were reduced for 88.7% and 97.6%, respectively, which can be ascribed to favourable chemical characteristics of WPO for the utilized combustion concept. In the least favourable operating point among those studied, indicated mean effective pressure covariance was kept below 2.5%, which is well below 5% being considered the limit for stable engine operation.

A comprehensive study on the performance and emission analysis in diesel engine via optimization of novel ternary fuel blends: Diesel, manganese, and diethyl ether

Ecosystem degradation and fossil fuel depletion are the two foremost concerns to look for alternative fuels. Rapid population growth is primarily accountable for higher consumption of fossil fuel sources, although engine technology is achieving milestones in terms of fuel efficiency and lower exhaust emissions in order to contribute towards a sustainable environment. The main root cause of global warming is carbon dioxide emissions; therefore, it is imperative to assess the impact of alternative fuels in diesel engines with an aim to minimize carbon emissions. A current study deals with the reduction of carbon emissions and improvement of efficiency through addition of manganese nano-additive to di-ethyl ether and diesel fuel blend in particulate form. Fuel blends were formed by adding various proportions of manganese to high-speed diesel fuel and stirring the mixture while heating it for 10 min. The blends were then tested in diesel engines at two distinct loads and five engine speed ranges. Emission analyzer was used to ascertain the CO2 output of engine. At higher loads for 10 % diethyl ether in diesel, the increase in brake thermal efficiency was 24.19, 28.17 and 26.86 % when the manganese amount in blend was changed as 250 mg, 375 mg and 500 mg respectively. On the other side CO2 emissions increase by 11.57, 30.52 and 20.33 % for manganese concentrations of 250 mg, 375 mg and 500 mg respectively. Analysis performed with Design Expert 13 showed that the desirability was 0.796 for a blend of 375 mg manganese at 1300 rpm and 4500 W load with 33.0611 % BTE, 334.011kg/kWh BSFC, 67.8821Nm torque, and 6.072 % CO2. Therefore, it can be deduced that manganese nanoparticle blends improved engine performance but CO2 emissions also increase which can be responsible for global warming and it should be reduced through catalytic converters.

A review of regeneration mechanism and methods for reducing soot emissions from diesel particulate filter in diesel engine

With the global emphasis on environmental protection and the proposal of the climate goal of "carbon neutrality," countries around the world are calling for reductions in carbon dioxide, nitrogen oxide, and particulate matter pollution. These pollutants have severe impacts on human lives and should be effectively controlled. Engine exhaust is the most serious pollution source, and diesel engine is an important contributor to particulate matter. Diesel particulate filter (DPF) technology has proven to be an effective technology for soot control at the present and in the future. Firstly, the exacerbating effect of particulate matter on human infectious disease viruses is discussed. Then, the latest developments in the influence of key factors on DPF performance are reviewed at different observation scales (wall, channel, and entire filter). In addition, current soot catalytic oxidant schemes are presented in the review, and the significance of catalyst activity and soot oxidation kinetic models are highlighted. Finally, the areas that need further research are determined, which has important guiding significance for future research. Current catalytic technologies are focused on stable materials with high mobility of oxidizing substances and low cost. The challenge of DPF optimization design is to accurately calculate the balance between soot and ash load, DPF regeneration control strategy, and exhaust heat management strategy.

Study on the Catalytic Characteristics of Precious Metal Catalysts with Different Pt/Pd Ratios for Soot Combustion

Soot particles in engine exhaust seriously pollute the atmosphere and endanger human health. For soot oxidation, Pt and Pd precious metal catalysts are widely used and are effective. In this paper, the catalytic characteristics of catalysts with different Pt/Pd mass ratios for soot combustion were studied through X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller analysis, scanning electron microscopy, transmission electron microscopy, the temperature-programmed oxidation reaction, and thermogravimetry. Besides, the adsorption characteristics of soot and O₂ on the catalyst surface were explored by density functional theory (DFT) calculations. The research results showed that the activity of catalysts for soot oxidation from strong to weak is Pt/Pd = 10:1, Pt/Pd = 5:1, Pt/Pd = 1:0, and Pt/Pd = 1:1. XPS results showed that the concentration of oxygen vacancies in the catalyst is the highest when the Pt/Pd ratio is 10:1. The specific surface area of the catalyst increases first and then decreases with the increase of Pd content. When the Pt/Pd ratio is 10:1, the specific surface area and pore volume of the catalyst reach the maximum. The following are the DFT calculation results. With the increase of Pd content, the adsorption energy of particles on the catalyst surface decreases first and then increases. When the Pt/Pd ratio is 10:1, the adsorption of C on the catalyst surface is the strongest, and the adsorption of O₂ is also strong. In addition, this surface has a strong ability to donate electrons. The theoretical simulation results are consistent with the activity test results. The research results have a guiding significance for optimizing the Pt/Pd ratio and improving the soot oxidation performance of the catalyst.

Effect of regeneration method and ash deposition on diesel particulate filter performance: a review

As countries around the world pay more attention to environmental protection, the corresponding emission regulations have become more stringent. Exhaust pollutants cause great harm to the environment and people, and diesel engines are one of the most important sources of pollution. Diesel particulate filter (DPF) technology has proven to be the most effective way to control and treat soot. In this paper, we review the latest research progress on DPF regeneration and ash. Passive regeneration, active regeneration, non-thermal plasma-assisted DPF regeneration and regeneration mechanism, DPF regeneration control assisted by engine management, and uncontrolled DPF regeneration and its control strategy are mainly introduced. In addition, the source, composition, and deposition of ash are described in detail, as well as the effect of ash on the DPF pressure drop and catalytic performance. Finally, the issues that need to be further addressed in DPF regeneration research are presented, along with challenges and future work in ash research. Over all, composite regeneration is still the mainstream regeneration method. The formation of ash is complex and there are still many unanswered questions that require further in-depth research.

Effects of ammonia on morphological characteristics and nanostructure of soot in the combustion of diesel surrogate fuels

The morphological characteristics and nanostructure of soot particles in pure n-heptane (C₇H₁₆) and n-heptane/ammonia co-flow diffusion flames were analyzed and compared using thermophoretic sampling and transmission electron microscopy (TEM) observation combining with quantitative image information extraction methods. The results showed that the overall formation and evolution of soot particles in NH₃-doped n-heptane flames along the flame centerline were similar with that without NH₃-doping. However, compared to n-heptane flame, the peak average diameter of primary soot particles and the peak gyration radius of soot aggregates in NH₃-doped flames were reduced by about 45% and 37%, respectively, which indicated that the growth of both primary soot particles via surface reaction/condensation and soot aggregates via coagulation were significantly decreased. Meanwhile, the fractal dimension of soot aggregates was lower with NH₃ addition as the structure of soot aggregates was looser and tended to be more chain-like. After NH₃ doping, the peak average fringe length inside soot particles was decreased by 13%, and the inter-fringe spacing and tortuosity of soot were increased by 8% and 3%, respectively. This represented a more disordered microcrystal structure and lower degree of graphitization of soot particles, meaningfully indicating a higher oxidation reactivity.

Combined feedforward and error-based active disturbance rejection control for diesel particulate filter thermal regeneration

In this paper, a novel control solution, which combines a feedforward control law and an error-based version of the active disturbance rejection control (ADRC) scheme, is proposed for the exhaust gas temperature control during the thermal regeneration process of a diesel particulate filter in the exhaust line of a diesel engine. Attributed to the complexity of the controlled upstream diesel oxidation catalyst (DOC), its thermodynamics is firstly captured and characterized by a set of linear models through identification modeling. Then, a novel error-based ADRC controller, in which the separated components in conventional ADRC such as the extended state observer (ESO) and the feedback compensator are restructured into a single, modularized control function block, is designed by applying the identified nominal DOC model. In order to further unburden the error-based ESO for better achievements, a combined feedforward compensator is well designed on the basis of the principle of energy balance. Thus a hybrid, 2-degree-of-freedom (2-DOF) controller is developed for better dynamic performance of the controlled DOC system. Its stability performance is also analyzed in the work. The robustness and advantages of the presented hybrid control scheme are finally validated and compared with a well-tuned regular PID-based controller by means of extensive simulation and experimental tests. The results show that the proposed hybrid controller is capable of providing more accurate and faster temperature response and is less sensitive to the variation of system parameters and external disturbances. Moreover, as the error-based ADRC in the hybrid scheme takes the reference tracking error as its direct input and is compatible with the regular PID controller in terms of input and output interfaces, it herein provides an appealing control scheme for existing applications as a substitute for the conventional PID-based controllers to achieve improved performance.

Diesel particulate filter regeneration mechanism of modern automobile engines and methods of reducing PM emissions: a review

Diesel particulate filter (DPF) is considered as an effective method to control particulate matter (PM) emissions from diesel engines, which is included in the mandatory installation list by more and more national/regional laws and regulations, such as CHINA VI, Euro VI, and EPA Tier3. Due to the limited capacity of DPF to contain PM, the manufacturer introduced a method of treating deposited PM by oxidation, which is called regeneration. This paper comprehensively summarizes the most advanced regeneration technology, including filter structure, new catalyst formula, accurate soot prediction, safe and reliable regeneration strategy, uncontrolled regeneration and its control methods. In addition, due to the change of working conditions in the regeneration process, the additional emissions during regeneration are discussed in this paper. The DPF is not only the aftertreatment device but also can be combined with diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) and exhaust recirculation (EGR). In addition, the impact of DPF modification on the original system of some old models has been reasonably discussed in order to achieve emission targets.

Effect of lubricating base oil on the oxidation behavior of diesel exhaust soot

In this study, the oxidation behaviors of soot particles from diesel engine when using neat diesel fuel (DF) and lubricating base oil-blended fuel (BBF) were investigated. The changes in the average particle size and nanostructure parameters during soot oxidation process were analyzed. Exhaust particulate matter (PM) samples were collected from a four-stroke, four-cylinder and turbo0charged diesel engine operated under 1200 rpm and 200 Nm. DF and BBF Soot samples with different oxidation weight losses of 20 %, 40 %, and 60 % were obtained by thermogravimetric isothermal oxidation experiments at 600 °C, and the particle size and nanostructure parameters (fringe length, L_a; fringe tortuosity, T_f) were characterized using high-resolution transmission electron microscopy (HRTEM). Results show that the DF soot particles exhibited an oxidation mode that was initially dominated by surface oxidation and gradually deviated to internal oxidation. Combustion of the base oil increased the soot internal oxidation tendency. HRTEM results showed that as the soot oxidation progressed, the primary particles showed a shell-core, onion-like and hollow structure gradually. The L_a of the primary particles gradually increased, and the T_f gradually decreased, indicating that the soot layer crystallites were rearranged during the oxidation process, which resulted in a disordered nanostructure that transitioned to a more graphitized nanostructure.

Advances in emission control of diesel vehicles in China

Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the exhaust gas recirculation (EGR) and high-efficiency selective catalytic reduction (SCR) routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, SCR for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH₃. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.

Insight into the penalty of exhaust emissions and fuel consumption by DPF regeneration of a diesel passenger car

In order to keep high fuel economy of diesel passenger cars, Diesel particulate filter (DPF) is periodically regenerated. In the regeneration process, extra fuel is injected into combustion chambers to achieve high exhaust temperature for the purpose of oxidizing particles accumulating on DPF substrate. It generates significant impacts on passenger car performance and exhaust emissions. In this paper, real-driving performance and exhaust emissions of a diesel car were tested over sixteen drivers under real-world conditions. DPF regeneration events were identified via exhaust temperature. Vehicle power output, fuel economy, and exhaust emissions in the trips both with and without DPF regeneration were analyzed. The results indicated that DPF regeneration events occurred in three of thirty-two test trips, and the maximum exhaust temperature was 250 °C during DPF regeneration. The DPF regeneration event led to the decrease of fuel economy and the increase of particle number, nitrogen oxides and carbon dioxides emission. Particle number emission factors were increased from approximately 10⁹ #/km to 5 × 10¹⁰ #/km during DPF regeneration. The average power output of the car was in the range of 14.5 kW-15.6 kW and 15.8 kW-18.4 kW for the trips with and without DPF regeneration, respectively. However, Carbon monoxide emission factors were insensitive to DPF regeneration in the test trips.

Effects of inlet velocity and structure parameters on the performance of a rotary diesel particulate filter for truck diesel engine based on fuzzy grey relational analysis

In this paper, a three-dimensional mathematical model of the rotary diesel particulate filter (RDPF) for truck diesel engine is established according to the fluid mechanics and porous media theory. The effects of inlet velocity and structure parameters (diameter ratio, expansion angle and filter length) on the flow uniformity in the RDPF are investigated. Furthermore, the Fuzzy grey relational analysis (FGRA) is employed to make a weight analysis of the influences of structure parameters on the regeneration performance and pressure drop of the RDPF. The results show that the velocity uniformity in the RDPF can be improved by properly reducing the inlet velocity, diameter ratio or expansion angle θ₁. The capture-regeneration volume ratio with 8-10 is appropriate range for the structural optimization. Finally, the expansion angle θ₁ is the most important structure parameter for the filter regeneration performance (regeneration time R = 0.8467; regeneration efficiency R = 0.6849) and the diameter ratio is the most important structure parameter for the pressure drop at the capture-regeneration "balance point" (R = 0.9352).

Assessment of particle and gaseous emissions and reductions from gasoline direct injection passenger car and light-duty truck during passive regeneration

This study evaluated the effectiveness of two passive regenerating gasoline particulate filters (GPFs) on reducing both gaseous and particle phase pollutants from a gasoline direct inject (GDI) passenger car (PC) and light-duty truck (LDT). In the absence of filter regeneration, observations from this study are consistent with other studies demonstrating how particle number (PN), particulate matter (PM), and black carbon (BC) emissions were reduced from the two vehicles with the use of GPFs. The significance of this study was to demonstrate the ability of the GPF to mitigate gaseous and particulate pollutants during severe passive filter regeneration, which was often observed on the LDT during aggressive US06 drive cycle testing. Partial filter regeneration happened on the LDT during some FTP-75 tests, as well as on the PC during some US06 drive cycles, however, this did not impact the GPF filtration efficiency (FE) to reduce particulate and gaseous pollutants. Using a cleaner fuel with lower overall tailpipe PM emissions could potentially lead to more frequent partial regenerations. This could produce the benefit of lower exhaust back pressure during and immediately after regeneration but still provide sufficient reduction in both particle and gaseous emissions.

Catalytic effect of diesel PM derived ash on PM oxidation activity

With diesel particulate filter and gasoline particulate filter periodical regeneration, more and more ash accumulates on the substrate of filter. Ash gathering on the substrate of filter leads to more contact area of particulate matter and ash. Specific ingredients in ash present catalytic effects on particulate matter oxidation. However, the catalytic effect of diesel particulate matter derived ash on its oxidation, mimicking the ash accumulating on filter substrate, is still uncovered using experiments. In this paper, diesel particulate matter derived ash was put at the bottom of particulate matter samples to imitating the soot loading on filter substrate which was covered by much ash. The results indicated that the burnout temperature of diesel particulate matter was in the range of 500-600 °C; while it was 600-700 °C for Printex (U). The burnout temperature drop by ash was lower than 10 °C for diesel particulate matter. The maximum mass loss rate corresponded to approximately 450 °C for diesel particulate matter, and it was changed minorly by ash and ramp rates. However, the temperature corresponding to the maximum mass loss rate was seriously retarded by high ramp rates for Printex (U), and ash presented limited effect on it. The maximum activation energy drop by ash was approximately 60 kJ/mol at the initial stage of oxidation for diesel particulate matter. The activation energy was approximately 132.19, 114.78, 157.26, and 144.67 kJ/mol for diesel PM, diesel PM-ash, Printex (U), and Printex (U)-ash, respectively. Organic compounds dropped gradually in the oxidation process of diesel particulate matter. Nanostructure evolutions of diesel particulate matter and Printex (U) were similar, experiencing smaller sizes and void cores at the end of oxidation process.

Study of durability of diesel vehicle emissions performance based on real driving emission measurement

Diesel vehicle emissions generally deteriorate with vehicle mileage due to the wear and deterioration of vehicle parts. Most of the experimental studies on vehicle emission durability were carried out based on the standard operation cycles of engine or vehicle, few research investigated vehicle emission deterioration characteristics under real driving conditions. In this research, the real driving emission (RDE) test method was used to investigate and evaluate the emission deterioration characteristics of two China-V diesel vehicles equipped with DOC and SCR systems. The experimental results show the emissions of CO and NOx from the N2 and N3 diesel vehicles increase with the vehicle mileage, showing the tendency of emission deterioration. The calculated deterioration factors of N2 and N3 diesel vehicle CO and NOx emissions are greater than the recommended values in China standard HJ 438-2008, which means experimental study on the vehicle emissions durability is necessary. The vehicle emissions deterioration depends on real driving conditions and the vehicle usage over vehicle lifetime.

Review of Particle Filters for Internal Combustion Engines

Diesel engines have gradually become one of the main forces in the human transportation industry because of their high efficiency, good durability, and stable operation. However, compared with gasoline vehicles, the high emission of diesel vehicles forces manufacturers to introduce new pollutant control technologies. Although the particulate matter emissions of gasoline vehicles are lower than that of diesel vehicles, with the popularity of gasoline vehicles and the continuous rise of power, the impact of these particles on the environment cannot be ignored. Therefore, diesel particulate filters and gasoline particulate filters have been invented to collect the fine particles in the exhaust gas to protect the environment and meet increasingly stringent emission regulations. This paper summarizes the research progress on diesel particulate filters and gasoline particulate filters at present and comprehensively introduces the diesel particulate filter and gasoline particulate filter from the mechanism, composition, and operation processes. Additionally, the laws and regulations of various countries and the impact of gas waste particulates on the human body are described. In addition, the mechanisms of the diesel particulate filter, gasoline particulate filter, and regeneration were studied. Finally, the prospects and future directions for the development of particle filters for internal combustion engines are presented.

Detailed Speciation of Non-Methane Volatile Organic Compounds in Exhaust Emissions from Diesel and Gasoline Euro 5 Vehicles Using Online and Offline Measurements

The characterization of vehicle exhaust emissions of volatile organic compounds (VOCs) is essential to estimate their impact on the formation of secondary organic aerosol (SOA) and, more generally, air quality. This paper revises and updates non-methane volatile organic compounds (NMVOCs) tailpipe emissions of three Euro 5 vehicles during Artemis cold urban (CU) and motorway (MW) cycles. Positive matrix factorization (PMF) analysis is carried out for the first time on proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) datasets of vehicular emission. Statistical analysis helped to associate the emitted VOCs to specific driving conditions, such as the start of the vehicles, the activation of the catalysts, or to specific engine combustion regimes. Merged PTR-ToF-MS and automated thermal desorption gas chromatography mass spectrometer (ATD-GC-MS) datasets provided an exhaustive description of the NMVOC emission factors (EFs) of the vehicles, thus helping to identify and quantify up to 147 individual compounds. In general, emissions during the CU cycle exceed those during the MW cycle. The gasoline direct injection (GDI) vehicle exhibits the highest EF during both CU and MW cycles (252 and 15 mg/km), followed by the port-fuel injection (PFI) vehicle (24 and 0.4 mg/km), and finally the diesel vehicle (15 and 3 mg/km). For all vehicles, emissions are dominated by unburnt fuel and incomplete combustion products. Diesel emissions are mostly represented by oxygenated compounds (65%) and aliphatic hydrocarbons (23%) up to C₂₂, while GDI and PFI exhaust emissions are composed of monoaromatics (68%) and alkanes (15%). Intermediate volatility organic compounds (IVOCs) range from 2.7 to 13% of the emissions, comprising essentially linear alkanes for the diesel vehicle, while naphthalene accounts up to 42% of the IVOC fraction for the gasoline vehicles. This work demonstrates that PMF analysis of PTR-ToF-MS datasets and GC-MS analysis of vehicular emissions provide a revised and deep characterization of vehicular emissions to enrich current emission inventories.

Emissions of Carbonaceous Particulate Matter and Ultrafine Particles from Vehicles—A Scientific Review in a Cross-Cutting Context of Air Pollution and Climate Change

Airborne particulate matter (PM) is a pollutant of concern not only because of its adverse effects on human health but also on visibility and the radiative budget of the atmosphere. PM can be considered as a sum of solid/liquid species covering a wide range of particle sizes with diverse chemical composition. Organic aerosols may be emitted (primary organic aerosols, POA), or formed in the atmosphere following reaction of volatile organic compounds (secondary organic aerosols, SOA), but some of these compounds may partition between the gas and aerosol phases depending upon ambient conditions. This review focuses on carbonaceous PM and gaseous precursors emitted by road traffic, including ultrafine particles (UFP) and polycyclic aromatic hydrocarbons (PAHs) that are clearly linked to the evolution and formation of carbonaceous species. Clearly, the solid fraction of PM has been reduced during the last two decades, with the implementation of after-treatment systems abating approximately 99% of primary solid particle mass concentrations. However, the role of brown carbon and its radiative effect on climate and the generation of ultrafine particles by nucleation of organic vapour during the dilution of the exhaust remain unclear phenomena and will need further investigation. The increasing role of gasoline vehicles on carbonaceous particle emissions and formation is also highlighted, particularly through the chemical and thermodynamic evolution of organic gases and their propensity to produce particles. The remaining carbon-containing particles from brakes, tyres and road wear will still be a problem even in a future of full electrification of the vehicle fleet. Some key conclusions and recommendations are also proposed to support the decision makers in view of the next regulations on vehicle emissions worldwide.

Variations of significant contribution regions of NOx and PN emissions for passenger cars in the real-world driving

Nitrogen oxides (NO_x) and particulate number (PN) emissions are the main concerns of the passenger cars in the real-world driving. NO_x and PN emissions are greatly dependent on the driving behaviors which differ significantly between standard driving cycles and real-world driving. However, the significant contribution regions (short durations corresponding to high proportions of total emissions) of NO_x and PN emissions regarding different driving behaviors (e.g. vehicle speed and acceleration) are still uncovered. NO_x20% and NO_x50% refer to instantaneous NO_x emission rates when NO_x emission rates are ranked from high to low level where the sums of NO_x emission rates being higher than NO_x20% and NO_x50% correspond to 20% and 50% of total NO_x emissions, respectively. t_20% and t_50% are corresponding durations where NO_x emission rates are higher than NO_x20% and NO_x50%. In this paper, three Euro-6 compliant direct injection gasoline passenger cars and a diesel passenger car are tested in a real-world driving trial in which nineteen drivers are involved. Novel key performance indicators with reference to the regimes of specific NO_x and PN contributions to total emissions are defined. Instantaneous NO_x and PN emissions are monitored using a portable emission measurement system (PEMS) in the test. The results indicate that the maximum and minimum average speed over the four cars being approximately 32.3 km/h s and 42.6 km/h, respectively. Average PN emission factor of the diesel car is the lowest among the four given cars. Average t_20% and t_50% corresponding to NO_x20% and NO_x50% are lower than 3% and 12%, respectively, for all the passenger cars; additionally, these two parameters show the same pattern. The corresponding t_20% and t_50% variations of the Euro-6a gasoline car and the diesel car are much lower than the other two. Average acceleration corresponding to 20% and 50% of total NO_x emissions for the given diesel car is approximately 1.25 m/s² and 0.6 m/s², respectively, being much higher than that of the other three gasoline cars (lower than 1 m/s² and 0.4 m/s² respectively) over the specific driving route and drivers. The average PN_20% and PN_50% of the given diesel car are approximately 7 × 10⁷#/s and 3 × 10⁷#/s respectively, being much lower than the three given gasoline cars (higher than 8 ×10⁹#/s and 2 ×10⁹#/s respectively) under the given test conditions; the corresponding t_20% and t_50% are lower than 4% and 17% respectively for all the three gasoline cars.

Potential hazards associated with interactions between diesel exhaust particulate matter and pulmonary surfactant

Long term exposure to diesel exhaust particulate matter (DEPM) can induce numerous adverse health effects to the respiratory system. Understanding the interaction between DEPM and pulmonary surfactant (PS) can be an essential step toward preliminary evaluation of the impact of DEPM on pulmonary health. Herein, DEPM was explored for its interaction with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), the major component of PS. The results indicated that the surface pressure-area (π-A) isotherms of DPPC monolayers shifted toward lower molecular areas and the compression modulus (C_S^-1) reduced in the presence of DEPM. Atomic force microscopy image showed that DEPM can disrupt the ultrastructure of DPPC monolayers along with the direction of lateral compression. In addition, DPPC can in turn condition the surface properties of DEPM, permitting its agglomeration in aqueous media, which was attributed to the adsorption of DEPM to DPPC. Furthermore, the particle-bound polycyclic aromatic hydrocarbons (PAHs) could be desorbed from DEPM by the solubilization of DPPC and it was positively correlated with the hydrophobicity of PAHs. These findings revealed the toxicity of DEPM-associated PAHs and the role of DPPC in facilitating the removal of the inhaled particles, which can provide a new insight into the potential hazards of airborne particles on lung health.

Fast Identification of the Failure of Heavy-Duty Diesel Particulate Filters Using a Low-Cost Condensation Particle Counter (CPC) Based System

The penetration of diesel particulate filters (DPFs) in the market is growing fast. However, in the current inspection/maintenance (I/M) regulation for these vehicles, particulate emissions were capped with smoke opacity, which is incompetent to identify the excessive particle number (PN) induced by non-major DPF failures such as small cracks in substrate. This research aimed at developing a fast identification method for such malfunctioning vehicles using a low-cost condensation particle counter (CPC). To verify the effectiveness of idle PN test, 33 China-5 and China-6 heavy-duty vehicles fueled with diesel and natural gas (NG) were tested using the regulatory portable emission measurement system (PEMS) as per China-6 protocol and idle PN tests using a low-cost CPC-based system. PN emissions from China-6 vehicles with malfunctioning DPFs were at a similar level to those from China-5 vehicles (without DPF), which were significantly higher than the proper counterparts. Idle PN tests using a CPC-based system managed to identify the vehicles with DPF failures. Volumetric PN concentrations of these vehicles were much higher than those of the proper ones. This study proved that an easy, fast, and low-cost procedure could be used to screen out those high emitters with DPF failure.

Experimental investigation into the oxidation reactivity, morphology and graphitization of soot particles from diesel/n-octanol mixtures

Aiming to investigate the impacts of n-octanol addition on the oxidation reactivity, morphology and graphitization of diesel exhaust particles, soot samples were collected from a four-cylinder turbocharged diesel engine fueled with D100 (neat diesel fuel), DO15 (85% diesel and 15% n-octanol, V/V) and DO30 (70% diesel and 30% n-octanol, V/V). All tests were conducted at two engine speeds of 1370 and 2150 r/min under a fixed torque of 125 N·m. The soot properties were characterized by thermogravimetric analyzer (TGA), transmission electron microscopy (TEM) and Raman spectroscopy (RS). The higher volatile organic fraction content, lower soot oxidation temperatures and lower activation energy from TGA results indicated that both the increasing n-octanol concentration and engine speed enhanced the soot oxidation reactivity. Additionally, quantitative analysis of TEM images showed that the soot derived from DO30 had the smallest primary particle diameters and fractal dimension, followed by those of soot produced by DO15 and D100. The RS results demonstrated that the n-octanol addition and higher engine speed led to a larger D1-FWHM (D1-full width at half maximum), A_D1/A_T (area ratio of D1 band and the total spectral) and A_D3/A_T (area ratio of D3 band and the total spectral) as well as a smaller L_a (crystallite width), revealing a lower degree of graphitization. Furthermore, the correlations between characterization parameters of soot properties and reactivity were nonlinear.

Emission inventory and control policy for non-road construction machinery in Tianjin

The establishment of a non-road construction machinery emission inventory forms the basis for the analysis of pollutant emission characteristics and for the formulation of control policy. We analyzed and investigated data on populations, emission factors, and activity levels for the construction machinery in Tianjin to estimate an emission inventory. Finally, a variety of emission reduction scenarios were used to simulate emission reductions and propose the most effective control policy. The results show that total emissions of CO, HC, NOx, PM₁₀, and PM_2.5 from non-road construction machinery in Tianjin of 2018 reached 4180.78, 951.44, 5833.85, 383.92, and 365.70 t, respectively. Forklifts, excavators, and loaders were the three most important emission sources in Tianjin. There are clear differences in the emissions of different districts. Large machinery emissions were mainly distributed across the Binhai New Area, which includes high volumes of port machinery and tractors in Tianjin Port. Based on various emission reduction scenarios, the effect of emission reductions is estimated. The IAD affected the reduction of CO and HC emissions with RR values of 17.6% and 17.3%, respectively, while EMO affected the mitigation of PM₁₀ and PM_2.5 emissions and RR values by 18.0% and 18.4%, respectively. The emission reduction control policy for non-road construction machinery is proposed, including the accelerated updating of non-road machinery emission standards; integrating diesel engine research and development institutions to accelerate the development of vehicle after-treatment technology; and establishing a cooperation mechanism for scientific research institutes, government departments, and enterprises in the control of non-road mobile machinery emissions.

Understanding the multiple interactions in vanadium-based SCR catalysts during simultaneous NOx and soot abatement

The multiple interactions during simultaneous removal of soot and NOx were systematically studied over a V-based catalyst, which is highly relevant for the development of more efficient 2-way SCRonDPF systems.

Filtration Efficiency and Regeneration Behavior in a Catalytic Diesel Particulate Filter with the Use of Diesel/Polyoxymethylene Dimethyl Ether Mixture

Polyoxymethylene dimethyl ether (PODEn) is a promising diesel additive, especially in particulate matter reduction. However, how PODEn addition affects the filtration efficiency and regeneration process of a catalytic diesel particulate filter (cDPF) is still unknown. Therefore, this experimental work investigated the size-dependent particulate number removal efficiency under various engine loads and exhaust gas recirculation (EGR) ratios when fueling with diesel (D100) and diesel/PODEn mixture (P10). In addition, the regeneration behavior of the cDPF was studied by determining the breakeven temperatures (BETs) for both tested fuels. The results showed that the cDPF had lower removal efficiencies in nucleation mode particles but higher filtration efficiencies in accumulation mode particles. In addition, the overall filtration efficiency for P10 particles was higher than that for D100 particles. Positioning the upstream cDPF, increasing the EGR ratio slightly decreased the number concentration of nucleation mode particles but greatly increased that of accumulation mode particles. However, increasing the EGR ratio decreased the removal efficiency of nanoparticles, and this effect was more apparent for the P10 case. Under the same period of soot loading, the pressure drop of P10 fuel was significantly lower than that of diesel fuel. In addition, a significantly lower BET was observed for the P10 fuel, in comparison with D100 fuel. In conclusion, adopting cDPF is beneficial for fueling with P10 in terms of the overall filtration efficiency in the particulate number and the lower input energy requirement for active regeneration. However, with the addition of EGR, the lower filtration efficiencies of nanoparticles should be concerned, especially fueling with diesel/PODEn mixture.

Oxidation of soot over supported RuRe nanoparticles prepared by the microwave-polyol method

The oxidation of soot over RuRe bimetallic nanoparticles (NPs) supported on γ-Al2O3 has been investigated. The catalysts were synthesized by a microwave-polyol method and characterized by ICP, BET, TEM, STEM-EDS, XRD and XPS techniques. The study revealed that the proper choice of the Re loading (0.4–2.0 wt%) is crucial for the catalytic behavior of the 2% Ru–Re/Al2O3 nano-catalysts.The best catalytic properties, in terms of overall activity and stability, were observed for the 2%Ru-0.8%Re/γ-Al2O3 nano-catalyst. The stability of all bimetallic 2% Ru–Re nano-catalysts in catalytic soot oxidation in the presence of oxygen is very high in contrast to the 2% Ru/γ-Al2O3 sample. The presence of rhenium in the catalytic system hinder the formation of large RuO2 agglomerates leading to a better dispersion of active ruthenium phase and a better catalytic performance. The relationship between the catalytic activity of Ru–Re/γ-Al2O3 and the synergetic roles of Ru and Re is discussed.

Impact Factors Analysis of Diesel Particulate Filter Regeneration Performance Based on Model and Test

In the application of DPFs (diesel particulate filters), temperature prediction and control technology during the regeneration phase has always been a great challenge, which directly affects the safety and performance of diesel vehicles. In this study, based on theoretical analysis and sample gas bench test results, a one-dimensional simulation model is built with GT-POWER software. The effects of soot loading quantity and oxygen concentration on regeneration temperature performance are studied. Simulation results show that, when the soot loading quantity exceeds 46 g (12.7 g/L), the maximum temperature inside DPF during the regeneration phase would be higher than 800 °C, and the risk of burning crack would be high. When the oxygen concentration in the exhaust gas is low (lower than 7%), the fuel injected into exhaust gas fails to give off enough heat, and the exhaust gas temperature fails to reach the target regeneration temperature, hydrocarbon emission could be found from the DPF outlet position; when the oxygen concentration in the exhaust gas reaches 7% or above, the DPF inlet temperature could reach the target temperature, accompanied by less hydrocarbon emission. Combined with the simulation results, engine test bench validation was carried out. The results show that the simulation results and test results agree well.

Catalytic Materials for Gasoline Particulate Filters Soot Oxidation

The energy efficiency of Gasoline Direct Injection (GDI) engines is leading to a continuous increase in GDI engine vehicle population. Consequently, their particulate matter (soot) emissions are also becoming a matter of concern. As required for diesel engines, to meet the limits set by regulations, catalyzed particulate filters are considered as an effective solution through which soot could be trapped and burnt out. However, in contrast to diesel application, the regeneration of gasoline particulate filters (GPF) is critical, as it occurs with almost an absence of NOx and under oxygen deficiency. Therefore, in the recent years it was of scientific interest to develop efficient soot oxidation catalysts that fit such particular gasoline operating conditions. Among them ceria- and perovskite-based formulations are emerging as the most promising materials. This overview summarizes the very recent academic contributions focusing on soot oxidation materials for GDI, in order to point out the most promising directions in this research area.

Effect of Operating Parameters on Oxidation Characteristics of Soot under the Synergistic Action of Soluble Organic Fractions and Ash

Diesel particulate filter is used to reduce particulate matter (PM) emission due to the stringent emission standards. The accumulated PM has been oxidized by the periodical regeneration method to avoid pressure buildup. The innovation of this study is to explore the oxidation performance of Printex-U (PU), which is mixed with ash and soluble organic fractions, under different operating conditions. Different aspects of operating parameters, such as the oxygen ratio in an O2/N2 atmosphere, total flow rate, initial PU mass, and heating rate, on PU oxidation properties have been critically discussed using a thermogravimetric analyzer. The oxygen ratio in the O2/N2 atmosphere is positively correlated with the oxidation characteristics of PU. The comprehensive oxidation index (S ) of PU under the 20% O2/80% N2 atmosphere increases by 184% compared with the 10% O2/90% N2 atmosphere. When the initial PU mass is 3 mg, the combustion stability coefficient (R w) and S reach the best values, which are 55.53 × 105 and 2.03 × 107 %2min-2 ° C-3, respectively. With the increase in the heating rate, the oxidation properties of PU become sensible and deflagration occurs easily, so that 10 °C/min heating rate is the best option. This study provides a theoretical basis for the optimization design of diesel particulates during the regeneration process.

Synergy Analysis of the Influence of the Connection Cone on the Thermal Distribution during Regeneration

Diesel particulate filters (DPF) are typically used for particle filtration in vehicle exhausts after a treatment system. The monolith inside a DPF is a symmetrical column structure, frequently an axisymmetric cylinder structure where filtration and regeneration occur. Due to the complex structure before the symmetric monolith, the internal particle distribution is not uniform, which leads to an uneven temperature change when regeneration occurs. During thermal regeneration, the temperature field inside a DPF is affected by the particle load, exhaust temperature and exhaust flow. The relationship between the temperature gradient and velocity vector is also a key factor influencing regeneration performance. Based on the particle-loading test method, a bench for thermal distribution testing during regeneration was built. Via experiments and simulations, the temperature field in an axisymmetric monolith during particle combustion given an uneven particle distribution was analyzed. Through field synergy analysis of the temperature and velocity fields in the monolith, the influence of connection cones with different structures on heat transfer enhancement was studied. The results indicated that compared with a monolith with a conventional linear cone, the radial temperature gradient is 1.1 °C/mm lower, the area of enhanced regeneration is larger, and the regeneration rate is improved in the monolith with a streamlined cone.

Analysis of the effect of particle-wall collision process in DPF on the spatial structure of smoke cake layer

Based on the rebound model of particle-wall collision, the influence of adhesion force on the deposition process of particles on the smoke cake wall was studied by using atomic force microscopy (AFM) and automatic specific surface area (BET) and pore size distribution analyzer. The interaction between the deposition process and the spatial structure of smoke cake was analyzed. The results show that with the increase of diesel engine speed, Young's modulus of particles decreases and the average particle size increases; the kinetic energy of particles impacting on the surface of smoke cake layer in diesel particle filter (DPF) increases; when the velocity of particles with the same particle size entering the wall increases, the maximum compression distance between particles and the surface of the smoke cake layer increases; and the adhesion force and adhesion energy increase. With the increase of diesel engine speed, the box counting dimension of smoke cake layer in DPF increases from 1.9478 to 1.996, the characteristic radius of pores decreases from 15.32 nm to 7.53 nm, the average pore diameter decreases, and the average pore volume increases. When the fractal dimension increases from 2.633 to 2.732, the deformation degree of particles increases, the smoke cake layer becomes more compact and dense, the internal structure of pores becomes more complex, the surface of pores is rougher, and particle adhesion requires overcoming larger adhesion barriers when particles adhere.