Gasoline Particulate Filters Research Articles

Effect of working conditions on oxidation activity and surface functional group of particulate matter emitted from China Ⅵ GDI engine

Gasoline particulate filter (GPF) is one of the most important means to solve particle emissions of gasoline direct injection (GDI) engines in the present and the future. In order to provide a theoretical guidance for the regeneration control and improvement of GPF, this paper analyzes the oxidation activity and surface functional group of particulate matter (PM) emitted from a China VI GDI engine at different working conditions, and the oxidation characteristics of ultrafine particles. The results show that ultrafine particles account for most PM emitted from the GDI engine, and the ratio of ultrafine particulates is affected by working conditions. The activation energy of PM changes in the range of 110 ∼ 180 kJ/mol under different working conditions. With the increase of engine load, the oxidation activity of PM decreases, which is manifested by the increase in characteristic temperatures of the oxidation activity. As the increase of engine speed, the oxidation activity increases. The activation energy of ultrafine particles is in the range of 88.0 ∼ 111.4 kJ/mol, and its oxidation activity is not significantly related to the particle diameter. The content of CO and C–H functional groups change obviously under different working conditions. IC-H/IC=C and IC=O/IC=C are in the range of 1.14 ∼ 1.8 and 1.25 ∼ 2.17. The oxidation activity of PM is positively correlated with the content of C–H functional groups.

Survey of strategies to reduce cold-start particulate, CO, NOx, and hydrocarbon emissions from direct-injection spark-ignition engines

Meeting cold-start emissions standards for particulate emissions and the criteria air pollutants, NO, CO and unburned hydrocarbons (HC), is critical for gasoline direct-injection spark-ignition (DISI) engines, including DISI engines in hybrid-electric powertrains. This work surveys recent strategies to reduce particulate mass (PM), particulate number (PN), NO, CO, and HC emissions during cold-start conditions. Results of studies that demonstrate progress using engine operating strategies (such as timing of fuel injection, spark-ignition, and valve events) and engine and after-treatment hardware development to mitigate and reduce cold-start engine-out and vehicle emissions are highlighted. Several methods are promising in terms of meeting more stringent cold-start emissions requirements, in particular, fuel injector design and operation have significant potential to reduce particulate emissions and advances in manufacturing can help reduce limitations from nozzle tip-wetting. Fast-heating of three-way catalysts also shows clear benefits, in addition to gasoline particulate filters to reduce vehicle PM and PN emissions. A clear challenge (and opportunity) is the dramatically larger parametric space for engine design and operation and the coupled interaction with after-treatment that should be considered to address cold-start emissions. Advances in modelling and physical experiments that allow more rapid development of DISI powertrain and after treatment systems are critical to meet future cold-start emissions requirements.

Impacts of engine lubrication oil-derived ash on soot oxidative reactivity on a catalytic gasoline particulate filter

Characterizing soot oxidation kinetics is crucial for understanding how gasoline particulate filters (GPFs) perform both in terms of filtration efficiency and pressure drop. The most common method for measuring soot oxidative reactivity is thermogravimetric analysis (TGA). Because TGA is an offline method, it may inaccurately predict how soot oxidizes on a GPF, especially if a catalytic washcoat is present that may enhance oxidation rates through surface interactions as the soot loads on the filter. In this work, a novel in-situ soot oxidative reactivity measurement method was developed. The method involved loading a catalytic GPF under high temperature conditions conducive to soot oxidation and measuring the filtration efficiency of 100 nm particles. A correlation was made between filtration efficiency and loaded soot mass on the filter to allow calculation of the soot oxidation rate. The method was evaluated in experiments using a 2.0 L gasoline direct injection (GDI) engine with three oils of varying additive packages, including an oil with a high zinc dialkyldithiophosphate (ZDDP) concentration, a non-additive, pure poly-alpha olefin (PAO) oil, and an oil with a high concentration of calcium sulfonate. Calculated specific soot oxidation rates ranged from ∼0.06–0.6 min−1 and showed strong dependence on GPF inlet gas temperature and lubrication oil additive type. The results clearly demonstrated a catalytic effect of calcium-containing ash particles. Reactivity of soot produced by the engine running with the high calcium containing lubrication oil was increased. Similarly, the results indicated that the catalytic washcoat on the filter increased soot oxidation rates on-filter, especially at low soot loading. Conversely, the ZDDP oil additive exhibited a reactivity inhibiting effect, resulting in lower soot oxidation rates. This work represents the first known in-situ soot oxidative reactivity measurements on a GPF and elucidates the effect of lubrication oil additives and catalytic washcoat on oxidation rate.

Effects of structural optimization design of gasoline particulate filter on soot emission and performance of GDI engine

Effects of structural optimization design of gasoline particulate filter on soot emission and performance of GDI engine

μ-CT Investigation into the Impact of a Fuel-Borne Catalyst Additive on the Filtration Efficiency and Backpressure of Gasoline Particulate Filters

μ-CT Investigation into the Impact of a Fuel-Borne Catalyst Additive on the Filtration Efficiency and Backpressure of Gasoline Particulate Filters

Challenging Conditions for Gasoline Particulate Filters (GPFs)

The emission limit of non-volatile particles (i.e., particles that do not evaporate at 350 °C) with size >23 nm, in combination with the real driving emissions (RDE) regulation in 2017, resulted in the introduction of gasoline particulate filters (GPFs) in all light-duty vehicles with gasoline direct injection engines in Europe. Even though there are studies that have examined the particulate emissions at or beyond the current RDE boundary conditions, there is a lack of studies combining most or all worst cases (i.e., conditions that increase the emissions). In this study, we challenged a fresh (i.e., no accumulation of soot or ash) “advanced” prototype GPF at different temperatures (down to −9 °C), aggressive drive cycles and hard accelerations (beyond the RDE limits), high payload (up to 90%), use of all auxiliaries (air conditioning, heating of the seats and the rear window), and cold starts independently or simultaneously. Under hot engine conditions, the increase of the particulate emissions due to higher payload and lower ambient temperature was 30–90%. The cold start at low ambient temperature, however, had an effect on the emissions of up to a factor of 20 for particles >23 nm or 300 when considering particles <23 nm. We proposed that the reason for these high emissions was the incomplete combustion and the low efficiency of the three-way oxidation catalyst. This resulted in a high concentration of species that were in the gaseous phase at the high temperature of the close-coupled GPF and thus could not be filtered by the GPF. As the exhaust gas cooled down, these precursor species formed particles that could not be evaporated at 350 °C (the temperature of the particle number system). These results highlight the importance of the proper calibration of the engine out emissions at all conditions, even when a GPF is installed.

Experimental investigation of particle number reduction in turbocharged GDI engines

Introduction (problem statement and relevance). Now it is difficult to imagine the automotive industry without constant improvement of the power plant. This is due to the constant tightening of environmental standards, so in environmental standards Euro 6 there is a limit of the countable concentration of particulate matters. To meet the Euro 6 environmental standard, vehicle manufacturers use catalytic converters, and gasoline particle filters (GPF). These methods of reducing the emissions of the exhaust gas are quite common, but they also have a limitation on the service life. The use of only catalytic converters and GPF may not be sufficient to meet the Euro 7 standards in the future. So, there is a need to reduce emissions with exhaust gases by improving the combustion process.The purpose of work is to investigate the combustion process of a turbocharged gasoline direct injection engine to reduce particulate matter by increasing the injection pressure and optimizing the injection timing. Methodology and research methods. The studies are of an experimental nature, the reliability of the data is confirmed by the use of modern measuring equipment and post processing of the measured data. Scientific novelty and results. The fuel injection parameters, which have a significant influence on the particulate matter formation and oxidation are defined.Practical significance. The recommendations to reduce particulate matter formation and to meet the requirements of the future Euro standards are given.

Gasoline Direct Injection Engine Emissions of OC and EC: Laboratory Comparisons with Port Fuel Injection Engine

To better understand carbonaceous aerosol emissions from gasoline vehicles, a gasoline direct injection (GDI) vehicle with and without a gasoline particle filter (GPF) installed and a port fuel injection (PFI) vehicle were tested on a chassis dynamometer using standard emission drive cycles. Carbonaceous particles emitted from the vehicles were collected on quartz filters and analyzed using three different thermal optical protocols to assess the sensitivity of organic carbon (OC) and elemental carbon (EC) emission estimates to the methods, showing OC obtained by the IMPROVE and EC by the NIOSH protocol was the lowest. Compared to the PFI vehicle, the GDI vehicle had higher EC and OC emissions under cold-start cycles by 1415% and 46%, respectively. However, the OC emission from the PFI vehicle was higher than GDI during an aggressive driving cycle by 146%. By considering OC collected on a quartz filter behind a Teflon filter, the emissions from PFI vehicle were found to be more volatile than the GDI vehicle. This is consistent with the OC forming characteristics for GDI and PFI engines, which are pyrolyzed particles from incomplete combustion and incomplete volatilization of fuel droplets, respectively. Generally, the particle phase OC emissions from gasoline engines are more volatile than other sources (e.g., biomass burning), supported by the very low level of pyrolyzed organic carbon (POC) and small differences among protocols in the current study. Once the GDI vehicle was equipped with a GPF, the removal efficiency of EC was > 98%, but OC emissions could increase as a result of regeneration, suggesting that the effect of a GPF on total carbon emitted to the atmosphere needs further evaluation, especially considering the formation of secondary organic aerosol.

Statistical capillary tube model for porous filter media: An application in modeling of gasoline particulate filter

A new statistical capillary tube model is presented to predict both filtration efficiency and permeability of particulate filters. The model considers the porous structure of the filter media as an assembly of curved capillary tubes with a statistical size distribution. The key model descriptors of pore microstructure are porosity, pore size, pore size distribution, and tortuosity. The model was validated by permeability and size dependent filtration efficiency measurements of bare and washcoated gasoline particulate filters (GPFs), using porosimetry data of the filter media as model inputs. Comparing with a more widely used spherical model for particulate filters with typical porosity range of 30–60%, the capillary tube model has similar input parameters but provides additional permeability prediction as well as better filtration predictions over a wider porosity range including the lower porosity of washcoated filters. Furthermore, it offers a more visually straightforward and intuitive correlation between filtration paths and filter performance. This allows convenient adoption of the capillary tube model in numerous applications that are currently based on spherical model assumption and provides improved guidance for filter optimization. Beyond ceramic automotive exhaust filters, this geometric model offers a new framework for examining porous filter media in general.

Using aerosols to create Nano-scaled membranes that improve gasoline particulate filter performance and the development of Wafer-based membrane coated filter analysis (WMCFA) method

The very high filtration efficiency of diesel particulate filters (DPF) derives from the soot cake that rapidly forms on the walls of honeycomb wall-flow substrates. However, one cannot count on this for gasoline direct injection (GDI) engines, because of their much lower soot rates and the soot oxidation due to their higher exhaust temperatures. Therefore, the present paper explores the use of artificial aerosols to synthesis nano-scale membranes that mimic the soot cake in DPFs. The paper has two major goals. The first is to introduce a new wafer-based approach for rapid screening and evaluation of new nanoscale membranes and show that this provides very good guidance for the performance of full-size gasoline particulate filters (GPF) by performing detailed experimental comparisons in aspects of filtration efficiency, pressure drop, and loading behavior. The second is to demonstrate the feasibility of using the nano-scale membranes to improve GPF performance and evaluate how choices of particle characteristics and aerosol flow rate influence the quality of the nano-scale membranes. Our experiments demonstrate that membranes produced 1) with particles of larger aggregate size or 2) under lower face velocity yield 25–36% and 13–34% better performance (particle number-based efficiency versus pressure drop tradeoff), respectively, under the range of tested conditions.

Evaluation of Solid Particle Number Sensors for Periodic Technical Inspection of Passenger Cars.

Following the increase in stringency of the European regulation limits for laboratory and real world automotive emissions, one of the main transport related aspects to improve the air quality is the mass scale in-use vehicle testing. Solid particle number (SPN) emissions have been drastically reduced with the use of diesel and gasoline particulate filters which, however, may get damaged or even been tampered. The feasibility of on-board monitoring and remote sensing as well as of the current periodical technical inspection (PTI) for detecting malfunctioning or tampered particulate filters is under discussion. A promising methodology for detecting high emitters is SPN testing at low idling during PTI. Several European countries plan to introduce this method for diesel vehicles and the European Commission (EC) will provide some guidelines. For this scope an experimental campaign was organized by the Joint Research Centre (JRC) of the EC with the participation of different instrument manufacturers. Idle SPN concentrations of vehicles without or with a malfunctioning particulate filter were measured. The presence of particles under the current cut-off size of 23 nm as well as of volatile particles during idling are presented. Moreover, the extreme case of a well performing vehicle tested after a filter regeneration is studied. In most of the cases the different sensors used were in good agreement, the high sub-23 nm particles existence being the most challenging case due to the differences in the sensors’ efficiency below the cut-off size.

Switzerland's PM10 and PM2.5 environmental increments show the importance of non-exhaust emissions

Atmospheric particulate matter (PM) is a priority pollutant for urban air pollution management because of its negative effects on human health and visibility. Emissions from road traffic have been a major focus of management over the past few decades, but non-exhaust emissions i.e. , emissions from brake, tyre, road wear, and the resuspension of dust have emerged to become a major source of unregulated PM in many locations. Here, a filter-based sampling campaign was conducted between 2018 and 2019 where a large number of PM constituents were quantified for five sites in Switzerland for both PM 10 and PM 2.5 . This had the objective of investigating urban and urban-traffic PM increments in Switzerland. The results show that PM concentrations increased as the sampling locations moved along a rural to urban-traffic gradient. However, source apportionment analysis showed that sulfate-rich, nitrate-rich, and biogenic sources were not enhanced in urban environments, but road traffic and mineral dust sources were. The total mass enhancement for PM 10 and PM 2.5 were 2.4 μg m −3 and 2.0 μg m −3 for the urban environment while the corresponding urban-traffic enhancements were 5.7 μg m −3 and 2.8 μg m −3 . Emissions from road traffic were estimated to contribute more than 75% to the urban increments and non-exhaust emissions contributed 48% (PM 10 ) and 25% (PM 2.5 ) to the total road traffic related increment at an urban background site and 62% (PM 10 ) and 49% (PM 2.5 ) at an urban-traffic site. Analysis of the composition of Switzerland's PM showed that elements associated with non-exhaust emissions, specifically the brake wear tracers of antimony, barium, copper, and iron were the metals with the greatest urban and urban-traffic enhancements. Critically, the urban increment of these elements was enhanced for both PM 10 and PM 2.5 by about the same magnitude as the urban-traffic increment (by 2–3 times), demonstrating non-exhaust emissions are encountered across urban areas, not just the urban-traffic environment. Therefore, non-exhaust emissions were an important contributor to the urban and urban-traffic PM 10 and PM 2.5 increments in Switzerland's urban areas. The relative contributions of non-exhaust emissions to the urban and urban-traffic increments could be expected to increase due to the introduction of further exhaust after-treatment technologies (such as gasoline particulate filters; GPFs) and the transition to a more electrified vehicle fleet. A management pivot will be required to control these non-exhaust emission pathways and although this work exclusively uses data from Switzerland, the conclusions are likely relevant to many other European urban areas. • Non-exhaust road traffic emissions significantly contaminate urban environments. • Non-exhaust emissions were a large contributor to Switzerland's urban increments. • Secondary and biogenic sources were not enhanced in Switzerland's urban areas. • Brake wear tracers were the most enhanced urban and urban-traffic PM components. • Characteristic elements from abrasion processes were enhanced in PM 10 and PM 2.5

Numerical analysis on a novel CGPFs for improving NOx conversion efficiency and particulate combustion efficiency to reduce exhaust pollutant emissions.

Improving the NOx conversion efficiency and particulate combustion efficiency under cold-start conditions (low-temperature conditions) is still the main challenge faced by catalytic gasoline particulate filter systems (CGPFs). In this study, the physical and mathematical models of novel CGPFs are proposed based on the computational fluid dynamics software. Then, the models are validated based on experiments, and the performances of conventional and novel CGPFs are analyzed comparatively. The comparison conclusions indicate that the NOx conversion efficiency of the novel CGPFs increases by 3.2% and the particulate combustion efficiency increases by 2.7% under the same operating condition. Finally, the effects of exhaust flow vf, exhaust oxygen mass fraction Co, exhaust NO mass fraction CNO, and electric heating power Pe on the NOx conversion efficiency and particulate combustion efficiency are investigated. The weights of each influencing parameter on the NOx conversion efficiency and particulate combustion efficiency are explored by orthogonal tests. The conclusions show that the NOx conversion efficiency is increased by 3.6% and the particulate combustion efficiency is increased by 16.7% compared to the initial condition. This study has an important reference value for improving the purification efficiency of vehicle emission under cold-start conditions.

Performance enhancement of equilibrium regeneration in a gasoline particulate filter based on field synergy theory

The optimization of exhaust parameters is conducive to improving the regenerative performance of the gasoline particulate filter(GPF) in the reaction equilibrium process. In this work, firstly, the regenerative model of the GPF is established to explore the effect of exhaust parameters on the index of the regenerative performance in the reaction equilibrium process. Secondly, based on the method of extreme difference analysis, a large number of parameters are optimized to intuitively study the variation law of the regenerative performance in the reaction equilibrium process. Finally, the multi-field synergy theory is used to analyze the field synergy effect after optimizing exhaust parameters. Research results show that when the exhaust mass flow, carbon loading amount, and m(NO2)/m(NO) decrease, while the oxygen concentration increases, both the regenerative performance and the effect of the field synergy are greatly improved. Through the calculation and analysis, after the exhaust parameters are optimized, the maximum increment of the soot oxidation rate is 30.38%, and the maximum decrement of the temperature non-uniformity coefficient(CTU), pressure drop in the reaction equilibrium process, and local maximum pressure drop gradient(GMP) are 23.40%, 69.38%, and 70.35% respectively. In addition, the increasing range of the field synergy coefficient of the GPF is 2.64–3.52%.

Modeling the Catalytic Performance of Coated Gasoline Particulate Filters under Various Operating Conditions

Coated gasoline particulate filters (cGPFs) can reduce gaseous as well as particulate emissions with the same device. However, their more complex design compared to conventional open monoliths requires accurate models in the development phase. We therefore present a new global kinetic model for cGPFs considering standard three-way catalyst reactions and extend it with the impact of lean–rich cycling, referred to as dithering. Submodels are introduced for the oxygen storage and for the extent of oxidation of the active centers. Therefore, the model captures the enhanced conversion of the catalyst under various dithering as well as steady-state conditions. Several steady-state and transient experiments were conducted on a specially equipped dynamic engine test bench in order to calibrate the approach. The proposed model accurately predicts the tailpipe emissions released in a worldwide harmonized light vehicles test procedure driving cycle that is not part of the original calibration data.

Global Kinetic Model of a Three-Way-Catalyst-Coated Gasoline Particulate Filter: Catalytic Effects of Soot Accumulation

In the present study, a global kinetic model of three-way-catalyst-coated gasoline particulate filters was developed to understand the relevant kinetic mechanisms taking place both in clean and real soot-loaded filters. The model involves reaction rate expressions for CO, C2H4, and C7H8 conversion over a model Pd/CeZr/Al2O3 catalyst, hydrothermally treated at 650 °C. Particularly, a new rate expression was proposed for ethylene based on the distinctive experimental trends observed for this hydrocarbon. The model predicted satisfactorily the conversion of all three reductants under different experimental conditions. The soot inhibition effect was also modeled by the reduction of the number of active sites. Interestingly, ethylene was less affected compared to other reductants by the presence of soot due to the formation of less stable and more reactive species on the catalyst surface.

Model Ag/CeO2 catalysts for soot combustion: Roles of silver species and catalyst stability

Ag/CeO2 has been regarded as a promising recipe for soot catalytic combustion in gasoline particulate filters, while lots of information about its reaction mechanism and practicability is yet missing. In this work, the reducibility and activity of three Ag/CeO2 model catalysts with different types of silver species (Agn+ nanoclusters, metallic Ag nanoclusters and metallic Ag nanoparticles) supporting on CeO2 nanorods were studied. It was suggested that silver facilitated the generation of Oxn- via Ag+-(Ce3+-VO)-induced O2 activation or ceria bulk-to-surface oxygen migration, both of which resulted in boosted soot combustion. From a practical point of view, the thermal ageing-induced silver sintering could be alleviated by the defective sites on CeO2, though certain degree of catalyst deactivation was still inevitable.

Impacts of Extreme Ambient Temperatures and Road Gradient on Energy Consumption and CO2 Emissions of a Euro 6d-Temp Gasoline Vehicle

The EU aims to substantially reduce its greenhouse gas emissions in the following decades and achieve climate neutrality by 2050. Better CO2 estimates, particularly in urban conditions, are necessary for assessing the effectiveness of various regional policy strategies. In this study, we measured the CO2 emissions of a Euro 6d-temp gasoline direct injection (GDI) vehicle with a three-way catalyst (TWC) and a gasoline particulate filter (GPF) at ambient temperatures from −30 °C up to 50 °C with the air-conditioning on. The tests took place both on the road and in the laboratory, over cycles simulating congested urban traffic, dynamic driving, and uphill driving towing a trailer at 85% of the maximum payloads of both the car and the trailer. The CO2 values varied over a wide range depending on the temperature and driving conditions. Vehicle simulation was used to quantify the effect of ambient temperature, vehicle weight and road grade on the CO2 emissions. The results showed that vehicle energy demand was significantly increased under the test conditions. In urban trips, compared to the baseline at 23 °C, the CO2 emissions were 9–20% higher at −10 °C, 30–44% higher at −30 °C, and 37–43% higher at 50 °C. Uphill driving with a trailer had 2–3 times higher CO2 emissions. In motorway trips at 50 °C, CO2 emissions increased by 13–19%. The results of this study can help in better quantification of CO2 and fuel consumption under extreme conditions. Additional analysis on the occurrence of such conditions in real-world operation is advisable.

Comparison of Olefin Copolymers and Comb Polymers in Engine Oil Formulations Tested for Fuel Efficiency Retention and CO <sub>2</sub> Emissions Under Advanced Emission Standards

<div class="section abstract"><div class="htmlview paragraph">This study presents the impact of two engine oil additives on fuel efficiency and CO<sub>2</sub> emissions. Formulations containing either Olefin Copolymer (OCP) or Comb polymer (Comb) were compared in tests for fuel efficiency retention, fine particle emissions, and ash accumulation in the gasoline particulate filter. The Comb formulations showed higher fuel efficiency throughout the testing, retaining this efficiency after three distinct engine aging test cycles. No significant differences between formulations were observed in oil consumption, ash accumulation, and filtration efficiency.</div></div>

Catalytic Diesel and Gasoline Particulate Filters

I am honored to be the Guest Editor of this Special Issue of the journal Catalysts dedicated to “Catalytic Diesel and Gasoline Particulate Filters” [...]