Effects of Nonthermal Plasma on Microstructure and Oxidation Characteristics of Particulate Matter

Effect of gas temperature on carbon soot oxidation via non-thermal plasma: two-dimensional numerical study integrating reactive flow and discharge models

Non-thermal plasma (NTP) efficiently regenerates diesel particulate filters by oxidizing carbon soot (CS) at low temperatures. However, numerical studies on the spatial characteristics of CS oxidation by NTP are scarce. In addition, the influence of background gas heating on the CS-oxidizing performance by NTP remains inadequately understood. This research investigates the impact of gas temperature (323-573 K) on heterogeneous CS oxidation using NTP in a two-dimensional configuration. The results indicate that CS is mainly oxidized by [Formula: see text], [Formula: see text], and [Formula: see text] during NTP treatment. The energy efficiency of CS removal by NTP ranges from 0.1 to 2.6 g kWh-1 for varying gas temperature and applied voltage, consistent with previous research. Higher gas temperatures enhance both CS removal rate and efficiency, whereas higher applied voltages enhance rate at the expense of efficiency. The study also assesses energy conversion efficiency from electrical power input to chemical bonding energy during CS oxidation by NTP, yielding 0.03 to 0.23% efficiency for the considered gas temperature and voltage ranges, with higher temperatures leading to better efficiency.

Performance evaluation of PM, NOx, and hydrocarbon removal in diesel engine exhaust by surface discharge-induced plasma

Diesel engines are characterized by low CO2 emissions and high fuel efficiency. However, their exhausts contain nitrogen oxides (NOx), particulate matter (PM), and hydrocarbons (HC) that require removal by aftertreatment. A novel low-temperature plasma-based aftertreatment method has been developed for the simultaneous removal of NOx, PM, and HC. NOx could be reduced by reacting with HC and CO in the exhaust gas. The particle and gas concentrations in the exhaust are measured using a scanning mobility particle sizer, a NOx analyzer, and a total hydrocarbon analyzer. The treatment performance is evaluated using the resulting measurements. The diesel engine is operated under 0%, 25%, 50%, and 75% loads (maximum output of 2 kW), and the exhaust gas is mixed with N2 + O2 (13%) gas. The power is adjusted to provide 100, 200, 300, and 400 W input power during the plasma reactor treatment. The aftertreatment removal of NOx, PM, and HC is evaluated, and the engine exhibits a removal efficiency of 70% for NOx, 98% for PM, and 67% for HC at 75% engine load and an input power of 100 W.

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.

Effect of temperature control conditions on DPF regeneration by nonthermal plasma

A regeneration test of a diesel particulate filter (DPF) was conducted under different temperature conditions with air as the gas source and a nonthermal plasma (NTP) injection system. We investigated the influence of the ambient temperature on the DPF regeneration performance and the oxidative decomposition amount of particulate matter (PM) and analyzed the changes in the PM oxidation characteristics by thermogravimetric analysis (TGA). The higher the temperature, the lower the decomposition amount of PM was under constant temperature conditions. The decomposition amount of PM was the highest at 80 °C (3.74 g), and the PM at interface P2 was not completely removed. The volume concentrations of the DPF regeneration products (CO and CO₂) were higher under variable than constant temperature conditions. In addition, the peak temperature of interface P1 occurred 10-30 min earlier, complete regeneration occurred at interface P2, and DPF regeneration occurred faster than under temperature conditions. The initial temperature of the control device was 110 °C, and the maximum mass of PM oxidation decomposition was 4.26 g after regeneration for 15 min cooling to 80 °C. The main form of elemental carbon (EC) transformed into the low ignition point component and the oxidation activity was improved after NTP injection.

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.

Investigation on the adsorption characteristics and influencing factors of diesel engine exhaust particulate matter

In the exhaust pipe, the adsorption process of diesel exhaust particulate matter (PM) is affected by the combination of its adsorption capacity and the environment. A diesel exhaust particle collection system was established to collect samples with different environmental conditions. The adsorption capacity of the samples was characterized by an isothermal adsorption test. Changes in sample characteristics were investigated by scanning electron microscope and thermogravimetric analyzer. The correlation analysis of the factors influencing the adsorption process was performed. The results showed that the diesel exhaust particulate matter has adsorption capacity, the pore diameter is distributed continuously in the range of 8 to 80 nm, and the specific surface area and pore structure parameters are similar to carbon black and belong to the category of mesopores and macropores. As the engine speed increased from 1500 to 3600 r·min^-1, the specific surface area of samples increased from 65.408 to 101.885 m²·g^-1, and the pore volume expanded from 0.093 to 0.152 mL·g^-1, with a more complex pore structure and enhanced adsorption capacity. The samples at the outlet of the exhaust pipe had increased box dimension (D_B), moisture, and soluble organic fraction (SOF) content compared to the samples at the inlet of the exhaust pipe. The activation energies (E) of the three samples were reduced by 34.77 kJ∙mol^-1, 38.88 kJ∙mol^-1, and 47.43 kJ∙mol^-1, respectively. Among the influencing factors, the increase of hydrocarbon concentration contributes to the increase of adsorption volume and the reduction of E. The increase of the average temperature inhibits the increase of the D_B, and the increase of the temperature difference between the inlet and outlet facilitates the adsorption of water and SOF by samples. The reduction of adsorption time is one of the main reasons for delaying the increase of D_B. Average pore diameter has the largest positive correlation with the variation amount of D_B, and the growth of the specific surface area and pore volume is the dominant reason for the improvement of adsorption capacity and oxidation activity.

Impact of High-Voltage Discharge After-Treatment Technology on Diesel Engine Particulate Matter Composition and Gaseous Emissions

Diesel particulate matter (DPM) and oxides of nitrogen (NOx) are the emissions from diesel engines (compression ignition engines) of the most concern and are currently strictly regulated. In this work, we present an alternative diesel emission control technique to assist in further emission reduction. An experiment-oriented study on diesel engine emission abatement using low-power, low-frequency, high-voltage discharge (HVD) treatment was carried out in a laboratory-scale reactor with whole diesel engine exhaust gas. A dielectric barrier discharge (DBD) reactor was used in direct contact with diesel exhaust gas at atmospheric temperature with an input energy density between 200 and 400 J/L. An investigation of the direct effect of the high-voltage discharge reactor on the diesel exhaust gas treatment was carried out to characterize both diesel particle and gaseous emissions. The proposed HVD system demonstrated up to 95% particulate matter reduction by mass or 64% reduction by number, and 63% reduction of the diesel soot particle geometrical mean diameter by HVD-generated O₃ oxidation. Thermogravimetric analysis revealed the significant change in the diesel soot compositions and oxidation characteristics. HVD-treated particulate matter demonstrated a lower reactivity in comparison to untreated soot. Gas composition analysis indicated the generation of free radicals (e, O, OH, O₃, and N) by the HVD system, as mainly indicated by the increase of the NO₂/NO ratio and concentration of CO and O₂. The pattern of CO₂ reduction while CO and O₂ increased indicated the dissociation of CO₂ by HVD. Free radicals generated by HVD directly affected DeNO, DeNOx, NO₂/NO ratio, and CO and CO₂ selectivities.

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.

Preparation of Cu–Cu2O–CuO by solid combustion ignited by dielectric barrier discharge and its activity towards p-nitrophenol reduction

Dielectric barrier discharge induces solid powder combustion at room temperature and atmosphere to prepare a high-activity catalyst for p-nitrophenol reduction.