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To reveal the effect of reaction temperature on the reduction of diesel particulate matter (PM) by non-thermal plasma (NTP) using oxygen as a gas source. The changes in the microcrystalline structure and the elemental state of PM before and after NTP oxidation at different temperatures were explored by Raman and X-ray photoelectron spectroscopy. After NTP oxidation, the disorder in the PM microcrystal structure and the amorphous carbon structure was reduced. The full width at half maximum (FWHM) of the D1 and D3 peaks decreased, and the FWHM of the G peak increased slightly. During the oxidation of PM, the carbon microcrystals grew and became restructured, and the graphitization of PM increased. After NTP oxidation, the content of O in PM increased as the reaction temperature increased, resulting in a gradual change in the binding form of O with C from C-O to C=O. The ability of temperature rise to promote the oxidation activity of NTP was gradually weakened for the thermal decomposition of NTP active substances. The microcrystalline structure and the occurrence state of C and O of PM changed with reaction temperature, indicating that the oxidizability of NTP on PM differed at different reaction temperatures.

To investigate the effect of nonthermal plasma (NTP) on the microstructure and oxidation characteristics of particulate matter (PM) from diesel engines at different oxidation stages, a self-designed NTP reactor was used to conduct a time-varying oxidation test on PM samples. The oxidized PM samples were analyzed via thermogravimetric analysis and Raman spectroscopy. The results indicated that the effect of NTP could allow the elemental carbon (EC) to more easily start ignition. The oxidation activity of the EC decreased when the action time of the NTP was less than 5 min. Conversely, when the NTP action time was more than 5 min, the EC oxidation activity gradually increased. When the NTP was active for more than 10 min, it rapidly reacted with the EC, and the oxidation priority of the volatile fraction was higher than that of the EC. During the oxidation process, there are many forms of carbon structures in the particles and they have a mutual transmission relationship. The variation trend of the graphitization degree was consistent with that of the thermogravimetric results, indicating that the degree of graphitization directly affected the PM oxidation activity.

Polyoxymethylene dimethyl ethers (PODE) was blended in diesel at volume ratios of 0 %, 10 %, 20 %, and 30 % (denoted as P0, P10, P20, and P30). The experimental study was carried on an unmodified YD480Q diesel engine. An engine exhaust particle sizer was introduced to analyze the particulate matter (PM) concentration and particle size distribution of diesel engine emission. The evaporation-oxidation characteristics of the PODE/diesel blends and the effect of the fuel blends on the oxidative activity of PM were investigated by thermogravimetric analysis and Arrhenius theorem. The results showed that blending PODE in diesel improved the evaporation-oxidation characteristics of the fuel and decreased the apparent activation energy of the fuel blends. PODE played a positive role in reducing PM emissions. The particle total number concentration of P30 decreased 28.29 ~ 66.60 % and the particle total volume density decreased 54.16 ~ 80.06 % compared to diesel. The particle size distribution shifted to a smaller particle size as the PODE blending ratio was increased. The mass fraction of the volatile substances (VS) increased and the mass fraction of the dry soot (DS) decreased by employing PODE as a diesel additive. Also, the oxidation activity of VS increased as the PODE blending ratio was increased. The oxidation activity of DS climbed to the peak when the PODE blending ratio was 20 % and then decreased.

Nonthermal plasma can achieve diesel particulate filter regeneration under much lower temperatures (≤200 °C), showing promise for potential applications. To investigate the evolution of particulate matter, partial regeneration of a filter was produced by active substances generated by a plasma injection system. The surface morphology, oxidation characteristics, and surface functional groups of particle samples inside the filters before and after regeneration were investigated using digital electron microscopy, scanning electron microscopy, thermal gravimetric analysis, and fourier transform infrared spectrometry. Results show that during the regeneration step, the soot cake surface changed from random irregular cracks to more uniform and relatively dense pores. Decreases in characteristic temperatures and the growth of oxygen-containing functional groups indicated that nonthermal plasma could improve the oxidizing activity of particulate matter. The reaction between nonthermal plasma and particulate matter was most intense but not limited to the regeneration interface area of the soot cake.

This study seeks to investigate the removal efficiency of particulate matter (PM) from the actual diesel exhaust at various reaction temperatures by using non-thermal plasma (NTP). The effect of the reaction temperature on removal efficiency was reflected by the change in the concentration of particles in different modes and the weight fraction of volatile organics in PM. The Arrhenius equation was used to determine the apparent activation energies Ea of the soot in PM. In addition, the difference in the oxidation reaction at various reaction temperatures and the effect of NTP on the properties of PM were discussed. After considering the decreasing ranges of the total concentration and the weight of the PM, it was determined that 120 °C is the optimal temperature choice for PM removal. The decreasing range of the total concentration reached 57.13% and 66.79% of PM was removed when the PM is measured by weight. NTP has better effect on the removal of smaller particles. The weight fraction of the volatile fraction markedly decreases after the reaction and the apparent activation energy of soot noticeably decreased. The oxidizability of the excited species in NTP was enhanced with the increase of the reaction temperature. However, the excited species concentration declined concurrently, resulting in the occurrence of the optimized range of reaction temperature. The particles were removed by the oxidation that occurred on the surface of the primary particle and the disintegration of the structure of the particles.

The emission tests were performed on a light-duty direct injection diesel engine. A polyoxymethylene dimethyl ethers (PODE) mixture was blended with diesel at a volume ratio of 0, 10, 20 and 30%, denoted as P0, P10, P20 and P30, respectively. The particle size distribution before and after the diesel particulate filter (DPF) was measured to evaluate the DPF filtering efficiency of various modal particles. The oxidation activity of the particles on the DPF intake end plane was analyzed by the Arrhenius method. The regeneration of the DPF was conducted using a non-thermal plasma (NTP) injection system. The results showed that blending PODE with diesel contributed to reducing the particle number concentrations. PODE adversely affected the improvement of the DPF filtering efficiency, especially that of P30. However, the DPF filtering efficiency of all fuels was still higher than 94%. Blending PODE with diesel increased the mass fraction of volatile substances (VS) and decreased the mass fraction of dry soot. Particles of P20 showed a better oxidation activity with lower apparent activation energy. In addition, PODE increased the DPF regeneration effect by NTP technology. The deposit removal mass of the DPF rose to the peak level and then decreased as the PODE blending ratio increased. The better DPF regeneration effect was observed when P20 was employed.

To study the effects of residual ash on the capture and regeneration of a diesel particulate filter (DPF), repeated capture and complete regeneration experiments were conducted. An engine exhaust particulate sizer was used to measure the particle size distribution of diesel in the front and back of DPF. Discrepancies in the size distribution of the particulate matter in repeated trapping tests were analyzed. To achieve complete DPF regeneration, a DPF regeneration system using nonthermal plasma technology was established. The regeneration carbon removal mass and peak temperatures of DPF internal measuring points were monitored to evaluate the effect of regeneration. The mechanism explaining the influence of residual ash on DPF capture and regeneration was thoroughly investigated. Results indicate that the DPF trapping efficiencies of the nuclear-mode particles and ultrafine particles have significant improvements with the increase quantity of residual ash, from 90 % and 96.01 % to 94.17 % and 97.27 %, respectively. The exhaust backpressure of the DPF rises from 9.41 kPa to 11.24 kPa. Heat transfer in the DPF is improved with ash, and the peak temperatures of the measuring points accordingly increase. By comparing the regeneration trials, the elapsed time for complete regeneration and time difference for reaching the peak temperature between adjacent reaction interfaces are extended with increased quantity of ash. The carbon removal mass rises by 34.00 %.

In order to investigate the influence of initial regeneration temperatures on diesel particulate filter (DPF) regeneration, an experimental study of DPF regeneration was implemented using a dielectric barrier discharge (DBD) reactor, aided by exhaust waste heat after engine flameout. DPF trapping characteristics and carbon deposit mass were discussed to facilitate further data analysis and calculation. DPF regeneration was then investigated by comparison analysis of deposit removal mass, backpressure drop, and internal temperature change. The results revealed that a large amount of particulate matter (PM) was deposited in DPF with a high filtration efficiency of about 90 %. The deposit removal rate and percentage drop of the backpressure both maximized at the initial temperature of 100 °C. During DPF regeneration, the sharp rise of internal temperature indicated vigorous PM incineration and high CO2 emission. The results successfully demonstrated DPF regeneration using non-thermal plasma injection during engine flameout, and prominent heat durability was achieved in this method.