| The frequent occurrence and the deterioration of haze weather in China has pushed the air pollution problem to the forefront of social broad attention. PM2.5 (particle diameter, Dp?2.5 ?m) is considered to be the main causes of haze weather. Since the PM emissions of diesel engine is outstanding, alternatives for diesel engine exhaust gas treatment methods is being a increasingly stringent challenge in face of increasingly stringent emission regulations. Diesel particulate filters (DPF) have been recognized as superior for the PM after-treatment technology for its relatively mature technology. With the increment of PM inside DPF, the gas flow is hindered and the backpressure of DPF rises. When the backpressure of DPF reaches a certain degree, it will affect the normal operation of diesel engine. For the reasons given above, the key of DPF technology lies in its regeneration. The using of traditional regeneration technology is limited by its own for thermal damage of carrier structure, low regeneration efficiency and high cost. The application of Non-thermal Plasma (NTP) technology is one of research hotspots in the field of DPF regeneration in recent years.Firstly of all, the chemical reaction mechanism of DPF regeneration based on NTP technology had been analyzed and based on this, the DPF regeneration system assisted by NTP is established. Then, with oxygen and air as gas source, the DPF regeneration tests under different initial temperatures were conducted and the comparison of two kinds of gas source was discussed. Based on PM its nature difference, in combination with PM particle size analysis, thermogravimetric analysis and the oxidation characteristic analysis, the effects of particle size and composition of PM on DPF regeneration were studied. In further, through changing the loading time of PM, the influences of PM loading quality on temperature inside DPF and oxidative decomposition of PM were investigated during the process of DPF regeneration. Finally, on the premise of the same amount of O2, three kinds of different gas source control strategies were designed. The effect of gas source control strategy on PM oxidation decomposition and DPF regeneration was explored. The specific research works are as follows:(1) On the basis of the NTP discharge theory, we discussed the chemical reaction model of the DPF regeneration based on the NTP technology. It is aimed to further study the chemical reaction mechanism of PM decomposition through NTP technology and provide theoretical guidance for the regeneration of DPF based on the NTP technology.(2) Thorough building the DPF regeneration system based on NTP technology, the DPF regeneration tests under different initial temperatures were conducted with oxygen and air as gas source. By monitoring the volume fraction of CO and CO2 and the internal temperature of DPF, the initial temperature of test on PM oxidation decomposition and DPF regeneration were studied. Besides, the experimental conclusions were verified. The results showed that NO2 and O3 in NTP have strong oxidizing to decompose PM to CO and CO2 within the temperature scope of the 17?-300?. In the process of DPF regeneration, both axial and radial temperatures and tempersture gradients are less than the use limit of DPF, so the internal structure of DPF remains intact. NTP tecnology have the ability to realize the regeneration of DPF without any catalyst at lower temperature.Compared to the traditional regenaration method, the NTP technology has significant superiority in practical application.(3) The comparative study of DPF regeneration assisted by oxygen-fed and air-fed NTP technology was conducted. The in-depth research had been focused on four aspects: the best initial temperature of DPF, PM decomposition quality, the decomposition effect of NTP active substances and the energy consumption of DPF regeneration. Moreover, the chemical reaction mechanism of the DPF regeneration based on air-fed NTP technology had been further perfected. The results showed that when the initial temperatures of test are lower than 180?, the DPF regeneration efficiency of oxygen source is higher than that of air source; when the initial temperature of test are higher than 180?, the situation is opposite. Since the cost of oxygen is relatively higher,air source has great advantage in the aspect of economy. When the temperature is changed from room temperature to 300?, both O3 and NO2 in NTP have the trend of self-decomposition, and the decomposition rate increases as the temperature rises. NO and N2 are proved to be the reduction product of the redox reduction of NO2 and PM, not exclude the existence of N2O. The energy consumption of NTP injection system is less than 3% of the engine power, which provides a powerful experimental basisthe feasibility for NTP technology.(4) Experimentation was conducted to analyze the DPF trap under four different engine loads with particle size analysis and thennogravimetric analysis introduced to PM samples. DPF regeneration was achieved utilizing the oxygen-fed NTP injection system.The decomposition quality of PM was calculated to measure the regeneration effect of DPF. Based on particle size analysis and oxidation characteristics analysis, the influence of PM itself nature difference on PM oxidation decomposition and DPF regeneration was investigated. Results indicated that accompanying the increase of engine load, the concentration of nucleation mode particles decrease while that of accumulation mode particles and the total concentration number increase at first and then decrease. H2O and SOF in PM demonstrate a downward trend while DS exhibits an upward trend in mass fraction with the increasing load. As the apparent activation energy of SOF is far lower than that of DS, SOF is more likely to be oxidized. The higher content of SOF helps promote the oxidation synergies of SOF and DS, resulting the decreasing of the apparent activation energy of DS component. Size distribution and ingredients of PM trapped by DPF under different loads vary, thus the intensity of reaction between PM and radical gases produced by NTP is different. The more the total number of PM and the content of SOF, the more likely PM are to break down. Mass of PM removal maximizes at 50%load while DPF regeneration effect is the most remarkable.(5) The quality of PM deposited DPF was changed and the time of PM sampling test was 120min, 240min, 360min, respectively. With oxygen as gas source, the regeneration experiment of three DPFs with different quality of PM deposited was carried out under the same regeneration condition. The initial temperature of DPF was 80?. The changing rule of internal temperature in the process of DPF regeneration was studied, and on this basis, the synergetic effects of PM loading and the internal temperature on DPF different regeneration stages were analysed. The results show that the temperature of each measuring point inside DPF increases at first and then decreases and the heating rate of temperatures show a trend of decline from the upstream to the downstream and from the axis to the periphery of DPF, respectively. Temperature peak of measuring points emerged from upstream to downstream in DPF, and time interval was obvious. The greater the quality of PM, the higher the peak value of measuring point temperature is. In the initial stage of DPF regeneration, the PM loading is the main influence factor of PM decomposition while along with the advancement of regenerative phase, the PM decomposition is mainly affected by temperature. High temperature has the ability to promote the oxidation decomposition reaction of PM, but on the other hand,it strengthens O3 decomposition reaction.For this reason, the excess temperature is being bottlenecks in the decomposition of PM. The utilization ratio of NTP active material is enhanced with the moderate amount of PM loading, not too little or too much.(6) DPF regeneration was achieved utilizing the oxygen-fed NTP injection system.Three control methods of oxygen flow were desiened: the oxygen flow of method 1 remained the same at 5 L/min; the oxygen flow of method 2 increased from 3L/min to 7L/min; the oxygen flow of method 3 decreased from 7L/min to 3L/min. The total amount of oxygen of three methods are the same. On the basis of O3 formation rule, the influence factors of CO and CO2 were analysed and the effect of the source gas control strategy on PM oxidation decomposition and DPF regeneration was explored. The results revealed that the mass flow rate of O3 increased remarkably with the increase of oxygen flow, which promoted the oxidation of PM. The mass of Ci, C2 and C12 have the same tendency: method 3 > method 2 > method 1. The quality of PM broken down of method 3 is 3.1 g, which is the maximum of the three control methods.The method of variable flow control has better regeneration effect of DPF than that of constant flow control. The remarkable effect of DPF regeneration can be got by making oxygen flow decrease with the passage of experimental time. It can been concluded that the optimization of gas source control strategy is an effective way to improve the efficiency of the NTP regeneration technology. |
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