| Particle produced by incomplete combustion is one of the main air pollutants in China. Particles emitted by cars have become the major source of inhalable particles and have serious harm to human health. Internal combustion engine fueled with oxygenated fuels can not only partially replace oil but also reduce the emissions. The soot precursors formation mechanism, intermediate species formation process, and particle state characteristics of ethanol, dimethyl ether (DME), dimethyl carbonate (DMC), and biodiesel were studied. Methods of molecular beam mass spectrometry with tunable synchrotron photoionization, thermogravimetric analysis, scanning electron microscope, transmission electron microscopy, small angle X-ray scattering, bench test, and numerical simulation were used in this dissertation. The mole fraction profiles of major and intermediate flame species were measured and analyzed. The numerical simulation of important soot precursors, such as benzene, naphthalene, phenanthrene, and pyrene, were carried out from the perspective of chemical reaction kinetics. The effects of molecular structure and oxygen content of oxygenated fuels on the oxidation properties, microstructures, size distribution, and fractal dimension of particles were discussed. The measurement of particle number was proposed.The formation paths of benzene and the growth mechanism of polycyclic aromatic hydrocarbon (PAHs) were summarized. According to the combustion characteristics of hydrocarbon fuels, the chemical kinetics model of ethanol, DME, DMC, and ethanol/n-heptane which containing the PAHs formation process were established. The shock tube, premixed flame, and internal combustion engine reaction models were adopted, and both the rate-of-production and sensitivity analysis methods were used to simulate the formation process of PAHs. The results showed that benzene was mainly formed by polymerization of propargyl. Multiple benzene rings were formed by hydrogen abstraction and acetylene addition (HACA) reaction. H and OH radicals consumed most of the PAHs. In the reactions with the third body "M", ethanol can inhibit the PAHs formation, DME had little effect on the PAHs formation, and DMC can promote the PAHs formation. During the combustion process of ethanol/n-heptane, PAHs mainly formed during the phase of rapid increase in cylinder temperature. The decomposition reactions of n-heptane and n-propyl group can inhibit the formation of phenanthrene and pyrene. The formation rate of PAHs and the amount of PAHs during one cycle were reduced by increasing the ethanol blending ratio.Major and intermediate species of ethanol/n-heptane premixed flame, such as acetylene, ethylene, propinyl, formaldehyde, and acetaldehyde, were identified using molecular beam mass spectrometry with tunable synchrotron photoionization. The effects of ethanol blending ratio and equivalence ratio on the mole fraction profiles of major and intermediate flame species were studied. Study results showed that the mole fractions of H2and CO increased with the increase of equivalence ratio. With the increase of ethanol blending ratio, the mole fractions of formaldehyde and ketene decreased while the mole fraction of acetaldehyde increased. By analyzing the migration pathways of oxygen from ethanol, it was found that part of the oxygen formed the final combustion product H2O and part of the oxygen formed the formaldehyde and acetaldehyde. According to the simulation results, the oxygen from ethanol led to an easier production of oxygenated intermediates, compared with oxygen from the oxidizer, which can reduce the mole fractions of benzene, acetylene, ethylene, and propinyl effectively.Particles produced by ethanol/diesel, DMC/diesel, and biodiesel/diesel combustion process were collected. The thermo gravimetric (TG) and derivative thermo gravimetric (DTG) curves of those particles were measured using thermo gravimetric analysis (TGA). The weight loss of particles mainly included three stages which were water evaporation, precipitation and combustion of volatile organic compounds, and combustion of soot. The initial weight loss temperature, precipitation temperature, ignition temperature, maximum weight loss rate and corresponding temperature, and activation energy were applied to evaluate the oxidation characteristics of particles. Study results showed that with the increase of oxygen content, the percentage of soot decreased and that of volatile organic compounds increased. With the increase of oxygenated fuels blending ratio, the ignition temperature of volatile organic compounds dropped and that of soot rose, the maximum weight loss rate of soot increased, and the activation energy of particles decreased. According to the molecular structure characteristics of ethanol, DMC and biodiesel, the oxygen-containing groups played a role in promoting the break of chemical bond and that resulted in the decrease of the percentage of elemental carbon. The oxygen-containing groups adsorbed in the surface of particles were increased by shortening the carbon chain length of oxygenated fuels. And the oxidization of volatile organic compounds was promoted with the increase of oxygen-containing groups.The indicator diagram of ethanol/diesel with different ethanol ratios was performed on YZ4DB3diesel engine and the combustion process was studied. The relationship between oxidation characteristics and combustion process was analyzed. The results showed that with the increase of ethanol blending ratio, ignition delay period extended and combustion duration shortened, the peak heat release rate of diffusion combustion increased at light load, and the peak heat release rate of premixed combustion increased at heavy load. After adding oxygenated fuels, the combustion process and the formation process of flame species were changed, the characteristic of particles changed as well. The size of particles decreased, the percentage of organic matter increased, the appearance of disordered structure of elementary particle decreased, the reunion level of particles increased, and the activation energy decreased.The particle morphology of ethanol/diesel, DMC/diesel and biodiesel/diesel were studied using scanning electron microscope, transmission electron microscopy, and small angle X-ray scattering. The disordered and shell-core structures of elementary particle were analyzed. The effects of molecular structure and oxygen content of oxygenated fuels on the size distribution, interracial thickness, and fractal dimension of elementary particle were discussed. The measurement of particle number was proposed according to the number of inflection point and arc length. The size distribution of elementary particle followed the Gaussian distribution and the size was between14nm and45nm. The average fringe separation distance was between0.32nm and0.44nm. The fringe length was about1nm and the tortuosity was between0.8and2.0. With the increase of ethanol and DMC blending ratio, the average fringe separation distance of elementary particle increased, the fringe length decreased, and the average tortuosity increased. With the increase of biodiesel blending ratio, it was more difficult for the elementary particle to be oxidized. There was a linear relationship between turning radius, interracial thickness and the oxygen content. After increasing the oxygen content by1%, the turning radius decreased by about2.3%and the interracial thickness increased by2%. The surface and mass fractal dimension surface roughness, irregularity, and aggregation level of particles formed by oxygenated fuels combustion process increased. |
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