| Ethanol and biodiesel, as alternative fuels of diesel engine, have been widely concerned and used. The composition and molecular structure of ethanol, biodiesel are different from diesel, leading the difference of physical and chemical properties which influence the combustion process and combustion products. In this paper, the combustion process and particulate matter(PM) of oxygenated fuel and fossil fuel have been studied. According to the characteristics of component and molecularstructure of ethanol, biodiesel, diesel, based on the theory of molecular hybrid orbital, similarity and intermiscibility, and solvation, the mechanism that biodiesel can improve the mutual solubility of ethanol and diesel was explained. Besides, the corrosion mechanism of rubber fuel tube of diesel engine in ethanol and biodiesel was explored from the perspective of polar force. Synchrotron radiation, premix burner and diesel engine in bench test were adopted in the study of combustion process. Changing laws of burning rate, temperature, combustion products and indicator diagram under different combustion mode were studied. According to different combustion modes, the simulation model was established to research free radical variation characteristic, producing characteristic of intermediate products and migration path of oxygen in combustion progress. The molecular structure of oxygenated fuels and formation mechanism combustion products were studied. SEM (scanning electron microscope) and synchrotron radiation small angle X-ray scattering were used to characterize the geometry size and PM micro-region structure of ethanol and biodiesel. The main conclusions are following:Solubility in diesel of ethanol with different proportion, at different temperature was tested. Biodiesel was used as cosolvent of ethanol and diesel, and the cosolvent mechanism was studied. Results showed that biodiesel molecule combined diesel molecule by Vad der Waals force on one hand, and combined ethanol molecule polar force on the other hand. Therefore, biodiesel molecule played a role as bidirectional affinity interaction to improve the solubility of ethanol in diesel.The corrosion and swelling performance of nitrile rubber which is the main material of diesel engine fuel injection system was studied by soak and SEM. Parameters like mass, volume and hardness before and after soaking in ethanol, biodiesel for672hours were studied. Inner surface of the rubber tube soaked in ethanol, biodiesel and diesel was photographed, and the action process of polar force in rubber was analyzed. Results showed that oxygenated fuels corroded and swelled nitrile rubber. Ethanol which had the strongest polar force corroded nitrile rubber most. Molecule polar force of oxygenated fuel was the reason that corroded rubber tube.The combustion process of ethanol, biodiesel, diesel under different pressure, different equivalence ratio and different blending ratio was studied, using the method of synchrotron radiation, normal pressure and temperature premixed and diesel engine bench test. The influence of ethanol, biodiesel in blends on combustion process and products was analyzed. Results showed that oil and gas mixing mode, equivalent ratio influenced the burned rate. Ethanol can improve the burning rate of ethanol/diesel. The ethanol premixed combustion temperature of outer flame, intermediate flame, and inner flame were respectively1.8,1.5and1.96times higher than diffusion combustion. Ethanol, biodiesel used in diesel engine can significantly reduce PM, but did influence NOX too much.Using laminar premixed flame reactor model, from the perspective of chemical reaction kinetics, the main reaction paths, free radicals and intermediate products producing characteristic of diesel, ethanol and biodiesel were studied by means of reaction rate and sensitivity analysis.The paper focused on the pathways of oxygen in oxygenated fuels to analyze the cracking paths of carbomethoxy in the combustion process of biodiesel. Results showed that the mole fraction of olefins was larger than kindred alkane and alkyne of combustion products. The point that ethanol generated into H2O, CO after dehydrogenation, cracking was proposed. The other point was also proposed that with the attack of free radicals, the biodiesel macromolecule would lose hydrogenatom at different positions and turn into different kinds of carbomethoxy, then lose C2H4further, turning into cracking products with odd and even carbon. And mole fraction of carbomethoxy with odd carbon was larger than carbomethoxy with even carbon.HCCI combustion of blends with different oxygen content was investigated. The variation law of temperature and free radicals were discussed. Results showed that free radicals were generated and consumed quickly near TDC, lots of heat was released and the temperature increased rapidly. With the increase of oxygenated fuel proportion, the in-cylinder temperature decreased, and the phase of peak mole fraction of radicals postponed.DME is the isomer of ethanol. The premixed combustion of ethanol and DME were studied to determine the reaction rate in the combustion process, and the key formation reaction of olefins and alkyne. According to the molecule structure characteristics of ethanol and DME, it was found that ethanol can be directly cracked into C2H4, while DME would firstly be dehydrogenized, then C-O bonds broken, and eventually polymerized into C2H4. A detail explanation about the influence caused by ethanol and DME on the, sensitivity of C2H4formation was given.After analyzing biodiesel cracking paths and formation process of aromatic hydrocarbon benzene, combining the biodiesel molecule structure, the influencing factors of formation process of biodiesel was proposed from the perspective of chemical kinetics. The influence law of oxygen content, saturation and carbon chain length of biodiesel on benzene formation were discussed.Examples of combustion particulate matter of ethanol/biodiesel with different proportional under normal pressure and temperature were collected. The geometry size and micro-region structure of combustion particulate matter of oxygenated fuels were studied from the perspective of electron density properties, by the method of SEM and synchrotron radiation small angle X-ray scattering, and got the variation law of particulate matter. Results showed that with the increase of oxygenated fuel proportion, the size of combustion particulate matter decreased, the gyration radius and the mean radius reduced and the average thickness of the interface lowered. The Porod curve of particulate matter was negative deflected, and the interface between particulate matter and dispersion medium was fuzzy, indicating that interface layers were existent. |
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