Theory Analysis And Experimental Research On The Formation Mechanism Of Unregulated Emissions Produced By Biodiesel Fuel

As the alternative fuel of diesel, biodiesel has been applied widely. In the process of burning biodiesel, apart from the regulated emissions like NOx,CO,HC,PM, the diesel engine also produces unregulated emissions, such as carbonyl, mono-aromatic hydrocarbons, polycyclic aromatic hydrocarbons and metal particles and so on. These unregulated emissions can be further oxidized and polymerized into other substances. The paper centers around the aspects of measuring method of unregulated emissions, the emission characteristics, forming process and emission control, etc., adopts the methods of chromatographic analysis, scanning electron microscopy, bench test and numerical simulation to measure the emission characteristics of unregulated emissions, and at the same time, carries out the numerical simulation of the generated factors and emission control for carbonyl and aromatic hydrocarbons from the view of fuel chemical reaction kinetics.According to the physical and chemical characteristics of the carbonyl and aromatic hydrocarbons, this paper chooses appropriate sampling method, sample pretreatment method and Sample separation and determination method, adopts derivatization method and high performance liquid chromatography(HPLC) method to measure carbonyl, uses activated carbon adsorption tube and Gas chromatography/mass spectrometry to Qualitatively and quantitatively analyze aromatic hydrocarbons, it proves that the Precision indexes of Sampling efficiency, Elution efficiency, Detection limit, Relative standard deviation (RSD) and recovery rate can meet the measurement requirements, so that can realize the rapid and accurate measurement of carbonyl and aromatic hydrocarbons of diesel engine. In a single-cylinder 186 diesel engine, this paper adopts biodiesel and blend fuel to carry out Diesel engine bench test. The emission rule of carbonyl and aromatic hydrocarbons in different proportion and different condition was investigated. The effects of fuel components, physical and chemistry properties, and Combustion process on the formation of Carbonyl were analyzed, so was the formation process of aromatic hydrocarbons. The monocyclic aromatics emissions of diesel engine include Benzene, Toluene, Ethyl benzene and Xylene. The concentration of benzene reduced with the increase of biodiesel blending ratio, Compared with diesel fuel, PAH emissions of biodiesel decreased by 31%; the concentration of particulate tetracyclic PAHs decreased by 35.4%; and the gas tetracyclic PAHs decreased by 55.4%, which greatly reduce the hazards of high ring number PAHs.Collecting the lubricating oil samples of different running time, adopting Scanning electron microscope (SEM) and X-ray spectroscopy, the changes of lubricant oil absorbance was measured, the morphology and particle size distribution characteristics of the combustion particles of biodiesel/diesel blend fuel were also studied, the type and quantity of metal elements were investigated, and the source of metal particle and the influence on the quality of total particles were discussed. With the prolonged of engine running time, the particle diameter increased and adhesion enhanced, and the type and quality of metal elements in the lubricating oil showed an upward trend. The combustion particles diameter of biodiesel was near normal distribution. The agglomeration of particles strengthened and arranged more closely when there was a higher blending ratio, and the average particle diameter decreased with the increase of blending ratio,After analyzing the formation process of Alkane, Alkene, aromatic hydrocarbons and other small molecule fuel aromatic hydrocarbon, this paper identifies the critical reaction of Carbonyl and aromatic hydrocarbon in the process of biodiesel combustion. At the same time, combining the characteristics of biodiesel and diesel molecular structure, this paper reconstructs the chemical reaction kinetics calculation model of biodiesel. Using the relevant experimental data to verify the effectiveness of the model, the reconstructed mechanism can reproduce the combustion chemical reaction process of biodiesel, which can better reproduce the concentration of overall reaction and predict reactants.According to the characteristics of the combustion process of diesel engine, adopting Shock tube and laminar premixed flame reactor model, using the reaction rate and the sensitivity analysis method in terms of chemical reaction kinetics, this paper studies the factors in the formation process of carbonyl and aromatic hydrocarbon pollutants, puts forward the methods of air pretreatment and fuel pretreatment to reduce Carbonyl pollutants, summarizes the formation approach of aromatic hydrocarbon in the process of biodiesel and diesel combustion. Adopting hydrogen, carbon monoxide and methane to carry out fuel pretreatment, which helps the oxidative decomposition of formaldehyde; The first benzene ring of biodiesel is formed by C3H3 polymerization and addition reaction of C4H5 and acetylene, the second benzene ring of biodiesel is formed by addition reaction of dehydrogenation and acetylene; The first benzene ring of diesel is formed by C3H3 polymerization, the second benzene ring of diesel is formed by the reactions of C4 and benzene, dehydrogenation and acetylene.