| Developing clean alternative fuels is an effective solution all over the world to confront with the increasing energy crisis and environment pollution. Because of its characteristics in cleaness, renewability, good combustion and emissions, biodiesel has won more and more attention. In this paper, the optimal preparation of soybean oil biodiesel was studied, and the importance of various factors, and their interaction mechanism was analyzed. The physical and chemical characteristics of biodiesel and its spray characteristics were studied according to the fuel design concept. Meanwhile, the combustion and emission characteristics of the biodiesel-diesel blends from an internal combustion engine was also studied. The research content and related conclusions are as follows:1. The optimum Production Procedure Parameter of Biodiesel was studied. The soybean oil was selected as the raw material of the biodiesel. According to the U12 (46) uniform design, the experimental arrangements were determined. Four factors like of methanol, catalyst, reaction temperature and reaction time were targets for the study. With the help of BP neural network, constrained optimization, and wavelet analysis, the optimum Production Procedure Parameter of soybean oil biodiesel was obtained. The working mechanism of the factors was analyzed, according to the function from the idea of "Wavelet Denoising first-and then Regression Analysis". The results showed that the four factors, mentioned above, have a significant impact on the yield of biodiesel, and there existed confrontation between the methanol and catalyst, the methanol and reaction temperature, catalyst and reaction time. However, there existed synergistic effect between the methanol and reaction time, reaction temperature and reaction time.2. The physical properties of biodiesel affect combustion and emissions characteristics. Based on the fuel design concepts, diesel-biodiesel fuel blended in different proportions was selected, and the effects of blended fuel on physical and chemical properties were investigated. The results showed that there were linear relationships between lots of the fuel properties and biodiesel percentage in blends. The viscosity of biodiesel was lager than that of diesel, and the viscosity of the biodiesel-diesel blends increased linearly with the content of the biodiesel increasing, varied according to the hyperbolic function, which was similar to that of the diesel. The surface tension of blends increased linearly with the content of the biodiesel increasing, decreased as the temperature increasing. Lubrication properties of biodiesel were significantly better than diesel, but the residual methanol, glycerin and other substances in biodiesel would decrease its ultimate bearing capacity. Biodiesel had swelling effect on nitrile rubber, and corroding effect on copper pipe and copper alloy.3. Spray performance of biodiesel has a significant influence on the combustion and emission characteristics. Compared with diesel, under the same injection pressure, biodiesel has higher mass flow due to its high density. Moreover, its higher viscosity makes cavitation more difficult which brings lower cavitation strength than that of diesel, causing poor atomization. Since the density, viscosity and surface tension were greater than diesel, biodiesel has finer elongating spray and longer spray penetration distance, while diesel spray is wider and its penetration distance is shorter. On the macroscopic of spray performance, the difference between diesel and biodiesel were obvious. With the content of the biodiesel in the blends increasing, the spray penetration increased, and the spray angle decreased under the same back pressure. Under high injection pressure, with the rail pressure increasing, spray angle of each blends showed little difference.4. After researching on preparation and physical property of biodiesel as well as its spray features, this thesis focused on combustion and emission of biodiesel and its blends in internal combustion engines.(1) By using DEWE-800 Engine Multi-channel Combustion Analyzer, the instantaneous in-cylinder combustion pressure and phase in the 490B diesel engine was measured, as well as heat rule was calculated. The results showed that as the content of the biodiesel in the blends increased, both the pressure peak of in-cylinder combustion and rising rate of pressure decreased. Compared with the diesel, the phase of the in-cylinder combustion pressure peak advanced 1-2℃A when the engine burn the blends’, and the peak of instantaneous heat release rate decreases with its phase advanced 2-3℃A. Under low loads, the combustion starting point of the blends was later than that of the diesel 6-8℃A, and the combustion end point was later than that of the diesel 29-38℃A, and the combustion duration was longer than that of the diesel 21-32℃A. Under high loads, the combustion starting point of the blended fuel was slightly sooner than that of the diesel 0.3-0.9℃A, and the combustion end point was later than that of the diesel about 5-8℃A, and the combustion duration was longer than that of the diesel about 6-8℃A. Under low loads, the combustion starting point of B100 approached to that of the diesel,and the combustion end point was sooner than that of the diesel 23℃A, and the combustion duration was shorter than that of the diesel about 22℃A. Under high loads, the combustion starting point of B100 approached to that of the diesel, and the combustion end point was later than that of the diesel about 0.7℃A, and the combustion duration was longer than that of the diesel about 1.6℃A.(2) The performance of the internal combustion engine was evaluated based on parameters like torque, power, fuel consumption rate and so on from a 490B diesel engine, which were measured by Y280S dynamometer. The results showed that the effective power and torque of the biodiesel-diesel blends were entirely lower than that of the diesel (B20 was relatively higher). The fuel consumption and its consumption rate of the biodiesel-diesel blends were higher than that of the diesel, meanwhile, and the difference between them became larger as the engine speed increased. The effective thermal efficiency of the biodiesel-diesel blends was significantly lower than that of the diesel (it was reversed under the full-load characteristics test). The exhaust gas temperature of the biodiesel-diesel blends was lower than that of the diesel, and the difference between them became larger as the engine speed increased.(3) The regulated and unregulated emissions of 490B diesel engine were measured by AVL SESAM-FTIR Multi-component Analyzer and NHT-6 Impervious Photometer. The results showed that the emission of HCHO, MECHO and C4H6 of B100 were relatively higher than that of diesel. Under high loads, the emission of HCOOH was also relatively higher. The emission of AHC, NO, NOx, CO2, SO2, HNCO, CH4 and soot of B100 were relatively lower. Compared with the diesel, the biodiesel blended fuel’s various types of HC emissions were lower, the reduction of B20, B50 and B75 were especially obvious. However, B100’s various types of HC emission were higher than that of the diesel under high loads and speed. As the content of biodiesel in the blends increased, the emission of NO, NOx, CO2, SO2, soot, CH4, C3H8, MECHO, C2H2, HCN and AHC of the blends decreased. Among the biodiesel blended fuels, the emission of MECHO, HCN, HCOOH, HNCO and various types of HC of the B20 were lowest. |
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