| Because of its cleaness and renewability, biodiesel has a great potential as the alternative of diesel fuel to confront with the increasing energy crisis and environment pollution. In this study, the fuel design concept was used to improve the elastomer compatibility, combustion and emission characteristics. In order to reduce both NOx and smoke emission of diesel engine, the combined method of fuel design concept with low temperature combustion mode was applied in this study.Effects of ethanol percentage in ethanol-biodiesel blends on the physical and chemical properties were investigated. The results show that there were linear relationships between lots of fuel properties and the ethanol percentage in blends. Different kinds of methyl esters and ethyl esters were also tested, in order to illuminate the effects of molecular structure on the physical and chemical properties of biodiesel, such as carbon chain length, number of double bonds and alcohol type. The nitrile rubbers were immersed in different kinds of fuels. After 168 hours, the properties, such as mass weight, volume, hardness, tensile strength, elongation and tearing strength, were measured to investigate the effects of biodiesel, ethanol-biodiesel blend and ester's molecular structure on the elastomer compatibility. Spray characteristics of diesel, biodiesel and ethanol-biodiesel blend were studied via high speed digital camera. Based on the elastomer compatibility and spray test results, it was found that the addition of ethanol in blends could not only slow down the change of elastomer, especially the change of mass weight, volume and hardness, but also improve the atomization.According to the fuel design concept, the combustion, regulated emission, unregulated emission and particulate emission characteristics were studied, when the four cylinders diesel engine was fueled with biodiesel and biodiesel blended with methanol and ethanol. It was found that with increase of methanol in methanol-biodiesel blends, NOx and PM emissions could be reduced, while formaldehyde, acetaldehyde and 1,3-butadine could be enhanced. Moreover, comparison on effects of methanol against ethanol has been conducted.The effect of intake charge dilution with carbon dioxide on the combustion and emission characteristics of a 4-cylinder diesel engine fueled with EuroV diesel fuel, biodiesel, biodiesel-diesel blends, methanol-biodiesel and ethanol-biodiesel blends were investigated. The results show that charge dilution combined with fuel design could reduce NOx emission of biodiesel, and maintain the PM emission at the releatively lower level.The low temperature combustion mode of biodiesel with high EGR rate was investigated in this study, in order to reduce NOx and smoke emission simultaneously. Influence of methanol-biodiesel blends on the combustion and emission characteristics were studied in low temperature combustion mode. It was found that the NOx and smoke could be reduced simutanously at releativley lower EGR rate when the engine is fueled with methanol-biodiesel blends. Moreover, the effects of combustion phase on the emission characteristics were studied in LTC mode and HTC mode. Meanwhile, a new trade-off relationship was formed in LTC mode. The principles of fuel design concept for LTC optimization were generalized from the experimental results of this study.Different kinds of esters were used in diesel engine, in order to illustrate the relationship between molecular structure (carbon chain length, unsaturation and alcohol type) and emissions. The esters are methyl laurate (C12:0), methyl palmitate (C16:0), methyl stearate (C18:0), methyl oleate (C18:1M) and ethyl oleate (C18:1E). In the end, a comparsion of NOx, smoke opacity and particulate composition between rapeseed oil methyl ester and palm oil methyl ester was made to explain the variances between them in molecular structure. The results show that the ester with shorter carbon chain length and double bond in molecular structure could well restrain the emissions of HC, CO and smoke. While, the ester with longer carbon chain length and without double bond could produce releativley lower NOx emission. |
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