Study On The Emission Performance Of Diesel Engine Affected By Biodiesel Quality

Biodiesel is a renewable energy, the application of biodiesel in diesel engine has been developed in our country. Biodiesel has a wide range of raw materials, and the preparation technology and methods have great influence on the quality of biodiesel. Especially in the case of high temperature, during the long-term storage of biodiesel, the composition and physicochemical properties of biodiesel will be changed, which will affect the normal use of biodiesel, and have a certain influence on the performance of the diesel engine.This paper analyzes the change of biodiesel quality. Four research contents,such as oxidation, cetane ratio, the proportion of alcohol and the proportion of ester of biodiesel were selected to research the effects of oil quality on physicochemical properties based on theory and experiments.The influence of quality change of biodiesel on the atomization of biodiesel,the combustion and emission of diesel engine was discussed.Based on the oxidation process of long term storage of biodiesel, the biodiesel was prepared in 720 and 2160 hours, and the effects of oxidation time on the physical and chemical indexes of biodiesel were analyzed. According to the different sources of biodiesel, the biodiesel of different cetane was formulated, the oil density, viscosity, surface tension,surface functional groups and normal temperature and pressure ignition temperature and ignition delay time etc of biodiesel were measured, and the physical and chemical indexes and ignition performance of biodiesel in ambient temperature was stydied. The results showed that, with the increase of oxidation time, the density and viscosity of biodiesel wereincreased, the double bond absorption peak in the infrared spectra of the oxidation of 720 and 2160 h were decreased, the double bond of biodiesel was broken, generating acid and aldehyde. Under normal temperature and pressure, the ignition temperature of 720 and 2160 h biodiesel was increased by 7℃ and 13℃, respectively. Ignition delay time was increased by 0.02 s and 0.07 s. There was little effect on the density,viscosity and surface functional groups of oil after adding cetane. Adding0.2% and 0.4% cetane improver, the ignition temperature was decreased by 10℃ and 18℃, the ignition delay time is increased 0.03 s and 0.10 s.According to the process of biodiesel production, the ester exchange reaction and separation of alcohol were not complete. Biodiesel with different the proportion of alcohol and the proportion of ester was prepared, and the parameters of biodiesel under normal temperature,density, viscosity, surface functional groups, ignition temperature etc were measured to analyze the effects of different preparation processes on the physical and chemical indexes and ignition performance of biodiesel.With the increase of the proportion of ethanol in biodiesel, the density and viscosity were decreased. In the analysis of infrared spectrum, with the increasing of the proportion of alcohol, the intensity of absorption peak of-OH was increased. Under normal temperature and pressure, the proportion of ethanol increased to 5% and 10%, the ignition temperature of biodiesel was increased by 3℃ and 8℃, and the ignition delay time was increased by 0.02 s and 0.04 s. With the increase of the proportion of glyceride in biodiesel, density and viscosity in biodiesel were increased,there is little change in the infrared spectrum of biodiesel, and no obvious difference between the functional groups of oil and fatty acid methyl esters with the proportion of glyceride in biodiesel. When the proportionof glyceride in biodiesel was increased by 3% and 6%, ignition temperature was increased by 1℃ and 2℃, and the ignition delay time was increased by 0.01 s and 0.03 s.The volatile pyrolysis and oxidation combustion characteristics of the biodiesel were analyzed by thermogravimetric test. The results showed that : Under a nitrogen atmosphere, When the biodiesel is oxidized with 720 h and 2160 h, the mass reduction curve was shifted to a higher temperature, the initial weight loss temperature was 204℃and207℃,respectively.With the increase of time, biodiesel volatile becomes deteriorated at high temperature. After adding cetane number of biodiesel,the mass reduction curve had little change, and the volatility of biodiesel had no obvious change. The mass reduction curve of biodiesel/ethanol was blended, there were two weight loss rate peaks on DTG curve. With the increase of the proportion of glyceride in biodiesel, the volatile of biodiesel deteriorated.Under the oxygen atmosphere, When the biodiesel was oxidized with 720 h and 2160 h,the initial weight loss temperature was increased. The weight loss rate was decreased and the weight loss bandwidth was increased.Weight loss process gentle and dispersion.When the cetane number of biodiesel was increased, oxidation initiation temperature was lowered, the temperature of the maximum weight loss rate was decreased, the width at half maximum was reduced,and weight loss process was severe and concentration. With the increase of the proportion of alcohol in biodiesel, there are two distinct weight loss curve process, biodiesel/ethanol blended fuel oxidation rate was improved. With the increase of glyceride in biodiesel, the weight loss rate of biodiesel was decreased, and the weight loss was shifted to high temperature zone.On the diesel engine, the effects of the different quality biodiesel onthe diesel engine emissions and fuel consumption were investigated. The results showed that:(1) With the increase of oxidation time 、 the proportion of alcohol and glyceride,fuel consumption was increased.When the cetane number of biodiesel was improved, fuel consumption was decreased.(2)With the increase of the degree of oxidation of biodiesel, the HC, CO and soot emissions were increased,and the NO_X emission was decreased;(3)With the increase of the proportion of ethanol, the HC emission was increased, while CO、NO_X and soot emissions were decreased simultaneously;(4) Adding cetane of biodiesel, the HC, CO and NO_X emissions were all reduced. When cetane improvers addition ratio was increased, HC, CO and NO_X emissions were increased at a little, while little change on soot emission.(5)With the increase of the proportion of glyceride in biodiesel, the HC, CO and soot emissions of diesel engine were increased, while the NO_X emission was decreased.