Research On Optimization Of Chlorella Biodiesel Fuel Combustion Reaction Kinetics Model And Its Combustion Characteristics

Biodiesel is an excellent renewable alternative fuel with no sulfur and relatively high oxygen content.Chlorella has the advantages of high oil content,short growth cycle and no occupation of cultivated land.It is of great significance to develop and promote the biodiesel made from chlorella which can make up for the shortage of traditional biodiesel raw material supply and reduce our dependence on foreign crude oil.The researches mainly focus on the cultivation and screening of algae species,the preparation process and characteristics analysis of Chlorella Biodiesel Fuel?CBF?.There are few studies on the CBF combustion characteristics.This thesis focused on the CBF combustion reaction kinetics model and its combustion characteristics.The CBF model was optimized which has been constructed and simplified by the research group.The CBF combustion reaction path and the influence of different boundary conditions on CBF combustion characteristics were analyzed in HCCI combustion mode.A bench test was carried out with a diesel engine burning CBF,providing a certain theoretical basis for the promotion and application of CBF.?1?The optimization of the CBF model was carried out to improve the prediction performance of simplified CBF model.Six different disturbances?referred to as V1,V2,...,V6?were applied to pre-exponential factor of critical elementary reaction.Based on the perturbation model,the ignition delays for different equivalence ratios and inlet pressures were calculated and compared with the results of detailed model,simplified model and experiment.The results showed that there was still a certain error between the predicted value under different perturbation,the experimental value and the predicted value of detailed model in low-temperature stage?800K?T?1000K?.However,the prediction accuracy of the model under the perturbation of V3 and V4 were still better than that of the simplified model.The prediction performance of the mode were good in high-temperature stage?1000K<T?1300K?.The predictive performance of the model under V4perturbation was better.When the equivalence ratio was 0.5 and the inlet pressure was 20 atm,the error was only 1.724%.In six different disturbances,the overall prediction accuracy under V4perturbation was better than simplified model and close to the detailed model.?2?Based on the optimized CBF model,Sensitivity analysis?SA?and rate of production?ROP?were used to determine the key elementary reactions and main intermediates,ascertain the CBF combustion reaction path in low and high temperature stage.The results showed that under low temperature stage,CBF reacted with OH,HO₂ and H to form CC8H17,AC8H17 and dealkylation groups such as MD2J,MD4J,MD5J,MD8J.These products were then oxidized,cracked,dehydrogenated and isomerized and eventually produced CO₂;Under high temperature stage,CBF produced C₇H₁₅-1 through the cleavage reaction and then C₇H₁₅-1 would continue to cleave to C₂H₄ and NC₃H₇.The subsequent reactions were mainly concentrated on small molecules,such as C₂H₄,NC₃H₇ and C₂H₂.These small molecules would generate CH₂O through the reactions such as cracking dehydrogenation and oxidation,then finally converted to CO₂.?3?Under HCCI combustion mode,the influence of different boundary conditions on the combustion characteristics of CBF has been studied.The results showed that the peak of pressure,temperature and HO₂,OH molar concentration in cylinder increased with the increase of inlet air temperature and compression ratio and decreased with the increase of engine speed.However,the peak concentration of CO and CO₂ presented little variation.The peak time of temperature,pressure and intermediate product molar concentration in cylinder was advanced with the increase of inlet temperature and compression ratio,and delayed with the increase of speed.MD and C₈H₁₈would produce a lot of CO and HO₂ when they were rapidly consumed.With the consumption of CO and HO₂,a lot of CO₂ and OH would be generated.The cylinder temperature and pressure increased with the increase of inlet air temperature and compression ratio,speeding up the elementary reaction and promoting the fuel combustion.The cylinder temperature decreased with the increase of speed which does not meet the requirements for combustion and the elementary reaction could not proceed.?4?Bench test of a 186FA diesel engine fueled with CBF/diesel blends was carried out,the influence of B0,B3,B5?the proportion of CBF was 0,3%and 5%respectively?on the economic,dynamic,combustion and emission characteristics of diesel engine was analyzed.The results showed that compared to the pure diesel,as the proportion of CBF increased,the fuel consumption rate and energy consumption rate increased slightly,while the power and torque changed little.The peak pressures and heat release rates in the cylinders decreased and the maximum drop was respectively 3.3%and 15.4%.The peak value of the pressure increase rate increased with the maximum increase of 13.6%.The peak time was advanced 1²°CA,the delay period was advanced 0.5¹°CA,and the duration of combustion was extended 1²°CA.NOx emissions increased with the maximum increase of 9.6%,HC CO and soot emissions were reduced with the largest decrease of respective 14.3%,12%and 31.6%.This was mainly caused by the CBF different fuel characteristics of higher cetane,density,viscosity and lower calorific value.