| In order to decrease the production cost of butanol,acetone-butanol-ethanol(ABE)as the intermediate product of butanol production is considered to be a promising renewable fuel of diesel to confront with the increasing energy crisis and environment pollution,which could improve combustion and emissions characteristics of diesel engines.However,the research of ABE-diesel blends in diesel engines still belongs to starting stage.The researches mainly focused on the combustion and emissions performance of ABE-diesel blends through the diesel engine and constant volume chamber,and we still lack the fundamental understanding of the evaporation and combustion characteristics of ABE-diesel blends.In this study,the experimental and theoretical studies have been conducted,focusing on the evaporation and combustion characteristics of ABE-diesel blends droplets.The main research contents are as follows:The evaporation characteristics of ABE-diesel blends droplets have been investigated experimentally through droplet suspension technique and photographic technique at different ambient temperatures.The droplet evaporation characteristics of ABE–diesel blends vary with ambient temperature.The ABE-diesel blends always evaporate faster than diesel.At high temperature,the droplets exhibit the expansion and shrinkage phenomena due to bubble formation and rupture.Thus the droplet evaporation shows the three-phase quick evaporation characteristics.In addition,the effects of blending ratio and droplet initial diameter on the ABE-diesel blends evaporation characteristics are also investigated.The multi-component evaporation model for ABE–diesel blend droplet coupled with six components to represent diesel and Universal Functional Activity Coefficient(UNIFAC)method has been built and validated with droplet fiber-suspension evaporation experimental results.The internal gasification mechanism as well as the effects of fuel physical properties on droplet evaporation are analyzed.The droplet temperature quickly exceeding the local boiling temperature of ABE components leads to the occurrence of droplet fluctuation evaporation behavior observed in experiments.On this basis,the effects rules of ambient temperature,ambient pressure,relative velocity,initial droplet temperature and diameter are summarized in the complex environment.Based on the further study of droplet evaporation characteristics of ABE-diesel blends,the droplet burning characteristics of ABE-diesel blends are investigated experimentally through the droplet free falling technique.The values of ignition delay,burning duration,burning rate,micro-explosion,flame color and structure etc are used to evaluate droplet burning characteristics.Adding ABE to diesel significantly suppresses the soot generation propensity,increases the ignition delay and average burning rate.The ABE-diesel blends droplets occur micro-explosion before the end of the flame,which observably shorten the combustion duration.Meanwhile,with the increase of ABE fraction,the variations of the intensity and the moment of micro-explosion are nonlinear,which leads the overall burning rates increase first and then decrease.The micro-explosion performance and overall burning rate is optimal around 30% ABE-diesel blends.The new reduced chemical kinetics model of ABE-diesel blend is developed.The reduced mechanism of acetone(32 species and 73 reactions),n-butanol(66 species and 250 reactions)and ethanol(37 species and 81 reactions)are generated respectively coupled with DRG,DRGEP and CSP methods.The reduced n-heptane mechanism including 52 species and 241 reactions through sensitivity analysis.Each reduced mechanism is validated against the detailed mechanism.Then,coupled with reduced PAH mechanism,the ABE-n-heptane-PAH reduced mechanism consisting of 108 species and 566 reactions is generated.According to the ABE-n-heptane-PAH reduced mechanism,the chemical kinetics analysis of ABE-diesel blends are conducted at the environmental condition of droplet free falling experiments. |
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