Study On Ignition Characteristics Of Hydrous Bioethanol

The increase in energy demand and the intensification of environmental pollution has made the study of alternative fuels more and more important.With the continuous breakthrough and development of cellulosic ethanol brewing technology,bioethanol fuel has once again gained advantages due to its reproducibility and fewer pollutants emitted after combustion,and thus becoming a hotspot for the alternative fuel research.The high cost of dehydration and purification of bio-ethanol fuels reduces the energy efficiency of ethanol throughout its entire life cycle.The continuous advancement of HCCI engine technology makes it practical for the engine to use hydrous ethanol.Based on the independently designed shock tube test device and the CHEMKIN PRO gas-phase chemical kinetics software,the experiments and numerical simulations were carried out to explore the influence of initial conditions and water content changes on the ignition characteristics of hydrous ethanol.The sensitivities and main oxidation pathways for the ignition process of hydrous ethanol under different initial conditions were further studied,and the effects of chemical and physical effects of water content on the ignition characteristics of hydrous ethanol were quantitatively studied.The main conclusions obtained are as follows:（1）The shock tube test device was used to measure the ignition delay time data of hydrous ethanol,and the results show that the ignition delay time of the hydrous ethanol increases exponentially with decreasing temperature;the ignition delay time decreases with increasing pressure;the effect of pressure on the ignition delay time of hydrous ethanol gradually decreases with the increase of pressure;when the temperature is lower,it decreases with the rise of the equivalence ratio.When the temperature is higher,it decreases first and then increases with increasing equivalence ratio,and reaches the minimum value at the equivalence ratio of 1.0;when the temperature is lower,the ignition time of the hydrated alcohol increases.The increase of water volume first decreases and then increases,but the overall change is small.When the temperature is low,the ignition delay time of hydrous ethanol increases with the increase of water content,and the range of change is large.（2）The results of sensitivity analysis show that the elementary reaction that has the greatest promoting effect on the ignition of hydrous ethanol at high temperature is H+O₂=OH+O（R1）,and the greatest inhibiting effect is HO₂+H=H₂+O₂（R12）.Path analysis shows that in the ignition process of ethanol,it reacts with the radicals such as H,O and OH firstly through the dehydrogenation reaction generating three isomers of C₂H₅O,and then undergoes cracking and other processes finally producing C1 and C2 components.And each intermediate product is ultimately oxidized to CH₃O or CH₂O by direct or indirect reaction with CH₃.while CH₃O and CH₂O get collided with H and OH groups forming HCO,and then HCO is further dehydrogenated to CO.In addition,a small amount of ethanol generates C₂H₄ by the collision reaction with the third body M.Then,C₂H₄ is dehydrogenated to C₂H₃,C₂H₂,and finally it is converted into HCCO.When blended with 50%of the volume fraction of water,the main oxidation pathway of ethanol does not change significantly,but the addition of water significantly increased the amount of ethanol that produced C₂H₄ through reaction with the third body M,and the amount of C2H4 generated in the reaction system changed.It will have an important effect on the dynamic equilibrium value of H in the reaction,and thus affect the binding rate of ethanol and each intermediate product to H or OH.（3）The analysis shows that the physical effects of water on the ethanol ignition process dominate.With the continuous increase of water content,the proportion of chemical effects in the total impact gradually increases.When the water content is constant,the chemical effect of water increases significantly with the increase of temperature.With the addition of water,the temperature of the reaction system decreases significantly.Both the chemical and physical effects of water are manifested in suppressing the increase of temperature in the reaction system;the chemical effect of water promotes the increase of OH concentration in the reaction system.