| The laminar burning velocity,,is one of the most important characteristic parameters of premixed combustible mixture,which is of great significance for validating and developing the chemical dynamic mechanism,simulating the turbulent combustion,optimizing the combustion devices and establishing the model to predict the flash point and the minimum ignition energy of fuels.At present,many researchers have used the constant volume bomb to measure the laminar burning velocities of different fuels.However,there are few researches on the temperature distribution inside the constant volume bomb,in which there is no detailed analysis of the three-dimensional temperature field distribution and the influence of temperature field inhomogeneity on the spherical flame propagation process.Therefore,in this thesis,the temperature distribution of fluid medium inside the constant volume bomb and its effect on the process of hydrogen-air spherical flame propagation are studied by means of numerical simulation and experiment.Firstly,the laminar burning velocities at different equivalence ratio of hydrogen-air are measured by using the constant volume bomb,and the temperature values at several fixed points inside constant volume bomb are measured too.Afterwards,the numerical models calculating the temperature distribution and the numerical model simulating the hydrogen-air spherical flame propagating process are established based on Fluent software,and the accuracy is validated by the experimental results.Furthermore,the temperature distribution of the fluid medium inside the constant volume bomb and the its effect on the hydrogen-air flame propagation process and the accarucy of the measurement of hydrogen-air laminar burning velocity are studied by using the above models.The main conclusions of this paper can be summarized as follows:(1)The temperature distribution of fluid inside the chamber exhibits significant gradient along the gravity direction,and it first decreases to the minimum near the bomb center and then rises along gravity direction.With the increase of the overall temperature inside the chamber,the non-uniformity of the temperature field gradually increases as well.When the heater voltage is 90,120 and 150 V,the maximum difference of identified values of initial temperature in experiment reach 25 K?40 K and60 K,and the maximum temperature differences along the gravity direction reach 14,23 and 35 K,respectively.The fluid in the bomb appears to flow along the inner surface of the glass at the two sides to the middle region at the bottom of the bomb.At the same time,the numerical results show that the arrangement of the heating device will directly affect the temperature distribution of the fluid inside chamber.Compared with heater band,the evenly arranged heaters are more advantageous for the uniformity of the temperature distribution of the fluid in the bomb(2)Due to the influence of non-uniformity of temperature distribution inside the constant volume bomb,the shape of flame is not a standard circle during flame propagation process.At non-uniform temperature field conditions,the distance from upper edges of 2-D spherical propagating flame front to the center of flame is longer than that of lower edges,and the variability is more obvious over the time of flame propagation.And with the increase of heating voltage,this phenomenon is more obvious too.(3)Comparing the numerical results of hydrogen-air spherical flame propagating process at uniform and non-uniform initial temperature field,it is observed that the predicted laminar burning velocities at non-uniform temperature field are slightly higher than those at uniform temperature fields under the same equivalent ratio condition.As the heater voltage increases,the difference in laminar burning velocity between uniform and non-uniform temperature fields becomes bigger accordingly.When the heater voltage is 90,120 and 150 V,the relative changes in are around 3%~4%,4%~5% and 5%~7%,respectively. |
PDF Full Text Request