Study On The Combustion Characteristics Of N-heptane Droplets And Droplet Array

The increasingly severe environmental and energy problems,as well as the urgent need for the development of high performance propulsion technologies,have forced people to explore the clean and efficient combustion methods and search for new energy conversion means.The deep understangding of the combustion law of liquid fuel,which accounts for 30% of the total primary energy,is the key to the development of high efficient combustion equipment,and it is also an important aspect of improving the comprehensive utilization of energy.In this thesis,the ignition and flame propagation characteristics of droplets and droplet arrays are investigated by means of CFD numerical simulation and experiments,using n-heptane as the target fuel.The main contents and results are as follows:1)The droplet evaporation combustion model is established by coupling the multiphase flow slover and combustion solver in open source CFD software OpenFOAM,as well as adding the evaporation source term into the control equations.Based on the model,the effects of different ignition modes and environmental factors such as temperature and pressure on the evaporation combustion characteristics of droplets are analyzed.The simulation results show that the evaporation combustion rate of droplets can be accelerated effectively by increasing the ambient temperature or decreasing the ambient pressure,and the droplets in different positions exhibit different evaporation combustion characteristics due to the interaction between droplets.2)The droplet combustion test bench is built based on the high-speed camera,pipettes and igniters,using 0.425 mm quartz fiber to suspend droplets.A series of experiments are carried out and the flame propagation modes of droplets at different positions under different droplet spacing parameters are compared and analyzed.Moreover,the corresponding flame propagation limit is obtained.The results show that the droplet spacing plays a decisive role in the flame propagation mode,and the heat transfer mode between droplets is the essential reason for the formation of different flame propagation modes.3)Based on the simulation and experimental results,the variation process of fuel droplet radius caused by evaporation and combustion under the condition of single droplet and multi-droplet coexistence is compared and analyzed.The simulation results are in good agreement with the experimental data,which fully proves the correctness of the model and the calculation method.The constructed model can be used for further research on the evaporation combustion characteristics of droplets and droplet arrays.This work has laid the foundation for the dynamic study of the droplet combustion process.The established mathematical model and combustion test platform can be used to study the combustion characteristics of other liquid fuels.