The Effects Of Swirl Flow On Combustion Performance Of Solid Fuel Ramjet With Carbon Black Additive Solid Fuel

With a series of advantages such as simple structure,high specific impulse,and high safety,solid fuel ramjet(SFRJ)is a propulsion system with a broad application prospects.The application of swirl-flow can enhance mixing of solid fuel pyrolysis products and inlet air,improve combustion efficiency,and increase regression rate.The addition of carbon black in solid fuel can increase radiative heat feedback strength of the flame to the combustion surface,and enhance combustion stability.The effects of swirl flow on combustion characteristics of solid fuel ramjet with carbon black additive solid fuel were studied with the method of experiment and numerical simulation.(1)In order to obtain high quality carbon black-polyethylene solid fuels,the processing mold was designed.The processing mold is characterized by avoiding shrinkage holes formed in the cooling process of carbon black-polyethylene solid fuels,so it can ensure the quality of the solid fuels,and the processing mold has the characteristics of simple structure and easy operation.(2)The effects of mass fraction of carbon black and environmental pressure on ignition and combustion performance of polyethylene were researched by laser irradiation ignition experiments.The results show that solid fuel polyethylene decomposed under radiation heating firstly,and then the decomposition gases diffusing into air will mix and react with air near the surface of the solid fuel,which demonstrates the ignition of polyethylene is a typical gas phase ignition.The ignition delay time decreases sharply with the increase of mass fraction of carbon black and environment pressure,but varies little when the mass fraction of carbon black is higher than 20%and environment pressure is higher than 0.2MPa.For the pressure from 0.1 to 0.5MPa,mathematical relationship between ignition delay time and mass fraction of carbon black were given by using the least square method.When environmental pressure are 0.1MPa,0.3MPa and 0.5MPa respectively,the burning rates of solid fuel with 5%carbon black decreased by 13.76%,20.76%and 26.07%than polyethylene,respectively.(3)Several groups of connected-pipe solid fuel ramjet tests were carried out to research the effects of carbon black on the combustion performance of SFRJ under different inlet flow conditions.The results that the addition of carbon black with mass fraction of 5%to polyethylene can change the initial ignition characteristics of polyethylene,and it can improve the combustion stability,regression rate,characteristic speed and thrust effectively.Moreover,it is better to improve the effect in the case of swirl flow.The regression rate and combustion stability of solid fuel are improved with the increase of swirl intensity.However,it also reduces the stability of flame to some extent because the length of the reflux region reduced with the increase of swirl intensity.With the increase of the step height,the combustion stability and combustion efficiency are increased,but the average regression rate of solid fuel is reduced.(4)The effects of carbon black on the combustion performance of SFRJ under different inlet flow conditions were numerically simulated by using Fluent.The results show that the introducing of swirl flow can help pyrolysis products and flow of air more fully mixing,improve the combustion efficiency of carbon black.And it also helps the high temperature burning flame closer to the fuel surface in recirculation zone.But,due to the introducing of swirl flow,the length of the reflux region is shortened,and high temperature flame is more away from solid fuel surface after the attachment point.With the addition of carbon black,high temperature flame is more close to the solid fuel surface,so it is indicated that the addition of carbon black can improve the stability of combustion.In the swirl flow case,there is a large amount of carbon black particles are accumulated in the solid fuel surface,but less in the convergent section of the nozzle.