Research On The Combustion Process And Combustion Technology Of Boron-based Gel Fuel Ramjet

The boron-based gel ramjet engine is a new concept ramjet engine that uses a high energy density boron-based kerosene propellant as fuel.It is an ideal power plant.In this paper,a comprehensive and in-depth exploratory study on the theoretical performance,working process organization and working characteristics of the engine was performed theoretically and experimentally.The numerical simulations were also performed.The key technologies were developed,such as a high combustion efficiency of boron particles.The energy characteristics of gel propellants with different energetic particle additives and different boron particle contents were analyzed under ramjet operating conditions by thermodynamic calculations respectively.The results showed that the volumetric energy density of the gel propellant is about 1.4 times that of pure kerosene when the boron particle mass fraction was 40% and the air-fuel ratio is 20.The atomization process of boron-based gel propellant was observed and measured by optical method.The effects of atomization gas flow rate,boron particle content and particle type on the maximum droplet diameter during atomization were analyzed.The results show that the air atomizing nozzle can achieve good atomization for the gel propellant.In the case where the flow rate of the gel propellant is constant,the size of the spray droplet decreases as the flow rate of the atomizing gas increases,and the droplet size becomes more uniform;As the content of boron particles increases,the droplet diameter after atomization decreases despite the viscosity of the gel is increased.The droplet size after atomization of the gel propellant containing aluminum particles is smaller than that of the gel propellant containing boron particles under the same conditions.The combustion process of boron-based gel droplets with a diameter of about 140 microns was observed by high-speed microscopic imaging.The results showed that the combustion process of the boron-based gel droplets generates agglomerated porous boron particles.Based on the experimental observation of the formation of porous boron particles during the combustion process of boron-based gel droplets,a boron particle agglomeration ignition and combustion model which is suitable for numerical simulation in a boron-based gel ramjet engine was established.The effects of agglomerate diameter,ambient gas temperature,water vapor content and oxygen content on the ignition process of boron particle agglomeration were analyzed.The influences of the agglomerate diameter,the oxygen content,the mass fraction of boron particles inside the agglomerate and the of environmental pressure on the combustion process of boron particles agglomerated were also analyzed.The ignition and combustion experiments of boron particle agglomeration were carried out by using a planar flame burner.The flame morphology during the ignition process of agglomerated boron particles was obtained.The influences of parameters such as gas phase temperature and oxygen concentration on the ignition of boron particles was analyzed.Ignition of a boron-based gel ramjet engine was achieved by using a high energy spark plug.It is found that the engine could be restarted using the residual heat of the engine without the reignition of spark plug.The maximum time interval for engine restart increases as the working time increases.Compared to kerosene,the gel propellant and the boron-based gel propellant have much better restart characteristics.The restarting performance of the boron-based gel is slightly better than that of the pure gel.Fuel flow regulation is achieved during the operation of the gel ramjet.The influences of the engine head intake gas flow rate,atomized intake gas flow rate,flame stabilization method,combustion chamber configuration,air-fuel ratio,combustion chamber length and boron particle content on the combustion process in the gel ramjet engine were analyzed using the connected-pipe tests and numerical simulations.With an effective combustion organization,the combustion efficiency calculated by the temperature rise was 80.1% in the test where the boron particle mass fraction is 40%.