Investigation On The Working Process Of Solid Fuel Ramjet

In recent years, solid fuel ramjet (SFRJ) has become a very attractive propulsion system for many researchers due to its high special impulse and simple structure compared to other air breathing engines, which has a wide application prospect on supersonic missile and extended-range projectile.The schematic design and performance analysis evaluation method, combustion and internal flow field characteristics and their relative conditions of Minor-diameter SFRJ extended-range projectile were studied detailedly and comprehensively by means of theoretical analysis, experimental investigation and numerical simulation, and the computational fluid dynamics software FLUENT was used as a tool. It has laid a foundation of theory and experiment for the SFRJ. In this paper, the work reads as follows:(1) The complex flow field of a minor-diameter supersonic mixed-compression ramjet inlet with blunted-lip cowl was numerically simulated by using the 2D-axisymmetric N-S equations, and the flow structures were clearly obtained. The two-equation RNG k-e turbulence model and the first order upwind scheme were used. The influence of different bluntness radius of cowl lips on the performance parameters of the inlet at design Mach number was studied. The results show that:the reasonable increase of bluntness radius of the cowl lip induces the stable operation range of inlet broadens, the total pressure recovery increases, and the only disadvantage was the increase of total drag of inlet. However, when the bluntness radius of cowl lip was too bigger(r/H=2%), the low speed area around the blunted-lip cowl makes the boundary layer become thicker. Consequently, the interior flow field of inlet was destroyed, and the stable operation range of inlet becomes narrower rapidly.(2) Under the condition of different angles of attack and inflow Mach numbers, the complex flow field of a mixed-compression inlet of minor-diameter SFRJ extended-range projectile with struts was numerically simulated by using the 3D Reynolds-averaged N-S equations, and also wind tunnel test has been achieved. The schlieren photographs of inlet and the distribution of static pressure along the inlet and the influence of different operations on total pressure at the exit of inlet were obtained. The results indicate that numerical flow structure and wind tunnel test schlieren photographs of inlet were identical. The experimental data, such as static pressure and total pressure, were in good agreement with the numerical results, and the reliabilities of the numerical simulation methods in this paper were verified.The results show that:under the the design(Ma=3) and off-design condition (Ma=2.5), the designed mixed-compression supersonic inlet both work effectively, and also has favorable angles of attack characteristic in?=0°?6°range. The Mach number of exit plane was about 0.3?0.4, which can satisfy the requirement of solid fuel ramjet combuston chamber on the Mach number of combustion chamber inlet.(3) Compared with Rihani-Doraiswamy and Benson group contribution method, the thermodynamics data of methyl methacrylate(C5H8O2) were estimated, such as special heat at constant pressure, standard enthalpy of formation and entropy. According to pyrolysis principle of propellant, based on secondary development technology by using the User Defined Functions, which was included in software FLUENT, the combustion model of (Polymethylmethacrylate) PMMA in SFRJ combustion chamber was established. Its combustion flow was described with two-step chemical reaction model, RSM turbulent model, Eddy Dissipation turbulent combustion model and first order upwind scheme, then the flow field structure, temperature and species distribution in SFRJ combustion chamber also were analyzed. Based on above, the flow field of SFRJ combustor chamber was numerically simulated, and the fuel was PMMA. It was analyzed the influence of the parameters, such as fuel port diameter, air total temperature, air mass flow rate etc.then. The flow field structure, temperature and species distribution in SFRJ combustion chamber also were obtained.The results show that:as the axial distance increases, the local regression rate increases at first then decreases gradually. In addition, the increase of inlet air temperature and mass flow rate both induces the mean regression rate of PMMA approximately exponential increase, and the combustion chamber temperature also increase.As the fuel port diameter increases, the reattactment point moves downstream, and the mean regression rate of PMMA approximately exponential decrease.(4) The SFRJ direct tube test motor was established. For the first time in domestic, the combustion behavior of PMMA in SFRJ was performed using a direct tube test facility, and the amorce was Mg/PTFE. In order to control the test time accurately, the electromagnetic value and digital display time relay were used.The experiments results prove that the ignition method was reliable, and the motor works stably. The effects of factors, such as air mass flow rate, air total temperature and fuel port diameter on regression rate and performance was investigated experimentally. The results show that:While the fuel port diameter was smaller (Dp=30mm), the SFRJ combustion chamber will produce phenomenon similar to erosion effect in solid rocket motor. As the combustion chamber pressure decreases, the fuel mean regression rate and aft -mixing combustion chamber temperature both decreases. However, at the condition of low pressure (0.8MPa), this effect was limited. In addition, the increase of fuel port diameter induces the total fuel combustion area increases. Although the fuel mean regression rate decreases, the total fuel mass flow rate still increases. Therefore, the aft-mixing combustion chamber pressure and temperature both enhances. For a given amorce, the mass and energy of amorce as well as combustion duration of amorce were governing factors of the success of ignition. When the amorce mass was a certain quality, increases the air mass flow rate and decreases the air total temperature both will have negative effect on the ignition process. In order to achieve ignition process successfully, increases the aomrce mass was the feasible method.The predicted results of the numerical model coincide well with the experimental data, the reliability of numerical model was verified. The error of mean regression rate was less than 7.7%, the error of pressure of aft-mixing combustion chamber was less than 15.3%, the error of temperature of aft-mixing combustion chamber was less than 22%.