Solid Fuel Ramjet Research Articles

비점성 유동을 가정한 포 발사 램제트 추진탄 설계

Operation area of corps was expanded under military reformation, and extending range of 155 mm howitzer became important issue. New approach is needed to extend range to 80 kim. Ramjet engine is air breathing engine, and it can provide specific impulse several times more than solid rocket motor so that range is extended using same weight of propellant. If the ramjet engine is gun-launched system, it does not require any other booster because muzzle velocity is near Mach 3. Especially solid fuel ramjet (SFRJ) does not have any moving part so that it is favorable for gun-launching system which is under high stress during launching. In this paper, we design air intake, combustion chamber, and nozzle of 155 mm gun launched ramjet propelled artillery shell with inviscid flow assumption. We conduct parameter study to have range more than 80 km, and maximum high explosive volume.

Numerical Simulation of Cold Swirl Field for Solid Fuel Ramjet with NACA Airfoil

In order to study the swirl flow characteristics in the solid fuel ramjet chamber, a new type of annular vane swirler with NACA airfoil is designed. The cold swirl flow field in the chamber is numerically simulated with different camber and t attack angle, while the swirl number , swirl flow field structure, total pressure recovery coefficient were studied. According to numerical simulation result, the main factors in swirl number are camber and angle of attack, the greater angle of attack, the greater the camber ,the stronger swirl will be. Results show that the total pressure loss is mainly concentrated in the inlet section, the total pressure loss cause by vane swirler is small. Radial velocity gradient exists in swirling flow, and increases with the swirl number. With the influence of centrifugal force and combustion chamber structure, the radial velocity gradient increases.

Inlet Air Temperature Effects on the Performance of the Solid Fuel Ramjet

Based on the Brayton cycle analysis for the performance and the combustion experimental tests, the following results are concluded: Higher inlet temperature produces higher combustion efficiency but lower performance efficiency. the normalized performance efficiency change rate is lower with a higher Mach number flow for the given free stream temperatures ratio

Bypass-Regulated Solid Fuel Ramjet Combustor in Variable Flight Conditions

A comprehensive experimental investigation aimed at the examination of a solid fuel ramjet (SFRJ) regulation concept using an air-division valve has been conducted. By controlling the ratio between the port and bypass flows, one can maintain a desirable working state over a wide range of flight conditions. A general regulation law based on maintaining a constant fuel-to-air ratio has been tested. The experimental strategy was to isolate key parameters influencing the fuel regression rate, testing them one at a time, keeping the other parameters constant. Experiments aimed at airflow rate, total air temperature and pressure, as well as port diameter effects, simulated a broad flight envelope, from Mach 1.5 to Mach 4.7 and from sea level to 13-km altitude. The test results showed a very good agreement with the theory, demonstrating the feasibility, effectiveness, and characteristics of the air-division valve regulation technique in SFRJ motors.

Flame Stability Analysis of Turbulent Non-Premixed Reacting Flow in a Simulated Solid-Fuel Ramjet Combustor

ABSTRACTTo investigate the flame stability in a solid-fuel ramjet combustor, time-accurate calculations using a compressible flow solver with a modified Godunov flux-splitting scheme have been performed on high Reynolds number turbulent non-premixed reacting flows over a backward-facing step with mass bleed on one wall. The combustion process considered was a one-step, irreversible, and finite rate chemical reaction. The numerical results for reacting flows show that the two-dimensional (2-D) simulations can provide reasonable predictions on the dimensionless particle number decay rate and residence time in the flame holding recirculation zone, evolutions of both axial and transverse mean velocity profiles, and critical characteristic exhaust velocity separating the sustained combustion from the non-sustained combustion. In addition to the validation of 2-D reacting flow calculations, two- and three-dimensionally computed mean-velocity profiles are compared with existing experimental data for isothermal flows to check the suitability of 2-D simulations on capturing the large-scale mean flows.

Fuel Regression Rate in Hydroxyl-Terminated-Polybutadiene/Gaseous-Oxygen Hybrid Rocket Motors

The results of a systematic experimental investigation on the methods of enhancing the regression rate in hydroxyl-terminated polybutadiene (HTPB) fuel used in an HTPB/gaseous oxygen hybrid motor are presented. The effects of the addition of ammonium perchlorate (AP) or aluminum in the fuel, the variation of oxidizer ‐fuel ratio, and the variation of characteristic dimensions of fuel grain are presented. For the extents of the parametric variations considered, while the addition of AP and/or Al and the reduction of grain port diameter enhance the regression rate, the effect due to the latter is the most signie cant one. Furthermore, the regression rate increases along theaxis, and it becomes essentially constant in the port region corresponding to a fuel-rich composition. The possible physical processes for all of these behaviors are discussed. The experimentally obtained exponents of the variables for regression rate (oxidizer mass e ux and port diameter ) are found to be signie cantly different from those of the conventional theory. The similarity between the fuel regression rate equation used in solid-fuel ramjet and that obtained in hybrid motor is discussed.

Solid-Fuel Ramjet Regulation by Means of an Air-Division Valve

An in-e ight regulation technique, which can provide an optimal operation of a solid-fuel ramjet (SFRJ) motor over a wide e ight envelope, has been analyzed. Regulation capability is essential for an efe cient use of the SFRJ propulsionforapplicationsinvolvingvariablee ightandoperatingconditions.Themethodisbasedonacontrollable air-division valve, which drivespart of the inlet airinto thesolid-fuel port, whiletherest of the aire ow ischanneled through a bypass to the aft-mixing section of the combustor. The model takes into account parameters ine uencing the burning rate of the solid fuel (e.g., port-e ow rate, port diameter ) and formulates a general regulation law in terms of the instantaneous opening state of the division valve fora constant fuel-to-air ratio operation. The control lawwascheckedforcertaincases,considering typicaltrajectories.Ithasdemonstrated agoodregulationcapability over a broad operational range (between sea level and 15-km altitude ). Nomenclature A = area d = diameter f = fuel-to-air ratio f (h) = function of altitude in the regulation law, Eq. (22) G = air mass e ux g(M) = function of Mach number in the regulation law, Eq. (23) H = inlet step height h = heat-transfer coefe cient; altitude L = fuel grain length M = Mach number m = temperature exponent C m = mass-e ow rate n = mass-e ow rate or mass e ux exponent C

Design and Control of Solid-Fuel Ramjet for Pseudovacuum Trajectories

A ballistic trajectory in air of a powered projectile where the thrust always balances the drag is termed as a pseudovacuum trajectory. For a solid-fuel-ramjet (SFRJ)-powered gun-launched projectile this trajectory can be achieved by the control of engine mass-e ow rate, either by a bypass control of inlet air or by a regression rate controloffuel. Based on one-dimensional considerations,theproceduresfora preliminary designofthepropulsion system for an SFRJ-assisted gun-launched projectile and the methods to calculate the control requirements are presented. Using these, typical cone gurations of SFRJ suitable for 155-mm gun-launched projectiles are analyzed for different launch angles. The results indicate that the control requirements by either method are minimal and thus, demonstrate the self-throttling characteristics of SFRJ.

Experimental Investigation of a Supersonic Combustion Solid Fuel Ramjet

An experimental parametric investigation of a solid-fuel supersonic combustion chamber in a scramjet configuration was conducted. A hydrogen-burning vitiated air heater was designed and built to simulate flight conditions of Mach 5.5 in high and medium altitudes in a static test facility (stagnation temperatures and pressures of up to 1500 K and 50 atm, respectively). Flow and combustion phenomena were studied by pressure measurements along the fuel grain and by analyzing video images, digitized from the video recording of each test. Self-ignition and flameholding characteristics were consistent with results from previous works. Flow and combustion characteristics changed as inlet conditions extended, exhibiting initially choked or unchoked flow patterns. In the parametric investigation, incoming airflow conditions (total pressure, total temperature, and mass flow rate) defined the parametric space, yielding a regression rate power law of these parameters. Combustion efficiency was found to decrease with the increase of each of the inlet parameters. Increasing the diversion semiangle of the diverging section of the solid grain resulted in lower regression rate values.

SOLID FUEL RAMJET COMBUSTOR DESIGN

Combustion aspects of solid fuel ramjet (SFRJ) are reviewed. On the point of view of the ability of an SFRJ to operate satisfactorily at all off-design conditions the areas of concern to propulsion system designer are (1) selection of a fuel type, (2) flame holding requirements that limit maximum fuel loading, (3) understanding the fuel regression rate behaviour as a function of flight speed and altitude, (4) diffusion-controlled combustion process and its efficiency enhancement, and (5) inlet/combustor matching. Considering these areas, the following aspects are reviewed from the information available in open literature: (1) different experimental set-up conditions adopted in combustor research, (2) various suitable fuel types, (3) flammability limits, (4) fuel regression rate behaviour, (5) methods of achieving high efficiency in metallized fuel, and (6) various modelling efforts. Detailed discussion is presented on two different types of regression rate mechanism in SFRJ: one that is controlled by the heat transfer processes downstream of the reattachment region and the other by that in the region itself. With a view to demonstrate the use of the information collected through this review, a preliminary design procedure is presented for an SFRJ-assisted gun launched projectile of pseudo-vacuum trajectory.

Velocities of Reacting Boron Particles within a Solid Fuel Ramjet Combustion Chamber

A 2D-laser doppler velocimeter was used to measure velocities of reacting boron (B) particles during the combustion of a metallised solid fuel slab inside a 20-combustion chamber. The solid fuel hydroxyl-terminated polybutadiene (HTPB) was enriched with B particles to increase its specific heat. To obtain information on the combustion process and on the movement of B particles, their velocities were measured. The experiments were performed at ambient pressure. The behaviour of the B particles concerning the exit velocities from the fuel slab has been discussed on the basis of the experimental results.

Flammability Limits and Probability Density Functions in Simulated Solid-Fuel Ramjet Combustors

A numerical analysis was performed to study turbulent reacting e ows in solid-fuel ramjet combustors. The time-dependent axisymmetric compressible conservation equations were solved with a subgrid-scale turbulence model. The combustion process considered was a one-step, irreversible, and ine nitely fast chemical reaction. The numerical code used the e nite volume technique, which involved alternating in time the second-order, explicit MacCormack’ s and modie ed Godunov’ s schemes. Computed temperature proe les are compared with existing experimental data and the previous calculations, incorporating the k-e turbulence model and two-layer near-wall treatment. The superiority of the present predictions is demonstrated. Flammability limits in solid-fuel ramjet combustors have been determined using the characteristic exhaust velocity. Moreover, a compact correlation relating the minimum step height to the combustor diameter, air mass e ow rate, and equivalence ratio for sustained combustion is provided for practical design reference. Probability density function (PDF) proe les of temperature and mixture fraction are also analyzed to understand the thermal structure of turbulent e ames, and to provide information for examining the applicability of the conserved-scalar approach incorporated PDF models to turbulentreacting e ows.

Solid-fuel regression during ignition transient in a ramjet

The transient regression and ignition of a solid fueld in a hot-oxidizing flow in a simulated combustor of a solid-fuel ramjet (SFRJ) were experimentally investigated. The local regression of solid fuel was measured at various intervals before ignition, and the controlled variables of the experiments were the inlet flow velocity, gas temperature, oxygen content, and step height. The maximum regression was located at 5.0–5.5 step heights from the entrance. The results of regression tests indicate that the influence of heat transfer was more important than the flow structure of the separated-reattaching flow. The regression rate increased with increasing the flow temperature and mass flow rate but decreased with increasing step height. The oxygen content had no significant influence on the regression before ignition. The transport phenomena in the combustor before ignition were closely related to the ignition mechanisms, which were diffusion control and chemical kinetics control. Diffusion control applied in the region of oxygen concentration greater than 20%, and the ignition delay decreased as pyrolyzed fuel vapor increased during the preignition period. Chemical kinetics control applied in the region of oxygen concentration less than, 15%, and the flow feature of flame stabilization was more important than pyrolysis for decreasing the ignition delay.

Investigation of solid-fuel, dual-mode combustion ramjets

An investigation was conducted to determine the feasibility of using a solid-fuel, dual-combustion mode ramjet (DMRJ) for hypersonic vehicles (e.g., tactical missiles) operating at a design point of Mach 6 and an altitude of 24.4 km. The analysis showed that, with a supersonic combustion efficiency of 90%, the DMRJ can exceed the performance of the solid-fuel ramjet (SFRJ) by as much as 20% at near stoichiometric fuel-to-air ratios, neglecting heat and wall shear losses in the supersonic combustor. It also seems that the combustion efficiency must be greater than 70% in order for the DMRJ to outperform the conventional SFRJ at the chosen design point. Chemical kinetics considerations revealed that the dual-mode configuration enables the efficient use of solid hydrocarbon fuels due to the existence of highly reactive species in the supersonic combustor, after the completion of the initial slow reaction stages in the subsonic gas generator. Preliminary laboratory tests demonstrated the operation of such a DMRJ system, including the establishment of sustained combustion in the supersonic chamber.

Fuel Regression Mechanism in a Solid Fuel Ramjet

AbstractA model relating the combustion characteristics, particularly the regression rate, to the fuel properties in a solid fuel ramjet (SFRJ), is presented. The analysis is based on inspecting the different phenomena (e.g., chemical kinetics and heat transfer) involved in the fuel decomposition process in order to determine the rate controlling steps, and modeling the important mechanisms. Model predictions were compared to experimental findings for four polymeric fuels, showing excellent qualitative agreement in classifying different fuels, as well as good quantitative predictions of the fuel regression rates. The model can serve as a useful tool for the selection of appropriate fuels, as well as for preliminary design of the engine and mission profile prior to static firings of the final SFRJ prototype.

Similarity and scale effects in solid-fuel ramjet combustors

Theoretical analysis has been conducted concerning the similarity conditions and rules in solid-fuel ramjet (SFRJ) combustors utilizing hydrocarbon fuels. Modeling the dominant, controlling combustion processes, it has been shown that the pd scaling method, often applied to gas turbine and liquid-fuel ramjet combustors, is appropriate for SFRJ combustors as well. Thus, experimental data obtained from a laboratorysize apparatus can be applied to a full-scale system. Experimental investigation has demonstrated good agreement between the theoretical predictions of key operational parameters, such as fuel regression rate, fuel/air ratio, thrust, and combustion efficiency, and the tests, verifying the similarity model and its resulting rules.

Solid-fuel ramjet fuel regression rate/thrust modulation

An experimental investigation was conducted to determine if inlet air swirl and/or secondary gaseous injection could be used effectively for fuel regression rate control or thrust modulation in a solid-fuel ramjet. Inlet swirl characteristics were measured in nonreacting flows. Tests were conducted at high and low air mass fluxes using three fuel compositions with equivalence ratios between 0.5 and 1.8. Swirl introduced downstream of the air inlet was found to be effective for obtaining limited increases in the fuel regression rate, but the magnitude was highly dependent upon motor geometry. Swirl interactions with the reattaching inlet flow and/or significantly increased near-wall mixing were found to be detrimental to efficient combustion. Energetic gaseous fuels (H2, C2H4) can be easily injected and efficiently burned under fuel-lean conditions to significantly enhance thrust.

Swirl and fuel composition effects on boron combustion in solid-fuelramjets

The objective of this experimental investigation was to determine the influence of swirl flow and fuel composition on boron combustion efficiency, combustion products, and specific thrust. A solid-fuel ramjet combustor that was directly connected with an air heater and an air supply was used. The experiments were conducted with and without inlet flow swirl. HTPB fuels containing up to 40% boron or boron carbide in varying compositions were applied. An exhaust particle sampling technique in connnection with a chemical analysis procedure was developed in order to measure the composition of the condensed combustion products. The principle of the sampling method was based on quenching the reaction products on a cold surface. The results show that boron combustion efficiency and specific thrust are strongly increased for swirl flow conditions. Boron combustion efficiency increases with increasing amounts of boron in the fuel until a maximum at about 20% boron is reached. Further addition of boron leads to a decrease in combustion efficiency. The observations also lead to a similar behavior of specific thrust. The results for boron carbide fuels were similar, but no maximum in combustion efficiency has been observed.

Temperature effects on solid-fuel ramjet fuel properties and combustion

Temperature effects on solid-fuel ramjet fuel properties and combustion

Ignition and combustion of boron particles in the flowfield of a solid fuel ramjet

Theoretical investigation on the behavior of individual boron particles in the flowfield of a solid fuel ramjet (SFRJ) combustor is presented. The study was motivated by the observed difficulties in achieving good combustion efficiencies of boron required to exploit its remarkable theoretical energetic performance. The equations describing the gas flowfield and the particle behavior are solved numerically. The solution presents the trajectory, temperature, and history of the boron particles due to the interactions with the surrounding gas, as well as the ignition envelope and combustion time. The results demonstrate the limited ranges of particle size and ejection velocity which enable ignition and sustained combustion, reveal why practical systems often exhibit poor combustion efficiencies, and predict the conditions where ignition and efficient combustion of boron are feasible. Nomenclature