Ramjet

Boron has been studied as a possible fuel for soHd fuel ramjets (10,11). Fine particle sized boron, where the average particle size is 0.3 )J.m, has been studied for use as a gas-generating agent for soHd fuel ram rockets (12). 

H2—HD and Ar— Ar binary gas mixtures have been measured (34,35). A vortex tube has been used for isotope separation (36), and for the separation of gases in nuclear rocket or ramjet engines. 

Bloodhound Wrap-round separating boost. Ramjet sustainer. 

Pressure Atomization Plain- Orifice 25-250 Diesel engines, Jet engine afterburners, Ramjets Simple, Rugged, Cheap Narrow spray angle, Solid spray cone... 

The values of laminar flame speeds for hydrocarbon fuels in air are rarely greater than 45cm/s. Hydrogen is unique in its flame velocity, which approaches 240cm/s. If one could attribute a turbulent flame speed to hydrocarbon mixtures, it would be at most a few hundred centimeters per second. However, in many practical devices, such as ramjet and turbojet combustors in which high volumetric heat release rates are necessary, the flow velocities of the fuel-air mixture are of the order of 50m/s. Furthermore, for such velocities, the boundary layers are too thin in comparison to the quenching distance for stabilization to occur by the same means as that obtained in Bunsen burners. Thus, some other means for stabilization is necessary. In practice, stabilization... 

Recirculation of combustion products can be obtained by several means (1) by inserting solid obstacles in the stream, as in ramjet technology (bluff-body stabilization) (2) by directing part of the flow or one of the flow constituents, usually air, opposed or normal to the main stream, as in gas turbine combustion chambers (aerodynamic stabilization), or (3) by using a step in the wall enclosure (step stabilization), as in the so-called dump combustors. These modes of stabilization are depicted in Fig. 4.52. Complete reviews of flame stabilization of premixed turbulent gases appear in Refs. [66, 67],... 

In either case, bluff body or aerodynamic, blowout is the primary concern. In ramjets, the smallest frontal dimension for the highest flow velocity to be used is desirable in turbojets, it is the smallest volume of the primary recirculation zone that is of concern and in dump combustors, it is the least severe step. 

In the case of supersonic combustion ramjet devices, instantaneous ignition must occur because the flow time in the constant area duct that comprises the ramjet chamber is short. As noted in Chapter 1, supersonic combustion simply refers to the flow condition and not to any difference in the chemical reaction mechanism from that in subsonic ramjet devices. What is unusual in supersonic combustion because of the typical flow condition is that the normal ignition time is usually longer than the reaction time. To assure rapid ignition in this case, many have proposed the injection of silane (SiH4), which is... 

Roy, G. D. 1999. Control of thermoaconstic instabilities in ramjets and gas tnrbine combustors An overview. 6th International Congress on Sound and Vibration Proceedings. Copenhagen, Denmark. 

COMBUSTION OF HIGH-ENERGY FUELS IN AN AXISYMMETRIC RAMJET... 

Although several different system configurations have been simulated, the focus of this paper will be on the unsteady, compressible, multiphase flow in an axisymmetric ramjet combustor. After a brief discussion of the details of the geometry and the numerical model in the next section, a series of numerical simulations in which the physical complexity of the problem solved has been systematically increased are presented. For each case, the significance of the results for the combustion of high-energy fuels is elucidated. Finally, the overall accomplishments and the potential impact of the research for the simulation of other advanced chemical propulsion systems are discussed. 

The geometry of the ramjet system simulated is shown in Fig. 7.1, which consists of a cylindrical inlet connected to a central dump combustor that has an exhaust nozzle. This specific geometry was chosen because extensive studies have been made in the past of the interaction between acoustics, vorticity dynamics, and chemical energy release in this system [17-20]. These earlier gas-phase flow studies are very helpful in interpreting the current multiphase flow simulations. 

This approach called MILES (monotonically integrated large-eddy simulation) is described in detail elsewhere [22]. This is the same approach used in previous simulations of ramjet combustor flows [17-20]. 

Kailasanath, K., J.H. Gardner, J. P. Boris, and E. S. Oran. 1987. Numerical simulations of acoustic-vortex interactions in a central-dump ramjet combustor. J. Propulsion Power 3 525-33. 

Chang, E. J., K. Kailasanath, and S. K. Aggarwal. 1995. Compressible flows of gas-particle systems in an axisymmetric ramjet combustor. AIAA Paper No. 95-2561. 

New computational approaches are developed to explore flame stabilization techniques in subsonic ramjets. The primary focus is statistical modeling of turbulent combustion and derivation of the adequate boundary conditions at open boundaries. The mechanism of flame stabilization and blow-off in ramjet burners is discussed. The criterion of flame stability based on the clearly defined characteristic residence and reaction times is suggested and validated by numerical simulations. 

The present study is to elaborate on the computational approaches to explore flame stabilization techniques in subsonic ramjets, and to control combustion both passively and actively. The primary focus is on statistical models of turbulent combustion, in particular, the Presumed Probability Density Function (PPDF) method and the Pressure-Coupled Joint Velocity-Scalar Probability Density Function (PC JVS PDF) method [23, 24]. 

Analyzing Fig. 12.3, it is noticed that the flame width in the bluff-body stabilized flame increases almost linearly with the distance from the baffle with the spreading angle of about 3° to 5°. Since the flame spreading angle directly affects the ramjet combustion efficiency, it is important to check the performance of the ABC by applying it to combustors with different tailpipes. 

The Presumed Probability Density Function method is developed and implemented to study turbulent flame stabilization and combustion control in subsonic combustors with flame holders. The method considers turbulence-chemistry interaction, multiple thermo-chemical variables, variable pressure, near-wall effects, and provides the efficient research tool for studying flame stabilization and blow-off in practical ramjet burners. Nonreflecting multidimensional boundary conditions at open boundaries are derived, and implemented into the current research. The boundary conditions provide transparency to acoustic waves generated in bluff-body stabilized combustion zones, thus avoiding numerically induced oscillations and instabilities. It is shown that predicted flow patterns in a combustor are essentially affected by the boundary conditions. The derived nonreflecting boundary conditions provide the solutions corresponding to experimental findings. 

Talantov, A. V. 1958. Fundamentals for evaluating the simplest ramjet combustor. Izv. Vuzov USSR, Ser. aviation techn. 2. 

Vlasov, K.P. 1961. To the evaluation of the simplest combustor of a ramjet type. In Flame stabilization and the development of combustion in turbulent Sow. Ed. G. M. Gorbunov. Moscow Oborongiz. 128. 

Frolov, S.M., V. Ya. Basevich, and A. A. Belyaev. 1999. Flame stabilization in a ramjet burner. 12th ONR Propulsion Meeting Proceedings. Eds. G.D. Roy and S.L. Anderson. University of Utah, Salt Lake City, UT. 76-81. 

Crump, J. E., K. C. Schadow, V. Yang, and F. E. C. Culick. 1986. Longitudinal combustion instabilities in ramjet engines Identification of acoustic modes. J. Propulsion Power 2 105-9. 

LIQUID-FUELED ACTIVE CONTROL FOR RAMJET COMBUSTORS... 

Model ramjet dump combustor with direct liquid-fuel injection for... 

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