• Advances in aircraft and spacecraft science
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• v.7 no.3
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• pp.187-202
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• 2020

The exhaust nozzle serves back pressure of Pulse detonation combustor, so combustion chamber gets sufficient pressure for propulsion. In this context recent researches are focused on influence of nozzle effect on single cycle detonation wave propagation and propulsion performance of PDE. The effects of various nozzles like convergent-divergent nozzle, convergent nozzle, divergent nozzle and without nozzle at exit section of detonation tubes were computationally investigated to seek the desired propulsion performance. Further the effect of divergent nozzle length and half angle on detonation wave structure was analyzed. The simulations have been done using Ansys 14 Fluent platform. The LES turbulence model was used to simulate the combustion wave reacting flows in combustor with standard wall function. From these numerical simulations among four acquaint nozzles the highest thrust augmentation could be attained in divergent nozzle geometry and detonation wave propagation velocity eventually reaches to 1830 m/s, which is near about C-J velocity. Smaller the divergent nozzle half angle has a significant effect on faster detonation wave propagation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1989-1998
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• 1995

Characteristics of the flame propagation for normal and abnormal combustion in hydrogen premixture in a cylindrical constant-volume combustion chamber are studied numerically. A detailed hydrogen oxidation kinetic mechanism, mixture transport properties and a model describing spark ignition process are used. The calculated pressure-time history of the stable deflagration wave propagation agrees well with the experiment. The ignition of the premixture in the unburned gas, initiated by the hot spot, causes a transition from deflagration to detonation under some initial temperature and pressure. Under the initial conditions with high temperature and pressure, excessive ignition energy initiates a strong blast wave and a detonation wave that follows. The chemical reaction in the detonation wave is much more vigorous than that in the deflagration wave and the peak pressure in the detonation wave is much higher than the equilibrium value.

• Journal of Powder Materials
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• v.17 no.1
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• pp.29-35
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• 2010

We produced cylindrical porous TiNi bodies by Self-propagating High-temperature Synthesis (SHS) process, varying the heating schedule prior to ignition of a loose preform compact made from (Ti+Ni) powder mixture. To investigate the effect of the heating schedule on the behaviour of combustion wave propagation and the structure of porous TiNi shape-memory alloy (SMA) body, change of temperature in the compact during SHS process was measured as a function of time and used for determining combustion temperature and combustion wave velocity. Microstructure of produced porous TiNi SMA body was observed and the results were discussed with the combustion characteristics. From the results it was concluded that the final average pore size could be controlled either by the combustion wave velocity or by the average temperature of the preform compact prior to ignition.

• Advances in aircraft and spacecraft science
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• v.10 no.3
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• pp.203-222
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• 2023

The detonation combustion is a supersonic combustion process follows on shock wave oscillations in detonation tube. In this paper numerical studies are carried out combined effect of blockage ratio and spacing of obstacle on detonation wave propagation of hydrogen-air mixture in pulse detonation combustor. The deflagration to detonation transition of stoichiometric (ϕ=1)fuel-air mixture in channel has been analyzed for effect of blockage ratio (BR)=0.39, 0.51, 0.59, 0.71 with spacing of 2D and 3D. The reactive Navier-Stokes equation is used to solve the detonation wave propagation mechanism in Ansys Fluent platform. The result shows that fully developed detonation wave initiation regime is observed near smaller vortex generator ratio of BR=0.39 inside the combustor. The turbulent rate of reaction has also a great significance role for shock wave structure. However, vortices of rapid detonation wave are appears near thin boundary layer of each obstacle. Finally, detonation combustor demonstrates the superiority of pressure gain combustor with turbulent rate of reaction of 0.6 kg mol/m3 -s inside the detonation tube with obstacle spacing of 12 cm, this blockage enhanced the turbulence intensity and propulsive thrust. The successful detonation wave propagation speed is achieved in shortest possible time of 0.031s with a significance magnitude of 2349 m/s, which is higher than Chapman-Jouguet (C-J) velocity of 1848 m/s. Furthermore, stronger propulsive thrust force of 36.82 N is generated in pulse time of 0.031s.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.16-23
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• 2013

An experimental study has been conducted to investigate the effects of equivalence ratio on the propagation characteristics of $CH_4$-air premixed flame intervened by an ultrasonic standing wave. A Schlieren photography was used for the flame structure visualization, and the flame propagation behavior was investigated in detail throughout the post-processing analysis. It is found that the structural variation of methane/air premixed flame caused by the intervention of ultrasonic standing wave give rise to the enhancement of combustion reaction and flame propagation velocity. Effectiveness of the standing wave on the flame velocity decreases as the equivalence ratio increases. Larger flame velocity with the standing wave becomes undistinguishable in a specific range of equivalence ratios.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.221-224
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• 2003

A numerical study is carried out for the detonation wave propagation through a T-branch. The T-branch is a crucial part of the combustion wave igniter, a novel concept of rocket ignition system aimed for the simultaneous ignition of multiple combustion chambers by delivering detonation waves. Euler equation and induction parameter equation are used as governing equations with a reaction term modeled from the chemical kinetics database obtained from a detailed chemistry mechanism. Second-order accurate implicit time integration and third-order space accurate TVD algorithm were used for solution of the coupled equations. Over two-million grid points enabled the capture of the dynamics of the detonation wave propagation including the degeneration and re-initiation phenomena, and some of the design factors were be obtained for the CWI flame tubes.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.83-91
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• 1996

A numerical study is carried out to examine the ignition and propagation process of detonation wave in SCRam-accelerator operating in superdetonative mode. The time accurate solution of Reynolds averaged Navier-Stokes equations for chemically reacting flow is obtained by using the fully implicit numerical method and the higher order upwind scheme. As a result, it is clarified that the ignition process has its origin to the hot temperature region caused by shock-boundary layer interaction at the shoulder of projectile. After the ignition, the oblique detonation wave is generated and propagates toward the inlet while constructing complex shock-shock interaction and shock-boundary layer interaction. Finally, a standing oblique detonation wave is formed at the conical ramp.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.628-631
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• 2017

An experimental study of the combustion characteristics according to the equivalence ratio of hydrocarbon fuel/air premixture excited by ultrasonic standing wave are presented. The image of the propagating flame was acquired using a high-speed camera, and the combustion characteristics of each fuel were closely observed through image processing. it was conformed that ultrasonic standing wave has been found to stimulate the combustion reaction in the stoichiometric ratio.

• 한국가시화정보학회:학술대회논문집
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• 2004.04a
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• pp.29-36
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• 2004

A numerical study is carried out on the detonation wave propagation through a T-shaped flame tube, which represents a crucial part of the combustion wave ignition (CWI) system aimed for simultaneous ignition of multiple combustion chambers by delivering detonation waves. The formulation includes the Euler equations and an induction-parameter model. The reaction rate is treated based on a chemical kinetics database obtained from a detailed chemistry mechanism. A second-order implicit time integration and a third-order TVD algorithm are Implemented to solve the theoretical model numerically. A total of more than two-million grid points are used to provide direct insight into the dynamics of the detonation wave. Several important phenomena including detonation wave propagation, degeneration, and re-initiation are carefully examined. Information obtained can be effectively used to facilitate the design and optimization of the flame tubes of CWI systems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.294-299
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• 2012

An investigation into the influence of ultrasonic standing wave on the structural behavior of propane/air premixed flame has been made to get a clue to the combustion reaction acceleration and combustion instability, as well. Visualization technique utilizing the Schlieren method was employed for the observation of structural variation of the premixed flame. The flame shape and propagation velocity were measured according to the variation of equivalence ratio. It was found that the standing wave distorted the flame front and expedited a transition to the flame with turbulent nature.