Effect of condensed powder phase reactions on the stability of steady-state combustion processes

A study has been made of the low-frequency stability of powder combustion in a semiclosed chamber, working within the framework of a linear theory with account taken of condensed-phase (k-phase) inertia and evolution of thermal energy. The case treated is that of the first-order reaction. It is shown that k-phase exothermic chemical decomposition increases the stability of the combustion process. The results of numerical computations are interpreted.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 102–111, September–October, 1973.     

Shock slip-relations for thermal and chemical nonequilibrium flows

This paper appears to be the first where the multi-temperature shock slip-relations for the thermal and chemical nonequilibrium flows are derived. The derivation is based on analysis of the influences of thermal nonequilibrium and viscous effects on the mass, momentum and emergy flux balance relations at the shock wave. When the relaxation times for all internal energy modes tend to zero, the multi-tmperature shock slip-relations are converted into single-temperature ones for thermal equilibrium flows. The present results can be applied to flow over vehicles of different geometries with or without angles of attack. In addition, the present single-temperature shock slip-relations are compared with those in the literature, and some defects and limitations in the latter are clarified. The project supported by the National Natural Science Foundation of China and the National Defence Science and Industry Commission of China.     

Relaxation oscillations in combustion models of thermal self-ignition

Combustion processes are classified into three types depending upon the amount of fuel supply: two of them are the stationary states with either low or high temperatures and the other is the periodic state with relaxation oscillation type. We analyze the dependency of these processes on the amount of fuel supply by using the fast and slow dynamics approach.     

Effect of freestream nonequilibrium on flow past a wedge

We examine the effect of flow freezing in the nozzle of a hypersonic wind tunnel on the parameters of nonequilibrium flow past a wedge.Zhigulev's solution [1] for vibrational relaxation is extended to the nonequilibrium freestream case.It is shown that in this case the perturbations of the frozen-flow parameters behind the oblique shock wave can change sign if the flow in the working section deviates significantly from equilibrium.A method is proposed for converting experimental results obtained in tunnels with frozen flow to the case of equilibrium freestream flow past the body.The author wishes to thank O. Yu. Polyanskyi and V. P. Agavonov for their interest in this study.     

The effects of local thermal nonequilibrium and MFD viscosity on the onset of Brinkman ferroconvection

The simultaneous effect of local thermal nonequilibrium (LTNE) and magnetic field dependent (MFD) viscosity on thermal convective instability in a horizontal ferrofluid saturated Brinkman porous layer in the presence of a uniform vertical magnetic field is studied analytically. The results indicate that the onset of Brinkman ferroconvection is delayed with increasing MFD viscosity parameter but the critical wave number is found to be independent of this parameter. When compared to the simultaneous presence of buoyancy and magnetic forces, it is observed that the onset of Brinkman ferroconvection is delayed more when the magnetic forces alone are present. Asymptotic solutions for both small and large values of scaled inter-phase heat transfer coefficient H _t are compared with those computed numerically and good agreement is found between them. Besides, the influence of magnetic and LTNE parameters on the stability characteristics of the system is also discussed. The available results in the literature are recovered as particular cases from the present study.     

Effect of inelastic electron — Atom collisions on nonequilibrium ionization rate

We study possible formulations of the processes taking place near the cathode of the low-voltage arc as a function of the relationship between the electron Coulomb free path (_ee) and the free path for elastic scattering of electrons by atoms (₀) on the one hand, and for inelastic scattering (₁), on the other hand. Expressions are obtained for the correction to the Maxwellian distribution function, the local and overall nonequilibrium ionization rate with atoms. Results of computer numerical calculations are presented.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 11, No. 3, pp. 42–46, May–June, 1970.     

Optical study on thermal radiation energy of diesel spray combustion in a shock tube

A tailored interface shock tube was used to measure the thermal energy radiated from diesel-spray combustion. Experiments were performed in a steel shock tube with a seven m long low-pressure section filled with air and a six m long high-pressure section. Pre-compressed fuel was injected through a throttling nozzle into air behind a reflected shock wave. Monochromatic emissive powers and emissive powers of the whole IR-wavelengths were followed with IR-detectors set along the central axis of the tube. Time-dependent-radii, where soot particles radiate, were also determined. Results were : (1) the tailored interface shock tube could be applied to a study of diesel-spray combustion. (2) thermal radiation energy could be described well from the ignition delay of the fuel spray.PACS: 47.40.Nm, 47.70.Mc     

A study of thermal nonequilibrium effects in low-pressure wet-steam turbines using a blade-to-blade time-marching technique

A theoretical analysis of the wet-steam flow in the low pressure cylinder of a 500 MW steam turbine using a blade-to-blade time-marching computer program is described. The calculating method can compute most types of wet-steam flow found in LP turbines, including those involving both primary and secondary nucleations in transonic and supersonic blading with shock waves. In particular, condensing flows in highly staggered rotor tip sections can be computed without difficulty. Extensive results are presented showing the effect of departures from thermal equilibrium on the blade surface pressure and velocity distributions, the blade outlet relative flow angle, the mass flow coefficient and the thermodynamic loss coefficient. On the basis of the analysis, recommendations are made concerning the application of nonequilibrium wet-steam theory to steam turbine design.     

Detonation combustion of hydrogen in a Laval nozzle under rarefied atmosphere conditions

Detonation combustion of a hydrogen-air mixture entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered under atmospheric conditions at altitudes up to 24 km. The investigation is carried out on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. The limiting altitude ensuring detonation combustion in a Laval nozzle of given geometry is numerically established for freestream Mach numbers 6 and 7. The possibility of the laser initiation of detonation in a supersonic flow of a stoichiometric, preliminarily heated hydrogen-air mixture is experimentally studied. The investigation is carried out in a shock tube under conditions simulating a supersonic flow in the nozzle throat region.     

Detonation combustion of hydrogen in an axisymmetric channel with a central body

The problem of initiation and stabilization of detonation combustion of a hydrogen–air mixture injected into an axisymmetric channel with a finite-length central body in a flow with a Mach number M₀ = 5–9 is solved. It is numerically demonstrated that the presence of the central body both in a convergent–divergent nozzle and in an expanding channel leads to stabilization of detonation combustion of a stoichiometric hydrogen–air mixture at free-stream Mach numbers M₀ > 7. Various channel configurations that ensure different values of thrust generated by detonation combustion of a stoichiometric hydrogen–air mixture are compared.     

Initiation and stabilization of combustion at low pressure and temperature by means of a nonequilibrium electric discharge

The pattern of supersonic (M = 2) flow near the surface of a plate at points on which propane jets are injected normal to the air flow direction is investigated. For the initiation and intensification of the chemical reactions a nonequilibrium discharge is used. This is created between an anode oriented along the flow, the plate surface, and a metal interceptor mounted on the plate. The results of a schlieren visualization of the flows developed are presented. Spectroscopic studies show that the distribution of plasmochemical reaction products has a number of fundamental differences as compared with the case of propane injection along the plate surface. A comparative analysis of these distributions for identical gasdynamical experimental conditions is important for testing calculation models of reactive-mixture supersonic flows in which electric discharges are used for ignition and the stabilization of combustion.     

Transverse and parallel injection of hydrogen with supersonic combustion in a shock tunnel

An experimental comparison has been made of the combustion induced pressure rise in a constant area duct when hydrogen is injected transverse to the flow by using a surface orifice, and when it is injected parallel to the flow by using a central injection strut. The experiments were conducted in a shock tunnel at a flow Mach number of 4.2 and stagnation enthalpies of 5.6, 6.5 and 8.9 MJ kg. Both room temperature and heated hydrogen were injected, and a method of heating the hydrogen by compression in a gun tunnel which was slaved to the shock tunnel is described. It was found that, for both unheated and heated hydrogen, the combustion pressure rise was not measurably dependent on the method of introducing the hydrogen, not withstanding the complicated shock related flow pattern arising from transverse injection. Received August 14, 1995 / Accepted February 14, 1996     

Numerical study on supersonic mixing and combustion with hydrogen injection upstream of a cavity flameholder

Characteristics of supersonic mixing and combustion with hydrogen injection upstream of a cavity flameholder are investigated numerically using hybrid RANS/LES (Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation) method. Two types of inflow boundary layer are considered. One is a laminar-like boundary layer with inflow thickness of $\delta_{\inf } = 0.0$ and the other is a turbulent boundary layer with inflow thickness of $\delta_{\inf } = 2.5\,{\text{mm}}$ . The hybrid RANS/LES method acts as a DES (Detached Eddy Simulation) model for the laminar-like inflow condition and a wall-modeled LES for the turbulent inflow condition where the recycling/rescaling method is adopted. Although the turbulent inflow seems to have just minor influences on the supersonic cavity flow without fuel injection, its effects on the mixing and combustion processes are great. It is found that the unsteady turbulent structures in upstream incoming boundary layer interact with the injection jet, resulting in fluctuations of the upstream recirculation region and bow shock, and induce quick dispersion of the hydrogen fuel jet, which enhances the mixing as well as subsequent combustion.