Diffusion flames and supersonic combustion 2

Some problems related to the fluid dynamical and chemical phenomena appearing near the injector exit of an idealized supersonic combustion burner, are theoretically investigated. When hydrogen is injected into a coflowing supersonic stream of air,a wake-like configuration appears in most cases,improving the mixing process. It is only natural to suggest that whenever the ignition delay length, computed assuming isobaric mixing and reaction, is not much larger than the recirculation zone length, the wake will influence the ignition zone. In order to calculate the ignition delay length, the usual assumption is made that fuel and oxidizer mix without appreciable concentration change and heat release resulting from chemical reactions, although radicals, mainly atomic hydrogen, are produced. The chemical kinetics scheme is reduced to one overall chemical reaction; and the presence of radicals introduced in the mixing zone from outside is taken into account. A two-dimensional mixing zone has been considered. Although many different mechanisms will be responsible for the fortuitous or provoked production of these radicals either in real flight or in ground testing facilities, dissociation at the injector outer boundary layer is considered in this paper as the main radicals producing mechanism. As it is shown, the temperature of the injector outer wall and, to a less extent, pressure, injector length and the conditions outside of the boundary layer, control the amount of radicals introduced in the mixing layer, and hence the ignition delay length. Finally, it is shown that ignition delay lengths are, in most cases of interest, comparable to the near-wake length. The paper ends with a discussion of the main weaknesses of the work presented and with some suggestions for further work

Hydrogen as a fuel. some aspects of its combustion processes

The possibility of utilizing hydrogen as a fuel in air breathing power plants or in other energy conversion systems in a near future has been extensively studied and discussed, as for example, in the First World Hydrogen Energy Conference, including the associated problems of energy storage and energy transportation. Research on combustion of hydrogen has been mainly pionered through aerospace programs, due to the fact of the high interest of hydrogen both as a propellant for liquid fueled rocket motors, and as a fuel of excellent characteristics for air breathing engines, for the propulsion of subsonic, supersonic and hypersonic vehicles

Zero-G Gauging systems. CONTRACT No 17/8/4

Various systems for measuring propellant content in spacecrafts under weightlessness conditions are reviewed. The cavity resonator method is found to be the most suitable measurement; technique. This method is analyzed in detail. A determination of errors intrinsec to the method is carried out

A theoretical model for the combustion of droplets in supercritical conditions and gas pockets

Supercritical combustion of droplets is studied by means of a physical model which assumes spherical symmetry, laminar conditions, constant pressure and a zero-thickness flame. Boundary conditions at the infinity state that temperature and composition of the mixture are given and constant. Initial distributions of temperature and mass fractions of the species are given, as well as the initial conditions at the droplet surface. As combustion proceeds, droplet surface is not considered to exist as a physical boundary allowing unrestricted diffusion of species through it. With some additional simplifications for the density and t r ansport coefficients, a numerical solution of the problem is obtained. An analytical solution of the problem is also obtained by means of an asymptotic analysis. This solution applies when the initial temperature of the droplet is small as compared with the temperature of the sourounding atmosphere. It is shown that this is the most impor t ant case from the technological point of view. For this case results show that an apparent droplet exists throughout most of the process, in which its surface is characterized by an abrupt change in temperature and composition of the chemical species. Results show burning rates, combustion times, flame radius and temperature at the droplet center as function of the principal variables of the process. In particular, the square of the apparent droplet radius is a linear function of time as occurs in subcritical combustion. It is shown that combustion times are faster in supercritical conditions than in subcritical conditions with the minimum value existing at critical conditions. A numerical application is carried out for the case of oxygen droplets burning in hydrogen and a comparison is carried out between the theoretical results obtained numerically and analytically as well as with those experimentally obtained

Estudio del aprovechamiento de la energía eólica para la agricultura en España

En el presente trabajo se lleva a cabo un estudio preliminar del posible aprovechamiento de la energía eólica para la Agricultura en España, centrándose fundamentalmente el estudio en el problema del riego. Se incluye en primer lugar en el trabajo un breve análisis de las particularidades que presenta la energía eólica en su aplicación a las diferentes tareas y demandas energéticas que se requieren en la Agricultura, analizándose el grado de aplicabilidad en cada caso

On diffusive supersonic combustion (chemical kinetic effects in diffusive supersonic combustion)

Simple analytical methods are presented for the analysis of chemical kinetic effects in supersonic combustion. Three different regions are shown to occur in supersonic diffusive combustion. The first region is close to the injector exit, where the flow may be considered frozen for the main reacting species and where the radical concentration is being built up. This is the ignition delay region. A simplified kinetic scheme of the H2-air reaction is deduced for this region. The linear differential equation giving the H concentration has been discussed and integrated in a representative case. In terms of this solution the limits of the ignition region may be determined. Far from the injector exit the flow is close to chemical equilibrium. The reaction region is very thin, so that convection effects may be neglected. Then the governing equations reduce to ordinary differential equations, that may be integrated by using an integral method. In this way, deviations from equilibrium may be determined in terms of the reaction kinetics. An extension of the integral method, developed for the analysis of the near-equilibrium region is proposed for the study of the transition region

On the formation of nitrogen oxides in the combustion processes of hydrogen in air

A research programme is being carried out at the Institute Nacional de Tecnica Aeroespacial of Spain, on several aspects of the formation of nitrogen oxides in continuous flow combustion systems, considering hydrogen and hydrocarbons as fuels. The research programme is fundamentally oriented on the basic aspects of the problem, although it also includes the study of the influence on the formation process of several operational and design variables of the combusters, such as type of fuels, fuel/air ratio, degree of mixing in premixed type flames, existence of droplets as compared with homogeneous combustion.This problem of nitrogen oxides formation is receiving lately great attention, specially in connection with automobile reciprocating engines and aircraft gas turbines. This is due to the fact of the increasing frequency and intensity of photochemical hazes or smog, typical of urban areas submitted to strong solar radiation, which are originated by the action on organic compounds of the oxidants resulting from the photochemical decomposition of nitrogen dioxide N02. In the combustion process almost all nitrogen oxides are in form of NO. This nitric oxide reacts with the oxygen of the air and forms N02, this reaction only taking place in or near the exhaust of tne motors, since the N0-02 reaction becomes frozen for the concentration existing in the atmosphere

The influence of launching errors on the trajectory of space probes

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