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At least 289 records · Page 16

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NASA NTRS1974

Development of a global pollution model for CO, CH4, and CH2O

The current status of a global pollution model for carbon monoxide, methane, and formaldehyde is described. The physico-chemical action is considered of these three pollutants in the troposphere. This geographic restriction is convenient since the tropopause provides a natural boundary across which little transport occurs. The data on sources and sinks for these pollutants is based on available information and assumptions relative to the major man-made and natural contributions. The distributions and concentrations of methane, formaldehyde, and carbon monoxide in the atmosphere are interrelated by the chemical reactions in which they participate. A chemical kinetic model based on the pseudo-steady state approximation for the intermediate species was developed to account for these reactions. The numerical procedure used to mathematically describe the pollution transport is a mass conservative scheme employing an integral flux approach.

Peters, L. K.↗

NASA NTRS1974

The chemistry and diffusion of aircraft exhausts in the lower stratosphere during the first few hours after fly-by

An analysis of the hydrogen-nitrogen-oxygen reaction systems in the lower stratosphere as they are initially perturbed by individual aircraft engine exhaust plumes was conducted in order to determine whether any significant chemical reactions occur, either among exhaust chemical species, or between these species and the environmental ozone, while the exhaust products are confined to intact plume segments at relatively high concentrations. The joint effects of diffusive mixing and chemical kinetics on the reactions were also studied, using the techniques of second-order closure diffusion/chemistry models. The focus of the study was on the larger problem of the potential depletion of ozone by supersonic transport aircraft exhaust materials emitted into the lower stratosphere.

Hilst, G. R.↗

NASA NTRS1973

Recent developments in shock tube research; Proceedings of the Ninth International Symposium, Stanford University, Stanford, Calif., July 16-19, 1973

Recent advances in shock tube research are described in papers dealing with the design and performance features of new devices as well as applications in aerodynamic, chemical, and physics experiments. Topics considered include a cryogenic shock tube for studying liquid helium fluid mechanics, studies of shock focusing and nonlinear resonance in shock tubes, applications in gas laser studies, very-low and very-high temperature chemical kinetic measurements, shock tube studies of ionization and recombination phenomena, applications in bioacoustic research, shock-tube simulation studies of sonic booms, and plasma research. Individual items are announced in this issue.

Bershader, D.↗

NASA NTRS1974

Decomposition of nitric oxide in a hot nitrogen stream to synthesize air for hypersonic wind tunnel combustion testing

A clean source of high enthalpy air was obtained from the exothermic decomposition of nitric oxide in the presence of strongly heated nitrogen. A nitric oxide jet was introduced into a confined coaxial nitrogen stream. Measurements were made of the extent of mixing and reaction. Experimental results are compared with one- and two-dimensional chemical kinetics computations. Both analyses predict much lower reactivity than was observed experimentally. Inlet nitrogen temperatures above 2400 K were sufficient to produce experimentally a completely reacted gas stream of synthetic air.

Zumdieck, J. F.↗

NASA NTRS1975

A study of reacting free and ducted hydrogen/air jets

The mixing and reaction of a supersonic jet of hydrogen in coaxial free and ducted high temperature test gases were investigated. The importance of chemical kinetics on computed results, and the utilization of free-jet theoretical approaches to compute enclosed flow fields were studied. Measured pitot pressure profiles were correlated by use of a parabolic mixing analysis employing an eddy viscosity model. All computations, including free, ducted, reacting, and nonreacting cases, use the same value of the empirical constant in the viscosity model. Equilibrium and finite rate chemistry models were utilized. The finite rate assumption allowed prediction of observed ignition delay, but the equilibrium model gave the best correlations downstream from the ignition location. Ducted calculations were made with finite rate chemistry; correlations were, in general, as good as the free-jet results until problems with the boundary conditions were encountered.

Beach, H. L., Jr.↗

NASA NTRS1975

The NATA code: Theory and analysis, volume 1

A computer program for calculating quasi-one-dimensional gas flow in axisymmetric and two-dimensional nozzles and rectangular channels is presented. Flow is assumed to start from a state of thermochemical equilibrium at a high temperature in an upstream reservoir. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. Electronic nonequilibrium effects can be included using a two-temperature model. An approximate laminar boundary layer calculation is given for the shear and heat flux on the nozzle wall. Boundary layer displacement effects on the inviscid flow are considered also. Chemical equilibrium and transport property calculations are provided by subroutines. The code contains precoded thermochemical, chemical kinetic, and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It provides calculations of the stagnation conditions on axisymmetric or two-dimensional models, and of the conditions on the flat surface of a blunt wedge. The primary purpose of the code is to describe the flow conditions and test conditions in electric arc heated wind tunnels.

Bade, W. L.↗

NASA NTRS1975

Gas turbine combustor stabilization by heat recirculation

The feasibility of heat recirculation for stabilization of lean mixtures and emission reduction has been studied in detail for a typical aircraft gas turbine combustor. Thermodynamic calculations have indicated temperature and heat recirculation rates for operation of the combustor over a range of combustion zone equivalence ratios and for varying modes of desired engine operation. Calculations indicate the feasibility of stabilizing the combustion zone at equivalence ratios as low as 0.2 with achievable heat recirculation rates. Detailed chemical kinetic calculations suggest that combustor heat release is maintained with reaction completion substantially before the NO forming reactions, even though CO is rapidly oxidized in this same region.

Ganji, A.↗

NASA NTRS1975

Further development of a global pollution model for CO, CH4, and CH2 O

Global tropospheric pollution models are developed that describe the transport and the physical and chemical processes occurring between the principal sources and sinks of CH4 and CO. Results are given of long term static chemical kinetic computer simulations and preliminary short term dynamic simulations.

Peters, L. K.↗

NASA NTRS1975

The NATA code; theory and analysis. Volume 2: User's manual

The NATA code is a computer program for calculating quasi-one-dimensional gas flow in axisymmetric nozzles and rectangular channels, primarily to describe conditions in electric archeated wind tunnels. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. The shear and heat flux on the nozzle wall are calculated and boundary layer displacement effects on the inviscid flow are taken into account. The program contains compiled-in thermochemical, chemical kinetic and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It calculates stagnation conditions on axisymmetric or two-dimensional models and conditions on the flat surface of a blunt wedge. Included in the report are: definitions of the inputs and outputs; precoded data on gas models, reactions, thermodynamic and transport properties of species, and nozzle geometries; explanations of diagnostic outputs and code abort conditions; test problems; and a user's manual for an auxiliary program (NOZFIT) used to set up analytical curvefits to nozzle profiles.

Bade, W. L.↗

NASA NTRS1976

Numerical analysis of a two-dimensional nonsteady detonations

In the present work a system of two-dimensional nonsteady hydrodynamic and chemical kinetic equations was numerically integrated for an exothermic system. Assumed two-step reaction model simulates practically an oxyhydrogen mixture. The calculation starts from a plane Chapman-Jouguet detonation as an initial condition. Two-dimensional disturbances are generated by artificially placing nonuniformities ahead of the detonation front. Regardless of the difference of the given initial disturbances, a fixed number of triple shock waves were produced for a fixed combination of mixture model and geometry when the transition period was over. This shows that for a given detonation tube geometry any exothermic system has its own characteristic multidimensional structure. The obtained number of triple shock waves contained in the detonation front was in agreement with existing experimental observations under the same condition.

Taki, S.↗

NASA NTRS1976

Composite propellant combustion modeling with a porous plate burner

A burner is designed to model on a large scale (millimeters) the complex vapor phase processes that take place on awkwardly small scales (about a hundred microns) in the combustion of practical AP/ composite propellants at conventional pressures. Binder vapor evolution is modeled with gaseous fuel (ethane in the experiments reported) flow through a porous plate and oxidizer vapor with the flow of a gaseous oxidizer (air and enriched air in the experiments reported) through discrete holes in the porous plate. Measured flame standoff distance and surface temperature variations are consistent with theoretical predictions at atmospheric pressure. Data obtained at several atmospheres are discussed in the light of the current theories of propellant burning that place varying emphasis on the roles of chemical kinetics and fluid dynamic diffusion/mixing in the vapor phase of a burning composite propellant. The potential and proposed future applications of the burner are indicated.

Kumar, R. N.↗

NASA NTRS1976

Hydrogen-fueled scramjets: Potential for detailed combustor analysis

Combustion research related to hypersonic scramjet (supersonic combustion ramjet) propulsion is discussed from the analytical point of view. Because the fuel is gaseous hydrogen, mixing is single phase and the chemical kinetics are well known; therefore, the potential for analysis is good relative to hydro-carbon fueled engines. Recent progress in applying two and three dimensional analytical techniques to mixing and reacting flows indicates cause for optimism, and identifies several areas for continuing effort.

Beach, H. L., Jr.↗

NASA NTRS1977

Modeling the complete Otto cycle: Preliminary version

A description is given of the equations and the computer program being developed to model the complete Otto cycle. The program incorporates such important features as: (1) heat transfer, (2) finite combustion rates, (3) complete chemical kinetics in the burned gas, (4) exhaust gas recirculation, and (5) manifold vacuum or supercharging. Changes in thermodynamic, kinetic and transport data as well as model parameters can be made without reprogramming. Preliminary calculations indicate that: (1) chemistry and heat transfer significantly affect composition and performance, (2) there seems to be a strong interaction among model parameters, and (3) a number of cycles must be calculated in order to obtain steady-state conditions.

Zeleznik, F. J.↗

NASA NTRS1977

The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 1: The one-dimensional model

A one-dimensional model of stratospheric trace constituents is described in detail. Specifically, the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations representing the chemical kinetic terms, and an appropriate method for simulating the diurnal variations of the species concentrations, are discussed. A specialized treatment of atmospheric photodissociation rates is outlined in the text. The choice of a vertical eddy diffusivity profile and its success in predicting the vertical tracer distributions (carbon 14, methane, and nitrous oxide) are also discussed.

Turco, R. P.↗

NASA NTRS1977

The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 2: The two-dimensional model

The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions.

Whitten, R. C.↗

NASA NTRS1977

An experimental study of reactive turbulent mixing

An experimental study of the turbulent mixing of two coaxial gas streams, which react very rapidly (pseudo-hypergolic chemical kinetics), was performed to investigate the mixing characteristics of turbulent flow fields. The center stream consisted of a CO-N2 mixture and the outer annular stream consisted of air vitiated by H2 combustion. The streams were at equal velocity (50 m/sec) and temperature (1280 K). Turbulence measurements were obtained using hot film anemometry. A sampling probe was used to obtain time averaged gas compositions. Six different turbulence generators were placed in the annular passage to alter the flow field mixing characteristics. The turbulence generators affected the bulk mixing of the streams and the extent of CO conversion to different degrees. The effects can be related to the average eddy size and the bulk mixing. Higher extents of conversion of CO to CO2 were found by increasing the bulk mixing and decreasing the average eddy size.

Cooper, L. P.↗

NASA NTRS1977

Modeling the complete Otto cycle - Preliminary version

Zeleznik, F. J.↗

NASA NTRS1977

Further calculations based upon a theory of flame spread across solid fuels

A theory of flame spread above solid fuel beds of finite or infinite thickness is considered. Heat transfer ahead of the flame is allowed through both the solid and gas phases. The simplifying assumption of a surface reaction is made. Temperature profiles in both phases, concentration profiles in the gas phase, heat transfer at the surface, and flame spreading rates are determined. It is found that chemical kinetic parameters together with transport properties strongly influence the spreading rate. Heat transfer through the gas phase is the dominant mechanism for energy transfer ahead of the spreading flame over a wide range of Peclet numbers for the gas and solid phases.

Feng, C. C.↗