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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Preliminary tests of an advanced high-temperature combustion system

A combustion system has been developed to operate efficiently and with good durability at inlet pressures to 4.05 MPa (40 atm), inlet air temperatures to 900 K, and exhaust gas temperatures to 2480 K. A preliminary investigation of this system was conducted at inlet pressures to 0.94 MPa (9 atm), a nominal inlet air temperature of 560 K, and exhaust gas temperatures to 2135 K. A maximum combustion efficiency of 98.5 percent was attained at a fuel-air ratio of 0.033; the combustion efficiency decreased to about 90 percent as the fuel-air ratio was increased to 0.058. An average liner metal temperature of 915 K, 355 kelvins greater than the nominal inlet air temperature, was reached with an average exhaust gas temperature of 2090 K. The maximum local metal temperature at this condition was about 565 kelvins above the nominal inlet air temperature and decreased to 505 kelvins above with increasing combustor pressure. Tests to determine the isothermal total pressure loss of the combustor showed a liner loss of 1.1 percent and a system loss of 6.5 percent.

Wear, J. D.↗
NASA NTRS1983

Summary of synfuel characterization and combustion studies

Combustion component research studies aimed at evolving environmentally acceptable approaches for burning coal derived fuels for ground power applications were performed at the NASA Lewis Research Center under a program titled the ""Critical Research and Support Technology Program'' (CRT). The work was funded by the Department of Energy and was performed in four tasks. This report summarizes these tasks which have all been previously reported. In addition some previously unreported data from Task 4 is also presented. The first, Task 1 consisted of a literature survey aimed at determining the properties of synthetic fuels. This was followed by a computer modeling effort, Task 2, to predict the exhaust emissions resulting from burning coal liquids by various combustion techniques such as lean and rich-lean combustion. The computer predictions were then compared to the results of a flame tube rig, Task 3, in which the fuel properties were varied to simulate coal liquids. Two actual SRC 2 coal liquids were tested in this flame tube task.

Schultz, D. F.↗
NASA NTRS1983

New trends in combustion research for gas turbine engines

Research on combustion is being conducted to provide improved analytical models of the complex flow and chemical reaction processes which occur in the combustor of gas turbine engines, in order to enable engine manufacturers to reduce the development time of these concepts. The elements of the combustion fundamentals program is briefly discussed with examples of research projects described more fully. Combustion research will continue to emphasize the development of analytical models and the support of these models with fundamental flow experiments to assess the models accuracy and shortcomings. Previously announced in STAR as N83-20947

Mularz, E. J.↗
NASA NTRS1984

Combustion characteristics in the transition region of liquid fuel sprays

A number of important effects were observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NO(x) formation. Unfortunately, because of differences in experimental facilities and limitations in the ranges of experimental data, a unified description of these transition region effects is not available at this time. Consequently, a fundamental experimental investigation was initiated to study the effect of droplet size, size distribution, and operating parameters on these transition region phenomena in a single well controlled spray combustion facility.

Cernansky, N. P.↗
NASA NTRS1984

Experimental and theoretical deposition rates from salt-seeded combustion gases of a Mach 0.3 burner rig

Deposition rates on platinum-rhodium cylindrical collectors rotating in the cross streams of the combustion gases of a salt-seeded Mach 0.3 burner rig were determined. The collectors were internally air cooled so that their surface temperatures could be widely varied while they were exposed to constant combustion gas temperatures. The deposition rates were compared with those predicted by the chemically frozen boundary layer (CFBL) computer program, which is based on multicomponent vapor transport through the boundary layer. Excellent agreement was obtained between theory and experiment for the NaCl-seeded case, but the agreement lessened as the seed was changed to synthetic sea salt, NaNO3, and K2SO4, respectively, and was particularly poor in the case of Na2SO4. However, when inertial impaction was assumed to be the deposition mechanism for the Na2SO4 case, the predicted rates agreed well with the experimental rates. The former were calculated from a mean particle diameter that was derived from the measured intial droplet size distribution of the solution spray. Critical experiments showed that liquid phase deposits were blown off the smooth surface of the platinum-rhodium collectors by the aerodynamic shear forces of the high-velocity combustion gases but that rough or porous surfaces retained their liquid deposits.

Santoro, G. J.↗
NASA NTRS1984

Measurement of spray combustion processes

A free jet configuration was chosen for measuring noncombusting spray fields and hydrocarbon-air spray flames in an effort to develop computational models of the dynamic interaction between droplets and the gas phase and to verify and refine numerical models of the entire spray combustion process. The development of a spray combustion facility is described including techniques for laser measurements in spray combustion environments and methods for data acquisition, processing, displaying, and interpretation.

Peters, C. E.↗
NASA NTRS1984

Fast algorithms for combustion kinetics calculations: A comparison

To identify the fastest algorithm currently available for the numerical integration of chemical kinetic rate equations, several algorithms were examined. Findings to date are summarized. The algorithms examined include two general-purpose codes EPISODE and LSODE and three special-purpose (for chemical kinetic calculations) codes CHEMEQ, CRK1D, and GCKP84. In addition, an explicit Runge-Kutta-Merson differential equation solver (IMSL Routine DASCRU) is used to illustrate the problems associated with integrating chemical kinetic rate equations by a classical method. Algorithms were applied to two test problems drawn from combustion kinetics. These problems included all three combustion regimes: induction, heat release and equilibration. Variations of the temperature and species mole fraction are given with time for test problems 1 and 2, respectively. Both test problems were integrated over a time interval of 1 ms in order to obtain near-equilibration of all species and temperature. Of the codes examined in this study, only CREK1D and GCDP84 were written explicitly for integrating exothermic, non-isothermal combustion rate equations. These therefore have built-in procedures for calculating the temperature.

Radhakrishnan, K.↗
NASA NTRS1984

Combustion diagnostics by nonintrusive methods; Thermophysics Conference, 18th, Montreal, Canada, June 1-3, 1983, Selected Papers

The state of the art in coherent anti-Stokes Raman scattering (CARS) and laser-induced fluorescence (LIF) is outlined, and current diagnostic capabilities in particle and combustion diagnostics are demonstrated. The development and application of CARS to combustion systems is discussed, and the use of LIF for flow diagnostics is addressed. Nonintrusive particle diagnostics is treated, and a variety of nonintrusive techniques applied to combustion environments is considered.

Mccay, T. D.↗
NASA NTRS1982

Combustion hot section technology

The Turbine Engine Hot Section Technology Combustion Program is briefly described. The overall objective of the project is to develop and verify improved and more accurate analysis methods for increasing the ability to design with confidence the combustion system for advanced aircraft turbine engines. The approach is to first assess and evaluate existing combustor aerothermal analysis models by means of a contracted effort initiated during FY-82. The program also includes both analytical and experimental research efforts in the areas of aerothermal modeling and liner cyclic life. It is expected that the combustor model development effort will generate improved understanding in the areas of high pressure flame radiation characteristics, model numerical methods and solution schemes, complex geometrical boundary conditions, fuel spray - flow field interactions, combustion kinetics, flow and mixing of dilution jets, turbulence and heat transfer, and soot and carbon formation.

Ercegovic, D. B.↗
NASA NTRS1985

Modeling the internal combustion engine

A flexible and computationally economical model of the internal combustion engine was developed for use on large digital computer systems. It is based on a system of ordinary differential equations for cylinder-averaged properties. The computer program is capable of multicycle calculations, with some parameters varying from cycle to cycle, and has restart capabilities. It can accommodate a broad spectrum of reactants, permits changes in physical properties, and offers a wide selection of alternative modeling functions without any reprogramming. It readily adapts to the amount of information available in a particular case because the model is in fact a hierarchy of five models. The models range from a simple model requiring only thermodynamic properties to a complex model demanding full combustion kinetics, transport properties, and poppet valve flow characteristics. Among its many features the model includes heat transfer, valve timing, supercharging, motoring, finite burning rates, cycle-to-cycle variations in air-fuel ratio, humid air, residual and recirculated exhaust gas, and full combustion kinetics.

Zeleznik, F. J.↗
NASA NTRS1985

Fuel-rich catalytic combustion: A soot-free technique for in situ hydrogen-like enrichment

An experimental program on the catalytic oxidation of iso-octane demonstrated the feasibility of the two-stage combustion system for reducing particulate emissions. With a fuel-rich (phi = 4.8 to 7.8) catalytic combustion preburner as the first stage the combustion process was soot free at reactor outlet temperatures of 1200 K or less. Although soot was not measured directly, its absence was indicated. Reaction products collected at two positions downstream of the catalyst bed were analyzed on a gas chromatograph. Comparison of these products indicated that pyrolysis of the larger molecules continued along the drift tube and that benzene formation was a gas-phase reaction. The effective hydrogen-carbon ratio calculated from the reaction products increased by 20 to 68 percent over the range of equivalence ratios tested. The catalytic partial oxidation process also yielded a large number of smaller-containing molecules. The fraction of fuel carbon in compounds having two or fewer carbon atoms ranged from 30 percent at 1100 K to 80 percent at 1200 K.

Brabbs, T. A.↗
NASA NTRS1984

Heat and mass transfer in combustion - Fundamental concepts and analytical techniques

Fundamental combustion phenomena and the associated flame structures in laminar gaseous flows are discussed on physical bases within the framework of the three nondimensional parameters of interest to heat and mass transfer in chemically-reacting flows, namely the Damkoehler number, the Lewis number, and the Arrhenius number which is the ratio of the reaction activation energy to the characteristic thermal energy. The model problems selected for illustration are droplet combustion, boundary layer combustion, and the propagation, flammability, and stability of premixed flames. Fundamental concepts discussed include the flame structures for large activation energy reactions, S-curve interpretation of the ignition and extinctin states, reaction-induced local-similarity and non-similarity in boundary layer flows, the origin and removal of the cold boundary difficulty in modeling flame propagation, and effects of flame stretch and preferential diffusion on flame extinction and stability. Analytical techniques introduced include the Shvab-Zeldovich formulation, the local Shvab-Zeldovich formulation, flame-sheet approximation and the associated jump formulation, and large activation energy matched asymptotic analysis. Potentially promising research areas are suggested.

Law, C. K.↗
NASA NTRS1985

Atomization data for spray combustion modeling

Computer models that simulate the energy release processes in spray combustion are highly dependent upon the quality of atomization data utilized. This paper presents results of analyses performed with a state-of-the-art rocket combustion code, demonstrating the important effects of initial droplet sizes and size distributions on combustion losses. Also, the questionable aspects and inapplicability of the generally available atomization data are discussed. One important and misunderstood aspect of the atomization process is the difference between spatial (concentration) and flux (temporal) droplet size distributions. These are addressed, and a computer model developed to assess this difference is described and results presented. Finally, experimental results are shown that demonstrate the often neglected effects of the local gas velocity field on the atomization process.

Ferrenberg, A. J.↗
NASA NTRS1984

Transient processes in combustion of single submillimeter metal droplets

A laser was used to ignite Al, Zr, Ti and Hf droplets in separate trials to study metal droplet combustion in air. The burning was recorded with high speed film at high magnification. Al was found to flash vaporize, melt, surface oxidize, revaporize, then combust. All species burned with a vapor diffusion flame surrounded by an oxide condensation front. The Zr, Ti and Hf droplets grew by condensation, coalesced, then convected toward the perimeter of the condensation zone. It is expected that the data will serve as bases for a theoretical vapor diffusion model. Finally, the introduction of a transverse acoustic field was observed to have no effect on either the luminosity or combustion zone geometry.

Pellett, G. L.↗
NASA NTRS1983

Combustion hot section technology

The overall objective of the Turbine Engine Hot Section Technology Combustion Project is to develop and verify improved and more accurate analysis methods for increasing the ability to design with confidence the combustion system for advanced aircraft turbine engines. The analysis methods developed will be generically applicable to combustion systems and not restricted to one specific engine or manufacturer. This project's approach was to first assess and evaluate existing combustor aerothermal analysis models by means of a contracted effort initiated during FY 1982. This evaluation effort has assessed and quantified known models' strengths and deficiencies. During FY 1984 the Aerothermal Modeling Program, Phase 2 will be initiated, which is expected to have contracted model development efforts in the areas of improved numerical methods for turbulent viscous flows, flow interactions, and fuel spray flow foekd interactions. A Phase 3 effort is planned to address remaining model deficiencies. The primary inhouse effort in this area will be the determination of high pressure flame radiation characteristics in a full annular combustor. This experiment will be conducted in the NASA LeRC High Pressure Facility with the results compiled into a comprehensive flame radiation and liner heat flux model.

Ercegovic, D. B.↗
NASA NTRS1986

Combustion characteristics in the transition region of liquid fuel sprays

A number of important effects have been observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NOx formation. A monodisperse aerosol generator has been used to form and deliver a well controlled liquid fuel spray to the combustion test section where measurements of ignition energy have been made. The ignition studies were performed on monodisperse n-heptane sprays at atmospheric pressure over a range of equivalence ratios and droplet diameters. A capacitive discharge spark ignition system was used as the ignition source, providing independent control of spark energy and duration. Preliminary measurements were made to optimize spark duration and spark gap, optimum conditions being those at which the maximum frequency or probability of ignition was observed. Using the optimum electrode spacing and spark duration, the frequency of ignition was determined as a function of spark energy for three overall equivalence ratios (0.6, 0.8, and 1.0) and for initial droplet diameters of 25, 40, 50, 60, and 70 micro m.

Cernansky, N. P.↗
NASA NTRS1985

Combustion in supersonic flow

A workshop on combustion in supersonic flow was held in conjunction with the 21st JANNAF Combustion Meeting at Laurel, Maryland on October 3 to 4 1984. The objective of the workshop was to establish the level of current understanding of supersonic combustion. The workshop was attended by approximately fifty representatives from government laboratories, engine companies, and universities. Twenty different speakers made presentations in their area of expertise during the first day of the workshop. On the second day, the presentations were discussed, deficiencies in the current understanding defined, and a list of recommended programs generated to address these deficiencies. The agenda for the workshop is given.

Northam, G. B.↗