Learn the basic structure of a proposal.
Proposals share a general document architecture, which is usually modified to suit specific circumstances. The overall structure of a proposal can be broken down into four parts:
End matter, or management requirements
The front matter of a proposal includes the following components:
Explain clearly how you will manage the development of your proposal project. Proposal reviewers pay strict attention to this section because here you show that you have the required know-how to bring a project to completion. In this section, you will present the following information:
See Work Plan for a discussion of work plans.
|Ian A. Waitz,
Assistant Professor, Aeronautics and Astronautics
|PERIOD OF INVESTIGATION:
|November 1, 1994 - October 31, 1997
|FIRST YEAR AMOUNT:
|Background and Motivation
|Applications for Tailored Strain Field Mixing for Low-Emissions Gas Turbines
|4.1 Numerical simulations of simplified model flows
|4.2 Diffusion flame experiments
|4.3 Review and analysis of mechanisms for driving controlled-strain mixing environments
|Resume of Professor Ian A. Waitz
|Descriptions of the MIT Aero-Environmental Research Laboratory (AERL) and the MIT Gas Turbine Laboratory (GTL)
|Budget Estimates for Proposed Project
|Strained diffusion interface
|Simplified computational flow model 1
|Simplified computational flow model 2
|Experimental model flow
Mixing enhancement is critical for implementation of low-NOx combustor technologies. Current mixing augmentation techniques being developed for application in low emissions gas turbine engines rest largely upon increased intensity of conventional turbulent mixing with relatively weak spatial and temporal coherence in length scales responsible for the majority of the critical fine-scale mixing. The objective of this project is to investigate mixing concomitant with spatially well-defined strain fields such that the emission of pollutant species is reduced. Strategies will be studied that use high strain rates to selectively enhance or attenuate pertinent reaction processes in the course of mixing.
A joint Massachusetts Institute of Technology/Naval Research Laboratory program of analysis, numerical simulation, and experimental research is proposed to determine the feasibility and impact of tailored strain field mixing for control of pollutant emissions in marine and aircraft gas turbine applications.
The strong sensitivity of pollutant formation processes to local temperature and mixture fraction dictates atomization and mixing with extreme rapidity and spatial uniformity in low- NOx combustion systems. In lean-premixed-prevaporized (LPP), lean direct injection (LDI), and rich burn-quench-lean burn (RQL) combustors, molecular mixing of fuel and air that minimizes stoichiometric burning (and the associated local heat release that leads to fixation of atmospheric nitrogen) is desired. This must be accomplished in a manner that allows complete oxidation of CO, soot, and unburned hydrocarbons, while achieving combustor performance objectives and satisfying a variety of design constraints.
The critical mixing requirements are set by the kinetic rates of pertinent oxidation and formation reaction mechanisms. These reaction rates are dependent on the local temperature and pressure, and relevant species concentrations. The progression of these reactions is also strongly dependent on the rate of strain in the fluid since this directly affects the fuel/air interfacial area, and diffusion of heat and chemical species.
For the most part, molecular mixing and transfers of momentum and energy in current low- NOx combustion systems are the result of turbulent processes (e.g., jet injection from dilution holes). That is, there is largely random organization of strain rates in length-scales responsible for the majority of the mixing. Mixing using well-defined, tailored strain fields may be used to exert greater control over chemical reactions during the course of molecular mixing and exchange of momentum and energy. As reviewed below, depending on magnitude, strain can either increase or decrease the progression of a given reaction.
Consider two semi-infinite planar regions separated by the x-axis, one containing fuel and the other oxidizer, as shown in Figure 1a. Infinitely-fast chemical kinetics are assumed so that locally the reaction
Because of the broad range of kinetic rates and heat release associated with primary and pollutant species chemistry, the reactions will be influenced differently by straining. Then, tailoring of the strain field may be used to satisfy the necessary fuel/air mixing and combustion requirements of gas turbine applications in a manner which minimizes pollutant emission.
Figure 1: Strained diffusion interface.
One candidate for leveraging the effects of strain is to allow a reaction interface or strip of reactants to be convected in the field of an axial vortex such as that shed downstream of a lobed or forced mixer nozzle. Strain rates on the order of 1000/s are realizable for such geometries at flow conditions gerinane to gas turbine combustor applications. This may allow quenching of the primary hydrocarbon reactions in regions where stoichiometric burning might otherwise occur. For gaseous hydrocarbon flames (e.g. propane) extinction at atmospheric pressures occurs for strain rates between 300/s and 1200/s. In addition, the characteristic chemical time for such a reaction is 10- 4 s. This is on the same order or faster than that for some pertinent reactions in gas turbine combustors, so similar impacts of strain on reaction processes are expected.
Four specific research questions are posed:
The research plan described below is designed to address these four questions.
A joint Massachusetts Institute of Technology/Naval Research Laboratory program of analysis, numerical simulation, and experimentation is proposed. The objective of the research is to determine the effects of time-varying strain rates on ignition and extinction of the primary hydrocarbon reaction, and on pollutant species formation/oxidation in gas turbine engines. The approach will be to investigate these effects using simplified model flow fields which capture the essential physics present in a gas turbine combustor setting. This will provide the greatest clarity in distinguishing the relevant mechanisms and opportunities for emissions reduction. The functional requirements for these simplified model flows are:
Numerical simulations will be performed by an MIT graduate student in residence at the Naval Research Laboratory. The student will work under the guidance of Dr. Elaine S. Oran. Simulations will be conducted using the CMRFAST-2D code, which is a fully-parallelized, twodimensional, reacting, Navier-Stokes solver currently running on the Thinking Machines CM-5 Connection Machine. The code was originally developed at NRL [Oran, Boris and DeVore, 1992] and employs a flux-corrected-transport algorithm.
Two model flows which satisfy the functional requirements described in the beginning of Section 4 will be investigated. The first, shown in Figure 2, is a fuel/product strip subject to a time-varying strain rate. A similar configuration was used as a basis for the simulations of Thévenin and Candel . The primary independent variables of interest are the fuel/product species composition and temperature, and the variation of strain rate with time.
The second model flow which will be studied is a fuel strip in the strain rate field of a vortex as shown in the schematic of Figure 3. This flow is more representative of a likely combustor implementation, containing both spatially and temporally varying strain rates. Large spatial variations in the strain rate field may limit the emissions reducing potential of the combustion strategies being investigated, and study of this model flow is intended in part to address this concern.
Experiments will be carried out in parallel with the numerical simulations both to validate the numerical results, and to study the impact of large-scale straining in reacting flows with embedded fine-scale turbulence. The work will be performed in a model combustor to be constructed using existing combustion lab facilities in the MIT Aero-Environmental Research Laboratory. The facilities provide air flow up to 0.7 lb/s and automated control of gaseous fuel flow rate and dilution, in addition to a hot exhaust capability.
A schematic of the experimental configuration is shown in Figure 4. Two splitter plates with a single convolution in the trailing edge will be stacked one upon the other. A gap between the plates will be used for introduction of gaseous fuels. The convolution in the trailing edge will generate a single counter-rotating vortex pair. The vortex pair strength, and thus the strain rate field, may be directly correlated with the slitter plate geometry (see for example, Waitz et al., 1994].
When the air and fuel velocities are matched, the experiment is similar to the simplified numerical model flow shown in Figure 3. Vortex strength and size with respect to the fuel strip width can be varied by changing the geometry of the stacked splitter assembly.
At the half-way point of the proposed program, after results of the numerical and experimental investigations begin to be obtained, analysis will commence of the (l) feasibility (2) impact, and (3) methods for application, of tailored strain field mixing in gas turbine engines. This will include analysis of existing streamwise-vorticity-enhanced mixing technology, as well as investigation of non-traditional approaches for introducing tailored strain fields.
A work schedule for the three year program is shown in Figure 5. The majority of the first year will be devoted to modifying the computational fluid dynamics code to enable its use for the flow fields of interest for this study. Simulations of the model flow fields will be carried out during the second year, followed by design and construction of the experimental test apparatus. 'Me experiments will be conducted during the third year of the effort.
The principal investigator for this project will be Professor Ian A. Waitz, Assistant Professor of Aeronautics and Astronautics, Director of the MIT Aero-Environmental Research Laboratory (AERL), and member of the MIT Gas Turbine Laboratory (GTL). A resume is attached in Appendix A; descriptions of AERL and GTL are included in Appendix B.
Co-investigators include Dr. Elaine S. Oran of the Naval Research Laboratory and Professor Emeritus Frank E. Marble of California Institute of Technology. Bi-annual meetings will be held among the program participants. Dr. Oran will be responsible for advising an MIT student on the implementation of the CMRFAST-2D code, and will participate as a consultant throughout the course of the program. She is an expert in the field of numerical modeling of reacting flows and has served a similar role in advising students from the University of Maryland. Professor Marble will serve as a consultant at a level of effort of approximately 15 days/year. He is a recognized leader in the field of combustion science and has extensive experience in modeling the effects of strain on diffusion flames. He is the author of a seminal paper on the interaction of a diffusion flame with a vortex [Marble, 1985]. Professor Marble has a long standing relationship, with the MIT Gas Turbine Laboratory and makes several visits each year. Interaction with Professor Marble will be through these visits and possibly through one visit each year of the MIT student to California Institute of Technology.
Funding is requested to support one MIT doctoral student for the three-year period. The program will take advantage of existing NRL facilities and personnel; funding for NRL is not requested for these activities. Budget estimates are contained in Appendix C.
Chomiak, J. "Application of Chemiluminescence Measurement to the Study of Turbulent Flame Structure", Combustion and Flame, Vol. 18, pp. 429-433, 1972.
Driscoll, J. F., Sutkus, D. J., Roberts, Wm., L., Post, M. E., and Goss, L. P., "The Strain Exerted by a Vortex on a Flame-Determined from Velocity Field Images", AIAA 93-0362,1993.
Macaraeg, M. G., Jackson, T. L., and Hussaini, M. Y., "Ignition and Structure of a Laminar Diffusion Flame in the Field of a Vortex," Combustion Science and Technology, Vol. 87, pp. 364- 387, 1992.
Marble, F. E., "Growth of a Diffusion Flame in the Field of a Vortex," Recent Advances in the Aerospace Sciences, Plenum Publishing, 1985.