RESEARCH PROJECTS IN COMBUSTION SCIENCES

[Kinetics] [Coal] [Turbulent] [Supersonic] [Ram Accelerator] [Active Control]

 

1. Combustion Kinetics Use of shock tube and flat flame burner techniques enables controlled study of chemical reactions relevant to combustion. Current research topics range from fundamental studies of chemical reactions that produce or remove nitrogen oxides (NO_x) in combustion systems, to studies of specific hydrocarbon oxidation and pyrolysis reactions critical to detailed modeling of natural gas combustion and combustion of nitrogen-based propellants. One study, involving the kinetics of methyl radicals, an important intermediate species in combustion of natural gas, is intended to improve understanding of the combustion process involving hydrocarbon fuels. In another study we are using a new type of chemical reactor, which combines shock-wave heating tube and laser-photolysis concepts, for fundamental investigations of reaction kinetics. Finally, we have recently initiated a new program to study combustion chemistry at very high pressures, which is relevant to proposed advanced combustion systems. In each of these research areas, the development and application of modern spectroscopic diagnostic techniques plays a significant role.

2. Pulverized Coal Combustion and Gasification Research efforts in this area are intended to extend our understanding of the chemical and physical processes that describe the behaviors of coal char particles at the temperatures and pressures of industrial importance. The objective of one study is to provide the information needed to allow the prediction of the effects of coal properties on char particle burning rates. Another study is concerned with char particle fragmentation and its effect on unburned carbon during pulverized coal combustion and gasification. Another is concerned with characterizing the inhibition effects of CO on the gasification of coal chars in CO₂ environments. Coals ranging in rank from lignite to low-volatile bituminous are employed in the studies. Because coal is so heterogeneous, we also employ synthetic chars having known densities, porosities, and mineral loadings to aid in data interpretation and to provide mechanistic insight. We use entrained flow reactors and thermogravimetric analyzers to observe coal combustion and gasification phenomena over wide ranges of temperature, composition, and pressure. A study concerned with pyrite combustion is also underway. The objective of this study is to characterize the various mechanisms of intraparticle mass transfer and chemical reaction that control overall pyrite conversion rates during coal combustion. Pyrite particles are found in coal and the conversion of pyrite particles to non-adhesive magnetite particles is key in reducing slag formation in coal-fired combustors. An important aspect of our work is the development of engineering models that can be applied to large scale, practical coal combustors and gasifiers. The models will yield accurate characterization of char particle temperatures and burning rates over wide ranges of gas temperatures, pressures, and compositions, and hence, will permit the accurate prediction of mass loss rates, pollutant and slag formation rates, and heat transfer rates in industrial coal-fired devices.

3. Turbulent Combustion Dynamics In this program, we are investigating the interaction between turbulence and chemical reaction rates in combustion gases. Optical diagnostic techniques are employed to make non-intrusive measurements of species concentration and velocity in well-defined turbulent reacting flows. These measurements are used to determine local reaction rates in the flow which, in turn, are used to develop phenomenological models for turbulent combustion. Jets in cross-flow are currently under investigation for a range of conditions and heat release. Our latest approaches involve the simultaneous use of Planar Laser-Induced Fluorescence (PLIF) for measurements of scalars, with Particle Image Velocimetry (PIV) for measurement of the velocity field.

4. Supersonic Mixing and Combustion The objective of this program is to understand the differences between supersonic and subsonic mixing and its effect upon combustion. A supersonic shear layer facility has been built for this purpose with high stagnation temperature and pressure capability. Advanced diagnostic techniques are being used to study the instantaneous scalar, velocity and reaction fields. These measurements reveal information about mixing, scalar transport and burning mechanisms when compressibility is important. The work proceeds in parallel with numerical simulation of the same flows. A related effort involves techniques to achieve mixing and combustion enhancements under compressible conditions. Supersonic Combustion Project

5. Ram Accelerator Phenomena and Detonation Waves This is a new program concerned with high-speed exothermic flows. The work is motivated by a new propulsion concept, known as a ram accelerator, in which a projectile is accelerated by combustion react ions as it moves at supersonic speeds through a tube filled with premixed fuel and oxidizer. Experiments are conducted in a new expansion tube facility using a variety of modern optical instrumentation. In a separate related study, planar fluorescence imaging will be used to study fundamental aspects of detonation wave structure and propagation.

6. Active Control of Combustion In this program we are investigating various approaches for the active control of combustor performance. Important aspects of the research include the development of actuators, sensors and robust control algorithms.