Scott Samuelsen

Basic research

In one area of fundamental inquiry, research is conducted using two-color laser anemometry, fine-wire thermocouples, and laser Rayleigh scattering to measure and map the transport of momentum, mass, and heat flux in turbulent, reacting and nonreacting flows, with swirl-induced recirculation. The goal is to (1) develop an understanding of the physics of fluid transport in flows dominated by a high degree of swirl, and (2) to establish benchmark quality, spatially resolved maps of the mean and fluctuating flow field properties for the purpose of developing and validating numerical models for elliptic flows.

In another fundamental study, laser diagnostics are employed to map the two-phase transport associated with liquid droplets (discrete phase) in air (continuous phase). Spatial maps of droplet size and velocity statistics, and gas phase velocity statistics are measured using a combination of laser anemometry, phase Doppler interferometry, laser diffraction, optical patternation, and shadowgraph photography. The goal is to develop an understanding of two-phase transport in recirculating flows.

Applied research

The applied research is directed to the formation and emission of nitrogen oxides and soot in gas turbine combustors, the application of active control to practical combustors and burners, combustion instability in liquid rockets, liquid-fuel mixing in gas turbine systems, and the measurement of nitrous oxide (N(2)O).

The applied research in soot formation is directed to resolving the problem of soot emission from combustion systems. In these studies, laser scattering is employed to map the local soot size and soot population and a specially designed rapid extractive probe is used to establish the morphology development of the soot using transmission electron spectroscopy. The objectives are to establish (1) the mechanisms of soot formation and burnout in flows dominated by complex aerodynamics, (2) the role of fuel properties, and (3) the role of additives.

Laser diagnostics and conventional diagnostic techniques are being used to study the fuel air mixing processes in complex swirl stabilized reacting flows. Of particular importance in the work to date is gaining an understanding of how inlet and boundary conditions affect both the detailed flow structure and the overall performance of the system. The goal is to optimize combustion efficiency and overall combustor stability, and to minimize the emission of air pollutants. An important contribution of this program has been the development of surrogate fuels to provide compositional control in the development of the required data bases, and a numerical code to predict the performance of these systems.

With the increasing understanding of the association between fuel/air mixing and burner performance, projects have been initiated to monitor and optimize burner performance through the use of direct performance sensors and a feedback control system. A key component of this multidisciplinary effort is the development of a control system that can minimize and assure the maintenance of minimum pollutant emission. This application of control technology to gas turbine engines and industrial burners will improve the performance of present-day and future designs.

In the area of nitrogen oxides emissions, the laboratory has four major grants and contracts. In the area of gas turbine engines, two NASA grants are addressing the effectiveness of mixing in rich-burn, quick-mix, lean-burn combustors and lean-burn combustors. In addition, the laboratory is conducting detailed studies of nitrogen oxides formation and emission from conventional gas turbine combustor configurations. This research is primarily directed to high altitude flight associated with the High Speed Civil Transport, and advanced air frames for subsonic transports. The fourth program is supported by the California Institute for Energy Efficiency and Southern California Gas. The focus is on the reduction of nitric oxide emissions from natural gas-fired industrial burners and the adaptation of active control to maintain performance during long-term operation.

In liquid rocket combustion, combustion instabilities occur due to unsteadiness in the combustion processes and their associated coupling with the feed system dynamics and/or acoustic modes of the combustion chamber. High frequency acoustic combustion instabilities can result in severe hardware damage due to the high pressure amplitudes and accelerated heat transfer rates. In a collaborative effort with Pratt & Whitney, the laboratory seeks to identify and investigate key physical mechanisms responsible for high frequency acoustic combustion instabilities. The effort focuses on "secondary atomization" in which the wave interactions promote an additional breakup of the droplets produced by the injector. The coupling between this breakup and the wave action is though to promote and amplify the instability.

N(2)O is a global air pollutant contributing both to the greenhouse effect and depletion of ozone in the stratosphere. Little is currently known about the formation mechanisms of N(2)O during the combustion process. A continuous gas analyzer for measuring N(2)O in combustion products has been developed, evaluated, and demonstrated in the field. The analyzer is used to measure the formation and emission of N(2)O from coal fired combustors. In addition, a combustion tunnel has been equipped to operate on coal and used to assess the effect of reburning on the emission of N(2)O. Both the Electric Power Research Institute and the Southern California Edison Company have been instrumental in supporting this effort.

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