Optimization of Propulsion Systems
Figure 2 shows two parcels of fuel and air mixtures. In the diagram that shows a high degree of unmixedness, the dark regions represent fuel, and the light regions represent air. The diagram that shows a low degree of unmixedness has the same overall average f, but the regions of fuel (dark) and the regions of air (light) have been reduced in size giving the diagram a uniform gray appearance; it is approaching a state of being completely mixed.
Thus, the goal of this study is to use numerical analysis, supported by experimental data, to determine the combination of the minimum f and the optimal spatial unmixedness necessary to minimize NOx and CO2 formation while maintaining a stable reaction. These numerical results will complement the work currently being performed for the UEET (Ultra-Efficient Engine Technology) at the NASA Glenn Research Center (Lewis Field). Once the ideal combination is determined, different techniques of atomization and mixing can be proposed to apply these findings to actual hardware application. The experimental data will be collected in a model gas turbine combustor that has been developed in the MFDC lab. This experiment fixture allows control over the stoichiometric ratio, the swirl number, the location and amount of secondary air injection, and is designed to function with both gaseous and liquid fuels.
This experiment fixture allows control over the stoichiometric ratio, the swirl number, the location and amount of secondary air injection, and is designed to function with both gaseous and liquid fuels.
As part of the laboratoryÂ’s goal to evaluate and validate CFD software, a CFD model of this combustor has been developed. Preliminary numerical results from this model show promise in accurately predicting the behavior of the physical model. Figure 4 shows an example preliminary data that correlates well with the experimental data.
The study of particulate emissions is a growing field in the area of air pollution. These emissions can contain many harmful substances such as Polycyclic Aromatic Hydrocarbons which are formed during the combustion of organic materials (carbon and hydrogen) and are suspected carcinogens and mutagens. Because particle emission measurements are a relatively new concern, techniques for collection and quantification are currently being developed. The MFDC Laboratory has performed some preliminary means of collecting data on these particles (Figure 5). The goal of this study is to improve these data collection techniques and to further study these Polycyclic Aromatic Hydrocarbons particles.
Another goal of the proposed research is to create a supersonic combustion platform. Many facilities and universities are investigating high speed flight in the attempt to create an air vehicle capable of reaching hypersonic speeds. In hypersonic flight, many optimizing factors such as premixing, ignition, and blow-out need to be considered. Hypersonic flight is viable, but there are many problems that arise that will be predicted, examined, and solved in this proposed research activity. The most challenging goal is maintaining supersonic combustion. To address this challenge, the MFDC Laboratory is proposing to perform both experimental and computational studies in combustion at sonic speeds. A supersonic combustion test bed is currently being designed and fabricated where flow will enter this fixture through a De Laval converging-diverging nozzle to produce supersonic air speeds while fuel is injected mid-stream with a coaxial fuel injector. Preliminary Fluent modeling (Figure 6) supports the concern that sonic combustion is difficult to achieve. The model predicts that combustion can be achieved at Mach 1.8 but not at Mach 3.
The subsonic, large-scale combustion projects use a combustor designed to model an actual jet engine combustion chamber to study combustion efficiency and the byproducts of combustion. The chamber is set up to test different fuels including kerosene, methanol, ethanol, diesel, and biofuel. Since the combustor is modeled like an aircraft combustion engine, it has swirling capability and a designed fuel injector for different operating conditions. When operating the chamber, the combustion efficiency as well as its byproducts are studied at different swirl numbers. Along with the study of combustion efficiency, sound and acoustic data are measured to investigate the combustor acoustic properties. In many experiments, the efficiency and emission studies can be correlated with flame temperature, swirl number, fuel type, product of combustion, acoustic and sound data, and flame structure.