The combustion facet of this project includes testing Jet-A fuel combustion in an attempt to lower emissions. This research is aligned with one of NASA's major missions outlined in its technology roadmap for future aircraft: To reduce NOx emissions by 70% within 10 years and by 80% within 25 years. Simultaneously, CO2 emissions will be reduced by 25% and 50% in the same timeframe. The objective of the MFDCLab combustion group is to develop expertise and competency in modeling and simulation of combustion processes and propulsion systems used in commercial and military aircraft. Once the physical and numerical analyses are completely understood, emissions will be minimized using optimization techniques seen in controls systems. A major component of research includes development of a combustion chamber for validation and verification of simulation models. The combustion chamber will be used to determine the effects of swirl and controlled mixing during combustion. Pollutant formation will be examined with the help of Computational Fluid Dynamics software. Various studies and systems were modeled to evaluate the CFD program FLUENT. Now with the understanding of the accuracy and limitations of Fluent, the combustion chamber is modeled to show emissions and property profiles given various inlet conditions. Using both a FLUENT model and a physical model of the combustion chamber, we are currently studying techniques to reduce the emission of pollutants during a combustion process. Background: Different data have been collected and analyzed over various swirl numbers and inlet conditions. The physical and numerical combustion chambers have been constructed and analyzed for a great number of varying conditions. Validation of the code has been established.
Experiments have been performed to test the sustainability of hydrogen combustion in supersonic Mach flows. Supersonic combustion leads to hypersonic flight viability. Compressed air was inlet at different pressures to combine with hydrogen which was inlet at a constant flow rate. Pressure ratios across the flow chamber corresponded to supersonic Mach numbers of about 2.5. The ensuing fuel-air mixture was excited to initiate combustion. Special attention was paid to the pre-mixture of the hydrogen fuel and incoming air because of its relationship to flame stability.
The stability of combustion is especially important in high-speed flight, as seen in ramjet and scramjet engine and vehicle design. Combustion within ramjets occurs under very harsh and unstable conditions due to the high pressure and shock waves. It is therefore important to study different parameters which might increase or decrease the possibility of sustainable combustion, such as the equivalence ratio, pre-mixture ratio, fuel inlet rifling, cavity design as a flame holder, and volumetric flow rates of the combustion reagents. The combustion reaction was shown to force convection and cause conduction both radially outwards and across the shroud. Various materials are used for shrouds as a combustion chamber to shield the reaction from the surroundings.
The difference in conduction heat transfer was examined in all materials used. The high temperature and high pressure flow caused shock waves, a high universal heat transfer coefficient, and considerable forced convection. Radiation cannot be ignored due to the high temperature of the hydrogen combustion gases, therefore surface to surface radiation as well as gas radiation for various species were examined in this experiment. Experimental results were verified using laser diagnostics in cold flow, and FLUENT CFD code was also used in parallel to anchor and check data collected by pressure, temperature and other static and dynamic sensors.
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Cal State University, Los Angeles