CHAPTER 1. INTRODUCTION 1 CHAPTER 2. PROBLEM FORMULATION 3 2.1 Setup 3 2.2 Assumptions 4 2.3 Governing Equations 4 2.4 Boundary and Initial Conditions 5 CHAPTER 3. GRID TOPOLOGY 6 CHAPTER 4. NUMERICAL METHODS OF SOLUTIONS 9 4.1 Dynamic Cell Remeshing 9 4.2 Volume of Fluid Model 4.3 Non-Iterative Time Advancement 4.4 Discretization Schemes 4.5 Variable Time-Stepping CHAPTER 5. RESULTS AND DISCUSSION 5.1 Verification 5.2 Effect of Drop Height 5.3 Validation 5.4 Effect of Modified UAV Geometry

In response to the NASA Environmentally Responsible Aviation program, United Technologies Aerospace Systems has designed, fabricated and tested a new Multipoint Lean Direct Injection system. This design consists of an array of pressure atomizing pilot injectors and novel high-shear airblast main injectors. Staging of the fuel injector manifolds allows the array to achieve low NO x at high power, in line with the program's goals of reducing landing and takeoff cycle NO x by 75%. Additionally, optimizing fuel splits between banks yields low power emissions in line with current state-of-the-art combustors. Emissions predictions of the design were computed utilizing computational fluid dynamics, and validated with a scaled power sector test on the NASA CE-5B-1 combustion rig. Rig testing indicated air leakage around the interface between the dome plate and the rig, which drove up emissions levels versus the design intent of the injector array. Even so, compared to a previously published multipoint array, the recorded emissions data showed lower levels of NO x at low power condition, but slightly higher levels at high power. There was also a good match to CFD predictions, although the discrepancy was larger at lower fuel-to-air ratios. This validates the CFD NO x predictions and shows that the array will be near the 75% reduction desired during actual takeoff conditions. NomenclatureCAEP = Committee on Aviation Environmental Protection CO = Carbon monoxide ΔP = Pressure drop across injectors as fraction of inlet pressure EI = Emissions Index (grams of constituent/kilogram of fuel) ERA = Environmentally Responsible Aviation program FAR = Fuel-to-air ratio by mass ICAO = International Civil Aviation Organization LTO = Landing and takeoff cycle MLDI = Multipoint lean direct injection NO x = Oxides of nitrogen P 3 = Combustor inlet pressure P4 = Absolute combustor pressure T3 = Combustor inlet temperature UHC = Unburnt hydrocarbons W 3 = Combustion air mass flow W f = Fuel mass flow

Periodic behavior in the reaction zone of a multiple nozzle combustor undergoing self-sustaining combustion oscillations is examined. This combustor has three stages: a high-swirl pilot stage, a lower-swirl intermediate stage, and a low-swirl outer stage. The high-power conditions reviewed in this paper have fuel supplied to all three stages. Four conditions are examined in which thermoacoustic coupling is observed at a well-defined frequency. The highest overall equivalence ratio case displays a significantly higher oscillation amplitude than the other cases. Changes to the fuel distribution (with constant overall equivalence ratio) results in smaller effects on the oscillation strength. Phase averaged images of the OH* chemiluminescence emission show dramatic changes in the OH* distribution and intensity over an average period of the oscillation. This variation in chemiluminescence is dominated by recurrent quenching and reignition downstream of the intermediate and outer fuel stages. The pilot stage reaction zone also displays periodic variation in intensity which is out-of-phase and precedes the intermediate and outer fuel stages. Proper orthogonal decomposition is used to extract the most energetic spatial components which form the periodic behavior in the OH* distribution. The POD modes allow direct field visualization of fluctuation location and magnitude. For all four cases, the phase and location of the OH* emission variations are generally similar with small differences in the location and rates of periodic changes in the reaction oscillation.

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Emissions measurements and OH chemiluminescence imaging were performed on a novel multipoint lean direct injection combustor designed for low-NOx emissions and with the flexibility to operate at both high-and low-power settings. The combustor has five rows of fuel nozzles that can be staged in three independent circuits as required. The fuel nozzle stages are not identical; instead, they are optimized for different power settings. NOx, CO, and unburned hydrocarbons were measured for a variety of settings, including lean blowout, idle, intermediate power, and simulated full power. Effects of pressure, inlet temperature, equivalence ratio, and fuel flow distribution were studied. OH chemiluminescence was used to observe flame structure and interpret emissions trends. The local equivalence ratio, calculated with the fuel and air flow rates particular to each combustor stage, was a useful parameter for interpreting emissions. The combustor demonstrated the ability to operate at a wide range of conditions, from an overall equivalence ratio of 0.55 to lean blowout at 0.079. Low-NOx operation was achieved at high power by using all fuel stages and controlling fuel flow to obtain an even distribution among the nozzles and reduce peak temperatures while using staging to provide good stability at low power.