No abstract

The objective of the Innovative High-Temperature Fuel Nozzle Program was to design, fabricate, and test propulsion engine fuel nozzles capable of performance despite extreme fuel and air inlet temperatures. Although a variety of both passive and active methods for reducing fuel wetted-surface temperatures were studied, simple thermal barriers were found to offer the best combination of operability, cycle flexibility, and performance. A separate nozzle material study examined several nonmetallics and coating schemes for evidence of passivating or catalytic tendencies. Two pilotless airblast nozzles were developed by employing finite-element modeling to optimize thermal barriers in the stem and tip. Operability of these prototypes was compared to a current state-of-the-art piloted, prefilming airblast nozzle, both on the spray bench and through testing in a can-type combustor. The three nozzles were then equipped with internal thermocouples and operated at 1600F air inlet temperature while injecting marine diesel fuel heated to 350F. Measured and predicted internal temperatures as a function of fuel flow rate were compared. Results show that the thermal barrier systems dramatically reduced wetted-surface temperatures and the potential for coke fouling, even in an extreme environment.

A wet low-NOx combustion system being developed for the AlliedSignal ASE40 industrial gas turbine is assessed using advanced 3-D CFD analysis. A PDF combustion-turbulence interaction model was modified to allow analysis of simultaneous injection of water with gaseous or liquid fuel. To the authors’ knowledge, such a CFD analysis is unique in the open literature. Analyses of the wet low-NOx combustion system were performed with and without water injection at full power engine conditions. Good qualitative agreement between engine emission data and predictions was seen. NOx reductions of 58% and 77% were measured for water-to-natural gas mass ratios of 0.5 and 1.0, respectively, compared to 75% and 93% for CFD calculations. Corresponding CO levels were measured to increase by factors of 3 and 9, compared to CFD predictions of 4 and 7. Similar trends were predicted for water injection with DF-2 diesel fuel. Predicted overall flow patterns were not significantly changed with water injection. NOx reductions were caused by a reduction in maximum flame temperatures in the primary and intermediate zones when water was injected. CO increases were caused by a reduction of CO oxidation downstream of the dilution zone (in the turn-around duct) due to lower gas temperatures with water injection.

The objective of the innovative high-temperature fuel nozzle program was to design, fabricate, and test propulsion engine fuel nozzles capable of performance despite extreme fuel and air inlet temperatures. Although a variety of both passive and active methods for reducing fuel wetted-surface temperatures were studied, simple thermal barriers were found to offer the best combination of operability, cycle flexibility, and performance. A separate nozzle material study examined several nonmetallics and coating schemes for evidence of passivating or catalytic tendencies. Two pilotless airblast nozzles were developed by employing finite-element modeling to optimize thermal barriers in the stem and tip. Operability of these prototypes was compared to a current state-of-the art piloted, prefliming airblast nozzle, both on the spray bench and through testing in a can-type combustor. The three nozzles were then equipped with internal thermocouples and operated at 1600°F air inlet temperature while injecting marine diesel fuel heated to 350°F. Measured and predicted internal temperatures as a function of fuel flow rate were compared. Results show that the thermal barrier systems dramatically reduced wetted-surface temperatures and the potential for coke fouling, even in an extreme environment.

The primary reaction zone of a modern propulsion engine combustion system has a profound effect on overall combustor performance, including efficiency, lean stability, exit temperature pattern factor, and emissions production rates. A unique full-annular, throughflow combustion system with interchangeable fuel injectors, dome mixing devices, and liners was used to evaluate the effects of several primary zone design variables on efficiency and exit temperature distribution. The combustor was tested in a rig designed for extreme exit temperatures, at heat release rates up to 30 M Btu/hr-ft3-atm (0.31 kW/M3-atm) and exit temperatures in excess of 3500F (1927C), through a range of overall fuel/air ratios up to stochiometric. An automated, six-port, rotating exit gas sampling system was used to map the exit gas concentrations for determining gas temperatures and combustion efficiency. Both liquid (JP-4) and natural gas fuels were used to examine the impact of evaporation and fuel momentum effects. Gaseous fuel was injected through nozzles designed to mimic the initial fuel spatial distribution and spray cone angle of the liquid nozzles. Thick thermal barrier coatings on the liners eliminated the need for and interference of film cooling. The high reference velocity, short residence time, and absence of any dilution zone further highlighted the primary zone design impact on exit conditions. Test results show that combustor efficiency becomes volume-limited at a point lean of stochiometric, with both the shape of the efficiency curve and the fuel/air ratio for maximum efficiency dependent on the primary zone design and fuel type. The average exit temperature raidal profile was outside diameter (OD)-peaked at low fuel/air ratios, rotating toward a flat profile at stochiometric for all of the configurations.