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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Swirl-Venturi Lean Direct Injection Combustion Technology for Low-NOx Aero Gas Turbine Engines

This paper summarizes research on the lean direct injection (LDI) combustor concept for aero-gas turbine combustors. The focus of this paper is one particular family of lean direct injection designs, swirl-venturi lean direct injection (SV-LDI). SV-LDI is characterized by the airpath: an air swirler followed by a converging-diverging venturi. For most SV-LDI configurations, a fuel injector is inserted through the center of the air swirler, with the fuel injector tip at or near the venturi throat. Several design variables were studied. These included fuel injector tip location, air swirler blade thickness, air swirler blade angle, and fuel-air mixer size. Moving the fuel injector tip slightly upstream or downstream of the venturi throat has at most a small impact on NOx emissions. Changing the blade thickness also does not affect NOx emissions. Changing the swirler blade angle has a significant effect on NOx emissions. Decreasing swirler blade angle, and thus decreasing swirl number, decreases the NOx emissions at lower flame temperatures (below about 1800 K). However, the slope of the NOx vs. flame temperature curve is higher for lower swirl numbers. Finally, decreasing the fuel-air mixer size initially decreases NOx emissions. However, there may be an optimum fuel-air mixer size below which NOx emissions do not continue to decrease.

lean direct injection↗
DOE OSTI2024

Design, Analysis, and Experimental Testing of Hydrogen Lean Direct Injection Nozzles at Elevated Pressure

Abstract There are many challenges of commissioning a hydrogen combustor into future gas turbine engines; especially regarding achieving emissions goals. Previously, Escudero et al. and Tran et al. conducted a study to adapt the liquid fuel Lean Direct Injection (LDI) concept from Jet-A to gaseous natural gas-hydrogen blends and pure hydrogen [1], [2]. Experimental data was collected at atmospheric conditions using a Box Behnken design of experiments. The design of experiments suggested that biasing the air split in favor of the inner air circuit and increasing the swirl strength of this inner air passage resulted in improved NOx emissions, while the inverse was true for stability, which was quantified by studying the lean blowoff point (LBO) [1], [2]. The trends revealed by the original experiment [1], [2] provided a design direction for further iterations of the experimental hardware. The study presented herein describes the further investigation of such LDI injectors through experimental methods and computational fluid dynamic (CFD) simulations at atmospheric conditions, which were used to identify potential flow behaviors driving enhanced emissions performance. Further evaluation of select injectors from both studies was then conducted at elevated pressures up to 6 atmospheres. The results from both experiments are presented in this study, which include flame observations, emissions measurements, and operational challenges. NOx emissions results are reported on a volume basis in ppmvd corrected to 15% O2 and corrected for fuel. A predictive model for relating NOx emissions to test conditions at atmospheric conditions show high significance to adiabatic flame temperature while little to no significance to fuel composition for the best performing configurations. The results illustrate the connection between atmospheric testing and testing elevated pressures. The design direction indicated by the initial tests and CFD results in promising configurations for implementation into a Multi-point LDI array.

08 HYDROGEN↗
NASA NTRS2002

Sector Tests of a Low-NO(sub x), Lean, Direct- Injection, Multipoint Integrated Module Combustor Concept Conducted

The low-emissions combustor development described is directed toward advanced high pressure aircraft gas-turbine applications. The emphasis of this research is to reduce nitrogen oxides (NOx) at high-power conditions and to maintain carbon monoxide and unburned hydrocarbons at their current low levels at low power conditions. Low-NOx combustors can be classified into rich-burn and lean-burn concepts. Lean-burn combustors can be further classified into lean-premixed-prevaporized (LPP) and lean direct injection (LDI) concepts. In both concepts, all the combustor air, except for liner cooling flow, enters through the combustor dome so that the combustion occurs at the lowest possible flame temperature. The LPP concept has been shown to have the lowest NOx emissions, but for advanced high-pressure-ratio engines, the possibility of autoignition or flashback precludes its use. LDI differs from LPP in that the fuel is injected directly into the flame zone, and thus, it does not have the potential for autoignition or flashback and should have greater stability. However, since it is not premixed and prevaporized, good atomization is necessary and the fuel must be mixed quickly and uniformly so that flame temperatures are low and NOx formation levels are comparable to those of LPP. The LDI concept described is a multipoint fuel injection/multiburning zone concept. Each of the multiple fuel injectors has an air swirler associated with it to provide quick mixing and a small recirculation zone for burning. The multipoint fuel injection provides quick, uniform mixing and the small multiburning zones provide for reduced burning residence time, resulting in low NOx formation. An integrated-module approach was used for the construction where chemically etched laminates, diffusion bonded together, combine the fuel injectors, air swirlers, and fuel manifold into a single element. The multipoint concept combustor was demonstrated in a 15 sector test. The configuration tested had 36 fuel injectors and fuel-air mixers that replaced two fuel injectors in a conventional dual-annular combustor. During tests, inlet temperatures were up to 870 K and inlet pressures were up to 5400 kPa. A correlation was developed that related the NOx emissions with the inlet temperature, inlet pressure, fuel-air ratio, and pressure drop. At low-power conditions, fuel staging was used so that high combustion efficiency was obtained with only one-fourth of the fuel injectors flowing. The test facility had optical access, and visual images showed the flame to be very short, approximately 25 mm long.

Tacina, Robert R.↗
NASA NTRS2010

Optical Characterization of a Multipoint Lean Direct Injector for Gas Turbine Combustors: Velocity and Fuel Drop Size Measurements

Performance of a multipoint, lean direct injection (MP-LDI) strategy for low emission aero-propulsion systems has been tested in a Jet-A fueled, lean flame tube combustion rig. Operating conditions for the series of tests included inlet air temperatures between 672 and 828 K, pressures between 1034 and 1379 kPa and total equivalence ratios between 0.41 and 0.45, resulting in equilibrium flame temperatures approaching 1800 K. Ranges of operation were selected to represent the spectrum of subsonic and supersonic flight conditions projected for the next-generation of commercial aircraft. This document reports laser-based measurements of in situ fuel velocities and fuel drop sizes for the NASA 9-point LDI hardware arranged in a 3 3 square grid configuration. Data obtained represent a region of the flame tube combustor with optical access that extends 38.1-mm downstream of the fuel injection site. All data were obtained within reacting flows, without particle seeding. Two diagnostic methods were employed to evaluate the resulting flow path. Three-component velocity fields have been captured using phase Doppler interferometry (PDI), and two-component velocity distributions using planar particle image velocimetry (PIV). Data from these techniques have also offered insight into fuel drop size and distribution, fuel injector spray angle and pattern, turbulence intensity, degree of vaporization and extent of reaction. This research serves to characterize operation of the baseline NASA 9- point LDI strategy for potential use in future gas-turbine combustor applications. An additional motive is the compilation of a comprehensive database to facilitate understanding of combustor fuel injector aerodynamics and fuel vaporization processes, which in turn may be used to validate computational fluid dynamics codes, such as the National Combustor Code (NCC), among others.

Heath, Christopher M.↗
NASA NTRS2015

Fundamental Study of a Single Point Lean Direct Injector. Part I: Effect of Air Swirler Angle and Injector Tip Location on Spray Characteristics

Lean direct injection (LDI) is a combustion concept to reduce oxides of nitrogen (NOx) for next generation aircraft gas turbine engines. These newer engines have cycles that increase fuel efficiency through increased operating pressures, which increase combustor inlet temperatures. NOx formation rates increase with higher temperatures; the LDI strategy avoids high temperature by staying fuel lean and away from stoichiometric burning. Thus, LDI relies on rapid and uniform fuel/air mixing. To understand this mixing process, a series of fundamental experiments are underway in the Combustion and Dynamics Facility at NASA Glenn Research Center. This first set of experiments examines cold flow (non-combusting) mixing using air and water. Using laser diagnostics, the effects of air swirler angle and injector tip location on the spray distribution, recirculation zone, and droplet size distribution are examined. Of the three swirler angles examined, 60 degrees is determined to have the most even spray distribution. The injector tip location primarily shifts the flow without changing the structure, unless the flow includes a recirculation zone. When a recirculation zone is present, minimum axial velocity decreases as the injector tip moves downstream towards the venturi exit; also the droplets become more uniform in size and angular distribution.

vortex↗
NASA NTRS2014

Fundamental Study of a Single Point Lean Direct Injector. Part I: Effect of Air Swirler Angle and Injector Tip Location on Spray Characteristics

Lean direct injection (LDI) is a combustion concept to reduce oxides of nitrogen (NOx) for next generation aircraft gas turbine engines. These newer engines have cycles that increase fuel efficiency through increased operating pressures, which increase combustor inlet temperatures. NOx formation rates increase with higher temperatures; the LDI strategy avoids high temperature by staying fuel lean and away from stoichiometric burning. Thus, LDI relies on rapid and uniform fuel/air mixing. To understand this mixing process, a series of fundamental experiments are underway in the Combustion and Dynamics Facility at NASA Glenn Research Center. This first set of experiments examines cold flow (non-combusting) mixing using air and water. Using laser diagnostics, the effects of air swirler angle and injector tip location on the spray distribution, recirculation zone, and droplet size distribution are examined. Of the three swirler angles examined, 60 deg is determined to have the most even spray distribution. The injector tip location primarily shifts the flow without changing the structure, unless the flow includes a recirculation zone. When a recirculation zone is present, minimum axial velocity decreases as the injector tip moves downstream towards the venturi exit; also the droplets become more uniform in size and angular distribution.

Tedder, Sarah A.↗
NASA NTRS2016

CFD Based Design of a Filming Injector for N+3 Combustors

An effort was undertaken to perform CFD analysis of fluid flow in Lean-Direct Injection (LDI) combustors with axial swirl-venturi elements for next-generation LDI-3 combustor design. The National Combustion Code (NCC) was used to perform non-reacting and two-phase reacting flow computations for a newly-designed pre-filming type fuel injector LDI-3 injector, in a single-injector and a five-injector array configuration. All computations were performed with a consistent approach of mesh-optimization, spray-modeling, ignition and kinetics-modeling. Computational predictions of the aerodynamics of the single-injector were used to arrive at an optimized main-injector design that meets effective area and fuel-air mixing criteria. Emissions (EINOx) characteristics were predicted for a medium-power engine cycle condition, and will be compared with data when it is made available from experimental measurements. The use of a PDF-like turbulence-chemistry interaction model with NCC's Time-Filtered Navier-Stokes (TFNS) solver is shown to produce a significant impact on the CFD results, when compared with a laminar-chemistry TFNS approach for the five-injector computations.

combustion chambers↗
NASA NTRS2016

CFD-Based Design of a Filming Injector for N+3 Combustors

An effort was undertaken to perform CFD analysis of fluid flow in Lean-Direct Injection (LDI) combustors with axial swirl-venturi elements coupled with a new fuel-filming injector design for next-generation N+3 combustors. The National Combustion Code (NCC) was used to perform non-reacting and two-phase reacting flow computations on a N+3 injector configuration, in a single-element and a five-element injector array. All computations were performed with a consistent approach towards mesh-generation, spray-, ignition- and kinetics-modeling with the NCC. Computational predictions of the aerodynamics of the injector were used to arrive at an optimal injector design that met effective area, aerodynamics, and fuel-air mixing criteria. LDI-3 emissions (EINOx, EICO and UHC) were compared with the previous generation LDI-2 combustor experimental data at representative engine cycle conditions.

combustion chambers↗
NASA NTRS2017

A Comparison of Combustion Dynamics for Multiple 7-Point Lean Direct Injection Combustor Configurations

The combustion dynamics of multiple 7-point lean direct injection (LDI) combustor configurations are compared. LDI is a fuel-lean combustor concept for aero gas turbine engines in which multiple small fuel-air mixers replace one traditionally-sized fuel-air mixer. This 7-point LDI configuration has a circular cross section, with a center (pilot) fuel-air mixer surrounded by six outer (main) fuel-air mixers. Each fuel-air mixer consists of an axial air swirler followed by a converging-diverging venturi. A simplex fuel injector is inserted through the center of the air swirler, with the fuel injector tip located near the venturi throat. All 7 fuel-air mixers are identical except for the swirler blade angle, which varies with the configuration. Testing was done in a 5-atm flame tube with inlet air temperatures from 600 to 800 F and equivalence ratios from 0.4 to 0.7. Combustion dynamics were measured using a cooled PCB pressure transducer flush-mounted in the wall of the combustor test section.

lean direct injection↗
NASA NTRS2017

Mars Organic Molecule Analyzer (MOMA) Laser Desorption/Ionization Source Design and Performance Characterization

The Mars Organic Molecule Analyzer (MOMA), a dual-source, ion trap-based instrument capable of both pyrolysis-gas chromatography mass spectrometry (pyr/GC-MS) and laser desorption/ionization mass spectrometry (LDI-MS), is the core astrobiology investigation on the ExoMars rover. The MOMA instrument will be the first spaceflight mass analyzer to exploit the LDI technique to detect refractory organic compounds and characterize host mineralogy; this mode of analysis will be conducted at Mars ambient conditions. In order to achieve high performance in the Martian environment while keeping the instrument compact and low power, a number of innovative designs and components have been implemented for MOMA. These include a miniaturized linear ion trap (LIT), a fast actuating aperture valve with ion inlet tube, and a Microelectromechanical System (MEMS) Pirani sensor. Advanced analytical capabilities like Stored Waveform Inverse Fourier Transform (SWIFT) for selected ion ejection and tandem mass spectrometry (MS/MS) are realized in LDI-MS mode, and enable the isolation and enhancement of specific mass ranges and structural analysis, respectively. We report here the technical details of these instrument components as well as system-level analytical capabilities, and we review the applications of this technology to Mars and other high-priority targets of planetary exploration.

Xiang Li↗
NASA NTRS2018

Fundamental Study of a 7-Element Fuel Injector Configuration for Gas Turbine Combustors - A Look at Cold Flow and Burning Measurements

Lean direct injection (LDI) is a combustion concept to reduce oxides of nitrogen (NOx) for next generation aircraft gas turbine engines. These newer engines have cycles that increase fuel efficiency through increased operating pressures, which increase combustor inlet temperatures. NOx formation rates increase with higher temperatures, and the LDI strategy is to avoid high temperature by staying fuel lean and away from stoichiometric burning. Thus, LDI relies on rapid and uniform fuel/air mixing. Additionally, in combustors for smaller core engines, the area and volume bring about mixing and time scale challenges not found in larger engines. As part of our parametric study in which we vary swirler angle and orientation and look at their effect on fluid mixing and combustion, we examine one configuration of a 7-point lean direct injector by looking at the non-combusting 2-D velocity field using PIV, and combusting system for chemical species using chemiluminescent imaging and flame spectroscopy. The circular 7-point array consists of axial swirlers, with the center 60° swirler surrounded by six 52° swirlers. The velocity results for this configuration show that the outer swirlers serve to isolate the center flow field near the injector exit. A recirculation zone forms downstream of the center swirler, but not behind the outer swirlers. The combusting results also show an isolated zone directly downstream of the center injector. The flame spectra show variation in speciation of combustion species such as OH*, C3*, CH*, and C2* as a function of position within the combustor.

lean direct injection↗
NASA NTRS2019

A Third-Generation Swirl-Venturi Lean Direct Injection Combustor with a Prefilming Pilot Injector

This paper presents experimental results for a low-NOxaero gas turbine combustor, in particular, a third-generationswirl-venturi lean direct injection (SV-LDI-3) combustor conceptcalled V4. The purpose of testing was three-fold. First,to evaluate the combustor against the 80% NOx reduction goalset by NASA’s AATT project. Second, to compare V4 to a previousSV-LDI-3 combustor concept called V3, especially at lowpower conditions. Third, to examine the accuracy of a type ofcorrelation equation frequently used by engine systems analysisgroups to estimate NOx emissions. All three testing goals weremet. For the first testing goal, with an estimated NOx reductionof 85%-90%, SV-LDI-3 V4 surpassed the AATT goal. For thesecond goal, however, V4 did not perform better than V3 at lowpower conditions. For the third goal, it was found that a majorassumption of the correlation equations — a simple dependenceon combustor inlet pressure — did not hold.

Tacina, K. M.↗
NASA NTRSDate not supplied

Comparison of Non-Combusting Spray Fields in a Model Combustor using Shadowgraphy

Droplet sizes were measured using shadowgraphy in the spray issuing from the center element of the baseline configuration of the NASA 7-element lean direct injector (LDI) array. Each LDI element consisted of a 60 degree clockwise axial air swirler, converging-diverging venturi, and a pressure-swirl atomizer positioned with its tip at the venturi throat. The non-combusting measurements were conducted using water spray in a 3-inch diameter research combustor operating at pressure of 5 bar and air inlet temperature of 700 K. At these inlet conditions, three air flow rates were used, producing reference velocities of 7.6, 15.2, and 22.9 m/s. Only the center nozzle was used. At each reference velocity, water flow rates were adjusted to simulate a common equivalence. Data were collected at a frame rate of 15 Hz over a range of positions near the LDI dump plane, and downstream, along the combustor centerline. Velocity measurements were achieved by use of a dual head Nd:YAG laser and frame transfer PIV camera. Droplet size and velocity, mass and number density, and volume fraction are compared at these inlet conditions to determine the effect of nozzle pressure drop on the measured properties.

lean direct injection↗
NASA NTRSDate not supplied

Comparison of Non-Combusting Spray Fields in a Model Combustor using Shadowgraphy

Droplet sizes were measured using shadowgraphy in the spray issuing from the center element of the baseline configuration of the NASA 7-element lean direct injector (LDI) array. Each LDI element consisted of a 60 degree clockwise axial air swirler, converging-diverging venturi, and a pressure-swirl atomizer positioned with its tip at the venturi throat. The non-combusting measurements were conducted using water spray in a 3-inch diameter research combustor operating at pressure of 5 bar and air inlet temperature of 700 K. At these inlet conditions, three air flow rates were used, producing reference velocities of 7.6, 15.2, and 22.9 m/s. Only the center nozzle was used. At each reference velocity, water flow rates were adjusted to simulate a common equivalence. Data were collected at a frame rate of 15 Hz over a range of positions near the LDI dump plane, and downstream, along the combustor centerline. Velocity measurements were achieved by use of a dual head Nd:YAG laser and frame transfer PIV camera. Droplet size and velocity, mass and number density, and volume fraction are compared at these inlet conditions to determine the effect of nozzle pressure drop on the measured properties.

lean direct injection↗
NASA NTRSDate not supplied

Characterization Progress of an Absorption Laser Differential Interferometer

An absorption laser differential interferometer (A-LDI) system can be used to provide simultaneous, colinear measurements of flow properties (pressure, temperature, concentration, velocity) and flow fluctuations. Further characterization work on the absorption aspect of the system is provided in this paper, including characterization of the laser operating parameters, comparisons of two etalons of different free spectral range, and the further evaluation of a fixed-wavelength absorption measurement that can be used to obtain absorption and LDI measurements with the same sampling rate. A 0.4 GHz etalon was demonstrated to provide sufficient fringe peaks at low modulation depths to be used for the low-pressure testing characteristic of hypersonic wind tunnel facilities. The use of a 3 GHz etalon as a low-cost relative wavemeter was tested and validated. Data taken with the fixed-wavelength strategy in a sub-atmospheric test cell using 100% O2was successful and will allow absorption and LDI data to be acquired simultaneously, colinearly, and at the same sampling rate, yielding a truly simultaneous measurement of the flow density fluctuations and the flow mean density.

Joshua M Weisberger↗
NASA NTRSDate not supplied

Characterization Progress of an Absorption Laser Differential Interferometer

An absorption laser differential interferometer (A-LDI) system can be used to provide simultaneous, colinear measurements of flow properties (pressure, temperature, concentration, velocity) and flow fluctuations. Further characterization work on the absorption aspect of the system is provided in this paper, including characterization of the laser operating parameters, comparisons of two etalons of different free spectral range, and the further evaluation of a fixed-wavelength absorption measurement that can be used to obtain absorption and LDI measurements with the same sampling rate. A 0.4 GHz etalon was demonstrated to provide sufficient fringe peaks at low modulation depths to be used for the low-pressure testing characteristic of hypersonic wind tunnel facilities. The use of a 3 GHz etalon as a low-cost relative wavemeter was tested and validated. Data taken with the fixed-wavelength strategy in a sub-atmospheric test cell using 100% O 2 was successful and will allow absorption and LDI data to be acquired simultaneously, colinearly, and at the same sampling rate, yielding a truly simultaneous measurement of the flow density fluctuations and the flow mean density.

Joshua M. Weisberger↗
NASA NTRSDate not supplied

CFD Evaluation of Radial Airflow Lean Direct Injectors for Commercial Supersonics Technology

An overview is provided of the impact on NOx emissions of replacing the six axial airflow Main swirlers of a seven-element lean-direct injection (LDI) module with radial airflow swirlers. The CFD study was motivated by the goal of reducing EINOx emissions of a combustor operating at supersonic cruise condition to a nominal value of 10 or below. The Open version of the National Combustion Code (OpenNCC) was used to perform two-phase reacting flow computations with various radial airflow swirler LDI flametube designs with an ‘average’ Jet-A (A2) fuel. The predicted EINOx emissions for the various radial airflow designs evaluated with OpenNCC were within 20% of each other, and 25% lower than current LDI injector designs using axial airflow swirlers.

gas turbine combustion↗
NASA NTRSDate not supplied

Effect of Liner Cooling Flow on Combustor Emissions for Commercial Supersonics Technology

An overview is provided of a parametric study conducted to study the effect of liner cooling airflow rates on NOx emissions of a seven-element lean-direct injection (LDI) module with radial airflow main swirlers. The goal of the CFD study was to determine the increase in cooling flow rate at which the NOx emissions would exceed 20% of the predicted emissions with zero liner cooling flow. The Open version of the National Combustion Code (OpenNCC) was used to perform two-phase reacting flow computations with a new LDI injection module design with radial airflow swirlers instead of axial airflow swirlers. CFD analysis with OpenNCC predicted a 20% increase in EINOx emissions was reached when the liner cooling airflow rate was increased to 15% of the baseline combustor airflow rate. The liner cooling flow rate was predicted to have a non-linear effect on increase in overall EINOx of the seven element LDI injection module.

CFD↗