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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Comparison of Center Nozzle Staging to Outer Nozzle Staging in a Multi-Flame Combustor

Combustion instability in gas turbines is often mitigated using fuel staging, a strategy where the fuel is split unevenly between different nozzles of a multiple-nozzle combustor. This work examines the efficacy of different fuel staging configurations by comparing axisymmetric and non-axisymmetric fuel staging in a four-around-one model gas turbine combustor. Fuel staging is accomplished by increasing the equivalence ratio of the center nozzle (axisymmetric staging) or an outer nozzle (non-axisymmetric staging). When the global equivalence ratio is ϕ = 0.70 and all nozzles are fueled equally, the combustor undergoes longitudinal, self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased above ϕ Staging = 0.79. This bifurcation equivalence ratio varies between ϕ Staging = 0.86 and ϕ Staging = 0.76 for the outer nozzles, and is attributed to minor hardware differences between each nozzle. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the staged flame has similar phase relationships for all staging configurations. It is found that axisymmetric staging can be as effective as non-axisymmetric staging; however, the aforementioned hardware variations can impact both the bifurcation equivalence ratio and the effectiveness of staging.

Culler, Wyatt↗
DOE OSTI2015

Effect of the number and position of nozzle holes on in- and near-nozzle dynamic characteristics of diesel injection

Despite the fact that all modern diesel engines use multi-hole injectors, single-hole injectors are frequently used to understand the fundamental properties of high-pressure diesel injections due to their axisymmetric design of the injector nozzles. A multi-hole injector accommodates many holes around the nozzle axis to deliver adequate amount of fuel with small orifices. The off-axis arrangement of the multi-hole injectors significantly alters the inter- and near-nozzle flow patterns compared to those of the single-hole injectors. This study compares the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole (3-hole and 6-hole) diesel injectors to understand how the difference in hole arrangement and number affects the initial flow development of the diesel injectors. A propagation-based X-ray phase-contrast imaging technique was applied to compare the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole injectors. The comparisons were made by dividing the entire injection process by three sub-stages: opening-transient, quasi-steady and closing-transient. (C) 2015 Elsevier Ltd. All rights reserved.

42 ENGINEERING↗
DOE OSTI2019

Nozzle tip wetting in gasoline direct injection injector and its link with nozzle internal flow

Fuel film in the gasoline direct injection injector tip, or so-called nozzle tip wetting, has been found to be an important contributor of particle emissions. Attempts have been made to reduce the nozzle tip wetting by optimizing nozzle geometry designs. However, the inherent mechanism of the nozzle tip wetting formation and its link with nozzle internal flow is still unclear yet due to the lack of direct observations. To overcome this insufficiency, here the nozzle internal flow and the formation process of the nozzle tip wetting were visualized in the real-scale aluminum nozzles using the X-ray phase-contrast technique. Results showed that the needle bouncing, injection pressure, and hole configuration affect the formation of the nozzle tip wetting, while the influence of needle bouncing is the most critical. A further study was conducted to examine the effect of nozzle counterbore diameter on the nozzle tip wetting. It was found that with an increase in counterbore diameter, the nozzle tip wetting slightly increased first and then decreased sharply after the counterbore diameter exceeded 0.40 mm. The mechanisms of the aforementioned phenomena were discussed in detail, which can contribute to the better understandings and control strategies of nozzle tip wetting.

42 ENGINEERING↗
DOE OSTI2020

Nozzle assembly and method for forming nozzle assembly

A nozzle assembly is disclosed, including a CMC nozzle shell, a nozzle spar, and an endwall. The CMC nozzle shell includes a CMC composition and an interior cavity. The nozzle spar is partially disposed within the interior cavity and includes a metallic composition, a cross-sectional conformation, a plurality of spacers protruding from the cross-sectional conformation, the plurality of spacers contacting the CMC nozzle shell, and a spar cap. The endwall includes at least one surface in lateral contact with the spar cap and maintains a lateral orientation of the CMC nozzle shell and the nozzle spar relative to the endwall. The lateral orientation maintains a predetermined throat area of the nozzle assembly. A method for forming the nozzle assembly includes inserting the nozzle spar into the interior cavity, rotating the CMC nozzle shell and the nozzle spar laterally relative to the endwall, and maintaining the lateral orientation.

Hafner, Matthew Troy↗
DOE OSTI2017

The Effect of Transient Fuel Staging on Self-Excited Instabilities in a Multi-Nozzle Model Gas Turbine Combustor

Combustion instability in gas turbines can be mitigated using active techniques or passive techniques, but passive techniques are almost exclusively used in industrial settings. While fuel staging, a common passive technique, is effective in reducing the amplitude of self-excited instabilities in gas turbine combustors at steady-state conditions, the effect of transients in fuel staging on self-excited instabilities is not well understood. This paper examines the effect of fuel staging transients on a laboratory-scale five-nozzle can combustor undergoing self-excited instabilities. The five nozzles are arranged in a four-around-one configuration and fuel staging is accomplished by increasing the center nozzle equivalence ratio. When the global equivalence ratio is φ = 0.70 and all nozzles are fueled equally, the combustor undergoes self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased to φ = 0.80 or φ = 0.85. Two transient staging schedules are used, resulting in transitions from unstable to stable operation, and vice-versa. It is found that the characteristic instability decay times are dependent on the amount of fuel staging in the center nozzle. It is also found that the decay time constants differ from the growth time constants, indicating hysteresis in stability transition points. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the instability onset process is different from the instability decay process.

Culler, Wyatt↗
DOE OSTI2018

Hole number effect on spray dynamics of multi-hole diesel nozzles: An observation from three- to nine-hole nozzles

For the simplicity of optical diagnostics, studies on fuel spray and combustion characteristics of modern diesel engines have been conducted using the investigation nozzles having the reduced number of holes (two- or three-hole nozzles) compared to the production nozzles. However, the similarity of spray dynamics between the investigation nozzles and production nozzles has not been confirmed yet. Also, the hole number effect on spray dynamics has been investigated only in a limited range of hole number making it difficult to derive the clear trend and understandings of the hole number effect. In this study, the hole number effect on spray dynamics of multi-hole diesel nozzles has been investigated in a wide range of hole number with sufficient data points (three, five, six, eight, nine-hole) by using the X-ray Phase-Contrast Imaging technique. The non-linear trend in the spray structure, as well as the dynamics results, was observed as increasing the hole number regardless of injection pressure. Discussions were made accordingly to understand the observed result trend. In conclusion, the study suggests that great attention is needed when deciding the number of nozzle holes for the optimized engine combustion.

42 ENGINEERING↗
DOE OSTI2016

Turbomachine combustor nozzle including a monolithic nozzle component and method of forming the same

A turbomachine combustor nozzle includes a monolithic nozzle component having a plate element and a plurality of nozzle elements. Each of the plurality of nozzle elements includes a first end extending from the plate element to a second end. The plate element and plurality of nozzle elements are formed as a unitary component. A plate member is joined with the nozzle component. The plate member includes an outer edge that defines first and second surfaces and a plurality of openings extending between the first and second surfaces. The plurality of openings are configured and disposed to register with and receive the second end of corresponding ones of the plurality of nozzle elements.

42 ENGINEERING↗
DOE OSTI2015

Ceramic micro-injection molded nozzles for serial femtosecond crystallography sample delivery

Serial femtosecond crystallography (SFX) using X-ray Free-Electron Lasers (XFELs) allows for room temperature protein structure determination without evidence of conventional radiation damage. In this method, a liquid suspension of protein microcrystals can be delivered to the X-ray beam in vacuum as a micro-jet, which replenishes the crystals at a rate that exceeds the current XFEL pulse repetition rate. Gas dynamic virtual nozzles produce the required micrometer-sized streams by the focusing action of a coaxial sheath gas and have been shown to be effective for SFX experiments. Here, we describe the design and characterization of such nozzles assembled from ceramic micro-injection molded outer gas-focusing capillaries. Trends of the emitted jet diameter and jet length as a function of supplied liquid and gas flow rates are measured by a fast imaging system. The observed trends are explained by derived relationships considering choked gas flow and liquid flow conservation. Finally, the performance of these nozzles in a SFX experiment is presented, including an analysis of the observed background.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Comparison of Equivalence Ratio Transients on Combustion Instability in Single-Nozzle and Multi-Nozzle Combustors

Low-emissions gas turbine combustion, achieved through the use of lean, premixed fueling strategies, is susceptible to combustion instability. The driving mechanism for this instability arises from fluctuations of pressure, fuel/air flow rate, and heat release rate. If these fluctuations are relatively in-phase, the combustion system will evolve to a self-excited state. The self-excited instability frequency and amplitude depend mainly on the operating condition and the geometry of the combustor. In this study, we consider the onset and decay of self-excited instabilities, resulting from transients in fuel/air ratio, in both single-nozzle and multi-nozzle combustors. In particular, we examine the differences in the instability onset and decay processes between these two flame configurations, as most gas turbine combustors have multiple nozzles, but most gas turbine combustor experiments utilize a single-nozzle. A nonlinear logistic regression analysis is applied to study the timescales of the decay and onset transients. Variations in the equivalence ratio change the heat release rate distribution inside the combustor, which is captured using chemiluminescence imaging. The normalized Rayleigh index, which shows the spatial distribution of the instability driving, is calculated to analyze the driving strength in different regions of the flame. Comparisons between the single- and multi-nozzle flame transients, including both center and outer flames for the multi-nozzle combustor, suggest that both confinement from the wall and flame-flame interaction are crucial to determining flame dynamics as the equivalence ratio transient changes the heat release rate distribution near corner recirculation zone and flame shear layers.

Chen, Xiaoling↗
DOE OSTI2018

Comparison of equivalence ratio transients on combustion instability in single-nozzle and multi-nozzle combustors

Low-emissions gas turbine combustion, achieved through the use of lean, premixed fueling strategies, is susceptible to combustion instability. The driving mechanism for this instability arises from fluctuations of pressure, fuel/air flow rate, and heat release rate. If these fluctuations are relatively in-phase, the combustion system will evolve to a self-excited state. The self-excited instability frequency and amplitude depend mainly on the operating condition and the geometry of the combustor. In this study, we consider the onset and decay of self-excited instabilities, resulting from transients in fuel/air ratio, in both single-nozzle and multi-nozzle combustors. In particular, we examine the differences in the instability onset and decay processes between these two flame configurations, as most gas turbine combustors have multiple nozzles, but most gas turbine combustor experiments utilize a single-nozzle. A nonlinear logistic regression analysis is applied to study the timescales of the decay and onset transients. Variations in the equivalence ratio change the heat release rate distribution inside the combustor, which is captured using chemiluminescence imaging. The normalized Rayleigh index, which shows the spatial distribution of the instability driving, is calculated to analyze the driving strength in different regions of the flame. Comparisons between the single- and multi-nozzle flame transients, including both center and outer flames for the multi-nozzle combustor, suggest that both confinements from the wall and flame-flame interaction are crucial to determining flame dynamics as the equivalence ratio transient changes the heat release rate distribution near corner recirculation zone and flame shear layers.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2016

Experimental study on the effect of nozzle hole-to-hole angle on the near-field spray of diesel injector using fast X-ray phase-contrast imaging

Fuel atomization and vaporization process play a critical role in determining the engine combustion and emission. The primary near-nozzle breakup is the vital link between the fuel emerging from the nozzle and the fully atomized spray. In this study, the near-nozzle spray characteristics of diesel injector with different umbrella angle (UA) were investigated using high-speed X-ray phase-contrast imaging and quantitative image processing. A classic ‘dumbbell’ profile of spray width (SW) composed of three stages: opening stage, semisteady stage and closing stage. The SW peak of two-hole injectors was more than twice of that of single-hole injector at the opening and closing stages, corresponding to the hollow-cone spray. This indicated the vortex flow was formed with the increase of the UA. The higher injection pressure had little influence on the SW while led to earlier breakup closer to the nozzle. Significant fuel effect on the SW at higher needle lift was found. However, this effect could be neglect at lower needle lift due to the leading role of internal flow and cavitation on the near-field spray characteristics. In addition, the morphology-based breakup process was observed, which highlighted the important effect of internal flow on the spray development. The possibility of using hollow-cone spray in diesel injector was also discussed.

biodiesel↗
DOE OSTI2018

Evaluation of Shot-to-Shot In-Nozzle Flow Variations in a Heavy-Duty Diesel Injector Using Real Nozzle Geometry

Cyclic variability in internal combustion engines (ICEs) arises from multiple concurrent sources, many of which remain to be fully understood and controlled. This variability can, in turn, affect the behavior of the engine resulting in undesirable deviations from the expected operating conditions and performance. Shot-to-shot variation during the fuel injection process is strongly suspected of being a source of cyclic variability. This study focuses on the shot-to-shot variability of injector needle motion and its influence on the internal nozzle flow behavior using diesel fuel. High-speed x-ray imaging techniques have been used to extract high-resolution injector geometry images of the sac, orifices, and needle tip that allowed the true dynamics of the needle motion to emerge. These measurements showed high repeatability in the needle lift profile across multiple injection events, while the needle radial displacement was characterized by a much higher degree of randomness. A robust and previously validated computational setup from the authors’ research group using a commercial computational fluid dynamics (CFD) code has been adapted for the eight-hole heavy-duty common-rail diesel injector used for the measurements. The simulation results obtained using the x-ray-scanned geometry have been validated against available experimental data of mass flow rate at the nozzle exit. The fuel mass flow rate has then been analyzed at three different injection pressures that cover the conditions at which the injector typically operates during normal engine operation. Finally, the average off-axis motion of the needle has been perturbed (based on the variability found in the experimental measurements) to generate three new cases that present different amplitude and phasing of the radial displacement with respect to the baseline average motion. Furthermore, this revealed the effects of off-axis motion on shot-to-shot and orifice-to-orifice variations.

42 ENGINEERING↗
DOE OSTI2013

Binary nucleation rates for ethanol/water mixtures in supersonic Laval nozzles: Analyses by the first and second nucleation theorems

We performed pressure trace measurements and small angle x-ray scattering measurements to determine the vapor-liquid nucleation rates of EtOH/H{sub 2}O mixtures including pure EtOH and pure H{sub 2}O in two supersonic Laval nozzles with different expansion rates. The nucleation rates varied from 0.9 × 10{sup 17} to 16 × 10{sup 17} cm{sup −3} s{sup −1} over the temperature range of 210 K to 230 K, EtOH activity range of 0 to 11.6, and H{sub 2}O activity range of 0 to 124. The first and second nucleation theorems were applied to the nucleation rates to estimate the sizes, compositions, and excess energies of the critical clusters. The critical clusters contained from 4 to 15 molecules for pure H{sub 2}O and EtOH/H{sub 2}O clusters, and from 16 to 23 molecules for pure EtOH clusters. Comparing the excess energies of the pure H{sub 2}O critical clusters with the results of a quantum-chemistry calculation suggested that the pre-factor of the theoretical nucleation rate is almost constant regardless of the monomer concentration. One possible explanation for this result is that cooling of the critical clusters limits the nucleation rate under the highly supersaturated conditions. The results of the analyses also yielded the relation between the surface energy and the composition of the critical clusters, where the latter are predicted to consist only of surface molecules. Applying this relationship to the EtOH/H{sub 2}O bulk liquid mixtures, we estimated the EtOH mole fraction in the surface layer and found it is higher than that derived from the surface tension based on the Gibbs adsorption equation when the EtOH mole fraction in the liquid is higher than about 0.2 mol/mol. This discrepancy was attributed to the existence of the EtOH depletion layer just below the surface layer of the liquid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗