Some aspects of steady-state propellant combustion as related to dynamic coupling mechanisms.
Composite solid propellant flame structure reaction zone, surface reactions and velocity dependence of linear regression rate
Povinelli, L. A.↗
SEARCH · Engineering Papers
Results for “Combustion dynamics”
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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Dynamic Stall Suppression Using Combustion-Powered Actuation (COMPACT)
Retreating blade stall is a well-known phenomenon that limits rotorcraft speed, maneuverability, and efficiency. Airfoil dynamic stall is a simpler problem, which demonstrates many of the same flow phenomena. Combustion Powered Actuation (COMPACT) is an active flow control technology, which at the outset of this work, had been shown to mitigate static and dynamic stall at low Mach numbers. The attributes of this technology suggested strong potential for success at higher Mach numbers, but such experiments had never been conducted. The work detailed in this report documents a 3-year effort focused on assessing the effectiveness of COMPACT for dynamic stall suppression at freestream conditions up to Mach 0.5. The work done has focused on implementing COMPACT on a high-lift rotorcraft airfoil: the VR-12. This selection was made in order to ensure that any measured benefits are over and above the capabilities of state-of-the-art high-lift rotorcraft airfoils. The detailed Computational Fluid Dynamics (CFD) simulations, wind-tunnel experiments, and system-level modeling conducted have shown the following: (1) COMPACT, in its current state of development, is capable of reducing the adverse effects of deep dynamic stall at Mach numbers up to 0.4; (2) The two-dimensional (2D) CFD results trend well compared to the experiments; and (3) Implementation of the CFD results into a system-level model suggest that significant rotor-level benefits are possible.
Matalanis, Claude G.↗
A study of high frequency nonlinear combustion instability in baffled annular liquid propellant rocket motors
Computer program contains mathematical model which provides relationship between engine gas dynamics and combustion processes. Mathematically simulated explosions initiate gas disturbances. Design methods for damping disturbances can be studied to prevent future engine shutdown or destruction.
Abreu, A.↗
Acoustic Database for Turbofan Engine Core-Noise Sources: Volume - I
In this program, a database of dynamic temperature and dynamic pressure measurements were acquired inside the core of a TECH977 turbofan engine to support investigations of indirect combustion noise. Dynamic temperature and pressure measurements were recorded for engine gas dynamics up to temperatures of 3100 degrees Fahrenheit and transient responses as high as 1000 hertz. These measurements were made at the entrance of the high pressure turbine (HPT) and at the entrance and exit of the low pressure turbine (LPT). Measurements were made at two circumferential clocking positions. In the combustor and inter-turbine duct (ITD), measurements were made at two axial locations to enable the exploration of time delays. The dynamic temperature measurements were made using dual thin-wire thermocouple probes. The dynamic pressure measurements were made using semi-infinite probes. Prior to the engine test, a series of bench, oven, and combustor rig tests were conducted to characterize the performance of the dual wire temperature probes and to define and characterize the data acquisition systems. A measurement solution for acquiring dynamic temperature and pressure data on the engine was defined. A suite of hardware modifications were designed to incorporate the dynamic temperature and pressure instrumentation into the TECH977 engine. In particular, a probe actuation system was developed to protect the delicate temperature probes during engine startup and transients in order to maximize sensor life. A set of temperature probes was procured and the TECH977 engine was assembled with the suite of new and modified hardware. The engine was tested at four steady state operating speeds, with repeats. Dynamic pressure and temperature data were acquired at each condition for at least one minute. At the two highest power settings, temperature data could not be obtained at the forward probe locations since the mean temperatures exceeded the capability of the probes. The temperature data were processed using software that accounts for the effects of convective and conductive heat transfer. The software was developed under previous NASA sponsored programs. Compensated temperature spectra and compensated time histories corresponding to the dynamic temperature of the gas stream were generated. Auto-spectral and cross-spectral analyses of the data were performed to investigate spectral features, acoustic circumferential mode content, signal coherence, and time delays. The dynamic temperature data exhibit a wideband and fairly flat spectral content. The temperature spectra do not change substantially with operating speed. The pressure spectra in the combustor and ITD exhibit generally similar shapes and amplitudes, making it difficult to identify any features that suggest the presence of indirect combustion noise. Cross-spectral analysis reveal a strong correlation between pressure and temperature fluctuations in the ITD, but little correlation between temperature fluctuations at the entrance of the HPT and pressure fluctuations downstream of it. Temperature fluctuations at the entrance of the low pressure turbine were an order of magnitude smaller than those at the entrance to the high pressure turbine. Time delay analysis of the temperature fluctuations in the combustor was inconclusive, perhaps due to the substantial mixing that occurs between the upstream and downstream locations. Time delay analysis of the temperature fluctuations in the ITD indicate that they convect at the mean flow speed. Analysis of the data did not reveal any convincing indications of the presence of indirect combustion noise. However, this analysis has been preliminary and additional exploration of the data is recommended including the use of more sophisticated signal processing to explore subtle issues that have been revealed but which are not yet fully understood or explained.
Aeroacoustics↗
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↗
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.↗
Scalability analysis of heavy-duty gas turbines using data-driven machine learning
With the increasing integration of variable renewable energy sources into power systems, the role of flexible power generation technologies like gas turbines (GT) in rapid grid balancing remains crucial. This sustained importance underscores the need for scaled and precise modeling of GT to ensure effective integration within evolving energy frameworks. While physics-driven GT models integrate thermodynamics, fluid dynamics, and combustion principles, they often rely on approximate mathematical representations to accommodate scaling that may not capture the actual complex dynamics for GTs and inertial effects associated to GTs with different ratings. In this study, a data-driven model is proposed using machine learning (ML) techniques to conduct GT scalability analysis and performance evaluation with high accuracy. The ML model, trained on data from various operating conditions and performance parameters, aims to uncover intricate relationships and patterns, resembling GT characteristics at different scales (ratings). The model is developed to capture complex system interaction and to adapt to changing operational scenarios at different capacities, providing valuable insights of power system dynamics. In this study, the real-time digital simulator platform was employed to generate training data for the ML model and assess its dynamic characteristics. The ultimate objective was to develop a detailed modeling framework based on governing equations and data-driven ML capable of predicting key performance indicators, in thermal systems such as GTs, including power output, speed, fuel consumption, and exhaust temperature under diverse operating conditions at different scales. The developed ML framework demonstrated high accuracy, with mean relative errors for GT power prediction, reference speed, exhaust temperature, and compressor pressure ratio (CPR) parameters consistently below 0.1% across typical load fluctuation scenarios. Maximum deviations were limited to approximately 0.5 K for exhaust temperature and 0.009 for CPR, underscoring the model’s ability to replicating dynamic GT behavior with high precision. The adaptability of the ML model enables its application across diverse operational conditions and its extension to other thermal systems. By leveraging advanced ML techniques, this study presents a robust and scalable modeling framework that enhances GT simulation precision, facilitating improved integration into evolving power systems.
24 POWER TRANSMISSION AND DISTRIBUTION↗
ELECTRONIC STRUCTURE METHODS AND PROTOCOLS WITH APPLICATION TO DYNAMICS, KINETICS AND THERMOCHEMISTRY
Hydrocarbon combustion involves the reaction dynamics of a tremendous number of species beginning with many-component fuel mixtures and proceeding via a complex system of intermediates to form primary and secondary products. Combustion conditions corresponding to new advanced engines and/or alternative fuels rely increasingly on autoignition and low-temperature-combustion chemistry. In these regimes various transient radical species such as HO2, ROO·, ·QOOH, HCO, NO2, HOCO, and Criegee intermediates play important roles in determining the detailed as well as more general dynamics. A clear understanding and accurate representation of these processes is needed for effective modeling. Given the difficulties associated with making reliable experimental measurements of these systems, computation can play an important role in developing these energy technologies. Accurate calculations have their own challenges since even within the simplest dynamical approximations such as transition state theory, the rates depend exponentially on critical barrier heights and these may be sensitive to the level of quantum chemistry. Moreover, it is well-known that in many cases it is necessary to go beyond statistical theories and consider the dynamics. Quantum tunneling, resonances, radiative transitions, and non-adiabatic effects governed by spin-orbit or derivative coupling can be determining factors in those dynamics. Building upon progress made during a period of prior support through the DOE Early Career Program, this project combines developments in the areas of potential energy surface (PES) fitting and multistate multireference quantum chemistry to allow spectroscopically and dynamically/kinetically accurate investigations of key molecular systems (such as those mentioned above), many of which are radicals with strong multireference character and have the possibility of multiple electronic states contributing to the observed dynamics. An ongoing area of investigation is to develop general strategies for robustly convergent electronic structure theory for global multichannel reactive surfaces including diabatization of energy and other relevant surfaces such as dipole transition. Combining advances in ab initio methods with automated interpolative PES fitting allows the construction of high-quality PESs (incorporating thousands of high-level data) to be done rapidly through parallel processing on high-performance computing (HPC) clusters. In addition, new methods and approaches to electronic structure theory will be developed and tested through applications. This project will explore limitations in traditional multireference calculations (e.g., MRCI) such as those imposed by internal contraction, lack of high-order correlation treatment and poor scaling. Methods such as DMRG-based extended active-space CASSCF and various Quantum Monte Carlo (QMC) methods will be applied (including VMC/DMC and FCIQMC). Insight into the relative significance of different orbital spaces and the robustness of application of these approaches on leadership class computing architectures will be gained. Synergy with other components of this research program such as automated PES fitting and multireference quantum chemistry will be used to address challenges encountered by the standard approaches to computational thermochemistry (those being single-reference quantum chemistry and perturbative treatments of the anharmonic vibrational energy, which break down for some cases of electronic structure or floppy strongly coupled vibrational modes).
74 ATOMIC AND MOLECULAR PHYSICS↗
Dynamic Temperature and Pressure Measurements in the Core of a Propulsion Engine
Dynamic temperature and pressure measurements were made in the core of a TECH977 propulsion engine as part of a NASA funded investigation into indirect combustion noise. Dynamic temperature measurements were made in the combustor, the inter-turbine duct, and the mixer using ten two-wire thermocouple probes. Internal dynamic pressure measurements were made at the same locations using piezoresistive transducers installed in semi-infinite coils. Measurements were acquired at four steady state operating conditions covering the range of aircraft approach power settings. Fluctuating gas temperature spectra were computed from the thermocouple probe voltage measurements using a compensation procedure that was developed under previous NASA test programs. A database of simultaneously acquired dynamic temperature and dynamic pressure measurements was produced. Spectral and cross-spectral analyses were conducted to explore the characteristics of the temperature and pressure fluctuations inside the engine, with a particular focus on attempting to identify the presence of indirect combustion noise.
Turbomachinery Noise↗
Low frequency instability - A comparison of theory and experiment.
Solid-propellant combustion instability models describing combustion zone dynamics applied to acoustic and nonacoustic instability in low frequency regime
COMBUSTION INSTABILITY↗
Miniaturized Laser Absorption Spectrometer for Combustion Calorimetry and Process Monitoring
A miniaturized tunable laser absorption spectrometer capable of measuring gas-phase concentrations of CO, CO2, and O2 has been developed for operation in spacecraft environments. As part of the Spacecraft Fire Safety Demonstration (Saffire) project, we previously demonstrated the Combustion Product Monitor (CPM) instrument to characterize pyrolysis of relevant test materials in low gravity aboard a transfer vehicle returning from low Earth orbit. Here, we adapted the CPM instrument design to achieve detection of CO, CO2, and O2 with improved minimum detection limits and dynamic range as well as reduced instrument size and power. The instrument can be operated in either an open or sealed configureation, allowing for ambient gas composition measuremnts or in-line monitoring of gas streams. By accurately monitoring CO, CO2, and O2 with broad pressure/temperature calibration and response time on the order of 1 s, the instrument can be used to characterize the dynamics of combustion reactions in a variety of environments.
Briggs, Ryan M.↗
Concentration Field of Reactants and Products Species in a Reacting Vortex Ring
The proposed paper will present experimental and numerical results on the concentration fields of both reactants and products species in a reacting vortex ring that is generated from the interaction between a diffusion flame and a laminar vortex ring. Flame-vortex interactions are canonical configurations used to study the underlying processes occurring in complicated turbulent reacting flows. This type of configuration contains many of the fundamental aspects of the coupling between fluid dynamics and combustion that could be investigated with more controllable conditions than are possible under direct investigations of turbulent flames. The current configuration has been studied experimentally by Chen and Dahm and Chen et al. under microgravity conditions, and by Park and Shin, and You et al. under normal gravity conditions. This configuration is similar to that used in the analyses of Karagozian and Manda of their 2-D vortex pair in which both fuel and entrained oxidizer are present. The vortex ring used in this study is generated by issuing methane into an air environment through the exit of an axisymmetric nozzle. The experiments were conducted under microgravity conditions in order to remove the undesirable effects of buoyancy that can affect both the flame structure and ring dynamics resulting in possibly asymmetric and nonrepeatable interactions. The experimental technique of diode laser wavelength modulation spectroscopy (WMS) is used to measure concentration fields of reactants, CH4 and O2, products, H2O, CO2, OH, and temperature fields which can be inferred from either line pairs of O2 or OH lines. This technique has been investigated previously by Silver and Bomse et al. This is the first time that the technique has been applied to reacting vortex rings under microgravity conditions. The effect of ring circulation and fuel volume on the species concentration fields will be investigated. The experimental results will be compared to the current numerical results, and used to validate the numerical studies. In addition, the existence of burned cores during the interactions will be determined, and the increase in reactant consumption with increased ring circulation will be examined. Numerical studies were also conducted by solving the Navier-Stokes and mixture fraction equations with the assumptions of unity Lewis and Schmidt numbers. Equilibrium chemistry and flamelet libraries were used to obtain the temperature and species mass fraction fields. The numerical results will serve as guidelines in conducting the experimental studies. Ring circulation and fuel volume effects on the interactions and species concentration fields will be investigated and compared to experimental results.
Chen, Shin-Juh↗
Parametric Modeling Investigation of a Radially-Staged Low-Emission Aviation Combustor
Aviation gas-turbine combustion demands high efficiency, wide operability and minimal trace gas emissions. Performance critical design parameters include injector geometry, combustor layout, fuel-air mixing and engine cycle conditions. The present investigation explores these factors and their impact on a radially staged low-emission aviation combustor sized for a next-generation 24,000-lbf-thrust engine. By coupling multi-fidelity computational tools, a design exploration was performed using a parameterized annular combustor sector at projected 100% takeoff power conditions. Design objectives included nitrogen oxide emission indices and overall combustor pressure loss. From the design space, an optimal configuration was selected and simulated at 7.1, 30 and 85% part-power operation, corresponding to landing-takeoff cycle idle, approach and climb segments. All results were obtained by solution of the steady-state Reynolds-averaged Navier-Stokes equations. Species concentrations were solved directly using a reduced 19-step reaction mechanism for Jet-A. Turbulence closure was obtained using a nonlinear K-epsilon model. This research demonstrates revolutionary combustor design exploration enabled by multi-fidelity physics-based simulation.
design analysis↗
Detonation structure in the presence of mixture stratification using reaction-resolved simulations
Many investigations of detonation-based combustors have identified reactant mixture inhomogeneity as having a leading-order impact on wave dynamics and combustion efficiency. To examine this phenomenon in a simplified context, an array of two- and three-dimensional channel detonation simulations are conducted in the present work. The reactant mixture consists of stratified fuel and air, wherein the randomly distributed equivalence ratio field features a characteristic stratification length scale. Detailed chemical kinetics are implemented in an adaptive mesh refinement solution framework where the region near the shock front is resolved with Ο (100) cells per representative ZND induction length. The results show that in comparison to baseline cases with uniform reactant mixtures, reactant stratification has a marked impact on the detonation structure. Increasing the stratification length scale increases the size and irregularity of the detonation cells, yielding larger variations in wave speed. Triple point collisions in fuel-rich regions lead to local wave speeds above the notional mean CJ speed, but wave passage through inert regions causes the local wave speed and strength to diminish. Further, conditional statistics show that increasing the stratification length scale increases the variance in pressure and temperature in the primary reaction zone, as well as the variance in heat release over a range of mixture conditions. In addition to the reactant mixture, the impact of the boundary condition behind the detonation is also investigated. The results show that an inflow boundary condition acts to over-drive the wave, leading to higher peak pressures, smaller detonation cells, and increased reactant consumption. On the other hand, cases with a wall behind the wave exhibit weaker waves with lower peak pressures and heat release rates, as well as greater variance in conditional quantities. Comparisons between complementary two- and three-dimensional simulations show reasonable qualitative agreement in wave structure, speed, and conditional statistics.
42 ENGINEERING↗
Cyclic dynamics of misfires and partial burns in a dilute spark-ignition engine
Here, this study investigates the cyclic dynamics of cumulative heat release data past the edge of stability in a dilute spark-ignition engine. Emphasis is placed on analyzing the cyclic dynamics near the dilute limit where partial burns and misfires are frequent. These events are often followed by a higher-energy cycle due to the feed-forward mechanism present in the residual gases. These patterns are deterministic and increase the coefficient of variation to undesirable levels. Symbol sequence analysis was used to investigate the cyclic dynamics of these low–high patterns. The heat release was partitioned on an energy basis to give physical meaning to each partition and each sequence created when analyzing the symbol sequence results. This partitioning method provided insight into the differences in the dynamics when operating in the misfire or partial burn regime. These differences could impact the control method used.
42 ENGINEERING↗
Dynamic Characteristics of Solid Propellant Combustion
Combustion instability - response of solid propellant combustion zone to normally incident one-dimensional pressure waves
COMBUSTION INSTABILITY↗
Low frequency instability - A comparison of theory and experiment.
Solid propellant combustion instability models describing combustion zone dynamics applied to acoustic and nonacoustic instability in LF regime
Beckstead, M. W.↗
Investigation of the starting transients of high performance solid-propellant motors
The starting transients of solid propellant engines were investigated to develop design principles for predicting transients in high performance igniter and engine configurations. Research and diagnosis were conducted on the processes affecting ignition transients, such as heat flux, igniter, flame spreading over the surface, and nonsteady combustion gas dynamics. Abstracts of published reports related to this research are presented. Topics discussed include: development of an analytical model, analytical prediction of the entire ignition transient, transient behavior of pressure and regression rate during reignition after shut-down, and problems associated with restarting hybrid rocket engines.
Summerfield, M.↗