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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Engine combustion control via fuel reactivity stratification

A compression ignition engine uses two or more fuel charges having two or more reactivities to control the timing and duration of combustion. In a preferred implementation, a lower-reactivity fuel charge is injected or otherwise introduced into the combustion chamber, preferably sufficiently early that it becomes at least substantially homogeneously dispersed within the chamber before a subsequent injection is made. One or more subsequent injections of higher-reactivity fuel charges are then made, and these preferably distribute the higher-reactivity matter within the lower-reactivity chamber space such that combustion begins in the higher-reactivity regions, and with the lower-reactivity regions following thereafter. By appropriately choosing the reactivities of the charges, their relative amounts, and their timing, combustion can be tailored to achieve optimal power output (and thus fuel efficiency), at controlled temperatures (and thus controlled NOx), and with controlled equivalence ratios (and thus controlled soot).

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2015

System and method for reducing combustion dynamics in a combustor

A system for reducing combustion dynamics in a combustor includes an end cap having an upstream surface axially separated from a downstream surface, and tube bundles extend from the upstream surface through the downstream surface. A divider inside a tube bundle defines a diluent passage that extends axially through the downstream surface, and a diluent supply in fluid communication with the divider provides diluent flow to the diluent passage. A method for reducing combustion dynamics in a combustor includes flowing a fuel through tube bundles, flowing a diluent through a diluent passage inside a tube bundle, wherein the diluent passage extends axially through at least a portion of the end cap into a combustion chamber, and forming a diluent barrier in the combustion chamber between the tube bundle and at least one other adjacent tube bundle.

42 ENGINEERING↗
DOE OSTI2016

Engine combustion control via fuel reactivity stratification

A compression ignition engine uses two or more fuel charges having two or more reactivities to control the timing and duration of combustion. In a preferred implementation, a lower-reactivity fuel charge is injected or otherwise introduced into the combustion chamber, preferably sufficiently early that it becomes at least substantially homogeneously dispersed within the chamber before a subsequent injection is made. One or more subsequent injections of higher-reactivity fuel charges are then made, and these preferably distribute the higher-reactivity matter within the lower-reactivity chamber space such that combustion begins in the higher-reactivity regions, and with the lower-reactivity regions following thereafter. By appropriately choosing the reactivities of the charges, their relative amounts, and their timing, combustion can be tailored to achieve optimal power output (and thus fuel efficiency), at controlled temperatures (and thus controlled NOx), and with controlled equivalence ratios (and thus controlled soot).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

System and method for engine combustion

A combustion system for use with one or more cylinder bores of an internal combustion engine includes at least one cylinder head defining first and second intake ports in fluid communication with the one or more cylinder bores. A flap is adjustably connected to the at least one cylinder head. The flap includes a first flap portion cooperating with the first intake port extending from an arm and a second flap portion cooperating with the second intake port extending from the arm and disposed adjacent the first flap portion. A controller in electrical communication with an actuator monitors the condition of the engine and actuates the flap to position the first and second flap portions between first and second positions to create a first combustion condition and a second combustion condition.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2019

COMBUSTION AND EMISSION CHARACTERISTICS OF A LEAN AXIAL-STAGE COMBUSTOR

Gas turbine engines with high operational flexibility represent an important area of research. In support of this, the reduction of NOx emissions at high-temperature, full-load conditions are the main target of this research study. To overcome the challenge of decreasing the residence time of hot exhaust gas in the burner, the approach of axial-staged combustion has been used, which aims to burn at lean conditions. A main combustion stage with a conventional burner is followed by a jet-in-crossflow (JIC) stage downstream. This second combustion stage, the test section, burns well over a third of the total fuel amount, which is added by a jet inlet. A steady Computational Fluid Dynamics (CFD) model in Star-CCM+ was created to analyze the JIC stage. A structured mesh grid with 1.7 million cells and local refinement domains was used along with RANS equations, Realizable k-ε turbulence, Complex Chemistry model with Laminar Flame Concept (LFC) applied. The findings of the computational model include a detailed description of the flow field, focusing on vortex formation and penetration depth. Three vortex types and local pressure losses of up to 6% in the mixing domain were identified. Results were compared with similar data from literature and a very good match was yielded. Optical laser diagnostics should work well to capture the predicted flow penetration. The highest local reaction rates were observed inside a thin flame front, 4 to 6 diameters downstream of the jet. The jet showed a limited expansion into the available channel domain, resulting in low heat release and a methane conversion of only 52%. Providing an enhanced amount of oxygen was proven to increase the CH4 conversion significantly. Emissions were analyzed for an estimated species composition from the main burner. A CO production of 9.85‰ and the reduction of an incoming NOx amount by 15% were determined, outlining the potential of axial-staged combustion. Further numerical investigation along with experimental verification is in progress.

03 NATURAL GAS↗
DOE OSTI2019

Additive-mixing fuel-injection system for internal combustion engines

A system and method for fast control of the timing of combustion in an internal combustion engine, comprising actuating a fast-acting fuel-additive supply valve to meter a variable amount of fuel additive into a fuel stream, thereby forming an additive-enhanced fuel with an additive concentration that can be dynamically adjusted as fast as each engine cycle; injecting the additive-enhanced fuel directly or indirectly into a combustion chamber or into an intake port; and combusting the additive-enhanced fuel.

42 ENGINEERING↗
DOE OSTI2020

Oxy-fuel combustion and power generation system

Integration of an oxyfuel combustion boiler at elevated pressures and a heat exchanger is achieved to produce carbon dioxide by feeding flue gas comprising carbon dioxide and water from the oxyfuel combustion boiler to a direct contact cooler column wherein water is condensed at a temperature of 0 to 10° C. lower than its dew point; feeding a portion of the condensed water from the direct contact cooler column to the oxyfuel combustion boiler; feeding a portion of the carbon dioxide from the direct contact cooler column to the oxyfuel combustion boiler; and recovering a portion of the carbon dioxide from the direct contact cooler column.

Alekseev, Alexander↗
DOE OSTI2018

Effects of equivalence ratio transient duration on self-excited combustion instability time scales in a single-nozzle combustor

Fuel staging is an effective way to attenuate combustion instability in lean, premixed combustion systems. Combustion instability occurs due to the coupling between heat release rate oscillations and combustor acoustics. In our experiments, we seek to understand how transient fuel staging affects the structure and dynamics of a single flame to help inform our previous studies of multi-flame systems. In the current experiments, fuel staging is achieved by changing the equivalence ratio in the nozzle. The equivalence ratio in the nozzle is varied over two different timescales, or transient durations, which are 1 ms and 4 s. For each duration, we also vary the percentage change in the equivalence ratio, with levels of ±3.57% and ±7.14% of the mean equivalence ratio, ϕ=0.7. Flame images recorded using CH* chemiluminescence imaging are analyzed to show the variations of the phase difference between pressure and heat release oscillations during transients. Phase difference transition behaves similarly in the flame base region but differently in flame/wall interaction region. More similarities between short and long duration transients are observed in combustion instability onset direction than decay direction.

Chen, Xiaoling↗
DOE OSTI2022

System and method for control of compression in internal combustion engine via compression ratio and elastic piston

The present disclosure relates to a system for controlling ignition of an air/fuel mixture intake charge directed into an internal combustion engine. The system may have a longitudinally movable inner cylinder liner configured to fit within a cylinder wall portion of an internal combustion engine, and able to receive a piston of the engine therein. A portion of the inner cylinder liner defines an internal volume forming a combustion chamber, and the internal volume controls a compression ratio of the cylinder. The system also has a cylinder head assembly operatively associated with the inner cylinder liner and able to move linearly to cause longitudinal displacement of the inner cylinder liner relative to the cylinder wall portion. This enables the volume of the combustion chamber to be further varied, to thus further vary the compression ratio.

Flowers, Daniel L.↗
DOE OSTI2018

Riemann solutions for counterflow combustion in light porous foam

The paper is motivated by a model for the injection of air into a porous medium that contains a solid fuel. In previous work, a system of three evolutionary partial differential equations that models combustion of light porous foam under air injection was considered. The existence and uniqueness of traveling waves were studied and the wave sequences appearing in Riemann solutions were identified. This analysis was done under assumption that the combustion wave velocity is positive. In the present work, this hypothesis was neglected and the results generalized including the case of negative combustion wave speed. The existence of such waves was proved and the uniqueness investigated for some particular cases using Melnikov’s integral. The wave sequences appearing in Riemann solutions were identified and the numerical examples using finite difference scheme were presented.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Plasma-based global pathway analysis to understand the chemical kinetics of plasma-assisted combustion and fuel reforming

The Global Pathway Analysis (GPA) algorithm helps analyze the chemical kinetics of complex combustion systems by identifying important global reaction pathways connecting a source species to a sink species through various important intermediate species (i.e., hub species). Here, the present work aims to extend GPA algorithm to plasma-assisted combustion and fuel reforming systems to identify the dominant global pathways in such systems at various conditions. In addition, the present study extends the ability of GPA algorithm to identify reaction cycles involving the excitation of high-concentration species (e.g., O 2 , N 2 , and fuel) to their vibrational and electronic states and the subsequent de excitation to their ground state, based on their significance on the reactivity of plasma-assisted systems in terms of gas heating and radical production. Provisions are made in the GPA algorithm to evaluate the reactivity of identified re action pathways and cycles based on the element-flux transfer (i.e., dominance), heat release, and radical production rate. The newly developed Plasma-based Global Pathway Analysis (PGPA) algorithm is then used to analyze the plasma assisted combustion of ammonia and reforming of methane. The PGPA analyses elucidated the significance of vibrational-translational cycles on the reactivity of NH 3 /air mixtures. Further, analyses on the production of NO ascribed the early reforming of NH 3 to N 2 and H 2 in impeding the production of NO during plasma-assisted NH 3 ignition. Lastly, the enhanced reforming of CH 4 /N 2 mixtures using plasma has been attributed to electron impact dissociation of CH 4 when compared to thermal reforming. In contrast, conventional path-Flux analysis (PFA) was found to require significant manual effort and pre-analysis intuitions from expert knowledge, making it arduous to provide valuable in sights into plasma chemistry. The user-friendly and automated nature of PGPA thus provides a valuable tool for assessing the kinetics of plasma-assisted systems helpful in analyzing and, further, a foundation in reducing plasma-assisted chemistry, without the needs of expert knowledge.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Combustion characteristics and detailed simulations of surrogates for a Tier II gasoline certification fuel

An experimental and numerical study of combustion of a gasoline certification fuel (‘indolene’), and four (S4) and five (S5) component surrogates for it, is reported for the configurations of an isolated droplet burning with near spherical symmetry in the standard atmosphere, and a single cylinder engine designed for advanced compression ignition of pre-vaporized fuel. The intent was to compare performance of the surrogate for these different combustion configurations and to assess the broader applicability of the kinetic mechanism and property database for the simulations. A kinetic mechanism comprised of 297 species and 16,797 reactions was used in the simulations that included soot formation and evolution, and accounted for unsteady transport, liquid diffusion inside the droplet, radiative heat transfer, and variable properties. The droplet data showed a clear preference for the S5 surrogate in terms of burning rate. The simulations showed generally very good agreement with measured droplet, flame, and soot shell diameters. Measurements of combustion timing, in-cylinder pressure, and mass-averaged gas temperature were also well predicted with a slight preference for the S5 surrogate. Preferential vaporization was not evidenced from the evolution of droplet diameter but was clearly revealed in simulations of the evolution of mixture fractions inside the droplets. Here, the influence of initial droplet diameter (D o ) on droplet burning was strong, with S5 burning rates decreasing with increasing D o due to increasing radiation losses from the flame. Flame extinction was predicted for D o =3.0 mm as a radiative loss mechanism but not predicted for smaller D o for the conditions of the simulations.

42 ENGINEERING↗
DOE OSTI2022

Octane Requirements of Lean Mixed-Mode Combustion in a Direct-Injection Spark-Ignition Engine

Here, this study investigates the octane requirements of a hybrid flame propagation and controlled autoignition mode referred to as mixed-mode combustion (MMC), which allows for strong control over combustion parameters via a spark-initiated deflagration phase. Due to the throughput limitations associated with both experiments and 3-D computational fluid dynamics calculations, a hybrid 0-D and 1-D modeling methodology was developed, supported by experimental validation data. This modeling approach relied on 1-D, two-zone engine simulations to predict bulk in-cylinder thermodynamic conditions over a range of engine speeds, compression ratios, intake pressures, trapped residual levels, fueling rates, and spark timings. Those predictions were then transferred to a 0-D chemical kinetic model, which was used to evaluate the autoignition behavior of fuels when subjected to temperature–pressure trajectories of interest. Finally, the predicted autoignition phasings were screened relative to the progress of the modeled deflagration-based combustion in order to determine if an operating condition was feasible or infeasible due to knock or stability limits. The combined modeling and experimental results reveal that MMC has an octane requirement similar to modern stoichiometric spark-ignition engines in that fuels with high research octane number (RON) and high octane sensitivity (S) enable higher loads. Experimental trends with varying RON and S were well predicted by the model for 1000 and 1400 rpm, confirming its utility in identifying the compatibility of a fuel’s autoignition behavior with an engine configuration and operating strategy. However, the model was not effective in predicting (nor designed to predict) operability limits due to cycle-to-cycle variations, which experimentally inhibited operation of some fuels at 2000 rpm. Putting the operable limits and efficiency from MMC in the context of a state-of-the-art engine, the MMC showed superior efficiencies over the range investigated, demonstrating the potential to further improve fuel economy.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1963

MODELING TECHNIQUES FOR LIQUID PROPELLANT ROCKET COMBUSTION PROCESSES

A qualitative physical processes description of stable and unstable combustion in rockets is presented to establish the basis for choosing model hardware design criteria. It is concluded that it is not possible to scale rocket combustion processes in the usual sense of the term. The studies conducted at Rocketdyne have shown that model chambers which satisfactorily model the steady state behavior of large engines must be designed to maintain (1) the propellant injection density, and (2) the chamber to throat Contraction ratio (hence chamber pressure). For studies of destructive acoustic modes of combustion instability a third parameter, the frequency, must also be maintained.

COMBUSTION↗
NASA NTRS2018

Pressure Gain Combustion 101

This presentation contains notes for a 30 minute lecture that is part of an AIAA Special Session titled, Pressure Gain Combustion Overview: Principles, Operation, and Applications. The presentation covers an introduction to Pressure Gain Combustion (PGC) and the devices used to implement it. The concept of PGC is discussed on a thermodynamic basis, the performance benefits are demonstrated, and methods of implementation are described. These include devices such as Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines.

pressure gain combustion↗
NASA NTRS1953

An Investigation of High-frequency Combustion Oscillations in Liquid-propellant Rocket Engines

An experimental investigation of high-frequency combustion oscillations (screaming) was conducted with a 100-pound-thrust acid-hydrocarbon rocket engine and a 500-pound-thrust oxygen-fuel rocket engine. The oscillation frequencies could be correlated as a linear function of the parameter C/L, where C is the experimentally measured characteristic velocity and L is the combustion-chamber length. The tendency of the engines to scream increased as chamber length was increased. With engine configurations that normally had a low efficiency, screaming resulted in increased performance; at the same time, a five to tenfold increase in heat-transfer rate occurred. It was possible, however, to achieve good performance without screaming.

COMBUSTION - EFFECT OF ENGINE OPERATING CONDITIONS↗
DOE OSTI2016

Investigating dominant characteristics of fires across the Amazon during 2005-2014 through satellite data synthesis of combustion signatures

Estimates of fire emissions remain uncertain due to limited constraints on the variations in fire characteristics. Here we demonstrate the utility of space-based observations of smoke constituents in addressing this limitation. We introduce a satellite-derived smoke index (SI) as an indicator of the dominant phase of large-scale fires. This index is calculated as the ratio of the geometric mean of observed fractional enhancements (due to fire) in carbon monoxide and aerosol optical depth to that of nitrogen dioxide. Here we assess the usefulness of this index on fires in the Amazon. We analyze the seasonal, regional, and interannual joint distribution of SI and fire radiative power (FRP) in relation to fire hotspots, land cover, Drought Severity Index, and deforestation rate estimates. We also compare this index with an analogous quantity derived from field data or emission inventories. Our results show that SI changes from low (more flaming) to high (more smoldering) during the course of a fire season, which is consistent with the changes in observed maximum FRPs from high to low. We also find that flaming combustion is more dominant in areas where deforestation fires dominate, while smoldering combustion has a larger influence during drought years when understory fires are more likely enhanced. Lastly, we find that the spatiotemporal variation in SI is inconsistent with current emission inventories. Although we recognize some limitations of this approach, our results point to the utility of SI as a proxy for overall combustion efficiency in the parameterization of fire emission models.

54 ENVIRONMENTAL SCIENCES↗