Nonpremixed Counterflow Flames: Scaling Rules for Batch Simulations

Fiala, Thomas; Sattelmayer, Thomas

doi:10.1155/2014/484372

Cited by 23 publications

(14 citation statements)

References 12 publications

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“…Figure 1 illustrates that thermal excitation exceeds chemical excitation at approximately 2700 K. This value is in agreement with earlier literature. 16,17,18,13 This relationship is pressure-independent.…”

Section: Thermal Vs Chemical Excitationmentioning

confidence: 97%

“…This has a positive effect on the modeling of the OH * radiation. 13 It must be concluded, however, that the radiation of the OH * molecule in liquid rocket combustion is not due to chemiluminescence. It is therefore not coupled to any form of reaction progress as it has been argued (ambiguously 19 ) for cooler flames.…”

Section: Thermal Vs Chemical Excitationmentioning

confidence: 99%

“…Several definitions of the strain rate can be found in literature, which are usually proportional to each other. 13 In this paper, the maximum absolute velocity gradient is used to identify the strain rate a max quantitatively. 14 To represent the ensemble of flamelets in turbulent combustion, a flamelet table is calculated.…”

Section: Numerical Setup Of the Counterflow Flame Simulationmentioning

confidence: 99%

“…14 To represent the ensemble of flamelets in turbulent combustion, a flamelet table is calculated. 13 This is done for pressures between 1 and 100 bar in steps of one bar. For representative pressure levels, the strain rate is varied from a low level at which the flamelet is close to equilibrium up to the extinction to the flame.…”

Section: Numerical Setup Of the Counterflow Flame Simulationmentioning

confidence: 99%

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On the Use of OH* Radiation as a Marker for the Heat Release Rate in High-Pressure Hydrogen Liquid Rocket Combustion

Fiala

Sattelmayer

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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The identification of the volumetric heat release rate is of great importance in combustion research, e.g. for the investigation of combustion instabilities in liquid rocket motors. Since it is not feasible to measure this quantity directly with reasonable effort, the heat release is often assumed to be directly proportional to the radiation of the excited hydroxyl radical (OH * ). This paper investigates whether this assumption can be used for diagnostics of the turbulent combustion in liquid rocket motors. The study is based on counterflow flamelet simulations. Using this model, the physical processes leading to both the OH * radiation and the heat release rate are examined.Within the calculated flamelets, only little spatial correlation exists between OH * radiation and the local heat release rate. This is in agreement with earlier experimental results. The relevance of this fact is discussed for turbulent liquid rocket combustion. Since the flame thickness in highly strained high pressure flames is usually much smaller than the detection length scale, the spatial discrepancy is disregarded. Instead, if the turbulent flame is represented by an ensemble of strained laminar flamelets, the integrated quantities of counterflow flames have to be considered.The correlation factor c f is defined as the proportionality of the flamelet-integrated heat release rate to the flamelet-integrated OH * radiation. Batch simulations show that c f increases linearly with the flamelet strain rate. A general proportionality between the heat release rate and the OH * radiation is therefore not given for arbitrary flamelet ensembles.Due to the linear dependence, a normal distribution of the strain rate maps on to a similar normal distribution of the correction factor. If the strain rate distribution in the flamelet ensemble is constant, there is also a constant mean correlation factorc f . Under this strict condition, the heat release rate is indeed proportional to the OH * radiation. Nomenclatureδ flame thickness [m] ω production rate [kmol/s] q volumetric heat release rate [W/m 3 ] a strain rate [1/s] C molar concentration [kmol/m 3 ] c f correlation factor [W/kmol] g 0 mf Gibbs enthalpy of formation [J/kg] h specific enthalpy [J/kg] M molar mass [kg/kmol] p pressure [bar] R m universal gas constant [J/(kmol K)] T temperature [K] X mole fraction

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Section: Thermal Vs Chemical Excitationmentioning

confidence: 97%

Section: Thermal Vs Chemical Excitationmentioning

confidence: 99%

Section: Numerical Setup Of the Counterflow Flame Simulationmentioning

confidence: 99%

Section: Numerical Setup Of the Counterflow Flame Simulationmentioning

confidence: 99%

See 2 more Smart Citations

On the Use of OH* Radiation as a Marker for the Heat Release Rate in High-Pressure Hydrogen Liquid Rocket Combustion

Fiala

Sattelmayer

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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“…The distance between fuel and oxidizer inlets is set to 20 mm. In order to reduce the computation effort of the counterflow flame simulations, the scaling rules of Fiala [60] are applied to improve the convergence behavior.…”

Section: Comparison Of Fundamental Combustion Propertiesmentioning

confidence: 99%

A Study on Electrofuels in Aviation

et al. 2018

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Abstract:With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study, five potential electrofuels are discussed with respect to the potential application as aviation fuels, being n-octane, methanol, methane, hydrogen and ammonia, and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly, the synthesis process of the electrofuel is described with its technological paths, its energy efficiency and the maturity or research need of the production. Secondly, the physico-chemical properties are compared with respect to specific energy, energy density, as well as those properties relevant to the combustion of the fuels, i.e., autoignition delay time, adiabatic flame temperature, laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel, except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition, the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly, a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels, but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally, a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels, more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however, the research is just at the beginning stage.

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Thermal Indices and Thermophysiological Modeling for Heat Stress

Havenith

Fiala

2015

Comprehensive Physiology

187

184

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The assessment of the risk of human exposure to heat is a topic as relevant today as a century ago. The introduction and use of heat stress indices and models to predict and quantify heat stress and heat strain has helped to reduce morbidity and mortality in industrial, military, sports, and leisure activities dramatically. Models used range from simple instruments that attempt to mimic the human-environment heat exchange to complex thermophysiological models that simulate both internal and external heat and mass transfer, including related processes through (protective) clothing. This article discusses the most commonly used indices and models and looks at how these are deployed in the different contexts of industrial, military, and biometeorological applications, with focus on use to predict related thermal sensations, acute risk of heat illness, and epidemiological analysis of morbidity and mortality. A critical assessment is made of tendencies to use simple indices such as WBGT in more complex conditions (e.g., while wearing protective clothing), or when employed in conjunction with inappropriate sensors. Regarding the more complex thermophysiological models, the article discusses more recent developments including model individualization approaches and advanced systems that combine simulation models with (body worn) sensors to provide real-time risk assessment. The models discussed in the article range from historical indices to recent developments in using thermophysiological models in (bio) meteorological applications as an indicator of the combined effect of outdoor weather settings on humans.

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Nonpremixed Counterflow Flames: Scaling Rules for Batch Simulations

Cited by 23 publications

References 12 publications

On the Use of OH* Radiation as a Marker for the Heat Release Rate in High-Pressure Hydrogen Liquid Rocket Combustion

On the Use of OH* Radiation as a Marker for the Heat Release Rate in High-Pressure Hydrogen Liquid Rocket Combustion

A Study on Electrofuels in Aviation

Thermal Indices and Thermophysiological Modeling for Heat Stress

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