Flame Extinction Limits of H2‐CO Fuel Blends

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Ahsan R. Choudhuri ◽  
Mahesh Subramanya ◽  
Subramanyam R. Gollahalli
Keyword(s):  
Laminar Flame ◽  
Critical Value ◽  
Mean Value ◽  
Flame Velocity ◽  
Flame Extinction ◽  
Hydrogen Fuel ◽  
Fuel Blend ◽  
Fuel Blends ◽  
Extinction Limit ◽  
The Mean

The flame extinction limits of syngas (H2‐CO) flames were measured using a twin-flame counterflow burner. Plots of extinction limits (%f: volumetric percent of fuel in air) versus global stretch rates were generated at different fuel blend compositions and were extrapolated to determine the flame extinction limit corresponding to an experimentally unattainable zero-stretch condition. The zero-stretch extinction limit of H2‐CO mixtures decreases with the increase in H2 concentration in the mixture. The average difference between the measured flame extinction limit and the Le Chatelier’s calculation is around 7% of the mean value. The measured OH chemiluminescence data indicates that regardless of blend composition the OH radical concentration reduces to a critical value prior to the flame extinction. The measured laminar flame velocity close to the extinction indicates that regardless of fuel composition, the premixed flame of hydrogen fuel blends extinguishes when the mixture laminar flame velocity falls below a critical value.

Interactions Between Self and Parametrically Excited Motions in Articulated Tubes

1984 ◽  
Vol 51 (2) ◽  
pp. 423-429 ◽  
Author(s):  
A. K. Bajaj
Keyword(s):  
Nonlinear Dynamics ◽  
Hopf Bifurcation ◽  
Parametric Resonance ◽  
Flow Rate ◽  
Critical Value ◽  
Mean Value ◽  
Vertical Position ◽  
Linearized System ◽  
The Mean ◽  
Stable Solutions

The nonlinear dynamics of a two-segment articulated tubes system conveying a fluid is studied when the flow is harmonically perturbed. The mean value of the flow rate is near its critical value when the downward vertical position gets unstable and undergoes Hopf bifurcation into periodic solutions. The harmonic perturbations are assumed to be in parametric resonance with the linearized system. The method of Alternate Problems is used to obtain the small nonlinear subharmonic solutions of the system. It is shown that, in addition to the usual jump response, the system also exhibits stable and unstable isolated solution branches. For some parameter combinations the stable solutions can become unstable and can then bifurcate into aperiodic or amplitude-modulated motions.

Turbulent mean reaction rates in the limit of large activation energies

1981 ◽  
Vol 110 ◽  
pp. 411-432 ◽  
Author(s):  
N. Peters ◽  
W. Hocks ◽  
G. Mohiuddin
Keyword(s):  
Reaction Rate ◽  
Laminar Flame ◽  
Mixture Fraction ◽  
Beta Function ◽  
Reaction Rates ◽  
Activation Energies ◽  
Premixed Combustion ◽  
Flame Velocity ◽  
Progress Variable ◽  
The Mean

Closed-form expressions for the turbulent mean reaction rate and its covariance with the temperature are derived for premixed and non-premixed combustion. The limit of large activation energies is exploited for a chemical reaction rate that, by virtue of coupling functions, depends on the mixture fraction and a non-equilibrium progress variable only. The probability density function (p.d.f.) formulation with an assumed shape of the p.d.f. is used; a beta-function distribution is assumed for the progress variable. The mean reaction rate is expressed in terms of the mean and the variance of the temperature and, for non-premixed combustion, of the mixture fraction. The reaction kinetics are represented by the non-dimensional activation energy and the laminar flame velocity. For non-premixed systems the possibility of local extinction by flame stretch is considered.

scholarly journals Correlation between results of functional lordosis test and digital pelvic inclinometer

2019 ◽  
Vol 17 (3) ◽  
pp. 247-252
Author(s):  
K. Kolev ◽  
R. Tasheva
Keyword(s):  
Lumbar Lordosis ◽  
Preliminary Investigation ◽  
Critical Value ◽  
Test Methods ◽  
Mean Value ◽  
Functional Test ◽  
Healthy Children ◽  
Pelvic Inclination ◽  
The Mean ◽  
The Difference

THE AIM of this study is to precise the diagnostics of lumbar lordosis in children at primary classes through applying the Digital Pelvic Inclinometer and to correlate the results with the Functional Test. METHODS. The screening examination involved 132 children with the average age 8, 7 from the beginning classes in Sofia. The lumbar lordosis was assessed through the Fuctional Test in all children during the period April - June 2016.. The DPI was applied for preliminary investigation in 25 children of measuring left and rigth pelvic inclination and therefore – torsion. RESULTS. The lordosis test is negative in 8 children and 16 are with functional lordosis. The mean value of the test with DPI - left sided, for healthy children is 7.1 degrees, and in children with functional lordosis is 10.90. The difference of 3.80 is statistically significant due to the value of T-Student criterion (t) of 2.63 at a critical value of 2.07. CONCLUSION. The results showed the correlation between the Digital Pelvic Inclinometer Test and the Functional Lordosis Test. Тhis study confirmed that the applying of the Digital Pelvic Inclinometer give an opportunity to precise the diagnostics of lumbar lordosis in children.

scholarly journals Study of the SCL-90 Scale and Changes in the Chinese Norms

2021 ◽  
Vol 11 ◽  
Author(s):  
Weimin Dang ◽  
Yajuan Xu ◽  
Jun Ji ◽  
Ke Wang ◽  
Songtao Zhao ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Detection Rate ◽  
Critical Value ◽  
Mean Value ◽  
Symptom Checklist ◽  
Measurement Standard ◽  
Standard Score ◽  
Usual Model ◽  
Significant Difference ◽  
The Mean

Objective: This study aimed to investigate the Chinese norms for the Symptom Checklist 90 (SCL-90) scale and its application.Methods: In total, 7,489 adults from Tianjin and Qingdao in China were included. Their data were compared with the norm data of 1,388 people published by Jin et al., the combined norms published by Tang et al., the data of 2,808 adults published by Chen and Li, and the data of 1,890 adults from Tong in China.Results: In five different periods, notable changes were observed in each factor of the SCL-90 that significantly differed from the previous norms. The scores of each factor showed an increasing annual trend. Compulsion consistently obtained the highest scores, and phobia consistently obtained the lowest scores. The scores tended to decrease from compulsion to anxiety, and psychosis scored lower than paranoia. There was a significant difference in the detection rate between the critical screening value of two points and the standard score. Using the standard score as the critical value, the detection rate ranged between 13 and 16% and was relatively concentrated. Using two points as the critical value, the detection rate ranged between 38 and 50%.Conclusion: The usual model in China is not consistent with social development. Using two points as the critical value is no longer suitable for the SCL-90. New Chinese norms and measurement standards should be developed. The mean value plus one standard deviation could be used as the new measurement standard.

Numerical Simulation and Experiments of Reformed Fuel Blends in a Lean-Burn Spark-Ignited Engine

2004 ◽  
Author(s):  
Scott B. Fiveland ◽  
Brett M. Bailey ◽  
Martin L. Willi ◽  
Joel D. Hiltner ◽  
Farzan Parsinejad ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Chemical Properties ◽  
Fuel Mixture ◽  
Lean Burn ◽  
Fuel Blend ◽  
Engine Simulation ◽  
Fuel Blends ◽  
Detonation Limits

Premixed, lean burn combustion research has focused for years on extending the lean flammability limit while maintaining both stables ignition and turbulent flame propagation. Operating with a leaner air-fuel mixture results in a lower temperature conversion of reactants to products (i.e. reduced NOx) while maintaining thermal efficiency. The lean limit, at some level, is dependent on both the fuel transport and chemical properties. This work sets out to numerically explore the effect of reformed fuels on both fundamental flame stability and the performance/emissions tradeoffs of the engine. The numerical simulations were conducted for a range of reformed fuel blends (10–40%) as well as mixture equivalence ratios (0.35–0.6). The laminar flame speed results clearly define the regime of stable flame propagations for equivalence ratio/reformed fuel blend combinations. Subsequently, a validated and predictive quasi-dimensional engine simulation is used to simulate the performance/emissions characteristics of the complete engine system operating on the reformed fuel blends (10–50%) for a range of ignition timings, and air-fuel ratios. The performance trends define not only the misfire and detonation limits associated with the air-fuel blends but also the thermal efficiency/NOx tradeoffs.

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

Partition Coefficient Ratios and Tumour Perfusion Studied with 85mKr and 133Xe

1987 ◽  
Vol 26 (06) ◽  
pp. 253-257
Author(s):  
M. Mäntylä ◽  
J. Perkkiö ◽  
J. Heikkonen
Keyword(s):  
Partition Coefficient ◽  
Partition Coefficients ◽  
Regional Blood Flow ◽  
Blood Perfusion ◽  
Compartmental Analysis ◽  
Malignant Tumour ◽  
Mean Value ◽  
Perfusion Rate ◽  
Biological Variables ◽  
The Mean

The relative partition coefficients of krypton and xenon, and the regional blood flow in 27 superficial malignant tumour nodules in 22 patients with diagnosed tumours were measured using the 85mKr- and 133Xe-clearance method. In order to minimize the effect of biological variables on the measurements the radionuclides were injected simultaneously into the tumour. The distribution of the radiotracers was assumed to be in equilibrium at the beginning of the experiment. The blood perfusion was calculated by fitting a two-exponential function to the measuring points. The mean value of the perfusion rate calculated from the xenon results was 13 ± 10 ml/(100 g-min) [range 3 to 38 ml/(100 g-min)] and from the krypton results 19 ± 11 ml/(100 g-min) [range 5 to 45 ml/(100 g-min)]. These values were obtained, if the partition coefficients are equal to one. The equations obtained by using compartmental analysis were used for the calculation of the relative partition coefficient of krypton and xenon. The partition coefficient of krypton was found to be slightly smaller than that of xenon, which may be due to its smaller molecular weight.

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