Limitations of the Reflected-Shock Technique for Studying Fast Chemical Reactions

Brabbs, Theodore A.; Zlatarich, Steven A.; Belles, F. E.

doi:10.1063/1.1731118

Cited by 21 publications

(8 citation statements)

References 3 publications

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“…We note that the first effect tends to make our computed I-number too small while the second and third effects tend to make it too large. A rough estimate of the first effect based on experimental data 15 , 16 and on Goldsworthy's theoretical relations 17 indicates an I-number increase of perhaps 20-40 per cent.…”

Section: Quantita Tive Spectroscopy and Gas Emissivitiesmentioning

confidence: 98%

Recent Studies on Quantitative Spectroscopy and Gas Emissivities

Penner

Olfe

Lapp

1963

Theory and Fundamental Research in Heat Transfer

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Representative theoretical and experimental studies relating to the determination of gaseous radiation from isothermal systems are discussed. The following recently concluded studies are described: f-number measurements for OH behind shock fronts; a method for the direct determination of radiative and collisional life times of vibrationally excited, molecules; emissivity calculations for CO 2 ; emissivity calculations for a hydrogen plasma at temperatures up to about 1O,OoooK.

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Section: Quantita Tive Spectroscopy and Gas Emissivitiesmentioning

confidence: 98%

Recent Studies on Quantitative Spectroscopy and Gas Emissivities

Penner

Olfe

Lapp

1963

Theory and Fundamental Research in Heat Transfer

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“…: XCH = (562,400 /T)exp(-T71087) (14) where k x is the spectral absorption coefficient (arm' 1 cm" 1 ) and T is the temperature in K. Equation 14 was used to estimate the effect of reflected-shock nonuniformities on the interpretation of CH 3 absorption data in the HPST.…”

Section: (13)mentioning

confidence: 99%

“…Strehlow and Cohen [12] and Skinner [13] attributed the uncertainties to shock-wave/boundary-layer interaction in other than monatomic gases. Underpredictions between 30 and 200 K were estimated, and Brabbs et al [14] observed significant reflected-shock temperature uncertainties even in argon. Strehlow and Case [15] in a later study found that temperatures in argon were overpredicted instead of underpredicted, while Johnson and Britton [16] claimed their Br decomposition measurements behind reflected shocks in an argon bath disagreed with similar data taken behind incident shock waves.…”

Section: Introductionmentioning

confidence: 97%

“…Unfortunately, when performing chemistry measurements in a shock tube, errors in the reaction temperature can lead to large uncertainties in the rate coefficient or ignition delay time [1]. For example, the high-pressure rate coefficient of N0 2 has an activation energy of 300 kJ/mol (i.e., k^T) = 4xl0 14 exp(300/RT) ) [2]. For an average temperature of 1500 K, a 15-K error in temperature (i.e., only 1%) can lead to a 25% uncertainty in the measured rate coefficient.…”

Section: Introductionmentioning

confidence: 99%

“…Early reflected-shock studies, however, uncovered large errors in T 5 which could seriously impact reflected-shock chemistry measurements [12][13][14][15]. Strehlow and Cohen [12] and Skinner [13] attributed the uncertainties to shock-wave/boundary-layer interaction in other than monatomic gases.…”

Section: Introductionmentioning

confidence: 99%

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Nonideal Effects Behind Reflected Shock Waves in a High-Pressure Shock Tube

Mathieu¹,

Hanson²

1999

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044REPORT Public reporting burden for this collection ot information is estimated to average 1 hour per response, including the time for review ng instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comment regarding this burden estimates or any aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and Shock tubes often experience temperature and pressure nonuniformities behind the reflected shock wave that cannot be neglected in chemical kinetics experiments. Because of increased viscous effects, smaller tube diameters, and nonideal shock formation, the reflected-shock nonidealities tend to be greater in higher-pressure shock tubes. Since the increase in test temperature (AT 5 ) is the most significant parameter for chemical kinetics, experiments were performed in the Stanford High Pressure Shock Tube using infrared emission from a known amount of CO in Argon. From the measured change in vibrationally equilibrated CO emission with time, the corresponding dT 5 /dt (or AT5 for a known time interval) of the mixture was inferred assuming an isentropic relationship between post-shock temperature and pressure changes. For a range of representative conditions in Argon (20-530 Atm, 1240-1900, the test temperature 2 cm from the endwall increased 3-8 K after 100 )J,s and 15-40 K after 500 u,s, depending on the initial conditions. Separate pressure measurements using a shielded piezoelectric transducer confirmed the isentropic assumption. An analytical model of the reflected-shock gas dynamics was also developed. The measured incident-shock axial velocity profile and a model of the boundary layer growth provide the upstream boundary conditions needed to define the properties behind the moving reflected shock. The calculated AT 5 's agree well with those obtained from experiment. The analytical model was used to estimate the effects of temperature and pressure nonuniformities on typical chemical kinetics measurements. When the kinetics are fast and occur in less than 300 |is, the temperature increase is typically negligible, although some correction is suggested for kinetics experiments lasting longer than 500 (xs. The temperature increase, however, has a negligible impact on the measured absorption profiles of OH and CH 3 when using laser absorption diagnostics at 306 and 216 nm, respectively, validating the use of a constant absorption coefficient. Infrared emission experiments are more sensitive to temperature and pressure changes, so T 5 nonuniformities should be taken into account when interpreting IR-emission data. NONIDEAL EFFECTS BEHIND REFLECTED SHOCK WAVES IN A HIGH-PRESSURE SHOCK TUBEEric L. Petersen f and Ronald K. Hanson AbstractShock tubes often experience temperature and pressure nonuniformities behind the reflecte...

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The thermodynamic state of the hot gas behind reflected shock waves: Implication to chemical kinetics

Michael

Sutherland

1986

Int J of Chemical Kinetics

127

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Procedures are discussed to correct for nonideality in a shock tube used in the reflected mode in conjunction with flash photolysis and atomic resonance absorption to measure chemical kinetics of atoms at high temperatures. Experimentally, pressure time profiles for the incident and reflected shock regions are made close to the location of the observation windows through which absorbance is measured. The corresponding temperatures are calculated from the adiabatic equation of state. Justification for this procedure is provided by extending Mirels' boundary layer theory to take into account interaction of the reflected wave with the flowing gas in the free stream and in the boundary layer. These theoretical methods are described for calculating the thermodynamic and hydrodynamic states behind the reflected wave from initial values of pressure and temperature and the measured velocity of the incident wave. The implication of these results to kinetic measurements at high temperature is discussed.

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Limitations of the Reflected-Shock Technique for Studying Fast Chemical Reactions

Cited by 21 publications

References 3 publications

Recent Studies on Quantitative Spectroscopy and Gas Emissivities

Recent Studies on Quantitative Spectroscopy and Gas Emissivities

Nonideal Effects Behind Reflected Shock Waves in a High-Pressure Shock Tube

The thermodynamic state of the hot gas behind reflected shock waves: Implication to chemical kinetics

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