Chemical kinetic modelers make extensive use of shock tube ignition data in the development and validation of combustion reaction mechanisms. These data come from measurements using a range of diagnostics and a variety of shock tubes, fuels, and initial conditions. With the wide selection of data available, it is useful to realize that not all of the data are of the same type or quality, nor are all the data suitable for simple, direct comparison with the predictions of reaction mechanisms. We present here a discussion of some guidelines for the comparison of shock tube ignition time data with reaction mechanism modeling. Areas discussed include definitions of ignition time; ignition time correlations (with examples taken from recent n-heptane and isooctane measurements); shock tube constant-volume behavior; shock tube diameter and boundary layer effects; carrier gas and impurity effects; and future needs and challenges in shock tube research. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:510–523, 2004

Interpreting shock tube ignition data

. 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 (
 
$\Delta T_5$
 ) is the most significant parameter for chemical kinetics, experiments were performed to characterize 
$\Delta T_5$
 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 d
 
$T_5/$
 dt (or 
$\Delta T_5$
 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 (24–530 atm, 1275–1900 K), the test temperature 2 cm from the endwall increased 3–8 K after 100 
$\mu$
 s and 15–40 K after 500 
$\mu$
 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, and the calculated 
$\Delta T_5$
 '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 (
 
$<300\mu$
 s), the temperature increase is typically negligible, although some correction is suggested for kinetics experiments lasting longer than 500 
$\mu$
 s. The temperature increase, however, has a negligible impact on the measured laser absorption profiles of OH (306 nm) and CH
 
$_3$
 (216 nm), validating the use of a constant absorption coefficient. Infrared emission experiments are more sensitive to temperature and density 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 Tube

The available information, up to mid‐1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant values are presented wherever possible with suggested error limits. The reactions considered involve the species H, O, C, N, S, OH, HS, S2, CS, SO, HSO2, NH2, NH3, NO, N2O, NO2, N2, O2, O4, N2, O2, O3, H2, H2O, SO2, SO3, CS2, OCS, H2S, and CO. Particular emphasis is given to reactions involving sulfur chemistry. The best available data for these reactions have been summarized in a table at the end of the paper. An appendix discussing the available evaluations and review articles published since 1960 also has been included to publicize these sources of either evaluated data or of extensive reference bibliographies.

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions

This report considers the adequacy of existing detailed reaction mechanisms for use in detonation simulation with chemical systems containing hydrogen, ethylene, and propane fuels. Shock tube induction time data are compiled from the literature and compared to detonation thermodynamic conditions to establish validation limits. Existing detailed reaction mechanisms are then used in constant-volume explosion simulations for validation against the shock tube data. A quantitative measure of mechanism accuracy is obtained from the validation study results, and deficiencies in the experimental data and reaction mechanisms are highlighted. Two mechanisms were identified which include the chemistry for all three fuels and simulated the experimental induction time data to within an average factor of three for temperatures above 1200 K. These mechanisms are incorporated into steady, one-dimensional detonation simulations to provide quantitative information on the reaction zone structure, characteristic reaction time/length scales, and activation and thermal energy parameters.

https://shepherd.caltech.edu/EDL/publications/reprints/galcit_fm99-5.pdf

Validation of Detailed Reaction Mechanisms for Detonation Simulation

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 reflectedshock 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 intoaccount 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

R. A. Strehlow

Papers

Shock Tube Technique in Chemical Kinetics