Chemical kinetic simulations behind reflected shock waves

Abstract

Chemical kinetic simulations that more accurately consider reaction conditions behind reflected shock waves in a high pressure shock tube have been conducted by accounting for (1) time-dependent temperature and pressure variations in contrast to assuming constant temperature and pressure, (2) the inclusion of reactions during quenching by cooling in contrast to the assumption of zero kinetic contributions, and (3) real gas behaviors in contrast to assuming ideal gas conditions. The primary objective of the current work is to assess the degree of uncertainty associated with assuming constant temperature and pressure and that no reactions occur during the finite time of quenching and prefect gas behavior. The assessment of the subsequent effect of the uncertainty on chemical kinetic modeling is evaluated by conducting extensive comparative studies. In order to achieve this purpose, available CHEMKIN II and CHEMKIN Real Gas codes were utilized and modified to adopt the proposed approaches. From our computational experiments, it is found: (1) For shock tube experiment with less than a 15% endwall pressure increase, the conventional assumptions lead to reasonable accuracy in predicting stable species; (2) during reaction quenching, the consumption of radical species occurs efficiently and is nearly complete once the pressure drops to 50% of its highest value, but concentrations of stable species are insignificantly perturbed by reactions occurring during quenching; and (3) at elevated pressures, the real gas effects, which are a combination of nonideal P-V-T (state variables), thermodynamic, and kinetic behaviors, affect kinetics by speeding the reaction progress up slightly and do not significantly influence the development or validation of a detailed kinetic model from shock tube data that are obtained in a wide temperature range. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 2006

The vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of kerosene

“…The uncertainties in shock tube experiments are mainly associated with nonideality and measurement uncertainty. Tang and Brezinsky [28] have investigated the nonideal behavior in a 5.6 m long shock tube with an inner diameter of 50.8 mm, and found that the temperature increase due to pressure variation, ∆T 5 , can be up to 55 K at 2.5 MPa and 1 270 K. They concluded that for shock tube experiments with a less than 15% end wall pressure increase, the conventional treatment is suited to study chemical kinetics. A 0.5% uncertainty in shock wave velocity measurements results in about 1% and 2% experimental errors in temperature and pressure behind reflected shock waves in the present study.…”

Very High Pressure Single Pulse Shock Tube Studies of Aromatic Species

“…The evaluations of these potential effects via numerical simulations are the subject of this study 67 aimed to better characterize the UIC HPST.…”

“…Definition of governing boundary conditions -Constant pressure adiabatic isenthalpic system (Defines condition behind a reflected shock wave) The numerical techniques employed are described in more detail elsewhere 67,70 . The RG-Senkin developed as part of this study 67 was used to calculate the time dependent endwall temperature T 5 (t) obtained from the observed pressure traces P 5 (t) and the calibrated temperature T 5-avg in the time interval from when reflected shock wave arrives (reaction starts) to when the pressure drops to its 30% highest value. The reason we limit our efforts to this range is that all reactions stop within this range, a phenomena that will be demonstrated later in this article.…”

“…Our computed temperature increase from the experimentally measured pressure profile and calibrated temperature in the UIC HPST is in a very good agreement with that of the Stanford HPST wherein they observed 58 an endwall temperature increase of ∆T 5 = 20−45 K at t = 500 µs. In our work 67 , we have defined an average quenching rate as the temperature change rate in the time range from the point at which pressure falls to its 80% highest value (where reaction time was empirically taken) to the point where a smooth pressure profile ends. Using this definition, the calculated quenching rate of UIC HPST was found to be 3.02×10 5 K/sec for the 600 bar shock which is almost half of Lifshitz's 71 estimate probably in a large part because of the different physical construction of the shock tubes.…”

“…the ideal gas assumption was applied. To account for real gas impacts more species property data are required and necessary critical properties and acentric factors of all the species in the models were obtained in this work 67 . This data was used with the Peng-Robinson (P-R) equation of state since, as Schmitt and Butler 72 demonstrated, the P-R equation compared with other types of EOS provided the most accurate correction for simulation of their observed detonation velocity at elevated pressures.…”