Chemical-kinetic modeling of ignition delay: Considerations in interpreting shock tube data

Abstract

High-pressure shock tube ignition delays have been and continue to be one of the key sources of data that are important to characterizing the combustion properties of real fuels. At pressures and temperatures of importance to practical applications, concerns have recently been raised as to the large differences observed between experimental data and chemical-kinetic predictions using the common assumption that the shock tube behaves as a constant volume (V) system with constant internal energy (U). Here, a concise review is presented of phenomena that can considerably affect shock tube data at the extended test times (several milliseconds or longer) needed for the measurement of fuel/air ignition at practical conditions (i.e., high pressures and relatively low temperatures). These effects include fluid dynamic nonidealities as well as deflagrative processes typical of mild ignition events. Proposed modeling approaches that attempt to take into account these effects, by employing isentropic assumptions and pressure- and temperature-varying systems, are evaluated and shown to significantly improve modeling results. Finally, it is argued that at the conditions of interest ignition delay data do not represent pure chemical-kinetic observations but are affected by phenomena that are in some measure facility specific. This hampers direct cross comparison of the experimental ignition data collected in different venues. In such cases, pressure/temperature histories should be provided in order to properly interpret shock tube ignition data. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 143–150, 2010