Historically, the development of chemical kinetics models of fuel oxidation has relied on information obtained in experimental setups such as jet-stirred reactors, flow reactors, ignition quality testers, rapid compression machines and shock tubes. The developed chemistry models are implemented in computational fluid dynamic (CFD) simulations to provide predictions of ignition timing, heat release rate and emissions in practical devices.

Shock tubes provide a nearly ideal chemical reactor to study ignition phenomena as a function of temperature, pressure and fuel/oxidizer mixture composition. They are commonly used as homogenous zero-dimensional batch reactors to investigate reaction kinetics, fuel pyrolysis and autoignition. The measurement of rate coefficients and ignition delay times in shock tubes provide highly valuable data for the development and validation of chemical kinetic models. Preignition, which leads to non-homogeneous combustion in otherwise ideal reactor conditions, has been observed in shock tubes and rapid compression machines, drifting the performance of these facilities away from ideal operation and, therefore, jeopardizing the accuracy of the measurements being taken.

Our research group has focused on the application of high-speed imaging diagnostics to the investigation of preignition in shock tubes and rapid compression machines with two main goals: characterizing the conditions of pressure, temperature and composition that promote preignition, and establishing ideal regimes of operation for these reactors. We have studied ethanol, methanol n-hexane and hydrogen ignition in shock tubes at low and high-pressures by the use of single-camera endwall imaging (Figueroa-Labastida et al., Combustion and Flame, 2018) and dual-camera simultaneous lateral and endwall imaging (Figueroa-Labastida et al., Combustion and Flame, 2020). An optical chamber was developed for a twin-piston rapid compression machine and was tested with fuels such as ethanol, iso-octane, diethyl ether (Figueroa-Labastida et al., 9th European Combustion Meeting, 2019). These studies have allowed the identification of different ignition regimes and their categorization in strong, intermediate and non-homogeneous ignition. Through mapping of different conditions, a regime criterion based on the ignition delay sensitivity, laminar flame speed and temperature inhomogeneities has been identified and validated, arising as a promising tool for combustion experimentalists (Figueroa-Labastida et al., Combustion and Flame, 2021).