Ethanol ignition in a high-pressure shock tube: Ignition delay time and high-repetition-rate imaging measurements

Ethanol is known to be prone to pre-ignition in internal combustion engines under high-load conditions and its ignition shows large deviations from ideal, spatially, and temporally-homogeneous ignition in shock tubes at moderate temperatures (800-950 K). In this context, the ignition of stoichiometric ethanol/O-2 mixtures with various levels of inert gas dilution was investigated in a high-pressure shock tube at congruent to 20 bar between 800 and 1250 K. Ignition delay times were determined from spatially integral detection of chemilu-minescence emission. Additionally, high-repetition-rate color imaging enabled the differentiation of the lu-minescence in time, space, and spectral range between various ignition modes. In the low-temperature range (800-860 K), different inhomogeneous ignition modes were identified. The addition of small amounts of helium into the undiluted fuel/air mixture was found to be efficient to mitigate pre-ignition, attributed to a variation in heat transfer and thus suppression of the build-up of local temperature inhomogeneities. The experiments in case of spatially homogeneous ignition show very good agreement with the predictions based on three detailed kinetics mechanisms (Zhang et al., CNF 190 (2018) 74, Frassoldati et al., CNF 159 (2012) 2295, and Zhou et al. CNF 197 (2018) 423), inhomogeneities, however, resulted in a shortening of the ignition delay times up to a factor of 2.6. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The study found that the addition of small amounts of helium in high-pressure shock tube can help mitigate pre-ignition of ethanol under different temperature conditions. The experiments showed good agreement between predictions based on detailed kinetics mechanisms and actual results for spatially homogeneous ignition, but inhomogeneities resulted in a shortening of the ignition delay times. Additionally, high-repetition-rate color imaging technology proved useful in differentiating between various ignition modes.