Abstract
Experimental and computational investigations are carried out to identify the generalized criterion to predict the preignition tendency of methanol and ethanol mixtures in shock tubes. Preignition or weak ignition in shock tubes has been reported to be a significant factor impacting the accuracy of the ignition delay times data. A systematic means to predict the extent of non-idealities needs to be established and validated with experimental data over a wide range of conditions. Measurements of ignition delay times of methanol and ethanol mixtures were performed to identify unexpectedly expedited ignition. Methanol mixtures showed preignition at low temperatures, similarly to ethanol mixtures. Endwall high-speed imaging was implemented to assess spatial uniformity of ignition for methanol and ethanol. Furthermore, 1-D simulations of ethanol/methanol mixtures, in the presence of ignition sources, were utilized to investigate various preignition criteria. The Sankaran number criterion (Sap), proposed earlier for ignition regime identification, was found to be the most successful predictor of the experimental observations.