A high pressure ignition delay time study of 2-methylfuran and tetrahydrofuran in shock tubes

Ignition delay time studies for tetrahydrofuran (THF) and 2-methylfuran (2MF) as well as optical investigations of combustion for 2MF have been carried out using two shock tubes. The experiments with undiluted THF/air mixtures were performed at 20 and 40 bar in a high pressure shock tube (HPST) at an equivalence ratio of Phi = 1 covering an overall temperature range of 780-1100 K and 691-1006 K, respectively. Undiluted 2MF/air mixtures (Phi = 1) were also investigated in the HPST at 40 bar in the temperature range of 820-1215 K. The experimental data of 2MF obtained at 40 bar were supported with kinetic simulations of existing models from literature. Additionally, sensitivity analyses of 2MF at several temperatures were performed for finding out the most sensitive reactions. Schlieren imaging was employed in a rectangular shock tube (RST) utilizing a high speed video camera through which the ignition process was captured for a stoichiometric 2MF/O-2/Ar mixture at pressures of about 10 bar and in the temperature range of 871-1098 K. The pressure signals of THF and 2MF at 40 bar indicate two types of pre-ignition at low temperatures: a short two-stage ignition for THF and a relatively long and smooth increase in pressure before main ignition for 2MF. Furthermore, in case of 2MF at 40 bar, far-wall ignitions at low temperatures could be observed. The deviation between simulation and experiment as well as the presence of pre-ignitions in the low temperature regime were the main reasons for undertaking optical investigations of 2MF. The Schlieren images show that the ignition process at low temperatures (T <= 940 K) begins as a deflagrative phase in the form of flame kernels and ends in a strong ignition (explosion in explosion). The current study analyzes the auto-ignition of THF and 2MF at engine relevant pressures and temperatures. The optical investigations have been conducted to analyze the ignition behavior of 2MF. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.