Shock tube investigations of ignition delays of n-butanol at elevated pressures between 770 and 1250 K

The ignition delays of n-butanol, a potential bio-fuel candidate, have been determined in a high-pressure shock tube. Conditions behind the reflected shock are approximately between 10-42 bar and 770-1250 K. To our knowledge, the ignition delay measurements of butanol at these high pressures are the first of their kind. CH emission and pressure time histories have been probed to determine ignition delay times for all experiments. For stoichiometric fuel-air-mixtures the influence of the temperature and pressure has been characterized. Interestingly the experimental data deviate from the Arrhenius behavior for temperatures lower than 1000 K. This is in contrast to simulation results which have been obtained by employing the simulation tool CANTERA with different reaction mechanisms applying the typical assumption of isochoric conditions. It has been found out that a positive pressure and temperature gradient behind the reflected shock has a significant influence on the ignition delay below 1000 K causing a pronounced decrease in the ignition delay times. This change of the conditions behind the reflected shock is attributed to the shock attenuation and probably from pre-ignition. Including the measured pressure gradients and assuming an isentropic compression behind the reflected shock, the simulation data and the experimental results show a same trend in the temperature dependence of the ignition delay. Nevertheless, striking differences between experiment and simulation persist especially for higher pressures. By performing sensitivity analysis at different temperatures some critical reactions could be identified and their role under our experimental conditions is discussed. In summary it can be stated that the employed reaction mechanisms may not be fully applicable to high-pressure conditions and it seems plausible that the lack of more detailed low temperature fuel specific reactions could be the probable cause for the discrepancies which calls for detailed investigations at elevated pressures. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.