Experimental Measurement of Ignition Delay Times of Thermally Cracked n-Decane in a Shock Tube

The ignition characteristics of endothermic hydrocarbon fuels (with different pyrolysis degrees) were investigated in a shock tube using n-decane as model compound. Six component surrogates (CH4/C2H4/C2H6/C3H6/C3H8/n-C10H22, marked as cracked n-decane) for thermally cracked n-decane were proposed based on the chemical compositions from the thermal stressing of n-decane on electrically heated tube under 5 MPa. Ignition delay times were measured behind reflected shock waves over a temperature range of 1296-1915 K, a pressure of 0.1-0.2 MPa, and equivalence ratios of 0.5-2.0. n-Decane showed a shorter ignition delay time than cracking gas at 0.1 MPa, demonstrating higher reactivity. For cracked n-decane, it was found that thermal cracking could improve the ignitability under certain conditions to a limited degree, i.e., at T > 1480 K for x = 37.97% and x = 17.61% and at T < 1480 K for x = 62.15% (x represents the conversion of thermal cracking of n-decane) in this work. Unimolecular decomposition reactions of n-decane producing active radicals and H atom would help chain initiation via H -abstraction reaction for unreacted fuels. This initial stage might accelerate ignition by activating cracking gas at these conditions. The empirical correlations for the ignition delay time of cracking gas and n-decane were also analyzed and compared with previous works. Two models were also used to simulate the experimental data of n-decane and cracking gas and showed good agreement with experimental results, and a combined model was utilized to predict results of cracked n-decane.