An experimental and modeling study of iso-octane ignition delay times under homogeneous charge compression ignition conditions

Autoignition of iso-octane was examined using a rapid compression facility (RCF) with iso-octane, oxygen, nitrogen, and argon mixtures. The effects of typical homogeneous charge compression ignition (HCCI) conditions on the iso-octane ignition characteristics were studied. Experimental results for ignition delay times, τ ign, were obtained from pressure time-histories. The experiments were conducted over a range of equivalence ratios (φ = 0.25–1.0), pressures (P = 5.12–23 atm), temperatures (T = 943–1027 K), and oxygen mole fractions (χO2 = 9–21%), and with the addition of trace amounts of combustion product gases (CO2 and H2O). It was found that the ignition delay times were well represented by the expression τign = 1.3 × 10−4P−1.05φ−0.77χ−1.41 O2 exp(33,700/R(cal/mol/K)T ), where P is pressure (atm), T is temperature (K), φ is the equivalence ratio (based on iso-octane to O2 molar ratios), χO2 is the oxygen mole percent (%), and τign is the ignition delay time (ms). Carbon dioxide was found to have no chemical effect on τ ign. Water was found to systematically decrease τ ign by a small amount (less than 14% for the range of conditions studied). The maximum uncertainty in the measured τ ign is ±12% with an average uncertainty of ±6%. The performance of several proposed chemical reaction mechanisms (including detailed, reduced, and skeletal mechanisms) was evaluated in the context of the current experimental results.  2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.