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

摘要

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 (χ_(O_2) = 9-21 %), and with the addition of trace amounts of combustion product gases (CO_2 and H_2O). It was found that the ignition delay times were well represented by the expression τ_(ign) = 1.3 x 10~(-4)P~(-1.05)φ~(-0.77) χ_(O_2)~(-1.41) 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 O_2 molar ratios), χ_(O_2) is the oxygen mole percent (%), and τ_(ign) 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.