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

Abstract

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 × 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.