THE SPONTANEOUS IGNITION BEHAVIOR OF ISO-OCTANE AIR MIXTURES UNDER STEADY FLOW CONDITIONS (COMBUSTION)

The spontaneous ignition behavior of homogeneous mixtures of 2,2,4 trimethylpentane (iso-octane) and air has been investigated in a steady flow apparatus. Rapid mixing of separately heated fuel and air streams was accomplished in a specially designed eddy diffusion device. The combustible mixture delivered from this mixing device was passed through an independently heated stainless steel tube having an internal diameter of 0.930 inches. The effective length of this tube was varied to a maximum of 14 feet by the positioning of a movable water cooled quenching probe inserted through the downstream end of the tube. By appropriate adjustment of the quencher position and the test conditions, spontaneous ignition was observed to occur near the tip of the water cooled probe. Information as to average mixture velocity and quencher position readily yielded a time of residence of the mixture within the test section, which was interpreted as the chemical reaction time required for ignition.;The results indicate that under conditions of fixed mass flow rate, the reaction times, (tau), can be described by the relationship (tau) = K (phi)('-1.04) P('-2.57) e('E/RT).;Determinations were also made of conditions prevailing in the pre-ignition zone within the test device. Temperature profiles along the reaction path were obtained. Mixture samples were also obtained to show the course of the chemical reactions leading to ignition. These samples were analyzed employing the techniques of gas chromatography.;The gas composition and temperature data thus obtained indicate that more than one-half of the thermal and chemical changes which take place do so over a period comprising about the last 25% of the ignition period. In addition, all changes which occurred were monotonic proceeding at nearly constant exponential rates.;Reaction times thus measured were obtained at velocities of from 1.3 to 3 feet per second in the test section. Temperatures of from 1075(DEGREES)F to 1170(DEGREES)F and pressures of from 1.25 to 2.0 atmospheres were employed over a fuel-air ratio range of from 0.5 to 2.2 times the stoichiometric ratio. Mass flow rates of from 0.0025 to 0.0065 pounds per second were used.;A set of reduced coordinates was established to correlate the temperature and composition profiles for all test conditions. (Abstract shortened with permission of author.).