The thermochemical changes occurring prior to spontaneous ignition were investigated for homogeneous mixtures of 2,2,4 trimethylepentane (isooctane) and air in a steady flow apparatus of unique design. Measurements were also made of the ignition times of these mixtures over a range of pressures, temperatures, and fuel-air ratios.
Most of the observable thermodynamic and chemical changes occurred in the last 10–25% of the ignition period. Principal among these changes were thermal decomposition of the isooctane to form isobutylene and probably isobutane; the appearance of significant quantities of propylene, ethylene, methane, hydrogen, carbon monoxide, and carbon dioxide; and a temperature rise of from about 200 to500 F.
Most significant among the results was the observation that the preignition changes for the entire range of conditions tested correlate with a normalized reaction time.