Auto-ignition of hydrocarbons behind reflected shock waves

Abstract

The paper reports on the study of auto-ignition of hydrocarbon-oxygen mixtures behind reflected shock waves. Because of their bearing on the problem of knock in internal combustion engines, n-heptane and iso-oc??ne were chosen as the combustible species. Their stoichiometric mixtures with oxygen had to be diluted with 70% argon to reduce the influence of the boundary layer. Photographic records demonstrated the existence of two different modes of ignition, as has been previously established for the hydrogen-oxygen system. One, called strong ignition, manifested itself by a shock wave generated in the immediate proximity of the back wall of the shock tube. The other, refered to as mild ignition, had chemical reactions starting at distinct points in the gaseous medium producing essentially constant pressure flames. The pressure-temperature limits between the regions of mild and strong ignition (strong ignition limit) were determined. From the same experimental tests, induction time data was obtained over the pressure range of 1–4 atm and the temperature interval of 1200–1700°K. The strong ignition limits were found to correlate best with the lines of constant partial derivatives of the logarithm of induction time with respect to temperature at constant pressure.