G070035 Low-temperature flames in shock-compression ignition

Abstract

To eliminate the influence of a preflame reaction for compression period, low temperature compression ignition of a stoichiometric n-heptane/oxygen/argon mixture (Ar mol%: 70) was carried out using an optically accessible shock tube. Experiments were performed over a wide temperature range from 686 K to 1207 K under the density condition of 50 mol/m^3. A high-speed digital video camera was used for photographic observation of low temperature flames and hot flame. Four temperature regions can be found from temperature dependence of ignition delay, namely the cool-flame dominant region, the negative temperature coefficient region, the blue-flame dominant region, and high temperature ignition region. In a cool-flame dominant region, the blue light emission history that corresponds to Emeleus's cool-flame band shows the typical degenerating behavior. Cool-flame appears near the tube end, and spreads spatially and homogeneously toward the high pressure chamber side afterwards. Hot flame, ruled by the low temperature oxidation reactions appears from the place apart from the tube end.