The spontaneous ignition of single n-heptane droplets in a closed constant volume filled with air was numerically calculated with a model that predicts pre-vaporized ignition. Initial pressure and initial air temperature were fixed at 3 MPa and 773 K, respectively. When the overall equivalence ratio (φ) was fixed to be sufficiently large, there existed no ignition limit in terms of initial droplet diameter (d0), and the ignition delay took a minimum value at certain d0. In such a case, transition from the heterogeneous ignition to the homogeneous ignition with decreasing d0 was observed. When d0 was fixed to be so small that the ignition would not occur in an infinite volume of air, the ignition delay took a minimum value at certain φ, which was less than unity. Two-stage ignition behavior was investigated with this model. Ignition delay of a cool flame had the dependence on d0 that is similar to that of ignition delay of a hot flame when φ was unity. When φ was almost zero, the ignition limit for cool flame in terms of d0 was not identified unlike that for hot flame. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Mechanical Engineering
- Physical and Theoretical Chemistry