The existing droplet ignition criterion was obtained by examining the initiation of chemical reaction in the far field under the assumption of gas-phase quasi-steadiness. However, it is precisely in this far field where transient diffusion becomes important. In order to incorporate this effect in an ignition analysis, we consider the simultaneous limits of a small gas-to-liquid density ratio and a large activation energy of the chemical reaction. The ignition dynamics is thus investigated; in particular, ignition delay times and ignitability criteria are obtained. Comparison of the ignition Damköhler number obtained in the present study with that corresponding to the quasi-steady case shows that they may differ significantly, hence demonstrating the qualitative importance of transient diffusion in droplet ignition.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)