THEORY OF SPHERICALLY SYMMETRICAL DROPLET COMBUSTION WITH GAS-PHASE FUEL PYROLYSIS

ABSTRACT

Simplified analyses of spherically symmetrical combustion of an isolated fuel droplet are developed to account for fuel pyrolysis. Fuel pyrolysis is modeled as a high activation-energy process that occurs within a thin zone between the droplet and the flame. Accounting for fuel pyrolysis changes classical expressions for the transfer number because the flame must supply energy for fuel pyrolysis, which requires the flame to be located closer to the droplet. Sample calculations for combustion of heptane droplets in air at one atm indicate that transfer numbers, burning rates, and quasi-steady flame standoff ratios can be appreciably reduced when fuel pyrolysis effects are included in the analyses.

Keywords:

• liquid droplets
• pyrolysis of fuel

Acknowledgments

Professor Forman A. Williams has been a leader in the field of droplet combustion for more than two decades. He has made exceptional contributions that have involved benchmark experiments as well as development of advanced theory. As a tribute to Professor Williams's significant contributions, I thought that an article focused on droplet combustion would be appropriate for this special issue of Combustion Science and Technology.

This research was supported by the NASA Microgravity Combustion Program. The Technical Monitor was Dr. Daniel L. Dietrich. The support and encouragement of Professor Williams are also gratefully acknowledged. The research described in the present article was an outgrowth of a series of communications between Professor Williams and me.