Combustion of single drops of fuel

An experimental study of the flame zone development about a spherical hydrocarbon fuel droplet burning in air has provided data which is compared to present quasisteady theories which predict mass-burning rates and flame-zone locations as a function of droplet size. The data show that only during part of the lifetime of the droplet do these quasisteady theories predict the observed mass-burning rates. All theories to date however, do not correctly predict the flame standoff distance. A simple heat-mass transfer analysis which incorporates the observed time variation of the ratio of the flame diameter to liquid-droplet diameter shows that the D² law is not necessarily a good test of the correctness of the burning rate equation as derived in the past using the standard quasisteady assumptions. A new mass burning-rate relation is derived. It is concluded that the inherent transient burning behavior must be described by any theory that hopes to predict the proper combustion behavior of droplets and sprays.