Jet fuel is used to cool military aircraft. Unfortunately,
heated jet fuel reacts with dissolved
oxygen to form products which foul fuel system components. Two
categories of surface deposits
which form in the autoxidative regime have been recently identified.
The first forms in heated
regions as the fuel is oxidized. The second accumulates in cooled
regions as certain compounds
within the reacted fuel become insoluble at reduced temperatures.
This paper seeks to improve
understanding of fouling at reduced temperatures and to develop a
global chemistry model that
can be used in computational fluid dynamics codes. Experiments
were conducted in a flowing
system using JP-8 fuel with different thermal stability additives.
Some thermal stability
additives reduced fouling in heated regions but were not as effective
in cooled regions. The
deposition and oxidation measurements obtained for specific flow
conditions were used to
calibrate a chemical kinetics model which uses global reactions to
simulate deposition. The
calibrated model yielded reasonable predictions within the thermal and
flow regimes considered.
Dispersion and vaporization behavior of liquid fuel droplets in a heated axisymmetric jet is studied using detailed flow visualization based on numerical simulations. Results show that the gravity has a strong effect on the dynamics of jet shear layer and droplets. The presence of gravity introduces the buoyancy-induced hydrodynamic instability, causing the large vortical structures to appear without any external perturbation. The droplet dispersion and vaporization behavior is influenced by both the vortex structures and the gravity. Three regimes, distinguished by the Stokes number St and the ratio of droplet terminal velocity to characteristic gas velocity Vr, are identified to characterize the effects of vortex structures and gravity on droplet dispersion. At low S/ and Vr, the droplets behave like gas particles. In the second regime, 0.1 < St < 0.64 and 0.04 < Vr < 0.3, due to the centrifugal action of the vortex structures the droplets are dispersed more than the gas particles. At the lower end of the third regime, the droplet motion is affected by both the vortex structures and the gravity, whereas at the higher end it is affected more by gravity. The effect of vaporization is to shift the Stokes number range for the three regimes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.