Ignition and combustion of fuel droplets and the ignition of premixed fuels by hot cylindrical surfaces
Technical Report
·
OSTI ID:6010804
Two types of combustion problems relevant to the gasification, ignition and combustion of fuels in combustion chambers using sprays are theoretically analyzed using mathematical and numerical techniques. The problem of the vaporization, ignition and subsequent combustion of a fuel droplet in a hot convective flow at atmospheric or moderately elevated pressures is analyzed using boundary layer theory around a spherical fuel droplet. The preliminary stages leading to the onset of ignition are treated as a perturbation of the boundary-layer non-reacting flow using the method of matched asymptotic expansions. The quasi-steady laminar combustion regime of the fuel droplet is analyzed using the flame-sheet approximation. The internal circulation of the liquid phase is also included in the analysis. The results show that ignition occurs towards the rear of the droplet where the residence time is longer. The droplet burning rate, however, is maximum at the forward stagnation point where the boundary layer is thinner. Liquid internal motion has only a minor influence on the burning characteristics of the droplet. A second group of problems studied is the quasi-steady thermal ignition of a premixed combustible gas flowing in mixed-convective conditions past a hot cylindrical, inert or catalytic, surface. The laminar boundary-layer equations including finite-rate kinetics are solved and the location of the ignition region is determined using the method of matched asymptotic expansions for large activation energies. Ignition is shown to occur very close to the surface where the temperatures are higher and downstream of the forward stagnation point where the heat losses are smaller.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6010804
- Report Number(s):
- LBL-20712; ON: DE86009262
- Country of Publication:
- United States
- Language:
- English
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