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ABSTRACT
This work is devoted to the use of detonative combustion of a liquid fuel in technical devices to obtain a jet thrust. The experimental and theoretical aspects of the organization of detonation in heptane/air/oxygen mixtures are considered. The pulsed regime of detonation at a frequency of 50 Hz has been implemented for the first time in a small-size tube (25 mm in diameter and 740 mm in length). The physical and technical methods that could accelerate the deflagration-to-detonation transition have been studied. The influence of thermal activation of a combustible mixture prior to its ignition and of the special form of a porous obstacle on the magnitude of the predetonation distance is established. The degree of this influence depends on the component composition, equivalence ratio, and the degree of filling the tube with a mixture.
Acknowledgments
The authors are grateful to the National Center for Aeronautical Technology, KACST, and Luikov Heat and Mass Transfer Institute of the National Academy of Sciences of Belarus for financial and scientific and methodical support.
Nomenclature
| Т0 | = | initial temperature of mixture |
| ϕ | = | equivalence ratio |
| ϕ1 | = | equivalence ratio in a three-component mixture (heptane + oxygen + air) |
| ϕ2 | = | equivalence ratio in a two-component mixture (heptane + air) |
| = | nitrogen-to-total oxygen ratio in a mixture | |
| DCJ | = | detonation velocity at the Chapman–Jouguet point calculated using the CHEMKIN program |
| DDT | = | deflagration-to-detonation transition |
| ТА | = | thermal activation of mixture |
| PPMC | = | porous packing of metal chips |
| ℮ | = | porous packing-free chamber in the absence of thermal activation |
| → | = | points to the transition of flame front from a three-component (heptane + oxygen + air) mixture to a two-component (heptane + air) one when oxygen is supplied with a certain delay |
| λ | = | degree of filling the pulsed combustor with a mixture being the ratio of the real mixture volume supplied per cycle to the geometric volume of the entire tube cavity |
| ψ | = | detonation intensity coefficient equal to the ratio of the actual wave velocity to the detonation velocity at the Chapman–Jouguet point for a given mixture |
| ψ1, ψ2, ψ3 | = | detonation intensity coefficient on the first, second, and third measuring bases, respectively |
| u | = | wave velocity in the combustion process |
| p | = | pressure |
| T | = | temperature |