![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
The purge layer of a semi-valveless pulse detonation cycle (PDC) needs to be minimized for operating at a gas-dynamic upper frequency limit. Therefore, it is essential to better understand the process of burned gas backflow for minimizing the purge layer thickness. The flow field of the semi-valveless PDC was visualized to illustrate the movement of burned gas. A combustor of length of 95 mm with a 10-mm-square cross section was used. Supercritical ethylene and oxygen gas were used as fuel and oxidizer, respectively, and the operation frequency was 604 Hz. The unsteady refilling process of the detonable mixture was modeled by an isentropic flow. In addition, the detailed burned gas blowdown process with deflagration-to-detonation transition (DDT) and the backflow were captured. It was shown that the retonation wave generated by the DDT process was the primary trigger of the burned gas backflow. When the duration required for the DDT process was sufficiently shorter than that of the burned gas blowdown process, it was found the latter could be reproduced with approximately 90% accuracy by one-dimensional numerical analysis without the DDT process.
Nomenclature
| A | = | speed of sound |
| A | = | cross-sectional area |
| cp | = | specific heat at constant gas pressure |
| DCJ | = | Chapman–Jouguet detonation speed |
| ER | = | equivalence ratio of detonable mixture |
| fope | = | operating frequency |
| fupper | = | upper limit frequency |
| Id | = | inner diameter |
| Lc | = | length of combustor |
| ṁ | = | mass flow rate |
| P | = | pressure |
| R | = | gas constant |
| T | = | temperature |
| tDDT | = | time to DDT occurrence from ignition time |
| tspark | = | time to ignition from starting fuel injection |
| Δtexhaust | = | duration to exhaust burned gas from exhaust detonation wave |
| Δtcycle | = | duration of one cycle |
| Δtinj | = | duration of fuel injection |
| Δtpurge | = | duration of purging burned gas |
| v | = | velocity |
| xDDT | = | DDT distance from spark plug |
| γ | = | ratio of specific heat |
Subscript
| a | = | atmosphere |
| b | = | inside of gas cylinder |
| c | = | combustor |
| cal | = | calculation |
| d | = | detonable mixture |
| exp | = | experiment |
| f | = | fuel |
| o | = | oxidizer |
| s | = | static |
| steady | = | steady flow by cold gas test |
| t | = | total |
Acknowledgments
This study was subsidized by Grant-in-Aid for Young Scientists (A) (17H04971), and the Tatematsu Foundation.