What the cut shows
Looking down into the annulus, nozzle end up. The gas path is the published 138.7 mm by 153.9 mm channel, 101.6 mm long, so the gap is 7.6 mm. The thick outer ring is the 25.4 mm GE124 quartz tube from the optically accessible rig, not a metal closeout. Air enters through the circumferential slot on the 123 mm diameter and turns into the channel. Fuel comes through 120 separate holes of 0.89 mm on the 134 mm circle, just inboard of the inner wall, as a jet in crossflow. The air plenum and the fuel plenum are separate, as in the optical rig. The ring at the top of the quartz is a schematic retainer; the abstracts do not give a bolt count, so none is drawn. The fuel holes are drawn on the injector face, on the published 134 mm circle, 2.35 mm inboard of the inner wall. The center body covers that circle when assembled and lifts off it in the explode. The abstracts do not give a shoulder height, so none is drawn. The radial tube is the hydrogen-oxygen pre-detonator. The cone on the center body is a schematic aerospike, the nozzle family on the AFRL six-inch SIMR, not a traced contour.
The wave is drawn at 1675 m/s, 0.85 of a 1970 m/s stoichiometric hydrogen-air Chapman–Jouguet speed. On the mean circumference that is 3.64 kHz for one wave and 7.29 kHz for two co-rotating waves. The motion on the page is slowed so the front can be followed; the readout keeps the real frequency. The unwrapped sketch shows the front, the fresh fill ahead of it, the triple point, the contact surface, and the oblique shock into the products. Products leave axially past the plug. Two waves use a shorter fill, which is the direction AFRL reported when the optical rig went from one wave to two at high air flow. Neither fill height is a measured frame.
Dimensions and assumptions
| Item | Value | Where it came from |
|---|---|---|
| Hardware | AFRL optically accessible 6-inch RDE | Hydrogen and air, separate plenums. Not the N2O/kerosene chamber. |
| Channel inner diameter | 138.7 mm (5.46 in) | Rankin et al., ICDERS 2015-017 and 2017-0833. |
| Channel outer diameter | 153.9 mm (6.06 in) | Same abstracts. Gas-side diameters, inside the quartz. |
| Radial gap | 7.60 mm | Gap/outer diameter = 0.049. Gap/mean diameter = 0.052. |
| Channel length | 101.6 mm (4.0 in) | ICDERS 2015-017. Axial height of the annulus. |
| Outer body | 25.4 mm GE124 quartz | The optical tube in those abstracts. A metal heat-sink wall is a different build. |
| Air injection | Circumferential slot, 123 mm diameter, 1.78 mm high | ICDERS 2017-0833 also states an area of 3.46 cm2. π·D·h is 6.88 cm2; the stated area matches π·(D/2)·h. The figure uses the stated diameter and height. |
| Fuel injection | 120 × 0.89 mm holes on a 134 mm circle | Area 0.75 cm2, against the stated 0.75 cm2. Jet in crossflow into the air slot. The holes are drawn on the injector face, 2.35 mm inboard of the inner wall. No shoulder height is taken from the abstracts. An impinging rocket element is a different injector (Purdue). |
| Initiation | H2/O2 pre-detonator, 6.35 mm × 63.5 mm | ICDERS 2015-017. Spark, DDT in the small tube, three pulses into the annulus. The axial station on the drawing is schematic. |
| Wave speed | 1675 m/s (0.85 × 1970 m/s) | 1970 m/s is a stoichiometric H2/air Chapman–Jouguet speed near 1 atm, the SP-273 class of number. The 0.85 factor is a viewing assumption: real waves run below CJ. Not a single test point. |
| Mean circumference | 459.6 mm | Mean of the inner and outer channel diameters. |
| Frequency, one wave | 3.64 kHz | Speed divided by the mean circumference. The picture is slowed; the label is this number. |
| Frequency, two waves | 7.29 kHz | Two co-rotating waves. ICDERS 2017-0833 saw the one-wave to two-wave change at high air flow, with a shorter fill. |
| Fresh-fill height | 30 mm (one wave), 16 mm (two waves) | Illustrative. About 0.3 and 0.16 of the channel. The abstracts show the height changing with flow rate; these are not a measured frame. |
| Plug | 46 mm taper to 28 mm radius | Schematic of the aerospike on the AFRL SIMR (Fotia, ICDERS 2015-015 and 2017-0819). Not a traced contour, and no area ratio is claimed for this cone. |
Checks run with the figure
- Pass: gap is the published channel width. 7.60 mm
- Pass: fuel circle sits just inside the inner wall. 2.35 mm inboard
- Pass: air slot is inboard of the fuel circle. slot radius 61.5 mm
- Pass: fuel hole area matches the stated 0.75 cm2. 0.747 cm2
- Pass: one wave and two waves are integer. co-rotating, same direction
- Pass: fill is shorter with two waves. 30 mm then 16 mm, both illustrative
Sources
- Rankin, Richardson, Caswell, Naples, Hoke, and Schauer, ICDERS 2015, paper 017, ICDERS2015-017. Optically accessible annulus 138.7 mm by 153.9 mm, length 101.6 mm, GE124 outer body 2.54 cm thick, hydrogen and air from separate plenums, pre-detonator 6.35 mm by 63.5 mm.
- Rankin, Fugger, Richardson, Cho, Hoke, Caswell, Gord, and Schauer, ICDERS 2017, paper 0833, ICDERS2017-0833. Air slot 123 mm diameter and 1.78 mm high, 120 fuel holes of 0.89 mm on a 134 mm circle, and the one-wave to two-wave change with a shorter fill at high air flow.
- Fotia, Hoke, and Schauer, ICDERS 2015, paper 015, and ICDERS 2017, paper 0819. Six-inch SIMR, center body 138.6 mm, gaps from 7.62 mm to 22.86 mm, aerospike plug, hydrogen and ethylene with air.
- Bykovskii, Zhdan, and Vedernikov, “Continuous Spin Detonations,” Journal of Propulsion and Power, Vol. 22, No. 6, 2006. The front, the contact surface, and the oblique shock in a continuous spin detonation.
- Rankin, Fotia, Naples, Stevens, Hoke, Kaemming, Theuerkauf, and Schauer, “Overview of Performance, Application, and Analysis of Rotating Detonation Engine Technologies,” Journal of Propulsion and Power, Vol. 33, No. 1, 2017. The same AFRL hardware family.
- Purdue rocket-mode chambers (Heister, Slabaugh, and co-authors) have used impinging injectors. This figure keeps the AFRL slot-and-orifice gas injector. Michigan (Gamba and co-authors) and UCF (Ahmed and co-authors) have imaged the same wave topology.
- Gordon and McBride, NASA SP-273, NTRS 19780009781, local note
library/notes/nasa-ntrs/19780009781.md. The equilibrium program that computes Chapman–Jouguet speeds. 1970 m/s is the stoichiometric hydrogen-air order of magnitude from that method, not a line copied from a run of this annulus.