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Acta Astronautica 63 (2008) 565574

www.elsevier.com/locate/actaastro

Recent progress in scramjet/combined cycle engines at JAXA,Kakuda space center

Tetsuo Hiraiwa, Katsuhiro Ito, Shigeru Sato, Shuichi Ueda, Kouichiro Tani,Sadatake Tomioka, Takeshi Kanda

Kakuda Space Center, Japan Aerospace Exploration Agency, 1 Kimigaya, Kakuda, Miyagi 981-1525, Japan

Received 22 December 2006; received in revised form 6 February 2008; accepted 28 April 2008

Abstract

This report presents recent research activities of the Combined Propulsion Research Group of Japan Aerospace Exploration

Agency. Aerodynamics and combustion of the scramjet engine and the rocketramjet combined-cycle engine, structure and

material for the two engines and thermo-aerodynamic of a re-entry vehicle are major subjects. In Mach 6 condition tests, a

scramjet engine model produced about 2000 N net thrust, whereas a model produced thrust almost equal to its drag in Mach 12

condition. A flight test of a combustor model was conducted with Hyshot-IV. A rocketramjet combined-cycle engine model is

under construction with validation of the rocket engine component. Studies of combustor models and aerodynamic component

models were conducted for demonstration of the engine operation and improvement of its performances. Light-weight cooling

panel by electrochemical etching examined and C/C composite structure was tested. Thermo-aerodynamics of re-entry vehicle

was investigated and oxygen molecular density was measured also in high enthalpy flow.

2008 Elsevier Ltd. All rights reserved.

1. Introduction

An orbital vehicle needs large kinetic energy. Con-

ventional liquid rockets attain this speed with consump-

tion of onboard oxidizer such as liquid oxygen, which is

about 70% of initial weight of the rockets. Air-breathing

engines use oxygen in air and implementation of the en-

gine to a launch vehicle will cause larger payload to anorbit. The scramjet engine, a hypersonic air-breathing

engine, has a high performance in hypersonic speed, and

its application to a booster stage will increase payload

to an orbit, comparing to that by the conventional space

transportation systems. The Combined Propulsion Re-

search Group of Japan Aerospace Exploration Agency

Corresponding author.

E-mail address: [email protected] (T. Hiraiwa).

0094-5765/$ - see front matter 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.actaastro.2008.04.011

(JAXA), Kakuda Space Center (KSC) has progressed

research on a scramjet engine to establish its design

technologies from 1980s [1]. In the present paper, re-

cent progresses of scramjet and combined-cycle engine

research works in JAXA are presented.

2. Research history in KSC

The scramjet engine can operate only in the hy-

personic speed and needs other engines to flight in

other conditions, such as taking-off and space flight.

To obtain larger operability, the group has started to

study a rocketramjet combined-cycle engine. The

rocketramjet combined-cycle engine is a combination

of the rocket engine and the ramjet engine [2]. This

engine has rocket engines inside the ramjet engine duct

and can operate from take-off to orbital flight.
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566 T. Hiraiwa et al. / Acta Astronautica 63 (2008) 565 574

Fig. 1 shows an image of the engine and Fig. 2 shows

a series of operating schematics of the engine. The en-

gine operates in the ejector-jet mode in low speed. As

flight speed increases, its operating mode changes to

the ramjet, the scramjet and the rocket [3,4]. In order to

Fig. 1. Image of rocketramjet combined-cycle engine.

Fig. 2. Conceptual operating modes of rocketramjet combined-cycle engine.

change these operating modes, the engine should be a

variable geometry configuration. However, this compli-

cated configuration will make many kinds of difficulties

in its development, maintenance and cost. Fixed geom-

etry engine is presumed in the research activities in this

group.Fig. 3 shows the diagram of our research activities

for the scram and combined-cycle engines. Prior to

the activities listed in the figure, a study of the air-

breathing rocket (ABR) started in 1975 [5]. Around

1980s, component and system studies on the scramjet

engine started. For further research activities in 1990s,

three major facilities were constructed; the ramjet en-

gine test facility (RJTF), the numerical space engine

(NSE), and the high enthalpy shock tunnel (HIEST). At

RJTF, sub-scale engine combustion tests can be con-

ducted in hypersonic flight condition from Mach 4 to

8. At HIEST, tests at higher Mach number flight con-ditions can be operated. The NSE, the supercomputer

system for the combined-cycle engine, can simulate

operating conditions of the engine models tested at

RJTF, HIEST and other small facilities. Table 1 lists
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T. Hiraiwa et al. / Acta Astronautica 63 (2008) 565 574 567

Fig. 3. Research activities on scramjet and combined-cycle engines in JAXAKSC.

Table 1

Features of RJTF, HIEST and NSE

RJTF M4 and 6 at dynamic pres. 50 kPa

M8 at dynamic pres. 25 kPa

HIEST Maximum stagnation enthalpy: 25 M J kg1

Maximum stagnation pressure: 150 MPa

NSE 512 GFlops, 512 GB memory, 64 CPU

specifications of the facilities. RJTF was recently mod-

ified to conduct Mach 0 condition test, that is, the sea-

level still air condition test for the ejector-jet mode tests.

The design technology of the ejector-jet mode can

be applied to a booster engine of a rocket vehicle. The

technologies of the scramjet engine and this mode of

the combined-cycle engine can be also applied to a hy-

personic flight vehicle [6].

3. Scramjet engine studies

Studies on the scramjet engine, preceding studies to

those on the combined-cycle engine, have produced re-

markable results in experimental, numerical and system

Fig. 4. Thrust increment of scramjet model under Mach 6 condition

at RJTF.

investigations. Recent activities are introduced in this

section.

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Fig. 5. Schematic of scramjet engine model tested under Mach 6 condition at RJTF.

Fig. 6. OH distributions in scramjet engine model at Mach 6 con-

dition of RJTF.

From March to April of 2005, a scramjet engine

model was tested under Mach 6 condition at RJTF.

Staged fuel injection was tried and an effect of in-

flow boundary layer was investigated [7]. Fig. 4 shows

thrust increment against an equivalence ratio, and Fig. 5

shows a schematic of the model. Fuel was injected from

a strut, and three positions on the sidewalls indicated

with MV1, MV3 and MV4. The engine produced about1.9 kN net thrust and specific impulse of 9000 m s1.

The net thrust doubled the previous value by the single

fuel injection. Fig. 6 shows numerical simulation re-

sults with NSE, showing OH distributions at fuel flow

rates [8]. In HIEST, another scramjet engine model was

tested under Mach 1015 conditions [9]. Fig. 7 shows a

schematic of the engine model setup. The engine model

succeeded to produce thrust almost equal to its drag. In

the model, hydrogen fuel was injected from hypermixer

injector, which enhanced mixing by streamwise vortices

[10]. Fig. 8 shows distribution of H2O mole fraction by

CFD simulation by NSE and Fig. 9 shows the injector.

The engine model was modified, and recently another

model was constructed.

The effectiveness of the injector was tried to demon-

strate in an actual flight condition with Hyshot-IV at

Woomera, Australia, under contraction with University

of Queensland. The test was also aimed to validatetest results produced at the wind tunnel of HIEST. Ac-

cording to experimental results at HIEST, the injector

showed higher mixing performance [10]. The flight test

was operated on March 30 with a flight model with two

combustors (Fig. 10). The nose cone did not open and

the trial was failed. The cause of the failure is now un-

der investigation.

4. Rocketramjet combined cycle engine studies

4.1. Engine model for RJTF tests

A rocketramjet combined-cycle engine model

shown in Fig. 11 is now under construction for tests

at RJTF [2]. Operation of each mode will be demon-

strated and design technologies of the engine will be

validated. Propellants are gas hydrogen and gas oxy-

gen. The choking condition with no geometrical throat

at the engine exit requires a large equivalence ratio,

especially in the ramjet mode. To compensate, this

engine model has a throat at the exit for safety. First

test is scheduled around November 2006 at a sea-level,still-air condition. This model will have additional fuel

injection positions along the engine duct as well as in

the downstream combustor section to study an effect of

the fuel injection position on mixing and combustion

condition. Geometry of the cowl leading edge is also

exchangeable to study its effect on breathing ability

in the ejector-jet mode and air-capture ability in the

ramjet and scramjet modes.

The rocket component was tested before integration

[11,12]. It operated in wide ranges of chamber pressure

and a mixture ratio, O/F. In an actual engine, number

of combination of the pressure and the mixture ratio
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Fig. 7. M12-02 scramjet model at HIEST.

Fig. 8. H2O mole fraction in M12-02 model.

Fig. 9. Hypermixer injector.

will be limited. However, in the research process, lots

of combinations should be examined to make clear the

suitable operating condition and engine configuration.

Fig. 12 shows C* efficiency against O/F. The rocket

component showed sufficient efficiency. Durability of

the face plate was enforced through the series of the

combustion tests. Fig. 13 shows the damaged plate and

the modified one after firing tests.

4.2. Component studies

Prior to the test in RJTF, component tests were con-

ducted to demonstrate the operation of the combined-

cycle engine and these experimental results were used

to design the RJTF model. Fig. 14 shows an example of

wall pressure distributions of a combustor model in the

ejector-jet mode at sea-level-, still-air condition [13].

Breathed air was choked at the exit of the throat sec-

tion. Pressure became lower than the choking pressure

of an atmospheric air around the entrance of the diver-

gent section. The combustion gas choked at the exit of

the model. Fig. 15 shows wall pressure distributions in

the downstream-combustion ramjet mode [14]. In this

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mode, fuel is injected into the downstream combustor.

Subsonic combustion and subsequent choking at the exit

are attained.

The inlet section should satisfy contradicting require-

ments; sufficient air capture in the subsonic and tran-

sonic condition and sufficient compression in the su-personic and hypersonic condition. Experimental and

Fig. 10. Scramjet combustor model test by Hyshot-IV.

Fig. 11. Schematic of rocketramjet combined-cycle engine model.

numerical investigations were conducted to design the

engine model. Fig. 16 shows CFD results of the inlet

sections at Mach 10 [15]. The shock waves from the side

wall leading edges deformed the ramp shock around the

symmetric plane, and this interaction increased spillage.

The engine operation was examined in a transonicwind tunnel. Fig. 17 shows a wind tunnel model [16].

Nitrogen gas was used to simulate rocket exhaust. The

ejector-jet mode operation was demonstrated and aero-

dynamic improvements were achieved.

5. Fundamental research works

5.1. Cooling structure and material

As shown in Fig. 1, the scramjet engine and the

combined-cycle engine have a large duct and the

Fig. 12. C* efficiency of rocket component.

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Fig. 13. Face plate of rocket component: (a) before improvementand (b) after improvement.

structure. The engine requires the regenerative cool-

ing system composed in the engine structure. There-

fore, light-weight material and structure are requested.

In KSC, production technique of the large cooling panel

and light-weight material of C/C composite have been

investigated.

Machining to such a large panel will be difficult. Elec-trochemical etching was employed for creating cooling

passages on the nickel alloy plate [17,18]. Fig. 18 shows

a trial product of stainless steel panel with cooling pas-

sages by chemical etching.

Combination of the C/C material with metal cool-

ing channel was proposed to prevent leakage of coolant

through breathable C/C material [19]. Fig. 19 shows a

picture of the model. Effectiveness of SiC coating to

the C/C material against oxidization and mechanism of

oxidizing erosion were also investigated [20]. Fig. 20

shows damage of C/C composite piece after heating

test.

Fig. 14. Wall pressure distributions in ejector-jet mode combustor

model.

Fig. 15. Wall pressure distributions in a combustor model.

Fig. 16. Isobars in inlet section.
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Fig. 17. Engine model for transonic wind tunnel tests.

Fig. 18. A stainless steel panel with cooling passages by chemical

etching method.

5.2. Thermo-aerodynamics for re-entry

The re-entry technique is necessary to carry passen-

gers or payload from the space station. Future space

Fig. 19. C/C composite structure with metal cooling passage.

transportation vehicle with the scramjet engine and the

combined-cycle engine also have to re-enter the at-

mosphere. Studies for re-entry vehicle are also being

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Fig. 20. Damage of C/C composite piece after heating test: (a) surface of pinhole and (b) cross section of pinhole.

Fig. 21. Schlieren image of flow field around a model with large

cone angle.

conducted in HIEST, which can simulate re-entry con-

dition. A model with a large cone angle was used to

investigate the real gas effect on pressure distribution

[21]. Fig. 21 shows a schlieren image around the model.

Recombination of dissociated air on surface of the re-

entry vehicle affects heat flux. Oxygen molecular den-

sity was measured on a flat plate model surface by

laser absorption spectroscopy with measurement of heat

flux [22].

6. Summary

The combined Propulsion Research Group of JAXA

is conducting researches on the scramjet engine and the

rocketramjet combined-cycle engine for wide applica-

tions of space transportation. In the scramjet engine re-

search, net thrust was attained in lower Mach numbers

and is being tested in higher Mach numbers. The scram-jet is combined with the rocket engine to enlarge its

operating range, and this rocketramjet combined-cycle

engine is also studied. Based on results of component

and system studies, sub-scale model is now under con-

struction. Researches on cooling panel and light-weight

material are being progressed, which will be useful for

future air-breathing and combined-cycle engines. Ac-

tivities of thermo-aerodynamics on the re-entry vehicle

are also progressed.

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