Study and Development ofThrottleable Hybrid Rocket Motors

Alessandro Ruffin

University of PadovaCentro di Ateneo degli Studi e Attivita Spaziali ”Giuseppe Colombo”

September 22nd 2017

Alessandro Ruffin Throttleable Hybrid Rocket Motors September 22nd 2017 1 / 14

Throttleable Hybrid Rocket Motors

Nammo test, Spartan Project

Applications

Launchers

ADV

Flying test beds

For a fixed nozzle throat, throttleability isachieved by controlling the oxidizer flow ⇒Flow control valve (FCV)

Advantages

Increase trajectory efficency

Peculiar mission profiles requiring deepthrottling

Requires to control a single feeding line

Disadvantages

Increase system complexity

o/f shifting

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C ? Penalties

Circular port

Port fuel consumpion

Marxman power law

o/f =m1−n

ox Dport2n−1

4n π1−n a ρf L

n = 0.5 ⇒ no Dport sensitivity

n = 1 ⇒ no mox sensitivity

n ∈ [0.45 0.8]

2 4 6 8 10 12 14 16 18 20 22

o/f []

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

Cha

ract

eris

tic v

eloc

ity [m

/s]

HTPN

2O

LOX

90%HTP N2O LOX

Maximum c∗ [m/s] 1598 1559 1773

c∗ Sensitivity [m/s] −22.4 −16.3 −369.9

c∗ Penalty TR=5 (balanced) 95.3% 95.9% 96.2%

c∗ Penalty TR=5 (fuel rich) 88.0% 84.5% 82.7%

c∗ Penalty TR=10 (balanced) 91.6% 92.8% 93.2%

c∗ Penalty TR=10 (fuel rich) 78.3% 78.5% 75.4%

Arbitrary throttling ⇒ o/f shift ⇒ Performance reduction

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FCV selection

Techniques:

Pure dissipative valve

Variable area injection

Parallel feeding lines

Variable area cavitatingventuri

For a CV:

mox = Cd Ath

√2 ρox (p◦ − psat)

Peculiarities

variable area ⇒ flow control

if p◦up > [0.8 0.9] p◦down ⇒ tank -combustion chamber uncoupling

41 42 43 44 45 46

Time [s]

5

10

15

20

25

Pre

ssur

e [b

ar]

cat postcc

tank ox

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This year:

Flow control valve design concluded

Integration and testing

Flow control valve characterization

Static hybrid rocket motor fire tests

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FCV: Design

A

A

Step DC Motor EncoderFCV

VALVE ACTUATION

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FCV: Design

Minimum mass flow range 30 [g/s]

Maximum mass flow range 300 [g/s]

Maximum operating pressure 80 [bar ]

Venturi throat diameter 2.2 [mm]

Upstream throat radius 3.3 [mm]

Venturi divergence angle 10 [deg ]

Pintle apex angle 10 [deg ]

Maximum pintle stroke 11 [mm]

Useful pintle stroke 7 [mm]

Features

Conical pintle/spike

Manually moved pintle

Pressure tap for feedback

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FCV characterization: Set-up

N2 tank

PR1 PR2 V05

x

Vtes t

Vc

Vdump Vpurg e

Vtank

VACV

HTP tank

To collector

To collector

Low pressure N2

Pup PdownPtank

Features

HTP tank (piston separator)

Flow control valve

Catalytic bed (not shown)

Test motor (not shown)

Purging line

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FCV characterization: Results

H2O

1 2 3 4 5 6 7 8 9 10

Pintle stroke [mm]

0

50

100

150

200

250

300

350

400

Mea

sure

d m

ass

flow

[g/s

]

30 bar45 bar60 bar

91 % HTP

1 2 3 4 5 6 7 8 9 10

Pintle stroke [mm]

0

50

100

150

200

250

300

350

400

450

500

Mea

sure

d m

ass

flow

[g/s

]

30 bar45 bar60 bar

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FCV characterization: Results

H2O

1 2 3 4 5 6 7 8 9 10

Pintle stroke [mm]

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

Dis

char

ge c

oeffi

cien

t []

30 bar45 bar60 barfit

91 % HTP

1 2 3 4 5 6 7 8 9 10

Pintle stroke [mm]

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

Dis

char

ge c

oeffi

cien

t []

30 bar45 bar60 barfit

CD,H20 = 1.008− 2.626 x − 93.14 x2 − 4.643 · 10−5/x , R2 = 0.93

CD,HTP = 1.003− 0.7345 x − 174.5 x2 − 3.086 · 10−5/x , R2 = 0.86

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Test Motor: Fire test campaign

A test campaign was conducted to characterize the test motor behaviorwith different mass flows. Tests were conducted in the fuel rich region.

10 12 14 16 18 20 22 24 26 28 30

Time [s]

0

5

10

15

20

25

30

Pre

ssur

e [b

ar]

post catalytic

combustion chamber

Test # mHTP tb pcc[g/s] [s] [bar]

1 56.5 25 8.62 137.9 16 20.93 219.0 7 33.14 282.1 5 43.5

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Test Motor: Fire test campaign

A test campaign was conducted to characterize the test motor behaviorwith different mass flows. Tests were conducted in the fuel rich region.

50 100 150 200 250 300

Oxidizer mass flow [g/s]

5

10

15

20

25

30

35

40

45

Com

bust

ion

cham

ber

pres

sure

[bar

]

Test # mHTP tb pcc[g/s] [s] [bar]

1 56.5 25 8.62 137.9 16 20.93 219.0 7 33.14 282.1 5 43.5

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Conclusion and Future work

A variable area cavitating venturi to be used as flow controlvalve in hybrid rocket motors was developed and characterized

Our test motor was tested with four different oxidizer massflows reaching a 1:5 throttling ratio

Automatically control the pintle stroke implementing a DCmotor

Characterize the dynamic behavior of flow control valve andtest motor

Throttling tests

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Conclusion

Thank you! Any question?

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