Flame Holding in the Recirculation Zone of Ducted Rockets

―The Effects of Zirconium Particle Addition―

Aeroapace Engineering MajorGraduate School of Science and Technology

Kuwahara and Tanabe Laboratory

Young Researchers’ Session on Aerospace Technology

S3-18

★ 　 Kenro Obuchi

Takuo Kuwahara

Mitsuaki Tanabe

1 ． BackgroundRocket engines needs to carry fuel and oxidizer ．

Ducted RocketsThe air-breathing engines suited for supersonic flight.

Oxidizer is the oxygen in atmosphere.

Higher specific impulse than that of Rockets.

Fundamental Structure of a Ducted Rocket

Gas-Generator

Gas FlowNozzle

SupersonicAir-Intakes

Primary Combustor

Convergent-Divergent Nozzle

SecondaryCombustor

1. 　Background

A Fuel Rich Propellant

Fundamental Structure of a Ducted Rocket

Supersonic Flight （ Mach2~5 ）

Fuel-Rich Gas

Air Ram-Air Combustion Gas

1. 　Background

Recirculation Zone

Air-Fuel Mixture

Mixture Gas Temperature Tm

1. 　Background

Ram-AirTa

Air-Fuel MixtureTm

Fuel-Rich GasTg

Gas-GeneratorComposition

Flight altitude and speed

Depending on flight conditions, the air-fuel mixture temperature can falls instantaneously

below spontaneous ignition temperature.

gas mixture Residence Time t ｒ

1. 　Background

Gas-Flow Speedin the Secondary Combustor

ug=100~200 m/s

The gas mixture can be exhausted before ignite

Residence Timetr 10 ms≒

Ignition Sources

Ignition sources are needed to ignite the air-fuel mixture forcibly and continuously.

1. 　Background

Ignitable minute particle Minute particles were mixed into the gas generator and those were injected into the recirculation zone.

It is important to ignite and combust the air-fuel mixturein the recirculation zone

Minute particles addition1. 　

Background

Tem

pera

ture

T

Length

Gas Generator Ram-Air

Recirculation Zone

Tg: Fuel-Rich Gas

Tm: Air-FuelMixture

Tb: Burned Gas

Tu: Unburned Gas

Tp: Burned Gas

Spontaneoustemperature

Requirement for ignition sourcesT

empe

ratu

re T

Residence time and Chemical Delay Time

Particles are exhausted before ignite

Chemical Delay Timeτc

1. 　Background

Tg

Tm

Tp

Recirculation Zone

τc

Requirement for ignition sourcesT

empe

ratu

re

Chemical Delay Time

τc

1. 　Background

Recirculation Zone

Tg

Particles can ignite!

★Tm

Tp

Residence time and Chemical Delay Time

2. Objective

・ To clarify the possibility of minute particles being ignition source of the gas mixture.

3. Experiment

To select the most suitable minute particle for the ignition source, their chemical delay time τc

was obtained experimentally.

Candidates for the ignition source Zirconium (Zr), Titanium (Ti), Magnesium (Mg),

Almunium (Al), Boron (B)

Apparatus for measuring the ignition Delay Time

3. 　 Experiment 1

minigig

pigc

cpig

ig

Electronic Furnace

Result3. 　 Experiment 1

0

0.1

0.2

0.3

0.4

0.5

800 900 1000 1100 1200

Temperature in the Furnace, K

Che

mic

al D

elay

Tim

e, s

Zr 20（ μm)

Ti（20μm）B（２μm)

Mg 20（ μm)

4. Theoretical Analysis

The relationship between temperature history of particles cooled by gas mixture and the chemical delay time in the recirculation zone

was obtained theoretically.

Calculation conditions

Flight speed Mach 2.0

Flight altiture 11 km

Compression method Dual Lump

Limp Angle 10 degree

Ram air temperature, Ta 360K

Ram air pressure, Pa 0.1 MPa

Gas generator AP/HTPB Propellant

AP(Ammonium perchlorate) 65 wt%

HTPB(Hydroxyl-terminated polybutadien)

35 wt%

Combustor pressure, Pg 0.22 MPa

Hot fuel-rich gas temperature, Tg 1050 K

Air-fuel ratio stoichiometric ratio

4. 　 Theoretical Analysis

Air Fuel-Rich Gas

gas mixture Particles

Air-fuel ratiostoichiometric ratio

7.4

Result4. 　 Theoretical Analysis

600

700

800

900

1000

1100

1200

0 0.02 0.04 0.06 0.08

Residence Time　 and Chemical Delay time, s

Tem

pera

ture

, K

B

Ti

Mg

Zr

Tm

Tp

τc

ignite!

★

5.Conclusion

・ Zr particle has the highest ignitability, and the most suitable particle for an ignition source.

Thank you very much for your attention