Development of Shock Diffuser for Pulse Detonation Turbine Engines

K. Yoshinaga, T. Ofuka, A. OchiT. Yatsufusa, T. Endo, and S. Taki (Hiroshima univ., Japan)

S. Aoki, and Y. Umeda (Toho Gas Co., Ltd., Japan)

20th International Colloquium on the Dynamics of Explosions and Reactive Systems

McGill University, Montreal, CanadaAugust 1-5, 2005

1

Pulse Detonation Turbine Engine（PDTE）

• A pulse detonation turbine engine (PDTE) is a PDE which drives a turbine for power generation.

• For high turbine efficiency and safety, the pressure history at the turbine inlet should be smoothed enough.

2

shock smoothing

Multi-tube system

Thermal efficiency of an ideal PDTE is higher than that of a conventional gas turbine engine

pinlet

p1

One of the key issues is development of a shock-smoothing device, which should be installed between the combustor and turbine

C3H8-air mixture

3

Function of shock diffuser• Shock diffuser deforms a strong shock wave into a

series of weaker shock waves, or a gradually-rising compression wave in the mean time.

• Because the sound speed becomes higher when the pressure becomes higher, a compression wave deforms into a shock wave as it propagates.

4

The effect of the shock diffuse is intrinsically transient.

Principle of shock diffuser

• A shock wave is divided into several small-wave-front shock waves.

• These shock waves are weakened by wave-front expansion, and merged together with different phases.

5

Shock diffuser (prototype)

• The shock diffuser we developed consisted of the confinement chamber, the diffuser tube, and the multi-step reflector.

6

(Dimensions are in mm)

Diffuser tube

• The V-slit diffuser tube is installed inside the confinement chamber, and the direction of the V-slit is variable relative to the outlet.

‘0’ ‘π/2’ ‘π’

outlet

P3

Confinement chamber

7

Principle of diffuser tube

time

Pres

sure

• A shock wave is weakened by the geometrical expansion of its wave front.

• A shock wave coming out through a narrower portion of the slit is weakened more than that coming out through a wider portion of the slit.

8

At the outlet

Multi-step reflector

各段で長さ変更可能

71 87 100

1x

1x 1x 2x

• The cross-sectional area of each step, which reflects the corresponding portion of a shock wave, is the same.

• The lengths, and , are variable.

9

2x

1x

Before reflection

After reflection

w/o multi-step reflector w/ multi-step reflector

Principle of multi-step reflector

Before reflection

After reflection

A series of weaker shock waves

A strong shock wave

10

Detonation tube for shock diffuser experiments

• The flame speed is measured by the ionization probes I1 and I2.

• The pressure transducer P2 is located in the air-filled portion, where the inert shock wave propagates.

11

(Dimensions are in mm)

Experimental apparatus

Detonation tube Shock Diffuser

outlet

PTPT

PT: Pressure transducer

12

Experimental conditions

• We confirmed detonation propagation in all experiments

13

Mixture White gasoline-airEquivalence ratio 1.1Initial pressure 1atmC-J velocity 1820m/s

Measureddetonation speed 1670±100m/s

Effects of the confinement chamber • Pressure histories at P2 and P3

in the case of confinement chamber only.

14

Effects of the diffuser tube• Pressure histories at P3 in the case of no multi-step reflector.

The first shock wave was diffused

‘0’ ‘π/2’ ‘π’

outlet

P3

15

Effects of the length • Pressure histories at P3 in the case of confinement

chamber, diffuser tube and multi-step reflector.

Reflector lengths:X1=30,60,90mmand X2=130mm

The reflected shock wave was diffused

161x

17

• Pressure histories at P3 in the case of confinement chamber, diffuser tube and multi-step reflector.

Reflector lengths: X1=90mm and X2=130,195,260mm

The best parameters in our experiments were

mmxandmmx

26090,2/

2

1

18Effects of the length 2x

19

• We developed the prototype of a shock diffuser which deforms a strong shock wave into a series of weaker shock waves．

• The shock diffuse was tested by using a simplified pulse detonation engine in a single pulse operation.

• The shock diffuser worked.

Conclusions 20

衝撃波の減衰

体積比約2.2倍PDE本体の後ろにPDEと同じ内径で長さが2.14mの管を継ぎ足したようなもの

2.14m

PDE 体積比約2.2倍

PDE Shock diffuser

1m

ホワイトガソリン特性

化学式

CnHn+2(n=6~9) :83% C5H10, C6H12:12% C6H5(CH3) . C6H4(CH3)2 :5%

沸点 60℃~140℃ 発火点 272℃

爆発限界 1~7(V%)

沸点・発火点が低いためPDEに適している

イオンプローブを設置したところの当量比は約1.1

38.51820 CJCJ MDAISTJANにより計算

衝撃波前後の圧力差 p 11.6 pp2.1,4.1 21 として計算すると

実際の実験では 2.5~6.4)/(1001670 CJCJ MsmD

1)6.5~3.4( pp

ホワイトガソリン特性

2

2 1

2

22

1

22

1

2

22

1111 2

112

)1(CJ

CJCJAA M

MMpp