ICLASS-2006 Aug.27-Sept.1, 2006, Kyoto, Japan

1. INTRODUCTION

Several kinds of injectors are used as devices for the atomization, mixing and vaporization in liquid rocket engine, ramjet and scramjet engines. Among them, plain orifice injectors are used widely only and with the combination of themselves. In general, a feasibility study is performed for injector design through the experimental method. Many times and efforts are required for these experimental study. Fuel injection devices have been developed as a procedure of fundamental research on ramjet and scramjet engines. Optimization technology and numerical simulation was adopted for high performance of plain orifice injectors. In this paper, computational simulation and experimental results performed in the development process of plain orifice injectors were reviewed 2. PLAIN ORIFICE INJECTORS AND SPILLING TEST Fig. 1 shows the configuration of the plain orifice injectors. The plain orifice injectors considered in this paper are used for ramjet and scramjet engines. So that the mass flow rate for an injector is relatively small. And therefore the configuration and dimension affect highly to performance of injectors. Consequently, the diameter and length for orifice, their ratio and chamfer dimension at orifice inlet including the ratio chamfer length to orifice diameter as a principal design factor were considered.

Fig.1. Geometries of the plain orifice injectors in this study Table 1. Geometries of the plain orifice injectors tested in

this study

Table 1 shows the main design parameters of plain orifice injectors manufactured for this research.

Paper ID ICLASS06-288 Design optimization of the plain orifice injector with RSM approximation

Poonggyoo Han, Hyuckjoon Namkoung

Technical Research Institute, Rotem 462-18, Sam-Dong, Uiwang-Shi, Gyeonggi-Do, Korea

and School of mechanical and Aerospace Engineering, Seoul National University, poong@rotem.co.kr.

Sanghwa Kim, Youngsoo Kim Technical Research Institute, Rotem

462-18, Sam-Dong, Uiwang-Shi, Gyeonggi-Do, Korea, 247622@mail.rotem.to

Kyoungsuk, Park School of mechanical Engineering, Kyung Hee University, ks2507@khu.ac.kr

ABSTRACT The authors studied the design optimization of the plain orifice injector with the methodology of Response Surface Model (RSM in order to reduce the required time of the development process of the injectors. The plain orifice injectors studied here would be used in the range of small mass flow rate and the principal design parameters of them were an orifice diameter, an orifice length, and their ratio, chamfer length in the inlet region and the ratio of a chamfer length to an orifice diameter, an angle of the chamfers. Among many combinations of the above-mentioned design parameters, several combinations were analyzed numerically to get the geometrical configuration for the maximum mass flow rate at the required pressure difference condition. Also, some plain orifice injectors were manufactured precisely and tested for the comparison with the calculation results. As a result, they were good agreement with test results and it was confirmed that this design procedure could be used with effect to develop above the injector. Keywords: plain orifice injector, discharge coefficient, RSM

XPO Do (mm)

Lo (mm)

Dc (mm)

ANGLE (℃) Dc/Do Lo/Do

1 1 0.65 0.3 50 0.3 0.652 1 2 0.3 50 0.3 2 3 1 5 0.3 50 0.3 5 4 1 0.65 0.1 50 0.1 0.655 1 0.65 0.45 50 0.45 0.656 1 0.65 0.3 20 0.3 0.657 1 0.65 0.3 60 0.3 0.658 2 1.3 0.6 50 0.3 0.659 0.5 0.33 0.15 50 0.3 0.66

10 0.3 0.2 0.1 50 0.33 0.67

Fig. 2 shows the sectional configuration of injector #9 used in spilling test which is captured by high powered optical microscope. Table 2 shows the results of inspection on the main design dimension.

Fig. 2 Inspection example of the principal geometry at plain

orifice injector, #9

As shown in Fig.2, all dimensions of the plain orifice injectors were machined precisely within the allowance range of a tolerance. While the spilling test was performed, the pressure difference was swept from 0 to around 8MPa continuously. The mass flow rate of the injectors was measured with the flowmeter. If the range of the mass flow rate was wide, 2 flow meters were used in the different range of the pressure difference. During the spilling test, the straightness of the jet injected from the plain orifice was inspected within ±1o from the central axis of the injectors 3. NUMERICAL CALCULATION

The governing equation was axisymmetric incompressible Navier-Stokes equation and water vapor model was used to predict the cavitation inside the orifice. Finite volume method was applied to spatial discretization as a numerical scheme. Standard k-ε Turbulent model was used for turbulent prediction. Hybrid grid system which use quadrilateral and tetra mesh was introduced to improve the accuracy on calculation of thermal boundary layer and the viscosity effect. Here, the value of Y+ was set up to 30 inserting prism layer [1] in the near wall. Pressure drop condition was setup to 2MPa (Back pressure is 1bar). RSM and MOGA (Multi-Objective Genetic Algorithm) were used for the optimization of the design parameters. The flow field inside the plain orifice injectors were calculated with Screw/Tetra, Fluent and iSIGHT. Fig. 3 shows the typical calculation grid distribution. 25,000 numbers of cell were generated. Table 2 shows ratio of the chamfer length to the orifice diameter, ratio of the length to diameter of the injectors with geometrical dimension of plain orifice injectors as a calculation condition

Fig. 3 Typical calculation grids used in the numerical

analysis

Table 2. Geometries of the calculated plain orifice injectors

4. RESULTS AND DISCUSSION

Fig. 4 ~ Fig. 8 show flow characteristics inside orifice according to variation of geometry scale in case of constant Lo/Do (See the Type 1 ~ Type 5 for Dimension).

Fig. 4 Static pressure distribution, velocity magnitude and

cavitation fraction (Case 1)

Type Do Lo Dc ANGLE Dc/Do Lo/Do1 0.15 0.1 0.05 50 0.33 0.67 2 0.3 0.2 0.1 50 0.33 0.67 3 0.45 0.3 0.15 50 0.33 0.67 4 0.6 0.4 0.2 50 0.33 0.67 5 0.9 0.6 0.3 50 0.33 0.67

Fig. 5 Static pressure distribution, velocity magnitude and

cavitation fraction (Case 2)

Fig. 6 Static pressure distribution, velocity magnitude and

cavitation fraction (Case 3)

Fig. 7 Static pressure distribution, velocity magnitude and

cavitation fraction (Case 4)

Fig. 8 Static pressure distribution, velocity magnitude and

cavitation fraction (Case 5)

Regarding model case 1, mass flow rate was increased according to increase of geometry scale when pressure drop is constant. However discharge coefficient was constant to about 0.91~0.92. Cavitation region was occurred on orifice wall after chamfer regarding all geometry. It also was occurred weakly at initial position of orifice according to

increase of geometry scale from case 3 to case 5. Averaged exit velocity remained constant in general when geometry scale was constantly increased, however averaged turbulent intensity was decreased at the condition of constant pressure drop. Afterward, analysis on flow characteristics will be performed according to the variation of Lo/Do ratio, pressure drop, chamfer angle etc.

Fig. 9 Calculated discharge coefficients

Fig. 9 is the discharge coefficients acquired from the calculation and the calculated discharge coefficients are very similar at the same Dc/Do and Lo/Do condition. The slight difference of the calculated discharge coefficients is thought to be caused by the different level of the cavitation. Here, cavitation effect varies according as the orifice diameter grows up. All plain orifice injectors listed in Table 1 were spill-tested which mass flow rates were measured with flow meter. Among the spill test results, as a typical result of the spilling tests, the mass flow rate of plain orifice injector, #9 was converted to the form of the nondimensional discharge coefficient, CD like Fig. 9. The pressure difference was controlled from 0 to 8MPa. Over 1MPa of the pressure difference, the discharge coefficients of 2 injectors are very coincident.

Fig. 10 Discharge coefficient of plain orifice injector, #9

Fig. 10 shows the discharge coefficients of the plain orifice injectors, #1~#9. The basic design criteria is Dc=0.3, Lo/Do=0.65, and chamfer angle=50o. From Fig. 10, at the design criteria, Cd was 0.862. In contrary, the calculation result of Fig. 10 shows that Cd is over 0.93. The difference of the measured and calculated discharge coefficient is caused by the unbalance of the real geometry and the

friction at the surface inside the plain orifice injector.

0 1 2 3 4 5 6 7 8 9 100.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Dc=0.6

Dc=0.15CF ANGLE=60

CF ANGLE=20

Lo/Do=5

Lo/Do=2

Design criteria1)Lo/Do=0.652)Dc/Do=0.33)CF ANGLE=50o

4)Dc=0.3

Dis

char

ge C

oeffi

cien

t

Injector #

Fig. 11 Discharge coefficients of the plain orifice injectors,

#1 to #9 According as Lo/Do increases up to 5, discharge coefficient decreases. This is thought to be from the occurrence and distinction of the cavitation inside the plain orifice. But, this phenomenon should be studied more experimentally and numerically. With the viewpoint of the chamfer angle, it is thought that the smaller a chamfer angle, the smaller a discharge coefficient. In case of the injectors, #8 and #9, it was found out that the discharge coefficient decreases proportionally with Dc. This is the same tendency with the calculation result in Fig. 11. The orifice length is very short, compared to the orifice diameter, in case Lo/Dc is 0.65. In can be thought that the separated flow at the edge point can not be re-attached before the exit of the orifice, when Lo/Dc is shorter absolutely. 5. REMARKS

The authors are still studying the influence of many numbers of geometrical parameters on the spray condition numerically and experimentally to obtain optimal conditions as shown in Fig. 12 ~ 15. From this work, they are expecting the design optimization procedure of the plain orifice injectors for ramjet and scramjet engines.

Fig. 12 Static pressure and velocity magnitude

(Chamfer24_Angle25)

Fig. 13 Static pressure and velocity magnitude

(Chamfer30_Angle24)

Fig. 14 Static pressure and velocity magnitude

(Chamfer30_Angle25)

Fig. 15 Static pressure and velocity magnitude

(Chamfer35_Angle25)

6. REFERENCES 1. SC/Tetra version 5, User's guide Preprocessor Reference,

2004 2. Arthur H. Lefebvre, Purdue University, Atomization and

Sparys 3. Ferrenberg, A. J., “Liquid Rocket Injector Atomization

Research, Liquid Particle Size Measurement Techniques, ASTM STP 848, J. M. Tishkoff. R. D. Ingebo, and J.B. Kennedy, eds., American Society for Testing and Materials, 1984, pp. 82-97

4. iSIGHT V9.0, User’s guide Reference, 2005 5. Joyce, J. R., The Atomization of Liquid Fuels for

Combustion, J. Inst. Fuel, Vol. 22, No. 124, 1949, pp. 150-156