• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.47-54
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• 2012

Single Stage To Orbit (SSTO) missions which require its engines to be operated at varying back pressure conditions, use engines operate at high combustion chamber pressures (more than 100bar) with moderate area ratios (AR 70~80). This ensures that the exhaust jet flows full during most part of the operational regimes by optimal expansion at each altitude. Aero-spike nozzle is a kind of altitude adaptation nozzle where requirement of high combustion chamber pressures can be avoided as the flow is adapted to the outside conditions by the virtue of the nozzle configuration. However, the thrust prediction using the conventional thrust equations remains to be a challenge as the nozzle plume shapes vary with the back pressure conditions. In the present work, the performance evaluation of a new aero-spike nozzle is being carried out. Computational studies are carried out to predict the thrust generated by the aero-spike nozzle in varying back pressure conditions which requires the unsteady pressure boundary conditions in the computational domain. Schlieren pictures are taken to validate the computational results. It is found that the flow in the aero-spike nozzle is mainly affected by the base wall pressure variation. The aerospike nozzle exhibits maximum performance in the properly expanded flow regime due to the open wake formation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2127-2132
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• 2003

A computational study is performed to better understand the choke phenomenon of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Navier-Stokes equations are solved using a finite volume method. In order to simulate the effects of back pressure fluctuations on the critical nozzle flow, a forced sinusoidal pressure wave is assumed downstream the exit of the critical nozzle. It's frequency is 20kHz and amplitude is varied below 15% of time-mean back pressure. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thereby giving rise to applicable fluctuations of mass flow through the critical nozzle. The effect of the amplitude of the excited pressure fluctuations on the choke phenomenon is discussed in details.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.426-431
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• 2001

This paper experimentally investigates the characteristics of dual coaxial jet issuing from inner supersonic nozzle and four kinds of outer converging nozzle of 40, 50, $60^{\circ}$ and $70^{\circ}$ in outer ejection angle. The pressure ratio of the stagnation to the exit ambient pressures in the inner supersonic nozzle of constant expansion rate is 7.5, which is corresponded to the condition of a slightly underexpanded, and that of outer nozzle is 4.0. Flow visualizations by using of shadowgraph method, impact pressure and centerline static pressure measurements are presented. It is found that the jet structure is changed significantly by the variation of outer nozzle ejection angle. Impact pressure level is lower and undulation of static pressure is higher, as the injection angle of outer jet increases.

• Journal of ILASS-Korea
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• v.7 no.1
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• pp.36-42
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• 2002

The objective of this investigation was to obtain an excellent spray at the low injection pressure. When cavitation occurred in the nozzle hole the atomization of the liquid jet enhanced considerably. In this experiments, a acrylic nozzle which was installed the gap and installed the bypass in the nozzle hole was used to enhance the atomization of the liquid jet at the few injection pressure. The liquid flow in the nozzle hole was photographed by a transmitted light using a micro flash. The spray angle was measured by macroscope images of PMAS and the Sauter mean diameter was measured by PDA system. The pressure of the notate hole was measured by pressure transducer. It was found that enhanced atomization of the liquid jet at the low injection pressure was obtained by installing the gap and the bypass at the single hole nozzle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.5
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• pp.263-268
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• 2015

In this study, the performance of an ejector in the refrigeration cycle was experimentally studied using R600a. The performance of the ejector is analyzed according to the inlet pressure and nozzle position. The increase in the primary nozzle pressure decreased the pressure difference across the ejector. In the low entrainment region, the increased suction flow pressure led to an increase in the pressure difference. In the high entrainment region, the pressure difference was inversely proportional to the suction pressure. The effects of nozzle position ($L_n$) were also analyzed and for $L_n<0$, the decreased suction chamber volume led to a large pressure drop with the small increase in the suction mass flow rate. For $L_n>0$, the increased $L_n$ disturbed the primary nozzle flow and thus an increase in the primary nozzle flow increased the pressure lifting effect. In contrast, the increased suction mass flow rate decreased the pressure difference. When the nozzle outlet was located at the mixing part entrance ($L_n=0$), the ejector showed the highest pressure lifting effect.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.16-23
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• 2002

Electrostatic pressure-swirl nozzle for practical oil burner application has been designed. The charge injection method has been used in this design, where the nozzle consists of a sharp pointed tungsten wire as a charge injector and the nozzle body grounded. The spray characteristics of the nozzles have been investigated by using an insulating liquid, i.e. kerosene without active surface agent. Breakup length of liquid decreased with an increase in applied voltage and injection pressure, while the spray angle increased with an increased in both applied voltage and injection pressure. An empirical equations have been suggested to predict the breakup length for electrostatic pressure-swirl atomizer. The experimental result was within the range of the predicted equations. The SMD decreased between the ranges of 2.8 ${\sim}$ 33% when the conventional nozzle was compared to the electrostatic with -10 kV applied to the electrode at a radial distance from 5 to 20 mm.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.496-501
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• 2003

Computational study is performed to understand the fluidic thrust vectoring control of an axisymmetric nozzle, in which secondary gas injection is made in the divergent section of the nozzle. The nozzle has a design Mach number of 2.0, and the operation pressure ratio is varied to obtain the different flow features in the nozzle flow. The injection flow rate is varied by means of the injection port pressure. Test conditions are in the range of the nozzle pressure ratio from 3.0 to 8.26 and the injection pressure ratio from 0 to 1.0. The present computational results show that, for a given nozzle pressure ratio, an increase of the injection pressure ratio produces increased thrust vector angle, but decreases the thrust efficiency.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.10a
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• pp.81-85
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• 1992

Quality of cut is strongly dependent on the cutting pressure, so this relationship can be identified by pressure measuring system. In this paper, the experiments presented were performed with the devised pressure measuring system and the laser cutting of STS 304. Convergent type and convergent-divergent type nozzle were used for pressure variation of the distance between nozzle and workpiece. In laser cutting of STS 304, 1.0 kW CO $\_$2/ laser used. The convergent type nozzle(1.0 mm diameter) pressured above 3 kgf/cm $\^$2/, the MSD(Mach Shock Disk) created, which caused the the pressure variations of the distance between nozzle and workpiece. The maximum cutting pressure exists in accordance with the variation of distance. In spite of far distance the maximum cutting pressure is achieved by using the pressure measuring system. The higher cutting pressure beneath the workpiece the less quantity of dross and the kerf width. Since the higher cutting pressure helps to remove the quantity of dross and to stop the exothermic energy into the material. The optimum laser cutting parameter of STS 304(2.0 mm thickness) with the convergent type nozzle(1.0 mm diameter)is 0.75 mm and 2.5 mm distance between nozzle and workpiece, 4 kgf/cm $\^$2/ cutting pressure. In 3.0 mm thickness case, 1.5 mm and 2.25 mm distance is achieved for good quality.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.1
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• pp.37-44
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• 1993

Fuel injection system is an important tool in the exhaust emission and performance of a diesel engine. Effects of the fuel injection system in diesel combustion was investigated experimentally by measuring the performance and analyzing the combustion phenomena in a D.I. diesel engine. The selected injection parameters were nozzle opening pressure, nozzle projection length, and nozzle spray angle. From the measured results, it is shown that the fuel injection pipe diameter is an effective means to improve engine performance in a middle and high speed range and the 2 stage spring nozzle holder has the advantage of increasing the engine performance due to the initial injection pressure in a low speed range. It has been also shown that increasing nozzle opening pressure resulted in decrease in smoke, but increase in NO$_{x}$ from the engine.e.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.69-74
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• 2002

This study is object to structural analysis of high pressure injection nozzle. The finite element model was developed to compute the stress, strain for high pressure injection nozzle. For structural analysis using result from FEM code. This structural analysis results, many variables such as internal pressure, boundary condition, constraint condition and load condition are considered.