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Variations of spray cone angle and penetration length of pressure swirl atomizer designed for micro gas turbine engine.

Introduction

The process of breaking or atomization of the liquid fuel into tiny droplets in the form of a fine spray plays a vital role in various industrial and propulsion applications. The droplets provide a larger surface area than the liquid itself, thus, reducing the liquid vaporization time, which results in better mixing and increases the time available for complete combustion in liquid fueled combustion systems (Lefevbvre [1]). The influence of spray quality on combustion/ignition performance and efficiency is well depicted in various works of Lefebvre [2], Rink and Lefebvre [3], and Reeves and Lefebvre [4].

The simplest case of breakup of liquid jet has been studied theoretically for more than a hundred years, but the result of these studies has failed to predict spray characteristics to a satisfactory level. The physics is not well understood, the available data and correlations are of questionable validity and there is little agreement between various investigators at to exact relationship between liquid properties, nozzle dimensions and spray characterization.

Typical issues pertaining to spray combustion are the non-symmetrical spray flames and the hot-streaks that can cause serious damage to the combustion liner and can severely affect the combustor exit temperature distribution. These issues are highly related to the spray pattern provided by a particular spray device as discussed by Chigier [5]. Thus, significant improvements in the performance of the liquid fueled combustors can be achieved by having the ability to control the spray characteristics and spray structure. Various spraying devices operating on different principles and varied geometry have been developed with time signifying the importance and high dependence of spray characteristics on both the abovementioned factors. Detailed descriptions of such devices can be found in Giffen and Muraszew [6], Lefebvre [1, 7], and Bayvel & Orzechowski [8].

The experimental investigations are carried out for pressure swirl atomizer of tubular type combustion chamber for micro gas turbine. The designed nozzles are experimentally investigated to study the effect of injection pressure on spray cone angle and penetration length.

Design of Pressure Swirl Atomizer

The basic dimensions of pressure swirl atomizer are given in Figure 1. The input variables to the design are summarized in Table - 1 while Table - 2 gives the primary dimensions of designed nozzles at half spray cone angles of 30[degrees], 45[degrees] and 60[degrees]. The dimensional drawings of designed nozzles are given in Figures 2, 3 and 4 at spray cone angles of 30[degrees], 45[degrees] and 60[degrees], respectively.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Experimental Setup

Spray Cone Angle and Penetration Length

The experimental setups were developed for the measurement of the spray cone angle and penetration length. The schematic of the experimental setup for the spray cone angle and penetration length is shown in the figure 5. The dimensions of test chamber (TC) are selected as 800 mm x 800 mm with the diameter of the test section being 500 mm. The test chamber is having four sides of Quartz, having thickness of 6 mm. The main fuel tank (FT) contains the fuel. Its volume is 50 liters. The fuel is pumped to the test chamber by motor and pump (M & P) assembly. It is squirrel cage single capacitor, 250v, single phase, 2800 rpm motor and gear oil pump with maximum discharge pressure of 25 bar. The tube is connected to the nozzle assembly made up of brass which holds the nozzle (N).

[FIGURE 5 OMITTED]

Results and Discussions

The experimental results and discussions of spray cone angle, penetration length and drop diameter distribution is carried out at different injection pressure varying from 3 bar to 15 bar injection pressure differential for pressure swirl atomizers designed at half spray cone angle of 30[degrees], 45[degrees] and 60[degrees].

Figure 6 shows the spray half cone angle as a function of injection pressure for pressure swirl atomizers designed for micro gas turbine engine. The half cone angle tends to decrease with increase in injection pressure. This is expected as atomization improves with increase in the injection pressure differential.

[FIGURE 6 OMITTED]

Lefebvre [7], based upon theoretical and experimental investigations mentioned that, the spray angle is an inverse function of the injection pressure. However, this was so because in those investigations the injection pressure was analyzed in an isolated manner, the mass flow rate was kept constant and the injector dimensions were adjusted to fit the desired condition, i.e., a completely different case form the one performed here.

However, Pedro et.al [9] from the experimental investigations on pressure swirl atomizer has suggested the increase in spray cone angle with increase in injection pressure. But the results obtained herein suggest that the spray cone angle decreases with increase in injection pressure. This decrease in spray cone angle with injection pressure differential leads to increase in penetration length as depicted in Figure 7. Roel Peters [10] from the studies of penetration and dispersion of non reacting spray analytically suggested no variations of spray length with injection pressure.

[FIGURE 7 OMITTED]

Conclusions

The pressure swirl atomizer is designed and developed for tubular combustion chamber of micro gas turbine engine with spray cone angle of 60[degrees], 90[degrees] and 120[degrees]. Because of the complexity of the over-all process involved in atomizers, it would appear unlikely that this simplified theoretical treatment would be adequate for different applications of pressure swirl atomizer. The experimental investigations suggest that spray half cone angle tends to decrease with increase in injection pressure. This is expected as atomization improves with increase in the injection pressure differential. The decrease in spray cone angle has led to the increase in penetration length with increase in injection pressure.

References

[1] Lefevbre A H (1983), Gas Turbine Combustion, Hemisphere Publishing Corporation, Washington, DC, USA

[2] Lefevbre A H (1985), Fuel Effects on Gas Turbine Combustion--Ignition, Stability and Combustion Efficiency, ASME J Eng Gas Turbine Power 107:24-37

[3] Rink KK, Lefebvre AH (1987) Pollutant Formation in Heterogeneous Mixtures of Fuel Drops and Air, AIAA J Propulsion Power 3(1):5-10.

[4] Reeves C M, Lefebvre A H (1986), Fuel Effects on Aircraft Combustor Emissions, ASME paper 86-GT-212

[5] Chigier N A (1993), Spray Science and Technology, Fluid Mechanics and Heat Transfer in Sprays, ASME Fluid Eng Div Publ FED 178:1-18.

[6] Griffen E & Maraszew A (1953), The Atomization of Liquid Fuels, Chapman and Hall Ltd., London

[7] Lefevbre A H (1989), Atomization and Spray, Hemisphere Publishing Corporation, New York

[8] Beyvel L & Orzechowski Z (1993), Liquid Atomization, Taylor and Francis, Philadelphia, PA

[9] Pedro, T., Demetrio, B. & Amilcar, P. 2004, Design Procedure and Experimental Evaluation of Pressure-Swirl Atomizers, 24th International Congress of the Aeronautical Sciences, 1-9

[10] Peters, R. 2007, Penetration and dispersion research of non-reacting evaporating diesel sprays, Graduation Report, Eindhoven University of Technology Mechanical Engineering--Combustion Technology.

* Digvijay B. Kulshreshtha, # Saurabh B. Dikshit and $ S. A. Channiwala

*# Lecturer, Mechanical Engineering Department, C. K. Pithawalla College of Engineering and Technology, Surat 395007 Gujarat, India

Email: casanovicdigs@hotmail.com and Email: saurabhjdikshit@rediffmail.com

$ Professor, Mechanical Engineering Department, S. V. National Institute of Technology, Surat 395007 Gujarat, India

Email: sac@med.svnit.ac.in
Table 1: Input Variable to Design.

Sr. No.            Parameter                      Value

1         Mass Flow Rate                7.2 E-03 kg/s
2         Injection Pressure            18 bar
3         Spray Angle                   60 [degrees], 90 [degrees]
                                          and 120 [degrees]
4         Density of Atomizing Liquid   780 kg/[m.sup.3]
5         Kinematic Viscosity of
            Atomizing Liquid            2 E-06 m/[s.sup.2]

Table 2: Summary of Design of Pressure Swirl Atomizer.

                            Cone Angle     Cone Angle     Cone Angle
Design Data                60 [degrees]   90 [degrees]   120 [degrees]

Discharge Orifice
Diameter, [d.sub.0]         0.8866 mm       0.754 mm        0.8 mm

Distance of Tangential
Inlet Port from Central
Axis, R                       1.4 mm         1.4 mm         1.4 mm

Number of Tangential
Inlet Ports, i                  4              4               4

Tangential Inlet Port
Diameter, [d.sub.p]          0.49 mm        0.52 mm        0.6831 mm

Swirl Chamber Diameter,
[D.sub.s]                    3.68 mm       3.3574 mm        3.53 mm

Length of Swirl
Chamber, [I.sub.s]           7.36 mm       6.7148 mm        7.06 mm

Length of Inlet Port,
[I.sub.p]                    1.06 mm       1.1148 mm        1.46 mm

Length of Discharge
Orifice, l                   0.675 mm      0.5278 mm        0.56 mm
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Article Details
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Author:Kulshreshtha, Digvijay B.; Dikshit, Saurabh B.; Channiwala, S.A.
Publication:International Journal of Dynamics of Fluids
Article Type:Report
Geographic Code:9INDI
Date:Dec 1, 2009
Words:1390
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