Pulse detonatio. Zheng Long Xi 1,Li Na 2 and Yan Chuan Jun 3 Northwestern Polytechnical University, xi'an, Shaanxi, , P.R.China.

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1 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition - 8 January 9, Orlando, Florida AIAA 9-97 Investigation on Noise Radiation Characteristics of Two- Phase Multi-Cycle Pulse Detonation Engine Zheng Long Xi,Li Na and Yan Chuan Jun Northwestern Polytechnical University, xi'an, Shaanxi, 77, P.R.China The noise radiation characteristics of single pulse detonation combustor () and hybrid pulse detonation engine () were investigated under several operating frequencies, different equivalence ratio and fill fraction, while gasoline and air were selected as fuel and oxidizer. It is found that the noise radiation characteristics are intermittent and periodic. Pulse detonatio onation engine jet noise are mainly consisted of annuploe source and quardrupole source. The frequency spectrum of the noise is very broad, its radiation energy mainly concentrates es in the frequency range of - khz, and it is composed of principal frequency (namely the detonation frequency), which is caused by pulse jet and harmonic frequencies. The peak sound pressure level is not sensitive to operating frequencies of this two kinds of conformations, but it increases along with the increasing ing of equivalence ratio and fill fraction. The impulse sound pressure level increases with the increasing ing of operating frequency, equivalence ratio and fill fraction. The peak sound pressure level of is less than about 4dB, and the impulse sound pressure level reduces db. At the same measuring locations, the head pressure, pipe pressure and outlet pressure of the is greater than. In the condition of s equivalence ratio is a constant, when the detonation wave flows through the turbine, the reduction of the peak pressure between the outlet and the turbine exhaust decreases es with the increasing of fill fraction, and the greater fill fraction increases, the smaller reduction produces. The reduction is 9.74dB when fill fraction is.. ff = fill fraction of detonation tubes Φ = equivalence ratio of detonable mixture f = detonation tube firing frequency PDE = pulse detonation engine = hybrid pulse detonation engine = pulse detonation combustor L peak = peak sound pressure level L Imp = impulse sound pressure level P peak = peak sound pressure SPL = sound pressure level P = reference pressure p Nomenclature I. Introduction ulse Detonation Engine (PDE) is a propulsion system that obtains thrust from the intermissive detonation wave. As a propulsion device, it is necessary to investigate its noise radiation characteristics. Mastery of the noise generation rules and using the rules to control it effectively can reduce the noise disturbance and harm on environment as well as human. It is a issue which should be solved in research. The single detonation cycle of PDE is buildup as follows: ) combustible mixture gas fills in the detonation tube; ) ignite at the airproof end; ) produce deflagration-to-detonation transition (DDT) and propagate to the open associate professor, School of Power and Energy, 7Youyi west road. graduate student, School of Power and Energy, 7 Youyi west road. professor, School of Power and Energy, 7 Youyi west road. 997 Copyright 9 by Long-xi Zheng. Published by the, Inc., with permission.

2 end; 4) detonation wave propagates from the open end and expansion wave reflects in; ) hot combustion products expel from PDE. On a certain detonation frequency, above-mentioned process works to-and-fro, PDE enters the muti-cycle working state. In this working state, if a PDE use liquid fuel it is called Two-Phase Multi-Cycle Pulse Detonation Engine (TMPDE for short). Hybrid Pulse Detonation Engine () is constituted of a compressor, a pulse detonation combustor () and a turbine. The cycle process is buildup as following:) compressed air enters and mixes with gasoline; ) ignite and generate detonation in ; ) the combustion products flow through the turbine and drive the compressor; 4) hot gas exit the exhaust tube. From above-mentioned cycle processes, we can find that the whole system radiates noise from initial ignition to hot combustion products exit the nozzle. The definition of pulsed noise was brought forward in a China national standard of GJB-8, namely, the noise which is composed of one or more abruptly noise (its duration time is less than s) can be called pulse noise. According to its physical characteristics, the pulsed noise can be classified to two kinds: One is the impact noise, when solid objects impact, the elasticity vibration, distortion, and rupture can cause this kind of noise. The other is caused by pulse pressure which produces by blast, bang or turbulence. Obviously, PDE noise belongs to the second situation. Using gasoline as fuel and air as oxidant, the noise radiation characteristics of single and were investigated and compared in variety detonation frequencies, fill fractions (ff), and equivalence ratios (Φ). II. Experimental Setup Fig. is the sketch of experimental setup, it involves air inlet, compressor,, turbine, exhaust nozzle, oil supply system, startup air supply system, ignition frequency control system, lubricant system, measuring system, data acquisition system and test control system and so on. In order to make the test conveniently, we choose a turbocharger of a automobile engine to replace the compressor and turbine of Fig. Sketch of experimental setup According to the need of air mass flow of, the chosen turbocharger type is 6/HP6, its mass flow range is.~.kg/s, the highest compression ratio is.6, the highest rotate speed is 6,RPM, the highest temperature is 7, power range is between Kw to kw. The turbocharger contains a single stage centrifugal compressor and a single stage radial-inward turbine. The outlet connects with turbine inlet, and detonation products flow into turbine radial and effuses axially, impacts the turbine to provide power, drive the rotor running. The compressor compresses the air which comes from the air inlet, the gas of turbine oulet expels from the exhaust tube and provide thrust. The testing of noise use a high sound pressure level measuring sensor system which is made in G.R.A.S sound and vibration company of Danmark. This system makes up of "4DP-/8 pressure microphone, RA6 microphone adapter, 6AC microphone preamplifier and AD power module. The system performance parameters are as follows: a. sensitivity is.97mvpa; b.frequency range is Hz~7kHz (±db) or 6.Hz~4kHz (±db); c. the sound measure range is 4~78dB; d. working temperature range is -4~+ C Before measurement, we used B&K4 sound calibrator to calibrate the whole measuring system. 997

3 III. Results and Discussion A. Effect of frequency on noise The used in experiment constitutes of mixing chamber, ignition section, detonation chamber. The engine can work at -Hz steadily. Table show the characteristics of peak sound pressure level and impulse sound pressure level of and when they work at different frequencies and ff=.,φ=.. Fig (a) and (b) were drawn according to the table. We can find that the peak sound pressure level is not sensitive to operating frequencies on this two kinds of conformations, but impulse sound pressure level increases with the increasing of operating frequencies. The peak sound pressure level of hybrid pulse detonation engine is less than single pulse detonation combustor about 4dB, and the impulse sound pressure level reduces about db.this reduction is because that turbine drives compressor to work and consumes a part of energy, and then the noise reduced. Table Characteristic at different operating frequency f /Hz L peak /db L Im p /db L peak /db /db L Im p L Peak /db L Imp /db (a) (b) Fig. Effect of frequency on peak pressure level (a) and impulse pressure level (b) at ff=. and Φ=.. B. The effect of fill fraction on noise Fig is the effect of fill fraction on peak pressure level (a) and impulse pressure level (b) when and work at Φ=. and f=hz. We can find that the peak sound pressure level and impulse sound pressure level all increase with the augment of fill fraction when operating frequency and equivalence ratio are constants. C. The effect of equivalence ratio on noise The equivalence ratio defines the ratio of factual fuel mass and theoretical fuel mass. Fig 4 is the effect of equivalence ratio on peak sound pressure level (a) and impulse pressure level (b) at ff=. and f=hz. We can find that the peak sound pressure level and impulse sound pressure level all increase with the augment of equivalence ratio when operating frequency and fill fraction are constants. 997

4 L Peak /db ff L Imp /db (a) (b) Fig. The effect of fill fraction on peak pressure level (a) and impulse pressure level (b) at Φ=. and f=hz. ff L Peak /db Equivalence Ratio L Imp /db Equivalence Ratio (a) (b) Fig.4 the effect of equivalence ratio on peak sound pressure level (a) and impulse pressure level (b) at ff=. and f=hz. D. The peak pressure reduction characterstics of The pressure reduction inside system defines the value of pressure in one location to another location, it also calls the minus of level. The pressure reduction can be defined as: P P P SPL = SPL SPL = lg = lg () P P P Where P is reference pressure ( P = Pa ). Table is the effect of fill fraction on peak pressure reduction through turbine. Fig. is the effect of fill fraction on peak pressure reduction through turbine at f=hz,φ=..we can find that the reduction in the peak pressure of the detonation between and turbine exhaust decreases along with the increasing of fill fractions when equivalence ratio is a constant, while the greater fill fraction increases, the smaller reduction generates. It shows when the detonation wave pressure is higher, the reduction is less, and the influence of barrier to strong detonation wave is little. This results match with the result of references

5 Table Effect of fill fraction on peak pressure reduction through turbine f f P4/MPa P/MPa Reduction/dB Peak Pressure Reduction/dB ff Fig. Effect of fill fraction on peak pressure reduction through turbine E. The compare of pressure with P / M P a t/s t /s (a) (b) Fig.6 Pressure traces without turbine (a) and with turbine (b) at ff=. and Φ=. Fig.6 is the pressure traces in second without turbine (a) and with turbine (b) at ff=. and Φ=.. P is head pressure. P is pipe pressure. P is outlet pressure. P4 is turbine inlet pressure. P is turbine outlet pressure. The outlet peak pressure of is between to.mpa, it shows that it has already came into being the adequately detonation wave. The pressure wave through the turbine reduces obviously which shows turbine can weaken pressure wave intensity remarkably. Compare (a) to (b) of fig 6, we can find the head pressure, pipe pressure and outlet pressure of is obvious greater than the pressure at the same locations of single. This is because detonation pressure through turbine will be reflected to, and also of the flow from is throttled by turbine which can make the initial pressure of increased. During the experiment, we measured the P of and P of to obtain the peak sound pressure level of these two kinds configurations. According to P of fig 6 (b) and P of (a), we can compute the peak pressure reduction of and single comparatively, the value is about 4 to 6 db. This value just meet with the forenamed conclusion that the peak sound pressure level of is less than it of about 4 db. F. The noise frequency radiation characteristics of 6 mmpde model 997

6 The sound power level and sound power would not be measured direct, but by measuring the sound pressure level in a certain sound field, then use the following equation to calculate sound power and sound power level, the sound power level and sound power are defined as: Where L Pr L W = L + lg S Pr L W ( db) W = W ( W ) is the average sound pressure level which is measured in a distance of r(m) at multi-point; S is the whole area which surround the sound source in this measuring distance. W is the reference sound power, which is defined as: W = ( W ) The noise time history signal was analyzed by FFT method, and its frequency spectrum and power spectrum were obtained like fig 7. We can easily find that the noise frequency spectrum is very broad, there are various frequency components between and 6Hz. But the energy of noise radiation mainly concentrate in the frequency range of ~Hz., especially in the frequency range of ~Hz. It shows the low frequency characteristics obviously. When PDE works in other frequencies, the noise radiation frequency characteristics are similar with the frequency of Hz..4 () () Pressure/Pa Power/W Fig 7 the frequency spectrum and power spectrum of noise characteristics at Hz on 6mm PDE model.4 Pressure/Pa Power/W Fig 8 Zoom in the frequency spectrum and power spectrum of noise characteristics at Hz on 6mm PDE model Zoom in the frequency spectrum and power spectrum of 6mm PDE model noise characteristics at Hz and the frequency range of ~Hz like fig 8. We can find that the noise radiation and power spectrum are composed of principal frequency(namly the detonation frequency) which is caused by the pulsed jet and harmonic frequencies. G. Analysis noise source on two-phase multi-cycle PDE 6 997

7 In a general way, the dynamics noise caused by high temperature and high pressure gas of PDE coming from jet is higher than mechanism noise caused by the libration of detonation tube about many decades decibel. So, the pulse detonation engine noise can be considered as aerodynamic noise coming from nozzle outlet. We analyze PDE dynamics noise primary according to the Lighthill equation. Based on mass conservation equation, momentum equation, thermodynamics equation of movement fluid, Lighthill put forward the fluctuate equation of little amplitude wave diffuse in infinite medium. when there are mass source Q(t) in flow field, volume force Fi act on fluid and the distributing source of disturbed velocity fluctuation. The equation is defined as following: Where: T ij ρ C t = ρv v i j + P ρ Q Fi = x t x ij i c ρδ ij, i Tij + x x δ ij i j (4),i = j =,i j The three items in right side of Lighthill equation are source function of invigorative sound field, including mass source, force source and stress source, corresponding to annuploe source, even source and quardrupole source. Because the ratio of PDE nozzle outlet area and detonation combustor volume is bigger, in one detonation cycle, the time from detonation wave propagating out of the nozzle outlet to burned gas expanding sufficiently is very short. So, the time variety ratio dω/dt of mass flow is big, which make the first item in the right side of equation much bigger. When PDE works in the multi-cycle state, the high pressure and high temperature gas jet from exit is periodic, the pressure and density of circumference air is disturbed, and then it generate noise. This type of noise is a single source similarly to pulse globe, which is called annuploe source. Its noise spectrum can be divided into two parts: schism spectrum in low frequency range and continuous spectrum in middle and high frequency range. In low frequency range, the spectrum is mainly composed of principal frequency (namely the detonation frequency) caused by pulsed jet and harmonic frequencies. This conclusion is identical with the result of experiment in this paper, so we can draw a conclusion that there is annuploe source in jet noise of PDE. In addition, because detonation wave can generate high gas pressure (it is greater than to times of atmospheric pressure); During a detonation cycle, from detonation wave propagating out of nozzle outlet to burned gas expanding sufficiently, the pressure variety ratio of outlet is great. The initial pressure P c of every jet at outlet is greater than times of atmospheric pressure, which is greater than critical pressure P A (when the airflow velocity of PDE in the outlet is equal to local velocity of sound). So the jet process of one working circle in PDE can mark off P two phases which are sound velocity jet phase (when c P P A ) and subsonic jet phase ( c PA ). In the sound velocity jet phase, the airflow velocity achieves to local sound velocity, the pressure at the outlet can not influence the jet velocity. This state is the barrage jet state which is put forward in the acoustics. Because of the discontinuity pressure in outlet, which generates shock wave and these wave disturb each other, then forms string shock wave which radiates additional noise, called pulse noise. The radiated peak pressure noise in single detonation cycle is caused by pulsed noise. In the barrage jet phase and subsonic jet phase, when jet flow into quiescent air, it mix with relative quiescent medium, turbulence fluctuant can be formed in boundary layer, which make the stress tensor T ij of the third item of right equation change in flow field. Then it generates quardrupole radiate, also called turbulence noise. Because of the spectrum of turbulence noise is mainly in high frequencies, high frequencies part noise is mostly the contribution of noise which is produced by quardrupole source, which can say there is quardrupole source in PDE jet noise. IV. Conclusion We can draw some conclusions through comparing experiments of two-phase multi-cycle pulse detonation engines of and as follows: () The impulse sound pressure level of the two kinds of conformations all increase with detonation frequencies, but the peak sound pressure level is not sensitive to operation frequencies; The sound pressure level of hybrid pulse detonation engine is less than single pulse detonation combustor about 4dB, the impulse sound pressure level reduces about db. () The impulse sound pressure level and peak sound pressure all increase with equivalence ratio and fill fraction when detonation frequency is constant of these two kinds of conformations. () 7 997

8 () The head pressure, pipe pressure and outlet pressure of hybrid PDE is greater than the same locations of single. (4) The reduction of the peak pressure of detonation between and the turbine outlet decreas with the increasing of fill fraction when equivalence ratio is a constant, while the greater fill fraction increases, the smaller reduction produces, the reduction is 9.74dB when fill fraction is.. () It is found that the noise radiation characteristics are intermittent and periodic. Two-phase multi-cycle pulse detonation engine jet noise is mainly consisted of annuploe source and quardrupole source. (6) The frequency spectrum of the noise is very broad, and its radiation energy mainly concentrate in the frequency range of - khz, composed of principal frequency (namely the detonation frequency) caused by the pulsed jet and harmonic frequencies. Acknowledgments The coauthor would like to acknowledgement to the sponsorship of the national nature science fund. References Yan Chuang Jun,Fan Wei,et al. "The principle and key technology on pulse detonation engine", Edited by Wang Qin and Ji Su Ping,Northwestern Polytechnical University publishing company,,pp.4-8. Wang Bing Yi. "The noise characteristics and prevention on firearm noise and blast sound", National defence industry publishing company,,pp.-6. Zheng Long Xi,Yan Chuan Jun, Fan Wei,et al. "Preliminary exploration on noise radiation characteristics of pulse detonation engine model", Journal of Vibration, Measurement & diagnosis, Vol 6, No., 6, pp Nicholas Caldwell, Aaron Glaser, "Russell Dimicco,et al.acoustic measurement of an integrated pulse detonation engine with gas turbine system", AIAA paper -4,January. Nicholas Caldwell, Aaron Glaser, Ephraim Gutmark,et al."acousic interactions of a pulse detonation engine array with a gas turbine", AIAA paper 6-,January 6. 6 Adam Rasheed, Anthony Furman, Anthony J. Dean."Wave attenuation and interactions in a pulsed detonation combuster-turbine hybrid system", AIAA paper 6-,January. 7 Nicholas Caldwell, Aaron Glaser, Ephraim Gutmark."Performance measurements of a pulse detonation engine array integrated with a turbine", AIAA paper 6-47,July 6. 8 Ayaka Nango,Kazuaki Inaba. "Aerodynamic effect of turbine blade geometryin pulse detonation combustor", AIAA paper 7-76,January 7. 9 Fred Schauer."Interaction of a pulse detonation engine with a turbine", AIAA paper -89,January. John Hoke, Royce Bradley. "Integration of a pulse detonation engine with an ejector pump and with aturbocharger", AIAA paper -6,January