Numerial Simulation of Combustion Chamber for Button Turbojet Engine Hongpeng Ma, Shuzhou Fang, Hang Gao, Teng Li and Guanlin Fang Shool of Aerospae Siene and Engineering, Beijing Institute of Tehnology, Beijing,100081, China Abstrat. To provide referene data for ultra-miro ombustor, a new type button turbojet engine was designed and simulated the ombustion s steady-state proess. The boundary ondition of inlet was alulated using isentropi numerial alulation, taken into turbulent hemial reation, heat radiation, and so on, getting the ombustion hamber s steady-state of the veloity, temperature and omponent onentration, analysis the fuel/air flow and bakflow, ombustion effiieny and total pressure reovery oeffiient, and ompared with the experimental data. The alulation results an aurately reflet the atual ombustion. The results show that ombustion hamber exit veloity is about 65m/s, outlet temperature is around 1000K, the simulation and experimental data are similar, ombustion hamber struture design is reasonable, and this paper will provide a basis for the future improvement of the millimeter sale turbojet engine. 1 Introdution As a high energy density of tatial powerplant, Miro Turbojet Engine(MTE) an be applied to small UAV (Unmanned Aerial Vehile ), target drone, ruise missiles and other kinds of MAV(Miro Aerial Vehile). It will play an inreasingly important role in the future air war, military reonnaissane, environment monitoring and even anti-terrorism operations, et, [1]-[]. However, ombustion hamber as a key tehnology of MTE, due to the requirements of more and more miniaturization (millimeter level), there are many tehnial diffiulties: (1) the struture size is too small to MEMS proessing easily; () ompared to normal engine, bigger surfae-tovolume ratio will inrease its heat loss; () burning resident time is short, easy to appear the inomplete ombustion;(4) resistane fators are ompliated, many proess related to the struture size are diffenrent, suh as fule injetion, mixing of fluid mehanis, the flow field analysis will beome more diffiult, [4]-[6]. Up to now, both home and abroad researhes are mainly onentrated on the study of miro turbojet engine s traditional struture design and improvement, [7]-[9], the flow field analysis of the miro small engines are very rare, millimeter turbojet engine s threedimensional flow field researhes are basially in the blank stage. This paper disussion is based on the researhes at home and abroad [10]-[15], design a round Button Turbojet Engine (BTE), and do some numerial simulations for the ombustion hamber. Therefore, not only we got the ombustion effiieny fators, harateristi urve and total pressure reovery oeffiient, but also obtained the of temperature, veloity and omponent onentration about the internal ombustion hamber. This work will provide the foundation for the future development, proessing and prodution of the miro turbojet engine s ombustion hamber. Physial model and alulation method.1 Physial model Referene some of past design experiene, restrited to small struture size and MEMS proessing, ombustion hamber struture was finally onfirmed as follows: the ombustion hamber is divided into six independent fanshaped ombustion hamber, diffuser blade surfae form the outer wall of the ombustion hamber, ombustion hamber avity is omposed of bakflow region wall and the diffuser blade wall, hoose the methane as fuel, eah entrane of ombustion hamber set an intake pipe. The overall vertial view of engine (XOZ plane) and one sixth engine struture as shown in Fig. 1 and Fig. respetively. Figure 1. Overall vertial view of engine (XOZ plane) The Authors, published by EDP Sienes. This is an open aess artile distributed under the terms of the Creative Commons Attribution Liense 4.0 (http://reativeommons.org/lienses/by/4.0/).
Method and the Disrete Coordinate Method, et, [16]. This artile hoose the Disrete Transfer Method, beause it is wider using in engineering appliation and has higher preision in sloving flow equation. The radiation heat transfer s integro-differential equations is as following formula(): l K s kaib( kaks) I (, ) Id x 4 () j Figure. One sixth turbo engine struture Combustor design dimensions are as follows: outer diameter D 1 =16.mm, inner diameter D =15.74mm, ombustion hamber height H=1.mm, eah volume of the ombustion hamber V =.69mm, total volume V =16.15mm, outlet temperature of the ombustion hamber designed for 1000K, affordable for turbine materials, another innovation is an U-shaped reirulation zone at the entrane of the ombustion hamber in order to improve the stability of the ombustion flame.. Combustor thermodynami alulation The design of thermodynami parameters: inlet ombustor temperature T =400K, outlet ombustor temperature T =1000K, fuel initial temperature T f =50K, fuel mass flow rate m f =0.00(kg/s), the ombustor oil-gas ratio =0.05, methane ombustion heat value H =50.07(kJ/kg).. Combustion model u Calulation using the EBU-Arrhenius turbulent ombustion model, this model takes into aount the turbulene and hemial dynami fators influene on hemial reation rate. This model s average response rate is showed as following formula (1): w min w, w st sv (1) where wst CEBUg / k, exp( E w ) sv A YY 1, w is st T the response rate ontrolled by turbulene, C EBU is empirial onstant, g is determined by the orresponding transport equation, w sv is response rate ontrolled by laminar flow..4 Radiation model Common thermal radiation model inlude Zone Method, Heat Flux, Disrete Transfer Method, Monte-Carlo where I is radiation intensity, Ib is blak-body radiation intensity, s is diretion vetor, ka is medium absorbane, ks is medium sattering oeffiient, (, ) is phase funtion and show the sattering harateristis of spatial..5 Turbulene model In this paper, using double ombustion model to simulate the interior flow field, the Reynolds Number is based on ky the wall distane, Re y. Where k is turbulene energy, y is the distane between omputational grids and the wall, turbulene visosity ratio and Reynolds number have diret ratio relations, taken the experiene value between 1 to 10, turbulene intensity(i) an be alulated by the following formula() : I ( 1/8) 0.16 ( Re) () where Re is Reynolds number, given by the study of Alan h. Epstein, et al, [17]. In high Reynolds number turbulene model, ompared with standard k- model, k- / RNG model equation has a new additional generated item, it an improve the simulated result of omplex rapid flow. In the alulation software of FLUENT, double-layer model through turbulene model ombined with enhaned wall funtion. In order to guarantee the auray of alulation, the wall grid is enrypted, ensure wall boundary layer y 5, other parameters set as default..6 Computational zone, mesh and boundary onditions Beause of the engine ombustion hamber is divided into six same size single hamber, refer to Fig. 1. Computational zone is hoosen to one sixth ombustion hamber, using ICEM divides the unstrutured grids, the total number of grids are 4100, partial enryption, ombustion hamber inlet onditions set on the basis of the ompressor s integration simulation results, omputational mesh as shown in Fig.. Boundary ondition setting : - Adopt speed inlet onditions, the numerial simulation results of old ombustion flow field as the the
ombustion hamber s import speed border, get the entrane veloity vetor, and then adjust inlet veloity aording to the residual gas oeffiient, flow flux, import area, density and other onditions. - Set pressure-outlet for outlet onditions. - Two sides of setor surfaes are spin yle boundary, the ombustion hamber internal walls set as fluidstruture oupled wall. The following Fig. 6 is the veloity nephogram of Y=0.5mm ross setion. As seen in Fig. 6, the exit of guide vane hanged the originally vertial veloity vetor into an angle of oblique diretion whih is perpendiular to the export turbine rotor blade surfae, the high-speed fule gas impat the turbine rotor and get the power for driving the ompressor. Figure. Computational mesh Calulation result Beause the whole ombustion hamber around Y axis is symmetrial rotation period, data analysis are mainly seleted in X=0mm ross setion and Y=0.45~0.6mm ross setion whin an reflet the ombustion hamber internal omponent onentration and hemial reation..1 Veloity field analysis Fig. 4 is the veloity of X=0mm ross setion whih is the ombustion hamber s enter setion. The figure shows that primary ombustion zone is full of the whole ombustion hamber, outlet veloity is about 65m/s. Fig. 5 shows veloity nephogram marked primary ombustion zone and bakflow zone. As shown in Fig. 5, bakflow zone exists at the entrane of the ombustion hamber, whih is benefiial to air to enter, improves the gas s burning time and the stability of the flame. Figure 6. Y=0.5mm ross setion veloity nephogram. Temperature field analysis In order to analyze the main ombustion area, selet multiple onseutive ross setion and semi-setion X=0mm for the whole flow field s temperature analysis. The seleted ross setions are Y=0.45mm, Y=0.5mm, Y=0.55mm and Y=0.6mm. Fig. 7~Fig. 1 show the temperature nephogram respetively. As seen in these figures, burning mainly onentrate in the region of the Y=0.4~0.6mm, the mixture of fuel and air ombust suffiiently, the highest temperature is 1800K, the average temperature is about 1000K. Burning area presents a fan-shaped, fit with the shape of ombustion hamber design, and the wall temperature distribute uniformly, even there is no entralized hot point, all of these prove the rationality of the design of the ombustion hamber powerfully. Figure 7. X=0mm ross setion temperature nephogram Figure 4. X=0mm ross setion veloity nephogram Figure 5. Marked primary zone and bakflow zone of X=0mm ross setion veloity nephogram Figure 8. Y=0.45mm ross setion temperature nephogram
Figure 9. Y=0.5mm ross setion temperature nephogram in Fig. 1 and Fig. 14, it is observed that the highest fuel onentration entres on these areas of Y=0.4~0.6mm. Combustion ours in the primary zone, totally aord with the former analysis data of temperature. As the axis distane inrease, burning is ongoing, fuel onentration is getting lower and lower. The outlet fuel mass fration is very small, fuel ombustion effiieny is above 90%, it is proved that the overall design of the ombustion hamber is reasonable. Fig. 15 of O onentration in the setion of Y=0.5mm, it an be seen the onentration is in a triangular shaped diffusion, so as to ensure the stability of ombustion. Fig. 16 and Fig. 17 are for the onentration of ombustion produts of CO and H O omponents, the onentration in the diagrams proves one again the position of theoretial main ombustion zone. Figure 10. Y=0.55mm ross setion temperature nephogram Figure 1. X=0mm ross setion CH 4 onentration Figure 11. Y=0.6mm ross setion temperature nephogram Figure 14. Y=0.5mm ross setion CH 4 onentration Figure 1. Y=0.45~0.6mm D temperature nephogram. Component onentration field analysis Take the fuel inlet setion X=0mm and Y=0.5mm ross setion whih an perfetly present the main ombustion area to analyze the onentration of omponents. Fuel omponents of CH 4 onentration as shown Figure 15. Y=0.5mm ross setion O onentration 4
shorter and the flow resistane inreases exponentially aused by the smaller size of the ombustion hamber. But the hange trend of the ombustion effiieny harateristi is not very different from the ommon ones. It should be pointed out, although through the alulation, the ombustion effiieny an reah 90%, but in fat, due to the miro-sale visous resistane and ombustion residene time of various fators influene, the atual ombustion effiieny inevitably redue..5 Comparative analysis of experimental data Figure 16. Y=0.5mm ross setion CO onentration Beause of the limit of the MEMS proessing and material ost and other aspets of the onditions, at present home and abroad in terms of this new button type turbojet engine ((ombustion hamber diameter in 0mm), there is no atual experiments for omparison, so this paper hooses existing the experimental data of miro turbojet engine (ombustion hamber diameter in 50mm to 100mm) and the theoretial study of Massahusetts Institute of Tehnology in miro turbojet as the ontrast, the seleted data are as follows: (1) a study on tiny annular ombustion hamber by Nanjing University of Siene and Tehnology (NUST)(ombustion hamber diameter is 50mm), [18]. () a miro turbojet engine study by Beijing Institute of Tehnology (BIT) (the outer diameter of the ombustion hamber is 70mm), [19]. () researh on miro turbojet based on MEMS proessing method by the Massahusetts Institute of Tehnology (MIT), [17]. The ompared data are shown as Table 1. Table 1. Simulation and experiment ontrast Figure 17. Y=0.5mm ross setion H O onentration.4 Calulation and analysis of performane parameters of ombustion hamber It an be onluded that the main performane parameters of the ombustion hamber are as follows: - Total pressure reovery oeffiient = P P (4) In the formula (4), P and P respetively represent the average total outlet-pressure and the average total inlet-pressure. By alulating =0.9. -Total volumetri heat intensity Q V 600 mh f u PV =68. kj m Pa h volumetri heat intensity is bigger than ommon turbojet engines, This is beause the volume of the new type of turbojet engine hamber is smaller, surfae-to-volume ratio is bigger, the ombustion residene time is muh Q V NUST BIT MIT BTE 0.98 0.9 >0.9 0.9 QV 895 980 68. 0.9 0.91 >0.9 0.9 From the table, the total pressure reovery oeffiient, volumetri heat intensity and ombustion effiieny and so on is in the reasonable range, it shows that the design of the button type turbine engine design is reasonable. Limited by the MEMS proessing tehnology and experimental onditions, only do some simulation researh work at present, the follow-up will eventually need to go through the test of unity mahine working ondition. The researh of this paper has ertain referene value for the design and improvement of the future ultramiro turbojet engine. 4 Conlusion In this paper, a new ombustion hamber model was designed and simulated based on the onventional miro turbine engine, realizing the integration simulation of working proess in atmospheri environment and getting the following onlusions : (1) The average veloity of the ombustion hamber outlet is 65m/s, the ombustion hamber outlet 5
temperature is about 1000K, fuel and air are mixed evenly, the ombustion is suffiient. () The ombustion hamber is segmentation for six of the same fan ombustion hamber, respetively of fuel supply, effetively guarantee the reliability of the engine's thrust. And there is a reirulation zone at the entrane of the ombustion hamber, whih an effetively promote the stability of the flame. Also the wall temperature is well-distributed, no obvious hot spots. () The simulation data are ompared with the experimental and simulation data of the domesti and foreign engine. The results show that the design of the button type engine is reasonable. (4) One approah to realizing BTE utilizes the miromahining tehnology known as MEMS, the proess impat of these engines will be dependent on the performane levels and the manufaturing osts. It s possible that BTE may be ompetitive with onventional mahines. It will be very useful as power soures for small aero&spae vehiles. Referenes 1. Liang D W, Huang G P. Reent Development and Key Tehniques of Miro Turbine in Centimeter Size. Gas Turbine Experiment and Researh, 17():9-1, (001).. Yuan P Y. The Present Situation and Development Prospet of Miro Turbine Engine. International Aviation, 7 1996. S.W. Janson, H. Helvajian, MEMS, Miroengineering and Aeiospae Systems. AIAA, 99-80. 4. Li C, Fang S Z, Zhang P. Numerial Simulation of Annular Combustion Chamber for Miro Turbine Engine. Journal of Propulsion Tehnology, 5:51-518, (008) 5. Jaobson S A. Aero-thermal hallenges in the design of a miro-fabriated gas turbine engine. AIAA, 98-545. 6. Saburo Y, Kana O. Conept and experiment of a flatflame miro ombustor for ultra miro gas turbine. AIAA, 00-771. 7. Yuan Y Z, Wang L P, Guan L W. Numerial Simulation and Optimization od A Miro Annular Combustor. J Tsinghua Univ (Si&Teh), :198-01+09, (007) 8. Amit, et al. A Six-Wafer Combustion System for a Silion Miro Gas Turbine Engine. Journal of Miro-eletromehanial Systems, 9-4, (000) 9. Stuart A. Jaobson. Aero-thermal hallenges in the design of a miro-fabriated gas turbine engine, Albuquerque: 9 th AIAA Fluid Dynamis Conferene, 98-445. 10. A. H. Epstein, S. D. Serturia, et al. Miro-heat engines, gas turbines, and roket engines-the MIT miro-engine projet. Snowmass Village: 8 th AIAA Fluid Dynamis Conferene, 97-177. 11. C. M. Spadaini, et al. High Power Density Silion Combustion Systems for Miro Gas Turbine Engines, Journal of Engineering for Gas Turbines and Power,: 15: 709-719, (00) 1. P. J. Conelho. Numerial Simulation of a Mild Combustion Burner. Combustion and Flame,,14: 50-518, (001) 1. Denis Veynante, Lu Vervish. Turbulent ombustion modeling, Progress in Energy and Combustion Siene, 8:19-66, (00). 14. Jinsong Hua, Meng Wu, Kurihi Kumar. Numerial Simulation of The Combustion of Hydrogen Air Mixture in Miro-Saled Chambers. Part I: Fundamental study, Chemial Engineering Siene,: 60:497-506, (005) 15. Jinsong Hua, Meng Wu, Kurihi Kumar. Numerial Simulation of The Combustion of Hydrogen Air Mixture in Miro-Saled Chambers. Part II: CFD analysis for a miro-ombustor, Chemial Engineering Siene, 60:507-515, (005) 16. Wen Z, Shi L Y, Ren Y R. FLUENT Fluid Computing Appliations Course, Tsinghua University Press, 1 (009) 17. Alan H. Epstein. Millimeter-Sale, Miro-Eletro- Mehanial Systems Gas Turbine Engines, Journal of Engineering for Gas Turbines and Power, 16:05-6, (004) 18. Wang D. Experimental Study of Miro Turbojet Engine, Nanjing University of Siene and Tehnology, (011) 19. Li C. The Design and Numerial Simulation Performane of Miro Turbojet Engine, Beijing Institute of Tehnology, (008) 6