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Chinese Journal of Aeronautics

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Chinese Journal of Aeronautics 25 (2012) 854-863

CFD Study of NOx Emissions in a Model Commercial Aircraft Engine Combustor

ZHANG Mana,*, FU Zhenbob , LIN Yuzhenb, LI Jibaoa aAVIC Commercial Aircraft Engine Co.,Ltd., Shanghai 200241, China

bNational Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics, Beihang University, Beijing 100191, China

Received 11 August 2011; revised 16 September 2011; accepted 23 September 2011

Abstract

Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics (CFD) is utilized as the powerful design approach. In this paper, Reynolds averaged Navier-Stokes (RANS) equations of reactive two-phase flow in an experi-mental low emission combustor is performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literature of a lean direct injection (LDI) combustor. The test rig studied in this paper is called low emission stirred swirl (LESS) combustor, which is a two-stage model combustor, fueled with liquid kerosene (RP-3) and designed by Beihang University (BUAA). The main stage of LESS combustor employs the principle of lean prevaporized and premixed (LPP) concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabili-zation. Detailed numerical results including species distribution, turbulence performance and burning performance are qualita-tively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data at both idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis.

Keywords: air worthiness; computational fluid dynamics; low emission combustor; lean prevaporized and premixed; NOx reduc-tion

1. Introduction1

The foundation of AVIC Commercial Aircraft En-gine Co., Ltd. (ACAE) in Shanghai triggers the hot upsurge of the civil aircraft engine development in China [1]. The low emission combustor study group headed by Professor Lin Yuzhen at Beihang Univer-sity (BUAA) has conducted plenty of experimental tests of the ultra low emission combustor in recent years [2-4]. As the fruits of joint effort with the two

*Corresponding author. Tel.: +86-21-34290808-8213. E-mail address: zhangman@acae.com.cn 1000-9361 © 2012 Elsevier Ltd. doi: 10.1016/S1000-9361(11)60455-X

sides in the context of development of Chinese next generation civil and low emission combustor, nu-merical study of a single sector combustor is carried out in this paper, with the experimental data provided by BUAA.

The single sector combustor developed by BUAA is called low emission stirred swirl (LESS) combus-tor [4], which is a two-stage ultra low emission com-bustor, fueled with liquid kerosene (RP-3). In order to fulfill the next generation pollutant release stan-dard defined by International Civil Aviation Organi-zation (ICAO) [5], the main stage of LESS combustor employs the principle of lean prevaporized and pre-mixed (LPP) concept to reduce pollutant, while a non-premixed flame as pilot source for flame stabili-Open access under CC BY-NC-ND license.

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zation in pilot stage. Based on this test rig, Fu, et al. firstly conducted experimental study of the ignition performance of this chamber while assisted by some numerical simulation analysis [4]. Their work shows that the ignition position along the main stream di-rection has little influence on the lean ignition boundary of the whole chamber. This encouraging result indicates that LESS combustor has pretty good stabilization performance working under the lean burn condition.

Although some similar LPP concept combustors have been developed for many years, such as twin annular premixed swirler (TAPS) family of low NOx combustor developed by General Electric Aircraft Engines (GEAE) [6-8], there is still a lack of funda-mental understanding of LPP combustion mechanism. The latest studies focusing on the combustion mechanism of LPP reported is conducted by Dha-nuka, et al. [9], who use planar laser-induced fluores-cence (PLIF) to investigate unsteady flow character-istics with the motivation to reveal the inside physics of flame-flame interaction and to provide some sup-ported data for further computational fluid dynamics (CFD). Their work shows that the combustion inter-action of the main stage and pilot stage would be the source of combustion instability, and generates con-siderable unsteady turbulent phenomena. However, the influence of the flame-flame interaction in LPP scheme on NOx formation is still absent at current stage.

Experimental investigations of the complicated flow physics of the premixed combustion and the pilot flame are made more difficult due to the highly transient nature of the processes and their interac-tions. Thus the interaction of the pilot flame with premixed combustion is still an outstanding issue and needs further investigation as it has strong im-plication on the combustor performance and NOx reduction.

Developments of CFD techniques in the last 30 years have enabled more complicated engineering cases to be simulated. The numerical approaches to purely turbulent diffusion flame and perfectly pre-mixed flame are rapidly developing in the context of the studies of industrial combustion [10]. However, there is still a threshold lying on the development road of numerical simulation of LPP combustor. Because of premixed flame, partially premixed flame and non- premixed flame coexisting simultaneously in one unique chamber, a unified flame model which could handle these entire different combustion regimes seems much more necessary [11].

Recent progress developed by Veynante and Legier, et al. [12-13] shows that their extended flame model with the hypothesis that turbulence brings effects of thicken flame surface, could treat both partially premixed and purely premixed flames with some reasonable results. Its application to turbulent spray combustion for air-craft combustors has seen some successes [13]. Thus, it

is still believed that CFD could provide in-depth analysis where experimental study cannot go at current stage.

This paper presents a joint effort between ACAE and BUAA to study the combustion characteristics and NOx formation mechanism of the LESS com-bustor. To achieve better understanding on the in-teraction of LPP combustion and pilot flame under the lean burning conditions, Reynolds averaged Na-vier-Stokes (RANS) equations of reactive two-phase flow are performed. Results are compared against experimental data with good agreements. Prelimi-nary results of the flame structure are shown in this paper, which indicates that LESS combustor has large potential to reduce NOx emission. The flame stabilization mechanism and NOx reduction efforts are also discussed with in-depth analysis.

2. Numerical Approach

Numerical simulation is carried out in ACAE. The Reynolds averaged governing equations are discretized numerically by a finite volume approach. High solu-tion differencing scheme which is a hybrid of 1st and 2nd order is employed. Kerosene is modeled by the mixture of 40% of n-C10H22 (decanenormal) and 60% of TMB-C9H12 (tetramethyl benzidine), thus the averaged molar mass is about 128.8 g/mol. In this work, Sauter mean diameter (SMD) distribution close to downstream of the fuel nozzle obtained by fuel droplets mass weighted rate is described instead of direct modeling of the primary breakup processes of droplets. However, the spray fuel nozzle inlet condi-tions are also given by the half cone angle (45°), the injection mass, injection direction, initial temperature and the initial velocity. Atomization processes induced by aerodynamics inside the swirler cup are modeled by enhanced Taylor analogy breakup (ETAB) breakup model [14]. Detailed discussion with the application of the atomization model could be referred to the work of Raju [15] and Zhang, et al. [16-18].

Subsonic condition is imposed at the inflow by specifying the flow mass rate and temperature. While only for the main stage inflow boundary, the mass fraction ratio of fuel is also added with the assumption of perfectly premixing. The pressure information is given on the outflow boundary. The entire wall in the combustion chamber is treated as impermeable and no-slip. The droplets and wall interaction are neglected in this paper due to lack of trustable model [19].

2.1. Turbulence-combustion interaction model

The extended coherent flame model (ECFM) [20]

used in this paper for turbulence and combustion in-teraction is a hybrid model which combines classic flame surface density model (FSDM) with laminar flamelet model. The coupling of ECFM with the

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flamelet model for effects of non-premixedness ex-tends the range of applicability of the model to deal with different combustion regimes inside the gas tur-bine combustor.

Laminar burning velocity of kerosene which is modeled by SL in ECFM is obtained from experi-mental test data given by Eberius, et al. [21]. However, because the original test data only concentrate within the range of equivalence ratio of 0.9 to 1.4, SL in the entire flammability range and under any operation conditions is extended by a fifth order polynomial correlation and an experiential correlation proposed by Metghalchi and Keck [22], which can be written as

L L,refref ref

T pS ST p

α β⎛ ⎞ ⎛ ⎞

= ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

(1)

2.98 0.8

3.08 0.22α φβ φ

= −⎧⎨ = − +⎩

(2)

where subscript “ref” means reference condition, SL is the base value of burning velocity, α the preheat de-pendency exponent, β the pressure dependency expo-nent, T the temperature, p the pressure and φ equiva-lence ratio.

Laminar flame thickness is model by Blint’s ap-proximation [23], which can be written as

0.7b

L u2 TT

δ δ⎛ ⎞

= ⎜ ⎟⎝ ⎠

(3)

where δL is the laminar flame thickness, δ the diffusive flame thickness, bT burnt fluid temperature and uT unburnt fluid temperature.

The turbulent flame stretch accounts for the increase of flame surface area due to stretching and wrinkling of the flame front under turbulence. For ECFM this effect is described by the intermittent turbulent net flame stretch (ITNFS) model proposed by Meneveau and Poinsot [24],

tt

L L

,KluK

kSεΓ

δ⎛ ⎞′

= ⎜ ⎟⎝ ⎠

(4)

where Kt is the turbulent time scale, u′ the mean tur-bulent velocity fluctuation, lt the integral length scale of turbulence, k the turbulent kinetic energy, ε the tur-bulent dissipation rate, and KΓ an efficiency function taking into account the ability of all vortices to wrinkle the flame.

2.2. NOx emission modeling

The current approach to model NO production is solving the mass transport equation for the NO spe-cies, taking into account convection, diffusion, pro-

duction and consumption of NO and the related spe-cies.

As thermal NOx formation plays a dominate role in the whole different mechanisms, only thermal NOx is considered in this paper. The mechanism of thermal NOx formation is based on the extended Zel’dovich mechanism, which consists of the following equa-tions as described by Bowman [25] and Hanson and Salimian [26]:

2

2

N O NO NN O NO ON OH NO H

+ ⇔ +⎧⎪ + ⇔ +⎨⎪ + ⇔ +⎩

(5)

3. Validation

Numerical approach is validated by a lean direct in-jection (LDI) system developed by NASA Glenn Re-search Center. Detailed structure and test condition can be referred to Refs. [27]-[30]. Figures 1-2 give the geometry and the mesh solution of LDI test rig. The CFD and experimental data comparisons are shown in Figs. 3-4. From the comparison of both temperature and the velocity distribution, it shows that the adopted numerical approach in this paper gives a reasonable prediction of the lean burn system.

Fig. 1 Geometry of LDI swirler.

Fig. 2 Mesh of LDI combustor in CFD.

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Fig. 3 Comparison of temperature distributions.

Fig. 4 Comparison of velocity distributions.

4. LESS Combustor Test Rig Simulation

4.1. LESS combustor test rig

LESS combustor studied in this paper is designed by BUAA, which is a two-stage ultra low emission com-bustor, fueled with liquid kerosene (RP-3). The main stage of LESS combustor employs the principle of LPP concept to reduce pollutant, while a non-premixed diffusion flame is used as pilot source for flame stabi-lization in pilot stage, which can be seen in Fig. 5. The test rig of LESS is a single annular layout. The combus-tor channel height, overall length and effective length (defined as the ratio of combustor volume to combustor reference area) are 120, 190, 160 mm, respectively.

The pilot stage is similar to a typical swirl cup scheme which is equipped with a pressure swirl at-omizer in the center line and with two dual counter- rotating radial swirlers for aerodynamic atomization. The pilot flame forming inside of the swirl cup is a fuel rich diffusion flame, which has evident advan-tages of ignition and flame stabilization. The main stage surrounding coaxially with the pilot stage in-

cludes one annulus as premixer formed by two steel pipes of different radius and 14 plain orifice atomiz-ers with 14 small dual counter-rotating radial swirlers arranged uniformly on the dome of the annulus. There are a number of straight and inclined holes on the surfaces of the main stage annulus. Furthermore, the air injecting through the inclined holes can form swirl within the annulus, and hence the fuel can be premixed with the air and prevaporized in the annulus by jet stirred swirl before entering the combustor chamber, thereby leading to the main premixed flame. This therefore allows, to some degree, fuel/air premixing within the passages with attendant reduction in NOx and im-proved combustor exit temperature quality.

The mass flow distribution for the dome inlet air and the cooling air is about 7 to 3, while the mass flow ratio of main stage to pilot stage is about 6.64 to 1. In CFD work, wall film cooling holes are modeled by sev-eral equal area slots for mesh saving (see Fig. 5(c)).

Fig. 5 Sketch and model of LESS combustor.

4.2. Grid independency study

Three different gird sizes have been performed

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before the calculation of LESS test rig (see Fig.6 and Table 1). Comparisons of resolution of different grids show that all three mesh size cases have satisfactory consistency with the experimental data. Considering the accuracy and time cost of both results, it is be-lieved that the gird size of 1.0 million is accurate enough for RANS, thus this mesh size has been taken as the grid for all subsequent calculations.

Fig. 6 Grid independency study of test rig.

Table 1 Predicted NOx compared with experimental data for grid independence study

Grid size 0.5 million

1.0 million

2.5 million

Experimental data

NOx/10−6 300 319 320 325

CPU number 24 48 120 N/A Total CPU

time/h 6 10 16 N/A

4.3. Pollutant prediction validation

Several numerical simulated conditions have been performed to study LESS combustor while some of them are compared by experimental data provide by BUAA (see Table 2). Subscript “M” and “P” mean main stage and pilot stage relatively, and “expt” and “CFD” mean results from experimental test and CFD prediction.

Table 2 Numerical simulated case for LESS study

Case Conditions

1 2 3 4 5 6

φM 0 0 0.62 0.75 0 0.73 φP 0 0.8 0.8 0.8 3.0 0.52

pM/MPa 2.2 2.2 2.2 2.2 0.45 3.33 TM/K 663 663 663 663 524 840 NOexpt/10−6 N/A N/A 325 418 47 N/A NOCFD/10−6 N/A 15 319 409 48 429 Tolerance/% N/A N/A 1.8 2.2 2.1 N/A

In Table 2, Case 3, Case 4 and Case 5 have been

tested by experiments previously conducted in Low Emission Ground Test Laboratory of BUAA and stand for the full power operation conditions (Case 3 and Case 4) and idle condition (Case 5) of LESS combus-tor according to the limits of ground test capability. Case 6 stands for the real working condition during the engine takeoff, while Case 1 and Case 2 are used to compare with Case 3, Case 4 and Case 5 to find the differences with the variance of equivalence ratio of the main stage.

From the validation of predicted NOx amounts, we can see that numerical approach adopted in this paper shows good agreement with experiments, thus it could bring us the credible resolution of the inner flow field inside the chamber.

Furthermore, another aspect should be emphasized is that the NOx emission of Case 6 which stands for the engine takeoff also shows a limited value which still lowers the standard by 60% margin compared with CAEP6. The encouraging results mean that LESS cham-ber has large potential to reduce the NOx emission.

4.4. Pilot stage burning characteristics

Case 2 and Case 5 are compared to study the effects of variance of equivalence ratio of pilot stage. Figure 7 gives the temperature distribution on the center plane

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of the chamber; Fig. 8, streamline distribution while Fig. 9, the shear strain rate distribution. It should be noted that each figure contains two parts separated by the center dotted horizontal line of the chamber. The upper pattern in each figure is for Case 2 and the lower one is the description of Case 5.

Fig. 7 Temperature distribution under the conditions of Case 2 and Case 5.

Fig. 8 Streamline distribution under the conditions of Case 2 and Case 5.

Fig. 9 Shear strain rate distribution under the conditions of Case 2 and Case 5.

From the comparison of different equivalence ratios of the pilot stage, it shows that significant flow struc-tures can be caused due to the variance pilot stage fuel/air ratio. For the case of pilot stage under lean burn condition, although combustion could be main-tained, the pilot diffusion flame is weak. The burning area compressed by main stream recirculation fluid motion is adjacent to the dome. The pilot flame nearly burns in the shear layer between the main and the pilot stage.

The combustion intensity is improved with the in-

crease of pilot stage fuel/air ratio, which can be proved by temperature contour in Fig. 7. Large area of high temperature is shown in the center of the chamber, where the recirculation vortex core coincides with it. Due to the nature of diffusion combustion of the pilot stage, the maximum temperature value is achieved along the line of equivalence ratio of 1.0.

4.5. Pilot and main stage interaction

As mentioned above, the lasted study of LPP main stage interacted with the pilot flame is reported by Dhanuka and his fellows [9]. Due to lack of sufficient data of the reaction fluid structure at current stage, the PLIF results in their work are used here as a reference for LESS combustor under the conditions of pilot and main stage interaction (see Fig. 10).

Fig. 10 Numerical prediction of flame structure compared against PLIF results.

It can be seen that although the working conditions of LESS combustor have some discrepancy with Dha-nuka’s work [9], the flame structure for the pilot and main stage interaction looks similar.

Figure 10 shows that the lowest temperature occurs at the center of the pilot spray, where conditions are so fuel-rich that combustion is not possible. The flame is located where the equivalence ratio around the value is 1.0, which shows the nature of diffusion flame. Also, it can be seen that the main flame has a rounded shape and it appears that the main flame has some distance downstream of the main stage.

For the purpose of evaluating the effects of equiva-lence ratio of main stage, Case 3 and Case 4 are com-pared. Detailed difference of Case 3 and Case 4 can be referred to Figs. 11-13. Figure 11 gives the tempera-ture contour on the center plane of the chamber; Fig. 12, streamline distribution while Fig. 13, the shear

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strain rate distribution.

Fig. 11 Temperature distribution under the conditions of

Case 3 and Case 4.

Figure 11 shows that the area of equivalence ratio between the values of 1.0 to 0.72 has been extended in both Case 3 and Case 4 than the condition of only pilot flame on (refer to Case 2 in Fig. 7). This phenomenon must be influenced by the main stage. Meanwhile, within this region, the temperature gradient dissipates along the streamline, which is also the exclusive fea-ture belonging to the diffusion flame. However, the exact location of the interaction of the main flame and pilot flame is difficult to determine in the current CFD technique and Dhanuka’s work because of the lack of useful approach to separate the two kinds of combus-tion. The only judgment can be made is that inside the round shape adjacent to the swirl cup (equivalence ratio is 1.0), pilot flame holds the dominate position, and within the region of equivalence between the value of 0.72 and 0.68, pilot flame and main stage flame interaction take place.

Fig. 12 Streamline distribution under the conditions of Case 3 and Case 4.

What can be easily distinguished between Case 3 and Case 4 in Fig. 12 is the area of equivalence ratio from 0.72 to 0.68. As for Case 4, this area overlaps with the large scale recirculated motion, which should bring additional resident time for the fuel air mixture, thus inducing higher value of NOx formation. This point of view could be evidenced in Section 4.6.

Figure 13 gives the illustration of where the high intensity mixing process takes place. In the pilot and combustion interaction flow field, two evident mixing regions can be easily recognized. One is the shear

layer between the main stream and the pilot stream, and the other is the main stream mixed with the corner vortex. Furthermore, Figs. 11-12 show that the pilot stage fuel reacts with air along the shear layer as the reason for scalar transport within it.

Fig. 13 Shear strain rate distribution under the conditions

of Case 3 and Case 4.

4.6. NOx formation mechanism

Figures 14-17 present further information about the reacted species distribution inside LESS chamber to study the NOx formation mechanism. Figure 14 is the O radical mass fraction distribution contour, Fig. 15 the thermal NO reaction rate distribution contour, Fig. 16 the resident time of the fluid motion, and Fig. 17 the NO mass fraction contour.

Fig. 14 O radical mass fraction distribution in Case 3 and

Case 4.

Fig. 15 Thermal NO reaction rate distribution in Case 3

and Case 4.

From Fig. 14 it can be seen that O radical concen-trates in the region of high temperature level, i.e., along the equivalence ratio from 1.0 to 0.72 and dissi-pates quickly after the equivalence ratio below the

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value of 0.68 due to main decomposition process of O2 accompanied by heat absorption. Thus, the NO gen-eration process is followed by the accumulation of O radical, where high intensity of thermal NO reaction rate taking place coincides with the maximum amount of O mass fraction.

As we know, the net generation amount of NO is not only controlled by the chemical reaction rate, but also by the resident time in a flowing fluid. However, at current stage, the resident time scale of a moving fluid is hard to measure, especially in the case with complex geometry. In order to measure the resident time scale at any location inside the chamber, a novel approach has been developed in this work, as described below.

In CFD work, the Courant number (or called CFL number) is defined as

CFL

xU tC

xΔ

=Δ

(6)

where Ux is the local velocity, ∆x the local girds space, ∆t the time step defined artificially, and CCFL the Cou-rant number which could be easily obtained from any CFD codes, so the resident time τ could be defined by

CFLx

x tU C

τ Δ Δ= = (7)

According to the definition of resident time in this work, the entire fluid resident time scale based on each calculated node can be illustrated in Fig. 16.

Fig. 16 Resident time in Case 3 and Case 4.

Figure 16 shows that high value of resident time not only concentrates inside the core of the recirculation region, but also forms in the region next to the dome, where even the highest value of resident time in the chamber is. Referred to streamline distribution in Fig. 12, it can be easily found that due to the streamline turn-ing around, the value of resident time increases. From the mathematical point of view, we can say that the highest value of resident time takes place at Ux→0.

Considering the joint efforts of both reaction rate and the resident time, the NOx mass distribution is eas-ily understand (see Fig. 17). The overlapping region of both high level of NO chemical rate and the resident time controls NO mass rate. In this LESS chamber, one major location is between the equivalence ratio from 1.0 to 0.72 and the other one coincides with the

vortex core. It should be noted that both these regions are based on the zone of Ux equal to 0.

Fig. 17 NO mass fraction distribution in Case 3 and Case 4.

4.7. Analysis of reaction principle of LESS com-bustion

In terms of the above analysis including the pilot stage burning characteristics and pilot-main stage in-teraction feature, the mechanism of the pilot and main stage interaction could be summarized (see Fig. 18). Figure 19 gives the NOx formation mechanism in these fluid structures.

Fig. 18 Fluid structure inside of LESS combustor.

Fig. 19 NOx formation mechanism inside of LESS com-bustor.

It can be seen that Z.1 (Zone 1) stands for the pilot flame domination area, and Z.3 (Zone 3) is the loca-tion where the major amount of premixed combustion takes place. However, the transition area from pilot flame to premixed combustion is located in the region of Z.2 (Zone 2). However, it is still hard to give a

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quantitative measurement of level set of the interaction between pilot flame and the main stage in this work.

As the NOx formation mechanism illustrated in Fig. 19, the overlapping region of the higher value of tem-perature and the resident time will be the place where NO mass fraction achieves its maximum. The qualita-tive analysis of this work indicates that the maximum value of NOx formation appears in the region adjacent to the zero value axial velocity iso-surface. From this point of view, with the motivation to design the low NOx emission combustor, the basic design principle lies in the organization of this large-scale recirculation fluid motion.

5. Conclusions

Some findings of this work could be summarized as follows:

1) NOx predicted by CFD under the condition of en-gine takeoff indicates that LESS combustor has large potential to reduce NOx emission.

2) The flow pattern under the conditions of pilot stage and main stage interaction has been clearly re-solved by the current CFD approach, which is verified by PLIF results in open literature.

3) The principles of the fluid motion and NOx for-mation of LESS combustor have been illustrated in this work. Reaction zones could be divided into three parts inside of the LESS chamber under the condition of the pilot stage and main stage co-working.

4) The overlapping region of the higher value of temperature and the resident time is the place where NO mass fraction achieves its maximum. The qualita-tive analysis of this work indicates that the maximum value of NOx formation appears in the region adjacent to the zero value axial velocity iso-surface.

5) With the motivation to design the low NOx emis-sion combustor, the basic design principle lies in the organization of this large-scale recirculation fluid mo-tion.

6) It is still hard to give a quantitative measurement of level set of the interaction between pilot flame and the main stage in this work, which is critical for the design of LPP low emission chamber. Further efforts will be made in the coming research.

Acknowledgements

The author appreciates the technical guidance from senior engineer, Mr. HU Zhengyi of BUAA. The dis-cussion with Dr. WANG Xiaofeng and LI Lin of BUAA is also greatly acknowledged.

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Biographies:

ZHANG Man visited University of Southampton for one-year co-education from 2008 to 2009 and received Ph.D. degree at Northwestern Polytechnical University in the year of 2010. In his career now, his position is the deputy director of Department of Combustion Systems in R&D Center of ACAE. His main research interest is the numerical simula-tion of combustion, and he is participating in the project of CJ-1000AX low-emission combustor design. E-mail: zhangman@acae.com.cn FU Zhenbo is a Ph.D. candidate in Beihang University. He has been studying the aero-engine combustor since 2008. His main research fields focus on the design of aero-engine low emission combustor and the mechanism of combined com-bustion. He is credited with four patents on low emission combustor design, and three international and national pub-lications. LIN Yuzhen received Ph.D. degree from Beihang University in 1997. He is a professor of Beihang University since 2007. He has been engaged in the research of aero-engine com-bustor for almost 20 years since he suddied his master degree. Now his research interests are mainly the aero-thermal dy-namics, time-space evolution of combustion, and combustion instability of low emission combustor. He is credited with 15 patents on combustor design, and 80 international and na-tional publications.