application of computer fluid dynamics (cfd) to predict...

การประชุมวิชาการ ครั้งที่ 8 มหาวทิยาลัยเกษตรศาสตร วทิยาเขตกําแพงแสน

1586

การประยุกตใชการคาํนวณพลศาสตรของไหลจําลองในการทํานายปรากฏการณการถายโอน ในหองเผาไหมของกาซ

Application of Computer Fluid Dynamics (CFD) to Predict Transport Phenomena in Gaseous Combustion Chambers

นพพร รัตนชวง1 นัฐ กองแกว1 ทศพร อถากุล1 และสมบูรณ สุขพรรณเจริญ1

Nopporn Ruttanachung1, Nut Kongkaew1, Totsaporn Athakun1 and Somboon Sukpancharoen1

บทคัดยอ

การคํานวณพลศาสตรของไหลจําลอง (CFD)หลายมิติจากการสังเคราะหกาซที่ไดมาจากกระบวนการการ

เผาไหมภายใตเงื่อนไขตางๆ ผลของการสรางแบบจําลองถูกทํามาเปรียบเทียบเพ่ือทํานายขอมูลการทดลองที่

สอดคลองกัน โดยทํานายและวัดคาอุณหภูมิในหองเผาไหม ความเร็ว และเศษสวนมวลไดเปนอยางดี ซึ่งสรุปไดวา

การจําลองเศษสวนมวลที่มากที่สุดในสภาวะที่ไมเปลี่ยนแปลงเมื่อเวลาผานไปของ CH4, O2, CO2และ H2O คือ

1,0.230,0.145 และ 0.119 ตามลําดับ และในสภาวะที่มีการเปลี่ยนแปลงเมื่อเวลาผานไปคือ 1,0.230,0 และ 0

ตามลําดับ รูปแบบของซีเอฟดีสามารถนําไปวิเคราะหในกระบวนการเผาไหมไดอยางดีและพัฒนาตอไปจนเปน

ประโยชนสําหรับการจําลองในการเผาไหม

คําสําคัญ : การคํานวณพลศาสตรของไหลจําลอง (CFD) กระบวนการการเผาไหม ปรากฏการณการถายโอน

ABSTRACT

A multidimensional computational fluid dynamics (CFD) simulation of a constructed gaseous was

performed to evaluate the combustion of syngas in initial compositions under conditions. The modeled

results were validated by comparing predictions against corresponding experimental data. The predicted

and measured in-cylinder temperature, velocity magnitude and mass fraction data were in good

agreement. The results show that the simulated mass fraction of the maximum steady state conditions of

CH4, O2, CO2 and H2O are 1, 0.230, 0.145 and 0.119, respectively. Transient conditions are 1,0.230, 0

and 0, respectively. The present CFD model captured the overall combustion process well and could be

further developed into a useful tool for syngas-engine combustion simulations.

Key Words : CFD simulation, Gaseous Combustion, Transport Phenomena

E-mail : [email protected]

1 โครงการจัดตั้งสายวิชาฟสิกส คณะศลิปศาสตรและวิทยาศาสตร มหาวทิยาลัยเกษตรศาสตร นครปฐม 73140

Department of Physics, Faculty of Arts&Sciences, Kasetsart University, Nakorn Pathom 73140


1587

INTRODUCTION Computational fluid dynamics (CFD) is a powerful tool for the calculation of fluid flow. The

prediction of the flow field in the investigated combustion chamber is a great challenge because of the

need to account for homogeneous and heterogeneous reactions, phase changes, turbulent flow, as well

as convective and radiative heat transfer.

With the appropriate calculation models at hand the CFD results can be used for the optimization of

the combustor geometry and combustion parameters regarding the improvement of efficiency.

Advanced power systems that are projected to achieve high efficiency and low emissions rely on

synthesis gas (syngas) as a key intermediate energy carrier. Syngas consists of combustible gases

composed of mainly carbon monoxide (CO), hydrogen (H2), and methane (CH4), and non-combustible

gases composed of mainly nitrogen (N2), carbon dioxide (CO2) and water vapor (H2O).

Advanced reciprocating engines are considered a potential means of converting syngas into

power because of their role in distributed energy (DE) production and their combination of high efficiency

and low cost. Mixtures of H2 and CO have high antiknock behaviour and therefore could serve as fuels for

internal-combustion engines. However, the addition of H2 to CO or CH4 tends to increase combustion

temperatures and nitric oxide (NO) emissions under stoichiometric conditions. Therefore, such mixtures

are more appropriate for lean-burn applications, where combustion temperatures are moderated by

excess air.

MATERIALS AND METHODS 1. Materials

1.1 Personal Computer (PC):

- CPU [Intel(R) Pentium(R) Dual CPU T2310 1.46 GHz

- 2.00 GB of RAM

- 320 GB of Hard disk

1.2 Operating System: Microsoft Window 7 Professional

1.3 Software: Ansys Fluent 12.1, SolidWork 2011

2. Methods 2.1 Design of the combustion tube 0.5 m long, 2 m diameter cylindrical nozzle diameter of

0.01 m as shown in Figure 1.


1588

Figure 1 Combustion of Methane Gas in a Turbulent Diffusion Flame Furnace.

The area has 1615 quadrilateral cells to the grid and boundary conditions as shown in Figure 2.

Figure 2 The Quadrilateral Grid for the Combustor Model.

The simulation conditions with the engine specifications used in this study are given in Table 1.

Table 1 Engine specification and simulation conditions.

Simulation conditions Values

Engine type

Combustion area

Combustion system

Combustion chamber

Engine speed

Injection system

single-cylinder

0.5x2 m

Direct injection

Shallow dish

1000 rpm

Common-rail

The combustion will be modeled using a global one-step reaction mechanism. The reaction equation

(1) is:

CH4 + 2O2 ------> CO2+2H2O (1)

2.2 Calculated by using Computer Fluid Dynamic (CFD) by setting the wall temperature from

300 K, the speed of the air supply into the pipeline to burn 1.5 m/s and the speed of methane gas

charged tubes burned 120 m/s. The model used the energy equation in the equation (2) and k-epsilon is

shown in equation (3).


1589

The mass-averaged temperature will be computed in equation (4).

The area-weighted velocity-magnitude average will be computed in equation (5).

RESULTS AND DISCUSSION The experiments were performed to predict the two conditions in steady state and transient

conditions. It is presented in four profiles:

1. Iteration Profile

2. Temperature Profile

3. Velocity Magnitude Profile

4. Mass Fraction for CH4, O2, CO2 and H2O

1. Iteration Profile

Figure 3 The graph shows residuals from the process, (a) Steady state (b) Transient.

( ) ( )( ) ( ) αβ

ααβαβαβαααααααα λρρ SQhhThUrhrt

pN

SS ++Γ−Γ=∇−•∇+∂∂ ∑

=

++

1

( ) ( ) ρεσμμρρ

−+⎥⎦

⎤⎢⎣

⎡∇⎟⎟⎠

⎞⎜⎜⎝

⎛+∇=•∇+

∂∂

kk

t PkUktk

∫∫

•

•=

Adv

AdvTT rr

rv

ρ

ρ

∫= vdAA

v 1r

(2)

(3)

(4)

(5)

(a) (b)


1590

Figure 4 Convergence history of Mass Flow Rate on the pressure-outlet, (a) Steady state (b)Transient.

2. Temperature Profile

Figure 5. Contours of Static Temperature, (a) Steady state (b) Transient

Figure 3 and Figure 4 shows the repeatability of the calculation to find the answer and Figure 5

shows the temperature in the combustion chamber in a state that has a steady state temperature

distribution in the combustion chamber to isolate than the transient.

3. Velocity Magnitude Profile

Figure 6 Vector of Velocity Magnitude, (a) Steady state (b) Transient.

Figure 6 shows the velocity magnitude explained that both the state and the distribution of

velocity magnitude similar but steady state greater values than transient conditions as shown in Table 2.

(a) (b)

(a) (b)

(a) (b)


1591

4. Mass Fraction for CH4 , O2 ,CO2 and H2O

Figure 7 Contours of Mass fraction of CH4, (a) Steady state (b) Transient.

Figure 8 Contours of Mass fraction of O2, (a) Steady state (b) Transient.

Figure 9 Contours of Mass fraction of CO2, (a) Steady state (b) Transient.

Figure 10 Contours of Mass fraction of H2O, (a) Steady state (b) Transient.

(a) (b)

(a) (b)

(a) (b)

(a) (b)


1592

Figures 7, 8, 9 and 10 shows the contours of mass fractions of CH4, O2, CO2 and H2O,

respectively. Figure 7 shows that they are similar in both states and in Figures 8, 9 and 10, there is a

difference in the steady state conditions that have been described as the distribution of mass transfer

than in the transient state in which the values in Table 2.

Table 2 Represents the maximum value of the minimum values.

Steady state Transient Conditions

Profile Min Max Min Max

Static temperature(K)

Static pressure(kPa)

Velocity Magnitude(m/s)

Mass fraction of CH4

Mass fraction of O2

Mass fraction of CO2

Mass fraction of H2O

299.9999

-22.80333

0

0

0

0

0

302.797

141.7985

122.35427

1

0.2300001

0.145792

0.1193076

299.9997

-20.52435

0

0

0

0

0

300.0002

133.1841

121.7749

1

0.23

0

0

CONCLUSION

Computer Fluid Dynamics (CFD) can be used to predict the profile (temperature, velocity

magnitude, mass transfer etc.) in the combustion chamber more efficiently and robustly, which can be

used in industry to design a furnace to burn performance. It can be used for both steady state and

transient conditions.

ACKNOWLEDGEMENTS

This work was supported by the Department of Physics, Faculty of Arts&Sciences, Kasetsart

University.

REFERENCES

Rao AD, Samuelssen GS, Robson FL, Geisbrecht RA.Powerplant systemconfigurations for the 21st

century, vol. 1. ASME Int. Gas TurbInst, Turbo Expo IGTI; 2002. 831.

Wang L, Weller CL, Jones DD, Hanna MA. Contemporary issues in thermal gasification of biomass and its

application to electricity and fuel production. Biomass Bioenergy 2008;32:573-81.


1593

Shudo T, Takahashi T. Influence of reformed gas composition on HCCI combustion engine system fueled

with DME and H2-CO-CO2 which are onboard-reformed from methanol utilizing engine exhaust

heat. Trans JSME B 2004;70:2663-9.

Karim GA. Combustion in gas fueled compression: ignition engines of the dual fuel type. J Eng Gas Turb

Power 2003;125:827-36.

application of computer fluid dynamics (cfd) to predict...

Documents