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Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations

หน่วยงาน สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์

รายละเอียด

ชื่อเรื่อง : Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations
นักวิจัย : Watit Pakdee
คำค้น : Mechanical engineering , Chemical engineering , Turbulent , Nonpremixed , Combustion , Wood , Pyrolysis gas
หน่วยงาน : สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์
ผู้ร่วมงาน : -
ปีพิมพ์ : 2546
อ้างอิง : Ph.D., University of Colorado at Boulder, 2003, 157 pages , http://dspace.library.tu.ac.th/handle/3517/4071 , http://dspace.library.tu.ac.th/handle/3517/4071
ที่มา : -
ความเชี่ยวชาญ : -
ความสัมพันธ์ : -
ขอบเขตของเนื้อหา : -
บทคัดย่อ/คำอธิบาย :

The study of nonpremixed or diffusion flames established between wood pyrolysis gas and air is of great interest for wildland fire modeling. The primary source of fuel to largely gaseous flames in an intense wildfire is the gaseous fuel released during high temperature pyrolysis of wood. This fuel is a complex and highly variable mixture of four main gases (CO, H 2 , CH 4 , and CO 2 ). Current approaches to modeling the spread of wildland fire ignore the details of the gaseous combustion. In intense fires, a description of rapid transitions events requires treatment of the combustion of pyrolysis gases and its interaction with the turbulent fire environment. This research is motivated by the desire to develop physically based turbulent combustion submodels for implementation within a larger scale fire spread model. A characteristic wave analysis previously developed to specify boundary conditions for chemically reacting flows with realistic thermodynamic properties is derived with an alternative set of primitive variables. In a multicomponent reacting flow, it is sufficient to consider the time-integration of all species mass fractions, excluding one. This results in a primitive variable vector that contains one less element. The impact of this choice on the resulting characteristic equations and treatment of numerical boundary conditions is presented. The improved accuracy in the treatment of boundary conditions is assessed via three test problems including nonreacting and reacting situations. The method presented is found to provide accurate results as it allows acoustic wave, and vortex to propagate through the domain without discernable reflection. A fully compressible database of turbulent nonpremixed flames of wood pyrolysis gas is developed using direct numerical simulation (DNS). A previously derived reduced 4-step mechanism is used to model the combustion of pyrolysis mixture gas and air. The instantaneous flame surface density (FSD) evolution equation based on the concept of displacement speed is examined. The evolution of the FSD in regions of positive and negative curvature is consistent with predictions based on a one-step chemistry model in the literature. Effects of strain and curvature are analyzed by considering their correlations with reaction rates. Reaction rates are enhanced with increased positive strain rates due to an increase in flame surface area. On the other hand, reaction rates decrease as magnitudes of curvature decrease. A recently developed subgrid-scale reaction rate model was evaluated. In this method, the subgrid-scale reaction rate is represented as the product of the local reaction rate per unit flame area (flamelet consumption rate) and the filtered FSD. A new approach to model the flamelet consumption rate is developed and assessed from DNS data using a spatial filtering operation. In this approach, the filtered scalar dissipation rate [Special characters omitted.] is used as the new parameter, whereas the filtered value of scalar dissipation rate conditioned at stoichiometry [Special characters omitted.] is used in the existing model. Predictions of all the chosen filtered species reaction rates are more accurate when using the newly proposed model. Additionally, a new model for the subgrid-scale variance of scalar dissipation rate [Special characters omitted.] , based on a scale similarity approach, was proposed and examined. The comparison with DNS shows that [Special characters omitted.] is accurately predicted, resulting in a significant improvement over previous models.

บรรณานุกรม :
Watit Pakdee . (2546). Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations.
    กรุงเทพมหานคร : สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์ .
Watit Pakdee . 2546. "Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations".
    กรุงเทพมหานคร : สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์ .
Watit Pakdee . "Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations."
    กรุงเทพมหานคร : สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์ , 2546. Print.
Watit Pakdee . Analysis of turbulent nonpremixed combustion of wood pyrolysis gas via numerical simulations. กรุงเทพมหานคร : สถาบันวิจัยและให้คำปรึกษาแห่ง มหาวิทยาลัยธรรมศาสตร์ ; 2546.