A Simplified Approach to Model Particle Formation in a Annular Combustion Chamber (original) (raw)

ON THE SUITABILITY OF SOOT FORMATION MODELS IN TURBULENT FLAMES: A COMPARISON STUDY

2006

‫اﻟﻜﺮﺑﻮن‬ ‫ﺣﺒﻴﺒﺎت‬ ‫ﻟﺘﻜﻮن‬ ‫اﻻﺳﺘﺨﺪام‬ ‫ﺷﺎﺋﻌﺔ‬ ‫ﻧﻤﺎذج‬ ‫ﺛﻼﺛﺔ‬ ‫ﻟﻤﻘﺎرﻧﺔ‬ ‫دراﺳﺔ‬ ‫ﻋﻤﻞ‬ ‫ﺗﻢ‬ (Soot) ‫ﻄﺮب‬ ‫اﻟﻤﻀ‬ ‫اﻻﺣﺘﺮاق‬ ‫ﻓﻲ‬ . ‫ﺖ‬ ‫ﻗﻮرﻧ‬ ‫ﺚ‬ ‫ﺣﻴ‬ ‫ﺔ‬ ‫اﻟﻤﻌﻤﻠﻴ‬ ‫ﺎت‬ ‫اﻟﻘﻴﺎﺳ‬ ‫ﻊ‬ ‫ﻣ‬ ‫ﺬﻟﻚ‬ ‫وآ‬ ‫ﻬﺎ‬ ‫ﺑﻌﻀ‬ ‫ﻊ‬ ‫ﻣ‬ ‫ﻮن‬ ‫اﻟﻜﺮﺑ‬ ‫ﺎت‬ ‫ﻟﺤﺒﻴﺒ‬ ‫ﺎﻟﻲ‬ ‫اﻟﻌ‬ ‫ﺰ‬ ‫اﻟﺘﺮآﻴ‬ ‫ذو‬ ‫ﻄﺮب‬ ‫اﻟﻤﻀ‬ ‫ﺮاق‬ ‫ﻟﻼﺣﺘ‬ ‫ﺎذج‬ ‫اﻟﻨﻤ‬ ‫ﺘﻨﺘﺎﺟﺎت‬ ‫إﺳ‬ . ‫ﻧﻤﻮذﺟﻴﻦ‬ ‫ﻋﻠﻰ‬ ‫اﻟﺒﺤﺚ‬ ‫هﺬا‬ ‫ﻓﻲ‬ ‫اﻟﺪراﺳﺔ‬ ‫واﺷﺘﻤﻠﺖ‬ ‫اﻟﻤﺮﺣﻠﺔ‬ ‫ﺛﻨﺎﺋﻲ‬ ‫وﻧﻤﻮذج‬ ‫اﻟﻤﺮﺣﻠﺔ‬ ‫أﺣﺎدﻳﺔ‬ ‫اﻟﻨﻤﺎذج‬ ‫ﻣﻦ‬ . ‫اﻷﺣﺎدﻳﺔ‬ ‫اﻟﻨﻤﺎذج‬ ‫ﺗﻘﻮم‬ ‫ﺣﻴﺚ‬ ‫ﻮن‬ ‫اﻟﻜﺮﺑ‬ ‫ﺎت‬ ‫ﺣﺒﻴﺒ‬ ‫ﻮن‬ ‫ﺗﻜ‬ ‫ﺎب‬ ‫ﺑﺤﺴ‬ ‫ﺔ‬ ‫اﻟﻤﺮﺣﻠ‬ ‫ﺔ‬ ‫اﻟﺜﻨﺎﺋﻴ‬ ‫ﺎذج‬ ‫اﻟﻨﻤ‬ ‫ﺗﻘﻮم‬ ‫ﺣﻴﻦ‬ ‫ﻓﻲ‬ ‫ﻣﺒﺎﺷﺮة‬ ‫ﺑﻄﺮﻳﻘﺔ‬ ‫اﻟﻜﺮﺑﻮن‬ ‫ﺣﺒﻴﺒﺎت‬ ‫ﺗﻜﻮن‬ ‫ﺑﺤﺴﺎب‬ ‫اﻟﻤﺮﺣﻠﺔ‬ ‫ﻴﺔ‬ ‫اﻷﺳﺎﺳ‬ ‫ﺎ‬ ‫اﻟﻨﻮاﻳ‬ ‫ﻜﻞ‬ ‫ﺗﺸ‬ ‫ﻼل‬ ‫ﺧ‬ ‫ﻦ‬ ‫ﻣ‬ (Nuclei Radicals) . ‫وﻟﺘ‬ ‫ﻤ‬ ‫ﺜﻴ‬ ‫ﺔ‬ ‫اﻟﺤﺮآ‬ ‫ﺎل‬ ‫ﻣﺠ‬ ‫ﻞ‬ ‫ﺔ‬ ‫ﻃﺮﻳﻘ‬ ‫ﺘﺨﺪام‬ ‫اﺳ‬ ‫ﻢ‬ ‫ﺗ‬ ‫ﺮاق‬ ‫اﻻﺣﺘ‬ ‫ﺔ‬ ‫ﻏﺮﻓ‬ ‫ﻞ‬ ‫داﺧ‬ (Hybrid Eulerian-Lagrangian) . ‫ﺘﺨﺪام‬ ‫ﺑﺎﺳ‬ ‫ﺎز‬ ‫ﻟﻠﻐ‬ ‫ﺔ‬ ‫اﻟﺤﺎآﻤ‬ ‫اﻟﻤﻌﺎدﻻت‬ ‫وﺣﻠﺖ‬ ‫ﻰ‬ ‫ﻋﻠ‬ ‫ﺪ‬ ‫ﺗﻌﺘﻤ‬ ‫ﺔ‬ ‫ﻃﺮﻳﻘ‬ (Control volume) ‫ﺘﺨﺪام‬ ‫ﺑﺎﺳ‬ ‫ﻮد‬ ‫اﻟﻮﻗ‬ ‫ﻟﻘﻄﺮات‬ ‫اﻟﺰﻣﻦ‬ ‫ﻋﻠﻰ‬ ‫اﻟﻤﻌﺘﻤﺪة‬ ‫اﻟﺘﻔﺎﺿﻠﻴﺔ‬ ‫اﻟﻤﻌﺎدﻻت‬ ‫ﺗﻜﺎﻣﻞ‬ ‫ﺗﻢ‬ ‫ﺣﻴﻦ‬ ‫ﻓﻲ‬ ‫اﻟﻀﻤﻨﻲ‬ ‫ﺷﺒﻪ‬ ‫اﻟﻤﺤﺎوﻟﺔ‬ ‫ﺗﻜﺮار‬ ‫ﻋﻠﻰ‬ ‫اﻟﻤﺒﻨﻴﺔ‬ ‫اﻟ‬ ‫ﺒﻪ‬ ‫ﺷ‬ ‫ﺔ‬ ‫اﻟﻄﺮﻳﻘ‬ ‫ﺔ‬ ‫ﺘﺤﻠﻴﻠﻴ‬ . ‫ﺎت‬ ‫ﺣﺒﻴﺒ‬ ‫ﻮﻳﻦ‬ ‫ﺗﻜ‬ ‫ﺔ‬ ‫ﻋﻤﻠﻴ‬ ‫ﻲ‬ ‫ﻓ‬ ‫ﻮد‬ ‫اﻟﻮﻗ‬ ‫ﺰ‬ ‫ﺗﺮآﻴ‬ ‫دور‬ ‫ﺎدة‬ ‫ﺑﺰﻳ‬ ‫ﻮﻳﺮﻩ‬ ‫ﺗﻄ‬ ‫ﻢ‬ ‫ﺗ‬ ‫ﺔ‬ ‫اﻟﻤﺮﺣﻠ‬ ‫ﺎﺋﻲ‬ ‫ﺛﻨ‬ ‫ﻮذج‬ ‫اﻟﻨﻤ‬ ‫ﺔ‬ ‫دﻗ‬ ‫ﺎدة‬ ‫وﻟﺰﻳ‬ ‫اﻟﻜﺮﺑﻮن‬ . ‫ﻣ‬ ‫ﺗﻄﺎﺑﻖ‬ ‫أﻓﻀﻞ‬ ‫ﻳﻌﻄﻲ‬ ‫اﻟﻤﺮﺣﻠﺔ‬ ‫ﺛﻨﺎﺋﻲ‬ ‫اﻟﻤﻌﺪل‬ ‫اﻟﻨﻤﻮذج‬ ‫أن‬ ‫اﻟﻤﺨﺘﻠﻔﺔ‬ ‫اﻟﻨﻤﺎذج‬ ‫ﺑﻴﻦ‬ ‫اﻟﻤﻘﺎرﻧﺔ‬ ‫وأوﺿﺤﺖ‬ ‫ﻊ‬ ‫اﻟﻤﻌﻤﻠﻴﺔ‬ ‫اﻟﺒﻴﺎﻧﺎت‬ . ‫اﻟ‬ ‫ﻓﺈن‬ ‫ذﻟﻚ‬ ‫إﻟﻰ‬ ‫وﺑﺎﻹﺿﺎﻓﺔ‬ ‫ﺔ‬ ‫ﻣﺨﺘﻠﻔ‬ ‫ﺎﻓﺆ‬ ‫ﺗﻜ‬ ‫ﺐ‬ ‫ﻧﺴ‬ ‫ﺖ‬ ‫ﺗﺤ‬ ‫ﻖ‬ ‫اﻟﺘﻄﺒﻴ‬ ‫ﺪ‬ ‫ﻋﻨ‬ ‫اﻷدق‬ ‫هﻮ‬ ‫اﻟﻤﻌﺪل‬ ‫ﻨﻤﻮذج‬ ‫ﻮد‬ ‫ﻟﻠﻮﻗ‬ . ‫ﺎرﻩ‬ ‫اﻋﺘﺒ‬ ‫ﻦ‬ ‫ﻳﻤﻜ‬ ‫ﻪ‬ ‫ﻓﺈﻧ‬ ‫ﻢ‬ ‫ﺛ‬ ‫ﻦ‬ ‫وﻣ‬ ‫اﻟﻤﻀﻄﺮﺑﺔ‬ ‫اﻻﺣﺘﺮاﻗﺎت‬ ‫ﻓﻲ‬ ‫اﻟﻜﺮﺑﻮن‬ ‫ﺣﺒﻴﺒﺎت‬ ‫ﺗﻜﻮن‬ ‫ﺗﻤﺜﻴﻞ‬ ‫ﻓﻲ‬ ‫اﻷﻓﻀﻞ‬ .

Effect of soot model, moment method, and chemical kinetics on soot formation in a model aircraft combustor

Proceedings of the Combustion Institute

The simulation of turbulent sooting flames requires a host of models, of which the two critical components are the chemical kinetics that describe soot precursor evolution and the description of the soot population. The purpose of this study is to understand the sensitivity of soot predictions in a realistic aircraft combustor to model choices for these components. Two different chemistry mechanisms, three different statistical approaches, and two different soot inception models are considered. The simulations show that acetylene-based soot inception produces very high soot volume fraction, with the soot particles present predominantly in the inner recirculation zone of the swirl-stabilized combustor. The PAH-based nucleation models lead to soot generation in the shear layers emanating from fuel injection. The two advanced statistical approaches (Hybrid and Conditional Quadrature Method of Moments) also show significant differences. While the Hybrid method produces lower soot number density, it also generates larger soot particles due to a faster predicted rate of coagulation. The Conditional Quadrature approach produces much higher soot number density, but its particle sizes are smaller compared to the Hybrid method for all kinetic mechanisms considered. This experimental combustor is strongly dominated by surface growth based soot mass addition. As a result, even if nucleation/condensation rates are different, the final soot mass yield is comparable for PAH-based soot models. These results indicate the importance of not only the chemical mechanism, which may be less important in this surface growth dominated combustor, but also the soot statistical model, to which coagulation and the soot surface area are relatively sensitive.

A simplified model for soot formation and oxidation in CFD simulation of non-premixed hydrocarbon flames

Fire Safety Journal, 2005

A new approach to modeling soot formation and oxidation in non-premixed hydrocarbon flames has been developed and subjected to an initial calibration. The model considers only the phenomena essential for obtaining sufficiently accurate predictions of soot concentrations to make CFD calculations of fire radiation feasible in an engineering context. It is generalized to multiple fuels by relating the peak soot formation rate to a fuel's laminar smoke point height, an empirical measure of relative sooting propensity, and applying simple scaling relationships to account for differences in fuel stoichiometry. Soot oxidation is modeled as a surface area independent process because it is controlled by the diffusion of molecular oxygen into the zone of active soot oxidation rather than being limited by reaction of OH Á radicals with the available soot surface area. The soot model is embedded within a modified version of NIST's Fire Dynamics Simulator and used for a comparison of predicted and measured temperatures, soot volume fractions, and velocities in laminar ethylene, propylene, and propane flames. The

Modeling Formation and Oxidation of Soot in Nonpremixed Flames

Energy & Fuels, 2013

A detailed kinetic mechanism of aromatic growth, particulate formation, and oxidation is presented and is tested in nonpremixed laminar flames of methane and ethylene at atmospheric pressure. Model development is refined in strict connection with new experimental data on the formation and oxidation of high molecular mass compounds and incipient particles. Reaction pathways leading to the formation of incipient particles, their transformation to soot, their oxidation, and the oxidation-induced fragmentation of particles and aggregates have been included by using a multisectional approach for the particle process. Predictions within a factor of 2−3 are obtained for major oxidation and pyrolysis products as well as trace aromatic species and particulate concentrations. The newly developed model predicts the concentration of the particles, their sizes, morphology, and chemical properties in nonpremixed flames of methane and ethylene with a wide range of particle formation without any condition-dependent adjustments to the kinetic scheme. A wide range of particle sizes is covered from nanoparticles formed on the fuel side of the flames to larger soot particles and particle aggregates formed in the flame wings. The trend of the H/C ratio of the particles along the flame axis is also predicted well. It decreases to very low values typical of mature soot particles when large aggregates are produced. The new mechanism for particle oxidation, which includes the oxidation-induced fragmentation of particles and aggregates, has shown the importance of accurate modeling of particle oxidation to correctly predict particle burnout and particle size in nonpremixed flames.

On Numerical Simulation of Black Carbon (Soot) Emissions from Non-Premixed Flames

2014

Soot emissions (PM 2.5) from land-based sources pose a substantial health risk, and now are sub-ject to new and tougher EPA regulations. Flaring produces significant amount of particulate matter in the form of soot, along with other harmful gas emissions. A few experimental studies have pre-viously been done on flames burning in a controlled condition. In these lab-experiments, great ef-fort is needed to collect, sample, and analyze the soot so that the emission rate can be calculated. Soot prediction in flares is tricky due to variable conditions such as radiation and surrounding air available for combustion. Work presented in this paper simulates some lab-scale flares in which soot yield for methane flame mixture was measured under different conditions. The focus of this paper is on soot modeling with various flair operating conditions. The computational fluid dy-namics software ANSYS Fluent 13 is used. Different soot models were explored along with other chemistry mechanisms. The...

A Comparative Performance Study of Soot Formation Models in Methane Elevated Pressure Non-Premixed Flames

This paper presents results obtained from the application of a computational fluid dynamics (CFD) code Fluent 6.3 to modeling of elevated pressure methane non-premixed sooting flames. The study focuses on comparing the two soot models available in the code for the prediction of the soot level in the flames. A standard k-ε model and Eddy Dissipation model are utilized for the representation of flow field and combustion of the flame being investigated. For performance comparison study, a single step soot model of Khan and Greeves and two-step soot model proposed by Tesner are tested. The results of calculations are compared with experimental data of methane sooting flame taken from literature. The results of the study show that a combination of the standard k-ε turbulence model and eddy dissipation model is capable of producing reasonable predictions of temperature both in axial and radial profiles; although further downstream of the flame overpredicted temperature is evidence. With regard to soot model performance study, it shows that the two-step model clearly performed far better than the single-step model in predicting the soot level in ethylene flame at both axial and radial profiles. With a modification in the constant α of the soot formation equation, the two-step model was capable of producing prediction of soot level closer to experimental data. In contrast, the single-step soot model produced very poor results, leading to a significant under-prediction of soot levels in both flames. Although the Tesner's soot model is simpler than the current available models, this model is still capable of providing reasonable agreement with experimental data, allowing its application for the purpose of design and operation of an industrial combustion system.

Modelling of soot particle size distribution function under diesel engine like conditions

In this study the formation and oxidation of soot particles in diesel engine like operating conditions has been examined. A new detailed kinetic soot model for the particle size distribution, using the sectional method in diffusion flames has been developed [1]. A new tool was developed that could be implemented in an existing Computational Fluid Dynamic (CFD) code to get detailed information of soot particles distribution function in the combustor and to localise the regions where soot particles form, grow and are oxidised. Results from the model have been compared to experimental data at high pressure and at high temperature in an optically accessible constant-volume combustion vessel [2]. The investigation has been made for orifice diameters ranging from 69 µm to 180 µm at fixed ambient conditions (i.e. temperature and density). To study the soot particle formation as a function of ambient density, the orifice diameter of 100 µm, and ambient temperature of 1000 K, have been used. The dependence on nozzle orifice diameter is in qualitative accordance with measurements, increased nozzle diameter increase the amount of soot. Source terms for soot particle inception, surface growth, and oxidation describing the interaction of particles with gas phase species are taken from a flamelet library [3,4,5]. This library was generated using a detailed soot model [6,7,8] for the combustion of n-heptane containing 101 species and 841 reactions. Reactions up to four aromatic rings, i.e. pyrene are included in the gas phase aromatic chemistry. The pyrene formation is started from benzene following the HACA (hydrogen abstraction – carbon addition) reaction sequence. The combustion process itself is modelled using a progress variable model for the auto ignition of a diffusion flamelet [9,10,11]. The coagulation of particles is calculated as part of the CFD calculations, based on the mean of the weighted soot mass fractions.