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- Book ChapterYalnız künye2018Investigation of an optimal operating condition for a micro combustor regarding basic thermophotovoltaic system requirements
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker; Nizetic, S; Papadopoulos, A
In this study, effects of equivalence ratio and thermal power on combustion and emission behaviour of premixed hydrogen air mixtures were numerically investigated by constructing 3D micro combustor models. Combustion behaviour was analysed by examining combustor outer wall and centreline temperature profiles, and convective and radiative heat transfer quantities. Besides, emission behaviour was analysed in terms of centreline NOx profiles and NOx amounts emanated from exhaust of the micro combustor. Regarding these, optimal operating condition with respect to combustion performance and pollutant emissions was investigated by varying thermal power and equivalence ratio. Turbulence model used in this study is RNG k-ε (Yilmaz et al. Int J Hydrog Energy 42:25744–25755, 2017). Multistep combustion reaction process with 9 species and 19 steps was simulated using Eddy dissipation concept model. Data obtained from this study was validated against published experimental data (Tang et al. Int J Hydrog Energy 40:2396–2403, 2015). Results showed that optimal operating condition can be gained at 0.8 equivalence ratio and 1200 ml/min hydrogen flux.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017Effect of different turbulence models on combustion and emission characteristics of hydrogen/air flames
Yilmaz, Harun; Cam, Omer; Tangoz, Selim; Yilmaz, Ilker
This paper aims to present modeling results of hydrogen/air combustion in a micro-cylindrical combustor. Modeling studies were carried out with different turbulence models to evaluate performance of these models in micro combustion simulations by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are Standard k-ε, Renormalization Group k-ε, Realizable k-ε, and Reynolds Stress Transport. A three-dimensional micro combustor model was built to investigate impact of various turbulence models on combustion and emission behavior of studied hydrogen/air flames. Performance evaluation of these models was executed by examining combustor outer wall temperature distribution; combustor centerline temperature, velocity, pressure, species and NOx profiles. Combustion reaction scheme with 9 species and 19 steps was modeled using Eddy Dissipation Concept model. Results obtained from this study were validated with published experimental data. Numerical results showed that two equation turbulence models give consistent simulation results with published experimental data by means of trend and value. Renormalization Group k-ε model was found to give consistent simulation results with experimental data, whereas Reynolds Stress Model was failed to predict detailed features of combustion process.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017Effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air flames
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In this study, effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air mixtures is numerically investigated. An experimentally tested micro combustor geometry is varied by establishing a cavity or a backward facing step or micro channels inside the combustor. Considering effect of combustor geometry on the amount of heat transferred through wall based on outer wall and combustor centerline temperature distributions, combustion behavior is analyzed. Emission behavior is examined by means of mixing conditions, combustion efficiency and maximum temperature value which are highly bound to geometric properties of a micro combustor. Turbulence model used in this study is Renormalization Group k-ε. For turbulence chemistry interaction, Eddy Dissipation Concept model is used. Multistep combustion reaction scheme includes 9 species and 19 steps. Numerical results obtained from this study are validated with published experimental data. Results of this study revealed that combustion in such combustors can be improved by means of quality of mixing process, residence time, combustor centerline and outer wall temperature distributions, conversion rate of input chemical energy to utilizable heat and emanated NOx levels from combustor outlet with proposed geometric variations.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017A numerical study on combustion and emission characteristics of premixed hydrogen air flames
Cam, Omer; Yilmaz, Harun; Tangoz, Selim; Yilmaz, Ilker
Main challenges for micro power generators that utilize combustion process for energy production are inadequate residence time, destructive radical wall interactions and intensified heat loss which are mainly rooted from size limitation of such devices. To achieve high and uniform energy output, and bring in a solution to these challenges in an environment friendly manner without any kind of fundamental modification, effect of equivalence ratio on combustion and emission behavior of premixed hydrogen/air flames is numerically investigated in this study. For this purpose, an experimentally tested micro cylindrical combustor model is constructed and premixed hydrogen/air combustion in this model is simulated by varying equivalence ratio between 0.5 and 1.2 to find an optimal equivalence ratio with respect to drawbacks of micro power generators. Combustion and turbulence models implemented in this study are Eddy Dissipation Concept and Standard k-ε models, respectively. A detailed hydrogen/air reaction mechanism which consists of 9 species and 19 steps is employed to accurately gain insight into combustion process. Simulation results show that as the equivalence ratio decreases; centerline temperature distribution gets a lower value and the place where chemical reactions take place moves downstream. The most uniform temperature distribution is achieved between 0.8 and 1.0 equivalence ratios. The highest NOx formation is at 0.9 equivalence ratio and its mass fraction decreases sharply when the equivalence ratio reduces from 0.9 to 0.5.
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