A Numerical Prediction of Stabilized Turbulent Partially Premixed Flames Using Ammonia/Hydrogen Mixture

The objective of this work is to computationally assess the performance of a carbon free ammonia-hydrogen mixture when burnt in a gas turbine like combustor. Recently, utilizing ammonia as an alternative carbon-free fuel for future power, industry applications and achieving clean energy attracted enormous interest. Pure ammonia oxidation is facing many challenges such as high NOx emissions, high ignition energy, slow reactivity and lower laminar flame speeds. Therefore, the use of ammonia/hydrogen mixture provides flame stability and increasing flame speed. In this manuscript a numerical study for a new swirl stabilized combustor for oxidizing ammonia/hydrogen mixture. Numerical two dimensional model simulations of a turbulent flame on Reynolds Averaged Navier Stokes (RANS) including a realizable k-e turbulent scheme with the aid of chemistry mechanism were performed under various conditions. Partially premixed combustion model with flame-let concept was selected and radiation effects are also considered. Validation for the predicted results showed a reasonable agreement when validated with the experimental data. The results discuss the influence of changing inlet pressure and equivalence ratio on the stability and the characteristics of unburnt NH3 and NO emissions. Results show that for constant operating conditions such as constant equivalence ratio of 0.8 that increasing hydrogen content resulted in increasing NO emission. Also, for constant ammonia/hydrogen concentrations, NO emissions increases with equivalence ratio then reduced at rich conditions and NH3 emissions are generally low. Equivalence ratio lower than 1.2 will be preferable to reduce the amount of unburnt NH3 formation.

Download Full-text

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

Volume 2: Turbo Expo 2005 ◽

10.1115/gt2005-68565 ◽

2005 ◽

Cited By ~ 9

Author(s):

P. Griebel ◽

R. Bombach ◽

A. Inauen ◽

R. Scha¨ren ◽

S. Schenker ◽

...

Keyword(s):

Flame Front ◽

Gas Turbines ◽

Equivalence Ratio ◽

Turbulent Flame ◽

Flame Speed ◽

Operating Conditions ◽

Turbulent Flame Speed ◽

Front Position ◽

Preheating Temperature ◽

Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Download Full-text

Numerical Analysis of Equivalence Ratio Fluctuations in a Partially Premixed Gas Turbine Combustor Using Large Eddy Simulations

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4041656 ◽

2018 ◽

Vol 141 (4) ◽

Author(s):

Ping Wang ◽

Qian Yu ◽

Prashant Shrotriya ◽

Mingmin Chen

Keyword(s):

Reaction Mechanism ◽

Equivalence Ratio ◽

Flame Temperature ◽

Premixed Flames ◽

Large Eddy Simulations ◽

Combustion Model ◽

Inlet Channel ◽

Large Eddy ◽

Partially Premixed Flames ◽

Partially Premixed

In the present work, the fluctuations of equivalence ratio in the PRECCINSTA combustor are investigated via large eddy simulations (LES). Four isothermal flow cases with different combinations of global equivalence ratios (0.7 or 0.83) and grids (1.2 or 1.8 million cells) are simulated to study the mixing process of air with methane, which is injected into the inlet channel through small holes. It is shown that the fluctuations of equivalence ratio are very large, and their ranges are [0.4, 1.3] and [0.3, 1.2] for cases 0.83 and 0.7, respectively. For simulating turbulent partially premixed flames in this burner with the well-known dynamically thickened flame (DTF) combustion model, a suitable multistep reaction mechanism should be chosen aforehand. To do that, laminar premixed flames of 15 different equivalence ratios are calculated using three different methane/air reaction mechanisms: 2S_CH4_BFER, 2sCM2 reduced mechanisms and GRI-Mech 3.0 detailed reaction mechanism. The variations of flame temperature, flame speed and thickness of the laminar flames with the equivalence ratios are compared in detail. It is demonstrated that the applicative equivalence ratio range for the 2S_CH4_BFER mechanism is [0.5, 1.3], which is larger than that of the 2sCM2 mechanism [0.5, 1.2]. Therefore, it is recommended to use the 2S_CH4_BFER scheme to simulate the partially premixed flames in the PRECCINSTA combustion chamber.

Download Full-text

Scale-Resolving Simulation of a Propane-Fuelled Industrial Gas Turbine Combustor Using Finite-Rate Tabulated Chemistry

Fluids ◽

10.3390/fluids5030126 ◽

2020 ◽

Vol 5 (3) ◽

pp. 126 ◽

Cited By ~ 1

Author(s):

Kai Zhang ◽

Ali Ghobadian ◽

Jamshid M. Nouri

Keyword(s):

Gas Turbine ◽

Chemical Reaction ◽

Turbulent Flame ◽

Lower Amount ◽

Combustion Model ◽

Gas Turbine Combustor ◽

Finite Rate ◽

Chemistry Method ◽

Tabulated Chemistry ◽

Partially Premixed

The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental temperature and species mole fraction clearly showed the superiority of the shear stress transport, K-omega, scale adaptive turbulence model (SSTKWSAS). The model outperforms large eddy simulation (LES) in the primary region of the combustor, probably for two reasons. First, the lower amount of mesh employed in the simulation for the industrial-size combustor does not fit the LES’s explicit mesh size dependency requirement, while it is sufficient for the SSTKWSAS simulation. Second, coupling the finite-rate chemistry method with the SSTKWSAS model provides a more reasonable rate of chemical reaction than that predicted by the fast chemistry method used in LES simulation. Other than comparing with the LES data available in the literature, the SSTKWSAS-predicted result is also compared comprehensively with that obtained from the model based on the unsteady Reynolds-averaged Navier–Stokes (URANS) simulation approach. The superiority of the SSTKWSAS model in resolving large eddies is highlighted. Overall, the present study emphasizes the effectiveness and efficiency of coupling a partially premixed combustion model with a scale-resolving simulation method in predicting a swirl-stabilized, multi-jets turbulent flame in a practical, complex gas turbine combustor configuration.

Download Full-text

A predictive combustion model for one-dimensional gasoline engine simulation

International Journal of Engine Research ◽

10.1177/1468087420945905 ◽

2020 ◽

pp. 146808742094590

Author(s):

Yoshihiro Nomura ◽

Seiji Yamamoto ◽

Makoto Nagaoka ◽

Stephan Diel ◽

Kenta Kurihara ◽

...

Keyword(s):

Gasoline Engine ◽

Early Stage ◽

Burning Velocity ◽

Turbulent Flame ◽

Operating Conditions ◽

Combustion Model ◽

One Dimensional ◽

Turbulent Reynolds Number ◽

Proposed Model ◽

Wide Range

A new predictive combustion model for a one-dimensional computational fluid dynamics tool in the multibody dynamics processes of gasoline engines was developed and validated. The model consists of (1) a turbulent burning velocity model featuring a flame radius–based transitional function, steady burning velocity that considers local quenching using the Karlovitz number and laminarization by turbulent Reynolds number, as well as turbulent flame thickness and its quenching model near the liner wall, and (2) a knock model featuring auto-ignition by the Livengood–Wu integration and ignition delay time obtained using a full-kinetic model. The proposed model and previous models were verified under a wide range of operating conditions using engines with widely different specifications. Good agreement was only obtained for combustion characteristics by the proposed model without requiring individual calibration of model constants. The model was also evaluated for utilization after prototyping. Improved accuracy, especially of ignition timing, was obtained after further calibration using a small amount of engine data. It was confirmed that the proposed model is highly accurate at the early stage of the engine development process, and is also applicable for engine calibration models that require higher accuracy.

Download Full-text

Numerical Investigations of NOx Emissions of a Partially Premixed Burner for Natural Gas Operations in Industrial Gas Turbine

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2014-26906 ◽

2014 ◽

Cited By ~ 3

Author(s):

Alessandro Innocenti ◽

Antonio Andreini ◽

Andrea Giusti ◽

Bruno Facchini ◽

Matteo Cerutti ◽

...

Keyword(s):

Gas Turbine ◽

Turbulent Combustion ◽

Fuel Injection ◽

Formation Rate ◽

Operating Conditions ◽

Combustion Model ◽

Nox Emissions ◽

Air Concentration ◽

Partially Premixed ◽

Industrial Gas Turbine

In the present paper a numerical analysis of a low NOx partially premixed burner for industrial gas turbine applications is presented. The first part of the work is focused on the study of the premixing process inside the burner. Standard RANS CFD approach was used: k–ε turbulence model was modified and calibrated in order to find a configuration able to fit available experimental profiles of fuel/air concentration at the exit of the burner. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. An assessment of the turbulent combustion model was carried out with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. A reliable numerical setup was discovered by comparing predicted and measured NOx emissions at different operating conditions and at different split ratio between main and pilot fuel. In the investigated range, the influence of the premixer in the NOx formation rate was found to be marginal if compared with the pilot flame one. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of alternative fuel injection strategies allowed to define a set of advanced configurations to be investigated in future experimental tests.

Download Full-text

Design Improvement Survey for NOx Emissions Reduction of a Heavy-Duty Gas Turbine Partially Premixed Fuel Nozzle Operating With Natural Gas: Numerical Assessment

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4031144 ◽

2015 ◽

Vol 138 (1) ◽

Cited By ~ 5

Author(s):

Alessandro Innocenti ◽

Antonio Andreini ◽

Bruno Facchini ◽

Matteo Cerutti ◽

Gianni Ceccherini ◽

...

Keyword(s):

Gas Turbine ◽

Turbulent Combustion ◽

Operating Conditions ◽

Combustion Model ◽

Formation Mechanisms ◽

Heavy Duty ◽

Flamelet Generated Manifold ◽

Fuel Nozzle ◽

Partially Premixed ◽

Heavy Duty Gas Turbine

A numerical investigation of a low NOx partially premixed fuel nozzle for heavy-duty gas turbine applications is presented in this paper. Availability of results from a recent test campaign on the same fuel nozzle architecture allowed the exhaustive comparison study presented in this work. At first, an assessment of the turbulent combustion model was carried out, with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. In particular, the fluent partially premixed combustion model and a flamelet approach are used to simulate the flame. The laminar flamelet database is generated using the flamelet generated manifold (FGM) chemistry reduction technique. Species and temperature are parameterized by mixture fraction and progress variable. Comparisons with calculations with partially premixed model and the steady diffusion flamelet (SDF) database are made for the baseline configuration in order to discuss possible gains associated with the introduced dimension in the FGM database (reaction progress), which makes it possible to account for nonequilibrium effects. Numerical characterization of the baseline nozzle has been carried out in terms of NOx. Computed values for both the baseline and some alternative premixer designs have been then compared with experimental measurements on the reactive test rig at different operating conditions and different split ratios between main and pilot fuel. Numerical results allowed pointing out the fundamental NOx formation processes, both in terms of spatial distribution within the flame and in terms of different formation mechanisms. The obtained knowledge would allow further improvement of fuel nozzle design.

Download Full-text

Comparison of Flame Transfer Functions Acquired by Chemiluminescence and Density Fluctuation

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2016-57485 ◽

2016 ◽

Author(s):

Johannes Peterleithner ◽

Riccardo Basso ◽

Franz Heitmeir ◽

Jakob Woisetschläger ◽

Raimund Schlüßler ◽

...

Keyword(s):

Equivalence Ratio ◽

Transfer Functions ◽

Turbulent Flame ◽

Time Derivative ◽

Density Fluctuations ◽

Time Resolved ◽

Partially Premixed Flames ◽

Partially Premixed ◽

Premixed Turbulent Flame ◽

First Time

The goal of this study was to measure the Flame Transfer Function of a perfectly and a partially premixed turbulent flame by means of Laser Interferometric Vibrometry. For the first time, this technique is used to detect integral heat release fluctuations. The results were compared to classical OH*-chemiluminescence measurements. Effects of equivalence ratio waves and vortex rollup were found within those flames and were then investigated by means of time resolved planar CH*/OH*-chemiluminescence and Frequency modulated Doppler global velocimetry. This work is motivated by the difficulties chemiluminescence encounters when faced with partially premixed flames including equivalence ratio waves and flame stretching. LIV, recording the time derivative of the density fluctuations as line-of-sight data, is not affected by these flame properties.

Download Full-text

Numerical study of turbulent normal diffusion flame CH4-air stabilized by coaxial burner

Thermal Science ◽

10.2298/tsci110609042r ◽

2013 ◽

Vol 17 (4) ◽

pp. 1207-1219 ◽

Cited By ~ 2

Author(s):

Zouhair Riahi ◽

Ali Mergheni ◽

Jean-Charles Sautet ◽

Ben Nasrallah

Keyword(s):

Equivalence Ratio ◽

Numerical Study ◽

Mixture Fraction ◽

Turbulent Flame ◽

Flame Structure ◽

Premixed Combustion ◽

Air Jet ◽

Fuel Jet ◽

Jet Velocity ◽

Lift Off

The practical combustion systems such as combustion furnaces, gas turbine, engines, etc. employ non-premixed combustion due to its better flame stability, safety, and wide operating range as compared to premixed combustion. The present numerical study characterizes the turbulent flame of methane-air in a coaxial burner in order to determine the effect of airflow on the distribution of temperature, on gas consumption and on the emission of NOx. The results in this study are obtained by simulation on FLUENT code. The results demonstrate the influence of different parameters on the flame structure, temperature distribution and gas emissions, such as turbulence, fuel jet velocity, air jet velocity, equivalence ratio and mixture fraction. The lift-off height for a fixed fuel jet velocity is observed to increase monotonically with air jet velocity. Temperature and NOx emission decrease of important values with the equivalence ratio, it is maximum about the unity.

Download Full-text