Analysis of Autoignition Chemistry in Aeroderivative Premixers At Engine Conditions

2021 ◽  
Author(s):  
Sandeep Jella ◽  
Gilles Bourque ◽  
Pierre Gauthier ◽  
Philippe Versailles ◽  
Jeffrey M. Bergthorson ◽  
...  
Keyword(s):  
Residence Time ◽  
Real Life ◽  
Precursor Chemistry ◽  
Mode Analysis ◽  
Safety Factors ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Short Period ◽  
Large Eddy ◽  
Pure Methane

Abstract The minimization of autoignition risk is critical to premixer design. Safety factors based on ignition delays of homogeneous mixtures, are generally used to guide the choice of a residence time for a given premixer. However, autoignition chemistry at aeroderivative conditions is fast (0.5-2 milliseconds) and can be initiated within typical premixer residence times. The analysis of what takes place in this short period involves the study of low-temperature precursor chemistry. By coupling the evolution of the Chemical Explosive Modes to turbulence, it is possible to obtain a measure of spatial autoignition risk where both chemical (e.g. ignition delay) and aerodynamic (e.g. local residence time) influences are unified. In this article, we describe a method that couples Large Eddy Simulation to newly developed, reduced autoignition chemical kinetics to study autoignition precursors in an example premixer representative of real life geometric complexity. A blend of pure methane and dimethyl ether (DME), a common fuel used for experimental autoignition studies, was transported using the reduced mechanism (38 species / 238 reactions) at engine conditions at increasing levels of DME concentration until exothermic autoignition kernels were formed. The Chemical Explosive Mode analysis closely follows the large thermochemical changes in the premixer as a function of DME concentration and identifies where the premixer is sensitive and flame anchoring is likely to occur.

Analysis of Autoignition Chemistry in Aeroderivative Premixers at Engine Conditions

2020 ◽  
Author(s):  
Sandeep Jella ◽  
Gilles Bourque ◽  
Pierre Gauthier ◽  
Philippe Versailles ◽  
Jeffrey Bergthorson ◽  
...  
Keyword(s):  
Residence Time ◽  
Gas Turbines ◽  
Real Life ◽  
Precursor Chemistry ◽  
Mode Analysis ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Multi Stage ◽  
Short Period ◽  
Transport Effects

Abstract The minimization of autoignition risk is critical to the design of premixers of high power aeroderivative gas turbines as an increased use of highly reactive future fuels (for example, hydrogen or higher hydrocarbons) is anticipated. Safety factors based on ignition delays of homogeneous mixtures, are generally used to guide the choice of a residence time for a given premixer. However, autoignition chemistry at aeroderivative conditions is fast (0.5–2 milliseconds) and can be initiated within typical premixer residence times. The analysis of what takes place in this short period necessarily involves the study of low-temperature autoignition precursor chemistry, but precursors can change with fuel and local reactivity. Chemical Explosive Modes are a natural alternative to study this as they can provide a measure of autoignition risk by considering the whole thermochemical state in the framework of an eigenvalue problem. When transport effects are included by coupling the evolution of the Chemical Explosive Modes to turbulence, it is possible to obtain a measure of spatial autoignition risk where both chemical (e.g. ignition delay) and aerodynamic (e.g. local residence time) influences are unified. In this article, we describe a method that couples Large Eddy Simulation to newly developed, reduced autoignition chemical kinetics to study autoignition precursors in an example pre-mixer representative of real life geometric complexity. A blend of pure methane and dimethyl ether (DME), a common fuel used for experimental autoignition studies, was transported using the reduced mechanism (38 species / 238 reactions) at engine conditions at increasing levels of DME concentration until exothermic autoignition kernels were formed. The resolution of species profiles was ensured by using a thickened flame model where dynamic thickening was carried out with a flame sensor modified to work with multi-stage heat release. The paper is outlined as follows: First, a reduced mechanism is constructed and validated for modeling methane as well as di-methyl ether (DME) autoignition. Second, sensitivity analysis is used to show the need for Chemical Explosive Modes. Third, the thickened flame model modifications are described and then applied to an example premixer at 25 bar / 890K preheat. The Chemical Explosive Mode analysis closely follows the large thermochemical changes in the premixer as a function of DME concentration and identifies where the premixer is sensitive and flame anchoring is likely to occur.

scholarly journals Capturing Plume Rise and Dispersion with a Coupled Large-Eddy Simulation: Case Study of a Prescribed Burn

Atmosphere ◽  
2019 ◽  
Vol 10 (10) ◽  
pp. 579
Author(s):  
Nadya Moisseeva ◽  
Roland Stull
Keyword(s):  
Large Eddy Simulation ◽  
Numerical Models ◽  
Real Life ◽  
Plume Rise ◽  
Atmospheric Conditions ◽  
Prescribed Burn ◽  
Smoke Plume ◽  
Fire Emissions ◽  
Eddy Simulation ◽  
Large Eddy

Current understanding of the buoyant rise and subsequent dispersion of smoke due to wildfires has been limited by the complexity of interactions between fire behavior and atmospheric conditions, as well as the uncertainty in model evaluation data. To assess the feasibility of using numerical models to address this knowledge gap, we designed a large-eddy simulation of a real-life prescribed burn using a coupled semi-emperical fire–atmosphere model. We used observational data to evaluate the simulated smoke plume, as well as to identify sources of model biases. The results suggest that the rise and dispersion of fire emissions are reasonably captured by the model, subject to accurate surface thermal forcing and relatively steady atmospheric conditions. Overall, encouraging model performance and the high level of detail offered by simulated data may help inform future smoke plume modeling work, plume-rise parameterizations and field experiment designs.

Large Eddy Simulation of a Turbulent Spray Burner Using Thickened Flame Model and Adaptive Mesh Refinement

2020 ◽  
Author(s):  
Aleksandra Rezchikova ◽  
Cédric Mehl ◽  
Scott Drennan ◽  
Olivier Colin
Keyword(s):  
Large Eddy Simulation ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Two Phase ◽  
Jet Flame ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Large Eddy ◽  
Turbulent Spray

Abstract The accurate simulation of two-phase flow combustion is crucial for the design of aeronautical combustion chambers. In order to gain insight into complex interactions between a flame, a flow, and a liquid phase, the present work addresses the combustion modeling for the Large Eddy Simulation (LES) of a turbulent spray jet flame. The Eulerian-Lagrangian framework is selected to represent the gaseous and liquid phases, respectively. Chemical processes are described by a reduced mechanism, and turbulent combustion is modeled by the Thickened Flame Model (TFM) coupled to the Adaptive Mesh Refinement (AMR). The TFM-AMR extension on the dispersed phase is successfully validated on a laminar spray flame configuration. Then, the modeling approach is evaluated on the academic turbulent spray burner, providing a good agreement with the experimental data.

scholarly journals Large eddy simulation of diesel spray–assisted dual-fuel ignition: A comparative study on two n-dodecane mechanisms at different ambient temperatures

2020 ◽  
pp. 146808742094655
Author(s):  
Jeevananthan Kannan ◽  
Mahmoud Gadalla ◽  
Bulut Tekgül ◽  
Shervin Karimkashi ◽  
Ossi Kaario ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
High Reactivity ◽  
Dual Fuel ◽  
Ignition Process ◽  
Ambient Temperatures ◽  
Chemical Mechanisms ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Large Eddy

In dual-fuel compression ignition engines, a high-reactivity fuel, such as diesel, is directly injected to the engine cylinder to ignite a mixture of low-reactivity fuel and air. This study targets improving the general understanding on the dual-fuel ignition phenomenon using zero-dimensional homogeneous reactor studies and three-dimensional large eddy simulation together with finite-rate chemistry. Using the large eddy simulation framework, n-dodecane liquid spray is injected into the lean ambient methane–air mixture at [Formula: see text]. The injection conditions have a close relevance to the Engine Combustion Network Spray A setup. Here, we assess the effect of two different chemical mechanisms on ignition characteristics: a skeletal mechanism with 54 species and 269 reaction steps (Yao mechanism) and a reduced mechanism with 96 species and 993 reaction steps (Polimi mechanism). Altogether three ambient temperatures are considered: 900, 950, and 1000 K. Longer ignition delay time is observed in three-dimensional large eddy simulation spray cases compared to zero-dimensional homogeneous reactors, due to the time needed for fuel mixing in three-dimensional large eddy simulation sprays. Although ignition is advanced with the higher ambient temperature using both chemical mechanisms, the ignition process is faster with the Polimi mechanism compared to the Yao mechanism. The reasons for differences in ignition timing with the two mechanisms are discussed using the zero-dimensional and three-dimensional large eddy simulation data. Finally, heat release modes are compared in three-dimensional large eddy simulation according to low- and high-temperature chemistry in dual-fuel combustion at different ambient temperatures. It is found that Yao mechanism overpredicts the first-stage ignition compared to Polimi mechanism, which leads to the delayed second-stage ignition in Yao cases compared to Polimi cases. However, the differences in dual-fuel ignition for Polimi and Yao mechanisms are relatively smaller at higher ambient temperatures.

scholarly journals Large-Eddy Simulation of Air Parcels in Stratocumulus Clouds: Time Scales and Spatial Variability

2006 ◽  
Vol 63 (3) ◽  
pp. 952-967 ◽  
Author(s):  
Yefim L. Kogan
Keyword(s):  
Large Eddy Simulation ◽  
Spatial Variability ◽  
Time Scales ◽  
Residence Time ◽  
Turnover Time ◽  
Spatial Inhomogeneity ◽  
Cloud Base ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Stratocumulus Clouds

Abstract Large ensembles of air parcel trajectories driven by the (large-eddy simulation) LES-generated velocity fields from simulations of stratocumulus clouds were analyzed, focusing on statistics of air parcel in-cloud time scales, as well as their spatial variability. In the case of a drizzling stratocumulus cloud the in-cloud residence time is 2–5 times longer than the characteristic cloud eddy turnover time. About 70% of all air parcels cycle in the cloud more than 2 times and about 50% more than 3 times, thus indicating that air cycling is an essential feature of drizzling stratocumulus cloud dynamics. The extent of cycling is different in the case of nondrizzling stratocumulus cloud, where mean in-cloud time scales are on the order of eddy turnover time. Evidently air cycling in cloud depends on boundary layer stability and flow circulation; the latter is affected by cooling of evaporating drizzle and heating by solar radiation. Results show significant inhomogeneity of in-cloud time scales, which leads to inhomogeneity in cloud microphysical parameters. The potential effects of in-cloud residence time spatial inhomogeneity on cloud microstructure are obvious and significant. Older parcels will contain larger droplets and previously processed cloud condensation nuclei (CCN). Nonadiabatic mixing between old and new parcels provides new embryos for coagulation and accelerates drizzle formation. It is hypothesized that mixing of parcels with different histories, that is, with drop size distributions at different stages of their evolution, may contribute to the drop spectrum broadening. The results also suggest a possible positive feedback mechanism between drizzle and decoupling, namely, parcels with long time trajectories will favor enhanced drizzle growth, which, in turn, will lead to stronger evaporation below cloud base followed by a stronger increase in stability of the subcloud layer and stronger decoupling; all resulting in more air parcel cycling in cloud and more drizzle, which may eventually lead to stratocumulus cloud breakup.

Large Eddy Simulation of a Turbulent Spray Burner Using Thickened Flame Model and Adaptive Mesh Refinement

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Aleksandra Rezchikova ◽  
Cédric Mehl ◽  
Scott Drennan ◽  
Olivier Colin
Keyword(s):  
Large Eddy Simulation ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Two Phase ◽  
Jet Flame ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Large Eddy ◽  
Turbulent Spray

Abstract The accurate simulation of two-phase flow combustion is crucial for the design of aeronautical combustion chambers. In order to gain insight into complex interactions between a flame, a flow, and a liquid phase, the present work addresses the combustion modeling for the large eddy simulation (LES) of a turbulent spray jet flame. The Eulerian–Lagrangian framework is selected to represent the gaseous and liquid phases, respectively. Chemical processes are described by a reduced mechanism, and turbulent combustion is modeled by the thickened flame model (TFM) coupled to the adaptive mesh refinement (AMR). The TFM-AMR extension on the dispersed phase is successfully validated on a laminar spray flame configuration. Then, the modeling approach is evaluated on the academic turbulent spray burner, providing a good agreement with the experimental data.

scholarly journals Flow and deposition characteristics of nanoparticles in a 90° square bend

2015 ◽  
Vol 19 (4) ◽  
pp. 1235-1238 ◽  
Author(s):  
Zhong-Ping Dai ◽  
Zhao-Qin Yin
Keyword(s):  
Residence Time ◽  
Penetration Rate ◽  
Particle Model ◽  
Flow Conditions ◽  
Dean Number ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Discrete Particle Model ◽  
Schmidt Numbers ◽  
Bend Flow

Large eddy simulation and discrete particle model have been used to study the nanoparticles through a 90? square bend flow considering the effects of Brownian motion and turbulence diffusion. The penetration rate and the residence time of particles are evaluated under different flow conditions and various particle sizes. Results show that particles penetration rate increases with an increase in Dean and Schmidt numbers. The particle size and flow Dean number have significantly effects on the particles residence time in the bend.

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