FEM-SIMULATION OF LAMINAR FLAME PROPAGATION II: TWIN AND TRIPLE FLAMES IN COUNTERFLOW

2005 ◽  
Vol 177 (5-6) ◽  
pp. 955-978 ◽  
Author(s):  
B. MICHAELIS ◽  
B. ROGG
Keyword(s):  
Flame Propagation ◽  
Laminar Flame ◽  
Fem Simulation

Numerical study of pressure and composition influence on laminar flame propagation in nitrogen-diluted H2-O2 mixtures

2020 ◽  
Vol 65 (6) ◽  
pp. 529-537
Author(s):  
Domnina RAZUS ◽  
◽  
Maria MITU ◽  
Venera GIURCAN ◽  
Codina MOVILEANU ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Laminar Flame ◽  
Numerical Study

Optical and Numerical Investigations of Flame Propagation in a Heavy Duty Spark Ignited Natural Gas Engine

2021 ◽  
Author(s):  
Jinlong Liu ◽  
Christopher Ulishney ◽  
Cosmin E. Dumitrescu
Keyword(s):  
Natural Gas ◽  
Flame Propagation ◽  
Turbulence Intensity ◽  
Laminar Flame ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Heavy Duty ◽  
Piston Chamber

Abstract Increasing the natural gas (NG) use in heavy-duty engines is beneficial for reducing greenhouse-gas emissions from power generation and transportation. However, converting compression ignition (CI) engines to NG spark ignition operation can increase methane emissions without expensive aftertreatment, thereby defeating the purpose of utilizing a low carbon fuel. The widely accepted explanation for the low combustion efficiency in such retrofitted engines is the lower laminar flame speed of natural gas. In addition, diesel engine’s larger bowl size compared to the traditional gasoline engines increases the flame travel length inside the chamber and extends the combustion duration. However, optical measurements performed in this study suggested that a fast-propagating flame was developed inside the cylinder even at extremely lean operation. This was supported by a three-dimensional numerical simulation, which indicated that the squish region of the bowl-in-piston chamber generated a high turbulence intensity inside the bowl. However, the flame propagation experienced a sudden 2.25x reduction in speed when transiting from the bowl to the squish region. Such a phenomenon was caused by the large decrease in the turbulence intensity inside the squish region during the combustion process. Moreover, the squish volume trapped an important fuel fraction, and it is this fraction that experienced a slow and inefficient burning process during the expansion stroke. This resulted in increased methane emissions and reduced combustion efficiency. Overall, it was the specifics of the combustion process inside a bowl-in-piston chamber not the methane’s slow laminar flame speed that contributed to the low methane combustion efficiency for the retrofitted engine. The results suggest that optimizing the chamber shape is paramount to boost engine efficiency and decrease its emissions.

On the problem of laminar flame propagation in a gas with an inert dust

2011 ◽  
Vol 47 (4) ◽  
pp. 436-441
Author(s):  
A. A. Dement’ev ◽  
A. Yu. Krainov
Keyword(s):  
Flame Propagation ◽  
Laminar Flame ◽  
Inert Dust

The theory of flame phenomena with a chain reaction

1956 ◽  
Vol 249 (957) ◽  
pp. 1-25 ◽  
Keyword(s):  
Reaction Zone ◽  
Flame Propagation ◽  
Reaction Rate ◽  
Laminar Flame ◽  
Combustible Mixture ◽  
Flame Speed ◽  
Spontaneous Ignition ◽  
Chain Reaction ◽  
Hydrazine Decomposition ◽  
A Chain

For single-step reactions there is a unique relation between reaction rate and reactedness for a given combustible mixture at a specified pressure and initial temperature. This paper examines whether the relation is still unique when chain reactions are present, by considering three types of flame—spontaneous ignition, laminar-flame propagation, and the homogeneous steady-flow reaction zone—with a chain-reaction scheme proposed by Adams & Stocks for the decomposition of hydrazine. It is found that the relation is not unique but that similarities exist between the relation for laminar-flame propagation and the relation for the homogeneous reaction zone. Incidentally, a general method of calculating laminar-flame speeds with reaction schemes of arbitrary complexity is presented. When applied to the hydrazine decomposition flame the predictions of the theory are in fair agreement with experimental results. In particular, the variation of flame speed with temperature is correctly predicted. It is shown that the use of the Karman-Penner 'steady-state assumption' would lead to an overestimate of the flame speed. Consideration of the changes which would result if the chain reaction should branch shows that there would once again tend to be a unique reaction rate versus reactedness relation, and that the laminar-flame speed would be increased by a factor of about three for the hottest flame considered but by larger factors for cooler flames.

Effects of H2-Enrichment on the Propagation Characteristics of CH4-Air Flames

2006 ◽  
Author(s):  
Alejandro M. Briones ◽  
Suresh K. Aggarwal ◽  
Vishwanath R. Katta
Keyword(s):  
Flame Propagation ◽  
Laminar Flame ◽  
Mixture Fraction ◽  
Leading Edge ◽  
Tangential Component ◽  
Flame Speed ◽  
Axial Position ◽  
Stoichiometric Mixture ◽  
Jet Mixing ◽  
Flame Curvature

The propagation of H2-enriched CH4-air triple flames in a nonpremixed jet is investigated numerically. The flames are ignited in a nonuniform jet-mixing layer downstream of the burner. A comprehensive, time-dependent computational model is used to simulate the transient ignition and flame propagation phenomena. The model employs a detailed description of methane-air chemistry and transport properties. Following ignition a well-defined flame is formed that propagates upstream towards the burner along the stoichiometric mixture fraction line. As the flame propagates upstream, the flame speed, which is defined as the normal flamefront velocity at the leading edge with respect to the local gas velocity, increases above or decreases below to the corresponding unstretched laminar flame speed of the stoichiometric planar premixed flame. Although the flame curvature varies as a function of axial position, the flame curvature remains nearly constant for a given flame. As hydrogen is added to the fuel stream the flame curvature during flame propagation remains nearly constant. During the flame propagation process, the hydrodynamic stretch dominates over the curvature-induced stretch. Hydrogen increases the heat release and the component of the velocity perpendicular to the flame increases across the surface, whereas the tangential component remains unchanged. This jump in the perpendicular velocity component bends the velocity vector toward the stoichiometric mixture fraction line. This redirection of the flow is accommodated by the divergence of the streamlines ahead of the flame, resulting in the decrease of the velocity and increase in the hydrodynamic stretch.

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