scholarly journals Combustion of Air-Sheathed Kerosene Spray Jets Stabilized in a Stagnation-Point Reverse Flow

2018 ◽  
Author(s):  
Yukiya Arai ◽  
Takumi Saito ◽  
Takafumi Nakasu ◽  
Shigeru Hayashi
Keyword(s):  
Stagnation Point ◽  
Reverse Flow ◽  
Spray Jets

Effects of Second-Order Slip and Magnetic Field on Mixed Convection Stagnation-Point Flow of a Maxwellian Fluid: Multiple Solutions

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
M. M. Rahman
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Mixed Convection ◽  
Stagnation Point ◽  
Reverse Flow ◽  
Second Order ◽  
Dual Solutions ◽  
Stagnation Point Flow ◽  
Shrinking Sheet ◽  
Variable Surface

In this paper, we investigate the effects of second-order slip and magnetic field on the nonlinear mixed convection stagnation-point flow toward a vertical permeable stretching/shrinking sheet in an upper convected Maxwell (UCM) fluid with variable surface temperature. Numerical results are obtained using the bvp4c function from matlab for the reduced skin-friction coefficient, the rate of heat transfer, the velocity, and the temperature profiles. The results indicate that multiple (dual) solutions exist for a buoyancy opposing flow for certain values of the parameter space irrespective to the types of surfaces whether it is stretched or shrinked. It is found that an applied magnetic field compensates the suction velocity for the existence of the dual solutions. Depending on the parametric conditions; elastic parameter, magnetic field parameter, first- and second-order slip parameters significantly controls the flow and heat transfer characteristics. The illustrated streamlines show that for upper branch solutions, the effects of stretching and suction are direct and obvious as the flow near the surface is seen to suck through the permeable sheet and drag away from the origin of the sheet. However, aligned but reverse flow occurs for the case of lower branch solutions when the mixed convection effect is less significant.

Product Recirculation and Mixing Studies in a Stagnation Point Reverse Flow Combustor

2007 ◽  
Author(s):  
Mohan Bobba ◽  
Priya Gopalakrishnan ◽  
Karthik Periagaram ◽  
Jerry Seitzman
Keyword(s):  
Stagnation Point ◽  
Reverse Flow

Flame Structure and Stabilization Mechanisms in a Stagnation-Point Reverse-Flow Combustor

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Mohan K. Bobba ◽  
Priya Gopalakrishnan ◽  
Karthik Periagaram ◽  
Jerry M. Seitzman
Keyword(s):  
Stagnation Point ◽  
Reverse Flow ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Reaction Rates ◽  
Diagnostic Techniques ◽  
Flame Stabilization ◽  
Oh Radicals ◽  
Spontaneous Raman Scattering ◽  
High Turbulence

A novel combustor design, referred to as a stagnation-point reverse-flow (SPRF) combustor, was recently developed to overcome the stability issues encountered with most lean premixed combustion systems. The SPRF combustor is able to operate stably at very lean fuel-air mixtures with low NOx emissions. The reverse flow configuration causes the flow to stagnate and hot products to reverse and leave the combustor. The highly turbulent stagnation zone and internal recirculation of hot product gases facilitates robust flame stabilization in the SPRF combustor at very lean conditions over a range of loadings. Various optical diagnostic techniques are employed to investigate the flame characteristics of a SPRF combustor operating with premixed natural gas and air at atmospheric pressure. These include simultaneous planar laser-induced fluorescence imaging of OH radicals and chemiluminescence imaging, and spontaneous Raman scattering. The results indicate that the combustor has two stabilization regions, with the primary region downstream of the injector where there are low average velocities and high turbulence levels where most of the heat release occurs. High turbulence levels in the shear layer lead to increased product recirculation levels, elevating the reaction rates and thereby enhancing the combustor stability. The effect of product entrainment on the chemical time scales and the flame structure is quantified using simple reactor models. Turbulent flame structure analysis indicates that the flame is primarily in the thin reaction zone regime throughout the combustor. The flame tends to become more flameletlike, however, for increasing distance from the injector.

Flame Structure and Stabilization Mechanisms in a Stagnation Point Reverse Flow Combustor

2007 ◽  
Author(s):  
Mohan K. Bobba ◽  
Priya Gopalakrishnan ◽  
Karthik Periagaram ◽  
Jerry M. Seitzman
Keyword(s):  
Stagnation Point ◽  
Reverse Flow ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Reaction Rates ◽  
Diagnostic Techniques ◽  
Flame Stabilization ◽  
Oh Radicals ◽  
Spontaneous Raman Scattering ◽  
High Turbulence

A novel combustor design, referred to as a Stagnation Point Reverse Flow (SPRF) combustor, was recently developed to overcome the stability issues encountered with most lean premixed combustion systems. The SPRF combustor is able to operate stably at very lean fuel-air mixtures with low NOx emissions. The reverse flow configuration causes the flow to stagnate and hot products to reverse and leave the combustor. The highly turbulent stagnation zone and internal recirculation of hot product gases facilitates robust flame stabilization in the SPRF combustor at very lean conditions over a range of loadings. Various optical diagnostic techniques are employed to investigate the flame characteristics of a SPRF combustor operating with premixed natural gas and air at atmospheric pressure. These include simultaneous Planar Laser-Induced Fluorescence (PLIF) imaging of OH radicals, chemiluminescence imaging, Spontaneous Raman Scattering. The results indicate that the combustor has two stabilization regions, with the primary region downstream of the injector where there are low average velocities and high turbulence levels where most of the heat release occurs. High turbulence level in the shear layers lead to increased product recirculation levels, elevating the reaction rates and thereby, the combustor stability. The effect of product entrainment on the chemical timescales and the flame structure is quantified using simple reactor models. Turbulent flame structure analysis indicates that the flame is primarily in the thin reaction zones regime throughout the combustor. The flame tends to become more flamelet like, however, for increasing distance from the injector.

Characteristics of Combustion Processes in a Stagnation Point Reverse Flow Combustor

2006 ◽  
Author(s):  
M. K. Bobba ◽  
P. Gopalakrishnan ◽  
J. M. Seitzman ◽  
B. T. Zinn
Keyword(s):  
Stagnation Point ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Reverse Flow ◽  
Laser Sheet ◽  
Flame Structure ◽  
Stable Operation ◽  
Oh Radicals ◽  
Combustion Processes ◽  
Hot Products

The performance of dry, low NOx gas turbines, which employ lean premixed (or partially premixed) combustors, is often limited by static and dynamic combustor stability, power density limitations and expensive premixing hardware. To overcome these issues, a novel design, referred to as the Stagnation Point Reverse Flow (SPRF) combustor, has recently been developed. Various optical diagnostic techniques are employed here to elucidate the combustion processes in this novel combustor. These include simultaneous planar laser-induced fluorescence (PLIF) imaging of OH radicals and chemiluminescence imaging, and separate experiments with particle image velocimetry and elastic laser sheet scattering from liquid particles seeded into the fuel. The SPRF combustor achieves internal exhaust gas recirculation and efficient mixing, which eliminates local peaks in temperature. This results in low NOx emissions, limited by flame zone (prompt) production, for both premixed and non-premixed modes of operation. The flame is anchored in a region of reduced velocity and high turbulent intensities, which promotes mixing of hot products into the reactants, thus enabling stable operation of the combustor even at very lean equivalence ratios. Also, the flame structure and flow characteristics were found to remain invariant at high loadings, i.e., mass flow rates. Combustion in the non-premixed mode of operation is found to be similar to the premixed case, with the OH PLIF measurements indicating that nonpremixed flame burns at an equivalence ratio that is close to the overall combustor equivalence ratio. Similarities in emission levels between premixed and non-premixed modes are thus attributable to efficient fuel-air mixing in the nonpremixed mode, and entrainment of hot products into the reactant stream before burning occurs.

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