The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Jun Li - One of the best experts on this subject based on the ideXlab platform.
-
experimental study on standing wave regimes of premixed h2 air combustion in planar micro Combustors partially filled with porous medium
Fuel, 2016Co-Authors: Jun Li, Yuantao Wang, Jinxing ChenAbstract:Abstract Heat recirculation is of vital importance to micro/meso-scale combustion. Filling a micro-Combustor with porous medium is intended to enhance heat recirculation from the reaction zone, besides the Combustor wall. Typically, in large-scale porous burners with a constant cross-sectional area, once the fuel–air equivalence ratio ( Φ ) is fixed, there is only one corresponding filtration velocity ( U ) which gives rise to a stationary combustion wave. In our previous studies, a configuration of a planar micro-Combustor partially filled with stainless steel mesh was proposed, and three critical conditions corresponding to the flame stability limits of premixed H 2 –air combustion were experimentally identified. In addition, we observed a regime, rather than a point ( U and Φ ), within which stationary combustion waves exist. As a follow-up, this study investigates the effects of width, filling position, porosity and wire diameter of the porous medium on the standing wave regime in an H = 1 mm planar micro-Combustor. Furthermore, two more micro-Combustors with H = 1.5 and 2 mm, respectively, are studied and the results compared with the case with H = 1 mm. It is shown that the Combustor size has a significant influence on the standing wave regime. With the increase of Combustor size, the standing wave regime shrinks rapidly. The finding clearly reveals the scale effect on the standing wave regime in filtration combustion.
-
fundamental flame characteristics of premixed h2 air combustion in a planar porous micro Combustor
Chemical Engineering Journal, 2016Co-Authors: Jun Li, Qingqing Li, Yuantao WangAbstract:Micro-/meso-scale combustion represents a great potential in generating portable power in an efficient way. Heat recirculation is regarded as the most important factor that influences the combustion process in micro-Combustors. Adding porous medium to a free flame micro-Combustor is able to enhance thermal energy transport, thus allowing more heat recirculation. A CFD study on fundamental flame characteristics of premixed H2–air combustion in a planar porous micro-Combustor is carried out. Thermal radiation is not considered in order to focus on the contribution of enhanced thermal conduction. The effects of flow conditions and properties of the porous medium on the wall temperature, species concentration, flame temperature, flame location, and flame speed are examined individually. The numerical results indicate that a porous micro-Combustor gives a higher wall temperature and a lower flame temperature than a free flame counterpart. In the presence of porous medium, temperature distribution as well as species (OH) concentration becomes more uniform. Flame locations in a porous micro-Combustor exhibit a U-shaped pattern against the change of the inlet flow velocity. Choosing the porous material properly to have the effective thermal conductivity and the wall thermal conductivity in the same order of magnitude is helpful to localize flames. Finally, the flame speed is found to be in a linear relation with the inlet flow velocity. It is noted that the blocking effect incurred by the solid matrix renders some conclusions of free flame micro-Combustors ineffective in explaining the results of the porous micro-Combustor, which requires further studies or more sophisticated models.
-
study on premixed combustion in cylindrical micro Combustors transient flame behavior and wall heat flux
Experimental Thermal and Fluid Science, 2009Co-Authors: Jun Li, S K Chou, Guangbin Huang, Wenming Yang, Zicong LiAbstract:Abstract The micro Combustor is a key component of the micro thermophotovoltaic (TPV) system. Improving the wall temperature of the micro Combustor is an effective way to elevate the system efficiency. An experimental study on the wall temperature and radiation heat flux of a series of cylindrical micro Combustors (with a backward-facing step) was carried out. For the micro Combustors with d = 2 mm, the regime of successful ignition (under the cold wall condition) was identified for different Combustor lengths. Acoustic emission was detected for some cases and the emitted sound was recorded and analyzed. Under the steady-state condition, the effects of the Combustor diameter ( d ), Combustor length ( L ), flow velocity ( u 0 ) and fuel–air equivalence ratio ( Ф ) on the wall temperature distribution were investigated by measuring the detailed wall temperature profiles. In the case that the micro Combustor is working as an emitter, the optimum efficiency was found at Ф ≈ 0.8, independent of the Combustor dimensions ( d and L ) and the flow velocity. Under the experimental conditions employed in the present study, the positions of the peak wall temperature were found to be about 8–11 mm and 4–6 mm from the step for the d = 3 mm and d = 2 mm micro Combustors, respectively, which are 8–11 and 8–12 times of their respective step heights. This result suggests that the backward-facing step employed in the Combustor design is effective in stabilizing the flame position.
Ephraim Gutmark - One of the best experts on this subject based on the ideXlab platform.
-
Rotating Detonation Combustor Research at the University of Cincinnati
Flow Turbulence and Combustion, 2018Co-Authors: Vijay Anand, Ephraim GutmarkAbstract:Rotating detonation Combustors (RDC) are at the forefront of pressure gain combustion (PGC) research. The simplicity in design and the ease of assembly makes it a promising technology that could be integrated into existing Combustor architectures. This is, however, coupled with the considerable complexities of the detonation-based flow field, and the associated modes and coupling mechanisms. The current paper is an overview of the research done at the University of Cincinnati to address some of the challenges and questions pertaining to the physics of RDC operation. Issues such as Combustor geometry, injection schemes and mixing, varied reactants behavior and modes of RDC operation are discussed. The effects of pressurization of the Combustor, along with other detonation enhancement strategies are also deliberated upon. When appropriate, parallels are drawn to the phenomena of high frequency combustion instabilities to address the similarities in observations between the two fields.
-
rotating detonation wave mechanics through ethylene air mixtures in hollow Combustors and implications to high frequency combustion instabilities
Experimental Thermal and Fluid Science, 2018Co-Authors: Vijay Anand, Andrew St George, Charles Farbos De Luzan, Ephraim GutmarkAbstract:Abstract Recent investigations into the rotating detonation phenomenon have involved its inception and sustenance in hollow Combustors, in contrast to the traditional annular rotating detonation Combustor (RDC) designs. Despite this proof-of-concept, the mechanism of propagation of detonation waves in hollow Combustors is unclear. On the other hand, the decades-old issue of high frequency combustion instabilities, especially in rocket engines, has been known to produce distinct shock waves that are in-sync with regions of intense combustion, the reason for which is widely attributed to the Rayleigh criterion. In this paper, we argue that there is a considerable overlap in the physics behind the reported rotating detonations in hollow RDCs and the high frequency tangential combustion instabilities that are known to wreak havoc on engines. To support this notion, an atmospheric hollow Combustor is experimentally tested to attain the baseline performance. It is then ‘transformed’ into a hollow RDC by the use of a flow-turning obstacle that diverts the combustible ethylene-air mixture towards the outer wall. Two distinct mechanisms are found to cause rotating detonations in a hollow Combustor, and subsequently predicate its stability. The observed modes are analogous to the behavior exhibited by planar detonations at the near-limit. This explains not only the widely observed velocity and pressure deficits in rotating detonations, but also the “steep-fronted”, “detonation-like” behavior noted in high frequency combustion instabilities.
-
Performance of an Axial Flow Turbine Driven by Multiple Pulse Detonation Combustors
2013Co-Authors: Aaron Glaser, Nicholas Caldwell, Ephraim GutmarkAbstract:Experimental studies were carried out to investigate the performance of a hybrid propulsion system integrating an axial flow turbine with multiple pulse detonation Combustors. The integrated system consisted of a circular array of six pulse detonation Combustor (PDC) tubes exhausting through an axial flow turbine. Turbine component performance was quantified by measuring the amount of power generated by the turbine section. Direct comparisons of specific power output and turbine efficiency between a PDC driven turbine and a turbine driven by a traditional steady flow Combustor were made. It was found that the PDC driven turbine had comparable performance to that of a steady burner driven turbine across the operating map of the turbine.
Ian A Waitz - One of the best experts on this subject based on the ideXlab platform.
-
high power density silicon combustion systems for micro gas turbine engines
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2003Co-Authors: Christopher M Spadaccini, Stephen P Lukachko, A Mehra, Xin Zhang, Ian A WaitzAbstract:As part of an effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, fabrication, experimental testing, and modeling of the combustion system. Two radial inflow Combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration. Both Combustors were micromachined from silicon using deep reactive ion etching (DRIE) and aligned fusion wafer handing. Hydrogen-air and hydrocarbon-air combustion were stabilized in both devices, each with chamber volumes of 191 mm 3 . Exit gas temperatures as high as 1800 K and power densities in excess of 1100 MW/m 3 were achieved. For the same equivalence ratio and overall efficiency, the dual-zone Combustor reached power densities nearly double that of the single-zone design. Because diagnostics in microscale devices are often highly intrusive, numerical simulations were used to gain insight into the fluid and combustion physics. Unlike large-scale Combustors, the performance of the microCombustors was found to be mole severely limited by heat transfer and chemical kinetics constraints. Important design trades are identified and recommendations for microCombustor design are presented.
-
high power density silicon combustion systems for micro gas turbine engines
ASME Turbo Expo 2002: Power for Land Sea and Air, 2002Co-Authors: Christopher M Spadaccini, Ian A Waitz, Stephen P Lukachko, A Mehra, Xin ZhangAbstract:As part of an effort to develop a micro-scale gas turbine engine for power generation and micro-propulsion applications, this paper presents the design, fabrication, experimental testing, and modeling of the combustion system. Two radial inflow Combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration. Both Combustors were micro-machined from silicon using Deep Reactive Ion Etching (DRIE) and aligned fusion wafer bonding. Hydrogen-air and hydrocarbon-air combustion was stabilized in both devices, each with chamber volumes of 191 mm3 . Exit gas temperatures as high as 1800 K and power densities in excess of 1100 MW/m3 were achieved. For the same equivalence ratio and overall efficiency, the dual-zone Combustor reached power densities nearly double that of the single-zone design. Because diagnostics in micro-scale devices are often highly intrusive, numerical simulations were used to gain insight into the fluid and combustion physics. Unlike large-scale Combustors, the performance of the micro-Combustors was found to be more severely limited by heat transfer and chemical kinetics constraints. Important design trades are identified and recommendations for micro-Combustor design are presented.Copyright © 2002 by ASME
-
Combustors for micro gas turbine engines
Journal of Fluids Engineering-transactions of The Asme, 1998Co-Authors: Ian A Waitz, Gautam Gauba, Yangsheng TzengAbstract:The development ofa hydrogen-air microCombustor is described. The Combustor is intended for use in a 1 mm 2 inlet area, micro-gas turbine engine. While the size of the device poses several difficulties, it also provides new and unique opportunities. The combustion concept investigated is based upon introducing hydrogen and premixing it with air upstream of the Combustor. The wide flammability limits of hydrogen-air mixtures and the use of refractory ceramics enable combustion at lean conditions, obviating the need for both a Combustor dilution zone and Combustor wall cooling. The entire combustion process is carried out at temperatures below the limitations set by material properties, resulting in a significant reduction of complexity when compared to larger-scale gas turbine Combustors. A feasibility study with initial design analyses is presented, followed by experimental results from 0.13 cm 3 silicon carbide and steel microCombustors. The Combustors were operated for tens of hours, and produced the requisite heat release for a microengine application over a range of fuel-air ratios, inlet temperatures, and pressures up to four atmospheres. Issues of flame stability, heat transfer, ignition and mixing are addressed. A discussion of requirements for catalytic processes for hydrocarbon fuels is also presented.
Yuantao Wang - One of the best experts on this subject based on the ideXlab platform.
-
experimental study on standing wave regimes of premixed h2 air combustion in planar micro Combustors partially filled with porous medium
Fuel, 2016Co-Authors: Jun Li, Yuantao Wang, Jinxing ChenAbstract:Abstract Heat recirculation is of vital importance to micro/meso-scale combustion. Filling a micro-Combustor with porous medium is intended to enhance heat recirculation from the reaction zone, besides the Combustor wall. Typically, in large-scale porous burners with a constant cross-sectional area, once the fuel–air equivalence ratio ( Φ ) is fixed, there is only one corresponding filtration velocity ( U ) which gives rise to a stationary combustion wave. In our previous studies, a configuration of a planar micro-Combustor partially filled with stainless steel mesh was proposed, and three critical conditions corresponding to the flame stability limits of premixed H 2 –air combustion were experimentally identified. In addition, we observed a regime, rather than a point ( U and Φ ), within which stationary combustion waves exist. As a follow-up, this study investigates the effects of width, filling position, porosity and wire diameter of the porous medium on the standing wave regime in an H = 1 mm planar micro-Combustor. Furthermore, two more micro-Combustors with H = 1.5 and 2 mm, respectively, are studied and the results compared with the case with H = 1 mm. It is shown that the Combustor size has a significant influence on the standing wave regime. With the increase of Combustor size, the standing wave regime shrinks rapidly. The finding clearly reveals the scale effect on the standing wave regime in filtration combustion.
-
fundamental flame characteristics of premixed h2 air combustion in a planar porous micro Combustor
Chemical Engineering Journal, 2016Co-Authors: Jun Li, Qingqing Li, Yuantao WangAbstract:Micro-/meso-scale combustion represents a great potential in generating portable power in an efficient way. Heat recirculation is regarded as the most important factor that influences the combustion process in micro-Combustors. Adding porous medium to a free flame micro-Combustor is able to enhance thermal energy transport, thus allowing more heat recirculation. A CFD study on fundamental flame characteristics of premixed H2–air combustion in a planar porous micro-Combustor is carried out. Thermal radiation is not considered in order to focus on the contribution of enhanced thermal conduction. The effects of flow conditions and properties of the porous medium on the wall temperature, species concentration, flame temperature, flame location, and flame speed are examined individually. The numerical results indicate that a porous micro-Combustor gives a higher wall temperature and a lower flame temperature than a free flame counterpart. In the presence of porous medium, temperature distribution as well as species (OH) concentration becomes more uniform. Flame locations in a porous micro-Combustor exhibit a U-shaped pattern against the change of the inlet flow velocity. Choosing the porous material properly to have the effective thermal conductivity and the wall thermal conductivity in the same order of magnitude is helpful to localize flames. Finally, the flame speed is found to be in a linear relation with the inlet flow velocity. It is noted that the blocking effect incurred by the solid matrix renders some conclusions of free flame micro-Combustors ineffective in explaining the results of the porous micro-Combustor, which requires further studies or more sophisticated models.
Masahide Kazari - One of the best experts on this subject based on the ideXlab platform.
-
NOx Correlation for an Industrial 10 MW Non-Premixed Gas Turbine Combustor for High Hydrogen Fuels
Volume 4A: Combustion Fuels and Emissions, 2016Co-Authors: Daniel Kroniger, Kunio Okada, Atsushi Horikawa, Manfred Wirsum, Masahide KazariAbstract:This paper describes a model to predict the nitric oxides (NOx) emissions for a dry non-premixed flame gas turbine Combustor at full operation conditions. The NOx correlation considered the Combustor pressure, the Combustor outlet temperature and the fuel composition from natural gas (NG) to pure hydrogen (H2) fuel. The test data for parametrizing the model was acquired with a high pressure combustion test rig for industrial 10 MWth reverse-flow gas turbine Combustors. The experimental results confirm the typical dependencies of NOx emissions. As expected, higher NOx emissions occur with increasing Combustor pressure, Combustor outlet temperature and hydrogen content of the fuel. The reference NOx model has been derived on the basis of physical approaches for the pressure and temperature effects. The substitution of natural gas with hydrogen is taken into account by a variable pressure exponent and a variable factor in the exponent of the exponential temperature correlation. As a result, the pressure exponent increases with increasing hydrogen. The temperature exponent factor decreases with increasing hydrogen. The model can describe the data set with limitations at high pressure and high hydrogen content fuel operation conditions. Copyright © 2016 by ASME.