The Experts below are selected from a list of 11721 Experts worldwide ranked by ideXlab platform
Dongke Zhang - One of the best experts on this subject based on the ideXlab platform.
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effect of a Homogeneous Combustion catalyst on the characteristics of diesel soot emitted from a compression ignition engine
Applied Energy, 2014Co-Authors: Mingming Zhu, Dongke ZhangAbstract:The effect of a ferrous picrate based Homogeneous Combustion catalyst (FPC), known to improve diesel Combustion efficiency, on the morphological and chemical characteristics of diesel soot was studied in detail. Diesel soot samples emitted from a laboratory CI engine fuelled with a commercial diesel, with and without FPC doping, were collected and characterised using a combination of several advanced analytical techniques including a TEM fitted with EELS, an FT-IR, and a solid state 13C NMR, in addition to elemental analysis. Compared to the soot from the reference diesel, the soot particle sizes of both primary soot and aggregates from the FPC treated diesel were consistently smaller and decreased with increasing FPC dosage. Both types of soot showed similar fractal dimensions, indicating that there were no apparent changes in the formation mechanisms of the primary soot particles and their agglomeration processes. Furthermore, the types of the carbon bonds and organic functional groups in the soot were virtually unaffected by FPC, as indicated by the similar degrees of graphitisation and indistinguishable chemical structures in the two types of soot. However, the soot from the FPC treated diesel showed slightly higher C/H and C/O ratios than those from the reference diesel. Based on these observations, it was speculated that FPC enhanced the diesel Combustion process, leaving fewer soot precursors, and also promoted the oxidation of soot particles, resulting in smaller sizes of the primary soot and aggregates and reduced the overall soot emissions.
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the effect of a Homogeneous Combustion catalyst on exhaust emissions from a single cylinder diesel engine
Applied Energy, 2013Co-Authors: Mingming Zhu, Dongke ZhangAbstract:Abstract This paper reports a series of experimental investigations into the effect of an Fe-based Homogeneous Combustion catalyst on the emission characteristics from a four-stroke single cylinder diesel engine. The catalyst contained ferrous picrate as the active ingredient in a composite organic solvent mixture which could be Homogeneously dissolved into a commercial diesel fuel at ultra low dosage ratios. The engine tests were conducted at four different engine loads and at two steady speeds of 2800 rpm and 3200 rpm, respectively. Engine exhaust emissions of CO, unburnt hydrocarbons (UHCs) and NOx were measured using an AVL gas analyser and the particulate emissions were evaluated in terms of smoke opacity using a Bosch smoke meter. The results showed that, in addition to the benefit of improved fuel efficiency, the Homogeneous Combustion catalyst significantly reduced the emissions of particulate matter, CO and UHC from diesel engines. Compared with the reference diesel, up to 3.7% reduction in the brake specific fuel consumption was achieved when the diesel fuel was treated with the catalyst. The use of the catalyst also led to significant reductions in the particulate matter, CO and UHC emissions, with the maximum reductions being 39.5%, 21.1% and 13.1%, respectively. The NOx emissions, however, increased slightly, by ca. 6%, which was consistent with the improved Combustion performance as reasonably expected.
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nanostructure and oxidative properties of soot from a compression ignition engine the effect of a Homogeneous Combustion catalyst
Proceedings of the Combustion Institute, 2013Co-Authors: Dongke Zhang, Mingming ZhuAbstract:Abstract This study examined the influence of an iron-based Homogeneous Combustion catalyst on the oxidative behaviour and nanostructural characteristics of soot emitted from a single-cylinder compression ignition engine. The catalyst was Homogeneously added into a commercial diesel as the reference at ultra low dosage ratios. Smoke opacity was measured using a smoke opacimeter in the engine exhaust stream to indicate the overall soot emission intensity. Soot particles were also sampled while the engine was maintained in steady-state operations and fuelled with the reference diesel and the catalyst treated fuels, respectively. The soot samples were subjected to thermogravimetric analysis (TGA) to study their oxidation reactivities in air, and transmission electron microscopy (TEM) for morphological characterisations. The smoke opacity results showed 7.3–39.5% less soot emissions when the catalyst was applied, depending on the catalyst dosage ratio. The TGA results revealed that soot from the catalyst treated fuels possessed higher oxidative reactivity as indicated by ignition at lower temperatures and faster oxidation rates than those of soot from the reference diesel. This tendency was more remarked as the catalyst dosage ratio increased. Subsequent TEM imaging analyses observed that the irregularly shaped, aggregated soot particles were made of a number of spherical primary particles. Smaller and more narrowly-distributed primary soot particles with the catalyst treated fuels than those of the reference diesel were evident. High-resolution TEM imaging revealed graphitic crystallite structures of the soot samples from both catalyst-treated and -untreated fuels with no obvious variations in the nuclei core areas, suggesting that the internal structure of the soot was not affected by the catalyst. It was evident that iron ions from the catalyst were more involved in the soot oxidation process, rather than in the early soot formation stage, and eventually resulted in smaller and narrowly-distributed primary soot particles.
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effect of a Homogeneous Combustion catalyst on Combustion characteristics of single droplets of diesel and biodiesel
PROCEEDINGS OF THE COMBUSTION INSTITUTE, 2013Co-Authors: Mingming Zhu, Dongke ZhangAbstract:Abstract Combustion characteristics of single droplets of diesel and biodiesel in air at temperatures between 923 K and 1073 K, with and without being dosed with a ferrous picrate based homogenous Combustion catalyst, were studied. The time-resolved ignition and burnout behaviour of the droplets were observed with the aid of a CCD camera, which enabled the determination of the ignition delay period, the burnout time and the flame temperature using the thermal imaging taken by the CCD camera. A flame emission spectrometer was used for identification of the presence of iron ions in the flame and TGA experiments were carried out to study the thermal decomposition behaviour of pure ferrous picrate. It was found that the catalyst shortened the burnout time, increased the burning rate and the flame temperature of the droplets of both diesel and biodiesel. At the catalyst dosing ratio of 1:10,000 (by volume) in the diesel and biodiesel, the flame temperatures of the catalyst dosed droplets were about 40–50 K higher than those of the droplets without the catalyst while the burning rate was 0.05–0.1 mm 2 s −1 higher. It was also found that the biodiesel droplets had longer ignition delay period but shorter burnout times, higher burning rates and flame temperatures than those of the diesel droplets. Iron ions were detected to present in the flame of the Combustion of the catalyst droplet alone and it was found that the pure ferrous picrate decomposed at 523 K. This low decomposition temperature of the picrate ensured the release of the iron ions into the flame, which in turn promoted the Combustion rate of the fuel vapour.
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effect of a Homogeneous Combustion catalyst on the Combustion characteristics and fuel efficiency in a diesel engine
Applied Energy, 2012Co-Authors: Mingming Zhu, Dongke ZhangAbstract:The influence of a ferrous picrate based Homogeneous Combustion catalyst on the Combustion characteristics and fuel efficiency was studied using a fully instrumented diesel engine. A naturally aspirated four stroke, single cylinder, air cooled, direct injection diesel engine was tested at engine speeds of 2800rpm, 3200rpm and 3600rpm under variable load conditions, with different dosing ratio of the catalyst in a commercial diesel fuel. The results indicated that the brake specific fuel consumption decreased and the brake thermal efficiency increased with the addition of the catalyst. At the catalyst dosing ratio of 1:10,000, the brake specific fuel consumption was reduced by 3.3–4.2% at light engine load of 0.12MPa and 2.0–2.4% at heavy engine load of 0.4MPa due to the application of the catalyst. From the in-cylinder pressure and heat release rate analysis, it was found that the catalyst reduced ignition delay and Combustion duration of fuel in the engine, resulting in slightly higher peak cylinder pressure and faster heat release rate.
John Mantzaras - One of the best experts on this subject based on the ideXlab platform.
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heterogeneous and Homogeneous Combustion of fuel lean c3h8 o2 n2 mixtures over rhodium at pressures up to 6 bar
Proceedings of the Combustion Institute, 2020Co-Authors: John Mantzaras, Ran Sui, Chung King Law, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of C3H8/O2/N2 mixtures over Rh was investigated at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-based measurements were applied in a channel-flow catalytic reactor and involved 1-D Raman spectroscopy of major gas-phase species across the channel boundary layer for assessing the catalytic reactivity and planar laser induced fluorescence (PLIF) of the OH radical for monitoring Homogeneous Combustion. Simulations were carried out with a 2-D numerical code that included detailed hetero-/Homogeneous chemical reaction mechanisms. By comparing the Raman-measured and predicted transverse profiles of the limiting C3H8 reactant, the suitability of a detailed surface reaction mechanism was initially evaluated and subsequently a one-step reaction was constructed, which was applicable for the C3H8 total oxidation over Rh at pressures 1 to 6 bar. The catalytic reactivity of C3H8 over Rh displayed a ∼p0.14 pressure dependence, which was substantially lower than a previously reported ∼p0.70 dependence over Pt. The weak pressure dependence of the C3H8 reactivity on Rh suggested caution when selecting catalysts for high-pressure power systems (recuperative microreactors, small-scale turbines) fueled with C3H8 or LPG (liquefied petroleum gas). Comparisons of PLIF-measured and predicted distributions of the OH radical indicated that the employed gas-phase reaction mechanism captured the onset of Homogeneous ignition at pressures greater than or equal to 3 bar as well as the ensuing flame shapes. Predicted and measured Homogeneous ignition distances agreed within 2.5% at 6 bar. With decreasing pressure, the predictions yielded gradually increasing but still modest underpredictions (up to 11.2% at 3 bar) of the Homogeneous ignition distances. The key gas-phase reactions affecting Homogeneous Combustion at various pressures were finally identified.
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coupled reaction mechanism reduction for the hetero Homogeneous Combustion of syngas over platinum
Combustion and Flame, 2020Co-Authors: Ran Sui, John Mantzaras, Wenkai Liang, Chung K LawAbstract:Abstract Coupled reduced mechanisms were developed for the hetero-/Homogeneous Combustion of fuel-lean and fuel-rich H2/CO/O2/N2 mixtures in a Pt-coated planar channel, using a method based on the Directed Relation Graph (DRG) and for a wide range of operating conditions for which detailed measurements are available. It is demonstrated that catalytic and gas-phase reaction mechanisms can be reduced together for all the fuel-lean cases. On the other hand, when joint reduction is performed for low-pressure fuel-rich cases (using a strict threshold value to capture the relatively weak, yet still important coupling between the catalytic and gas-phase reaction pathways) the result is a less efficient reduction process. For the high-pressure fuel-rich cases the catalytic-gaseous chemical coupling is weak enough to be neglected such that the reduction can be conducted separately for higher reduction efficiency. The reduced mechanisms reproduced well the major gaseous species concentrations, gas temperatures and Homogeneous ignition distances obtained with the detailed mechanisms, thus demonstrating the capacity of the applied method in reducing catalytic/gas-phase reaction mechanisms. In addition, it is shown that for fuel-lean stoichiometries the reduction could provide a rapid indication if gas-phase Combustion is ignited, without the need of full simulations. The reduced mechanisms are expected to facilitate large-scale simulations, with fidelity, for the design and thermal management of practical catalytic Combustion systems.
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h2 and co heterogeneous kinetic coupling during Combustion of h2 co o2 n2 mixtures over rhodium
Combustion and Flame, 2019Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The chemical interactions between CO and H2 over rhodium were investigated for H2/CO/O2/N2 mixtures with H2:CO volumetric ratios 1:5–3:1, overall fuel-lean equivalence ratios φ = 0.13 and 0.23, a pressure of 5 bar, and surface temperatures 510-610 K. This temperature range was particularly important for catalytic ignition in hybrid hetero-/Homogeneous Combustion concepts of large gas-turbines operating at part-load or idling conditions and in recuperative micro-turbine-based microreactors at normal operation. In situ Raman measurements of major gas-phase species concentrations were carried out over the catalyst boundary layer, while 2-D simulations were performed with a detailed catalytic reaction scheme. Comparisons of simulations and measurements assessed the performance of the catalytic reaction mechanism for the oxidation of pure CO, pure H2 and H2/CO fuel blends. Transition temperatures were identified below (above) which H2 inhibited (promoted) the oxidation of CO. For a given equivalence ratio, the transition temperatures decreased significantly with increasing H2:CO volumetric ratio (595 K for H2:CO = 1:5 and less than 535 K for H2:CO = 3:1, at φ = 0.13) while for a given H2:CO volumetric ratio they dropped moderately with decreasing φ. This behavior was fundamentally different to that of platinum catalysts, whereby transition temperatures depended weakly on H2:CO volumetric ratio and stronger on equivalence ratio. The strong dependence of the transition temperatures on H2:CO volumetric ratio over rhodium pointed to the advantage of this catalyst when used for high-hydrogen-content (> 80% volume) fuels in power generation applications. The promotion effect of H2 on CO oxidation above the transition temperatures was a result of the increased importance of the indirect CO oxidation route via surface COOH.
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a comparative experimental and numerical investigation of the heterogeneous and Homogeneous Combustion characteristics of fuel rich methane mixtures over rhodium and platinum
Proceedings of the Combustion Institute, 2017Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of fuel-rich CH4/O2/N2/CO2 mixtures (equivalence ratios φ = 1.8–3.5) was investigated experimentally and numerically at 5 bar. Experiments were carried out in an optically accessible channel-flow reactor, which was coated with either rhodium or platinum, and involved in situ spatially-resolved Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous processes and planar laser induced fluorescence (LIF) of formaldehyde for the assessment of Homogeneous Combustion. Simulations were performed with an elliptic 2-D code that included detailed heterogeneous and Homogeneous chemical reaction mechanisms. The surface reaction mechanism for Rh modestly overpredicted the formation of partial oxidation products (H2/CO) and underpredicted the total oxidation products (H2O/CO2) at φ ≥ 3.0. Rhodium was shown superior to platinum in syngas production and, furthermore, it maintained a good catalytic partial oxidation (CPO) capacity even at the low φ = 1.8 where Pt showed minimal H2/CO yields. The higher syngas production in Rh, and in particular of the highly reactive hydrogen, had a drastic impact on the ensuing gas-phase Combustion characteristics. While vigorous Homogeneous Combustion was always established in Rh, it was altogether suppressed in Pt despite the higher attained surface temperatures in Pt. The agreement between LIF-measured and predicted flame anchoring positions and flame lengths in Rh was particularly good. The strong gaseous Combustion in Rh had profound implications, as it considerably reduced the length of the oxidation zone in CPO reactors such that the reforming zone could be initiated farther upstream. It was also shown that Homogeneous Combustion did not affect the reactor thermal management and that it promoted the syngas yields at the reactor outlet.
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Combustion stability and hetero Homogeneous chemistry interactions for fuel lean hydrogen air mixtures in platinum coated microchannels
Combustion and Flame, 2016Co-Authors: John MantzarasAbstract:Abstract The hetero-/Homogeneous Combustion and stability limits of fuel-lean hydrogen/air mixtures (equivalence ratio φ = 0.40) were investigated numerically in a platinum-coated planar microchannel with a length of 10 mm and a height of 1 mm. A two-dimensional numerical model was used for both the gas and the solid, which included elementary heterogeneous and Homogeneous reaction mechanisms, detailed transport, heat conduction in the solid, surface radiation heat transfer, and external losses via a heat transfer coefficient h. Pressures of 1 and 5 bar and solid thermal conductivities ks = 1 and 16 Wm-1K−1 were analyzed, while stability maps were constructed in terms of the critical extinction heat transfer coefficient hcr versus inlet velocity UIN (or mass throughput). For a given solid thermal conductivity, there existed a crossover mass throughput above (below) which the stability envelope was broader at 5 bar (1 bar). Simulations with a surface perfectly stirred reactor (SPSR) model qualitatively reproduced the crossover points, which originated from a shift in the pressure dependence of the catalytic reactivity of hydrogen. For the low solid thermal conductivity ks = 1 Wm-1K−1, a non-monotonic dependence of the stability limits on the mass throughput was shown, with local minima created below the crossover point. The stability limits of hydrogen were solely determined by catalytic chemistry, as it sustained Combustion at temperatures down to 320–380 K, at which gas-phase chemistry was frozen. Away from the critical extinction points, both catalytic and gas-phase reaction pathways were controlling. The diffusional imbalance of hydrogen, which led to catalytically-induced superadiabatic surface temperatures, and the suppression of the surface superadiabaticity by gaseous chemistry resulted in rich Combustion phenomena, such as increasing peak wall temperatures with increasing heat transfer coefficients h. Critical extinction heat transfer coefficients for hydrogen were three to four orders of magnitude higher than those reported for methane and propane fuels in a similar channel geometry.
Rolf Bombach - One of the best experts on this subject based on the ideXlab platform.
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heterogeneous and Homogeneous Combustion of fuel lean c3h8 o2 n2 mixtures over rhodium at pressures up to 6 bar
Proceedings of the Combustion Institute, 2020Co-Authors: John Mantzaras, Ran Sui, Chung King Law, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of C3H8/O2/N2 mixtures over Rh was investigated at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-based measurements were applied in a channel-flow catalytic reactor and involved 1-D Raman spectroscopy of major gas-phase species across the channel boundary layer for assessing the catalytic reactivity and planar laser induced fluorescence (PLIF) of the OH radical for monitoring Homogeneous Combustion. Simulations were carried out with a 2-D numerical code that included detailed hetero-/Homogeneous chemical reaction mechanisms. By comparing the Raman-measured and predicted transverse profiles of the limiting C3H8 reactant, the suitability of a detailed surface reaction mechanism was initially evaluated and subsequently a one-step reaction was constructed, which was applicable for the C3H8 total oxidation over Rh at pressures 1 to 6 bar. The catalytic reactivity of C3H8 over Rh displayed a ∼p0.14 pressure dependence, which was substantially lower than a previously reported ∼p0.70 dependence over Pt. The weak pressure dependence of the C3H8 reactivity on Rh suggested caution when selecting catalysts for high-pressure power systems (recuperative microreactors, small-scale turbines) fueled with C3H8 or LPG (liquefied petroleum gas). Comparisons of PLIF-measured and predicted distributions of the OH radical indicated that the employed gas-phase reaction mechanism captured the onset of Homogeneous ignition at pressures greater than or equal to 3 bar as well as the ensuing flame shapes. Predicted and measured Homogeneous ignition distances agreed within 2.5% at 6 bar. With decreasing pressure, the predictions yielded gradually increasing but still modest underpredictions (up to 11.2% at 3 bar) of the Homogeneous ignition distances. The key gas-phase reactions affecting Homogeneous Combustion at various pressures were finally identified.
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h2 and co heterogeneous kinetic coupling during Combustion of h2 co o2 n2 mixtures over rhodium
Combustion and Flame, 2019Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The chemical interactions between CO and H2 over rhodium were investigated for H2/CO/O2/N2 mixtures with H2:CO volumetric ratios 1:5–3:1, overall fuel-lean equivalence ratios φ = 0.13 and 0.23, a pressure of 5 bar, and surface temperatures 510-610 K. This temperature range was particularly important for catalytic ignition in hybrid hetero-/Homogeneous Combustion concepts of large gas-turbines operating at part-load or idling conditions and in recuperative micro-turbine-based microreactors at normal operation. In situ Raman measurements of major gas-phase species concentrations were carried out over the catalyst boundary layer, while 2-D simulations were performed with a detailed catalytic reaction scheme. Comparisons of simulations and measurements assessed the performance of the catalytic reaction mechanism for the oxidation of pure CO, pure H2 and H2/CO fuel blends. Transition temperatures were identified below (above) which H2 inhibited (promoted) the oxidation of CO. For a given equivalence ratio, the transition temperatures decreased significantly with increasing H2:CO volumetric ratio (595 K for H2:CO = 1:5 and less than 535 K for H2:CO = 3:1, at φ = 0.13) while for a given H2:CO volumetric ratio they dropped moderately with decreasing φ. This behavior was fundamentally different to that of platinum catalysts, whereby transition temperatures depended weakly on H2:CO volumetric ratio and stronger on equivalence ratio. The strong dependence of the transition temperatures on H2:CO volumetric ratio over rhodium pointed to the advantage of this catalyst when used for high-hydrogen-content (> 80% volume) fuels in power generation applications. The promotion effect of H2 on CO oxidation above the transition temperatures was a result of the increased importance of the indirect CO oxidation route via surface COOH.
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a comparative experimental and numerical investigation of the heterogeneous and Homogeneous Combustion characteristics of fuel rich methane mixtures over rhodium and platinum
Proceedings of the Combustion Institute, 2017Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of fuel-rich CH4/O2/N2/CO2 mixtures (equivalence ratios φ = 1.8–3.5) was investigated experimentally and numerically at 5 bar. Experiments were carried out in an optically accessible channel-flow reactor, which was coated with either rhodium or platinum, and involved in situ spatially-resolved Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous processes and planar laser induced fluorescence (LIF) of formaldehyde for the assessment of Homogeneous Combustion. Simulations were performed with an elliptic 2-D code that included detailed heterogeneous and Homogeneous chemical reaction mechanisms. The surface reaction mechanism for Rh modestly overpredicted the formation of partial oxidation products (H2/CO) and underpredicted the total oxidation products (H2O/CO2) at φ ≥ 3.0. Rhodium was shown superior to platinum in syngas production and, furthermore, it maintained a good catalytic partial oxidation (CPO) capacity even at the low φ = 1.8 where Pt showed minimal H2/CO yields. The higher syngas production in Rh, and in particular of the highly reactive hydrogen, had a drastic impact on the ensuing gas-phase Combustion characteristics. While vigorous Homogeneous Combustion was always established in Rh, it was altogether suppressed in Pt despite the higher attained surface temperatures in Pt. The agreement between LIF-measured and predicted flame anchoring positions and flame lengths in Rh was particularly good. The strong gaseous Combustion in Rh had profound implications, as it considerably reduced the length of the oxidation zone in CPO reactors such that the reforming zone could be initiated farther upstream. It was also shown that Homogeneous Combustion did not affect the reactor thermal management and that it promoted the syngas yields at the reactor outlet.
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Homogeneous Combustion of fuel lean h2 o2 n2 mixtures over platinum at elevated pressures and preheats
Combustion and Flame, 2011Co-Authors: Yohannes Ghermay, John Mantzaras, Rolf Bombach, Konstantinos BoulouchosAbstract:Abstract The gas-phase Combustion of H2/O2/N2 mixtures over platinum was investigated experimentally and numerically at fuel-lean equivalence ratios up to 0.30, pressures up to 15 bar and preheats up to 790 K. In situ 1-D spontaneous Raman measurements of major species concentrations and 2-D laser induced fluorescence (LIF) of the OH radical were applied in an optically accessible channel-flow catalytic reactor, leading to the assessment of the underlying heterogeneous (catalytic) and Homogeneous (gas-phase) Combustion processes. Simulations were carried out with a 2-D elliptic code that included elementary hetero-/Homogeneous chemical reaction schemes and detailed transport. Measurements and predictions have shown that as pressure increased above 10 bar the preheat requirements for significant gas-phase hydrogen conversion raised appreciably, and for p = 15 bar (a pressure relevant for gas turbines) even the highest investigated preheats were inadequate to initiate considerable gas-phase conversion. Simulations in channels with practical geometrical confinements of 1 mm indicated that gas-phase Combustion was altogether suppressed at atmospheric pressure, wall temperatures as high as 1350 K and preheats up to 773 K. While Homogeneous ignition chemistry controlled gaseous Combustion at atmospheric pressure, flame propagation characteristics dictated the strength of Homogeneous Combustion at the highest investigated pressures. The decrease in laminar burning rates for p ⩾ 8 bar led to a push of the gaseous reaction zone close to the channel wall, to a subsequent leakage of hydrogen through the gaseous reaction zone, and finally to catalytic conversion of the escaped fuel at the channel walls. Parametric studies delineated the operating conditions and geometrical confinements under which gas-phase conversion of hydrogen could not be ignored in numerical modeling of catalytic Combustion.
Ran Sui - One of the best experts on this subject based on the ideXlab platform.
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heterogeneous and Homogeneous Combustion of fuel lean c3h8 o2 n2 mixtures over rhodium at pressures up to 6 bar
Proceedings of the Combustion Institute, 2020Co-Authors: John Mantzaras, Ran Sui, Chung King Law, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of C3H8/O2/N2 mixtures over Rh was investigated at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-based measurements were applied in a channel-flow catalytic reactor and involved 1-D Raman spectroscopy of major gas-phase species across the channel boundary layer for assessing the catalytic reactivity and planar laser induced fluorescence (PLIF) of the OH radical for monitoring Homogeneous Combustion. Simulations were carried out with a 2-D numerical code that included detailed hetero-/Homogeneous chemical reaction mechanisms. By comparing the Raman-measured and predicted transverse profiles of the limiting C3H8 reactant, the suitability of a detailed surface reaction mechanism was initially evaluated and subsequently a one-step reaction was constructed, which was applicable for the C3H8 total oxidation over Rh at pressures 1 to 6 bar. The catalytic reactivity of C3H8 over Rh displayed a ∼p0.14 pressure dependence, which was substantially lower than a previously reported ∼p0.70 dependence over Pt. The weak pressure dependence of the C3H8 reactivity on Rh suggested caution when selecting catalysts for high-pressure power systems (recuperative microreactors, small-scale turbines) fueled with C3H8 or LPG (liquefied petroleum gas). Comparisons of PLIF-measured and predicted distributions of the OH radical indicated that the employed gas-phase reaction mechanism captured the onset of Homogeneous ignition at pressures greater than or equal to 3 bar as well as the ensuing flame shapes. Predicted and measured Homogeneous ignition distances agreed within 2.5% at 6 bar. With decreasing pressure, the predictions yielded gradually increasing but still modest underpredictions (up to 11.2% at 3 bar) of the Homogeneous ignition distances. The key gas-phase reactions affecting Homogeneous Combustion at various pressures were finally identified.
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coupled reaction mechanism reduction for the hetero Homogeneous Combustion of syngas over platinum
Combustion and Flame, 2020Co-Authors: Ran Sui, John Mantzaras, Wenkai Liang, Chung K LawAbstract:Abstract Coupled reduced mechanisms were developed for the hetero-/Homogeneous Combustion of fuel-lean and fuel-rich H2/CO/O2/N2 mixtures in a Pt-coated planar channel, using a method based on the Directed Relation Graph (DRG) and for a wide range of operating conditions for which detailed measurements are available. It is demonstrated that catalytic and gas-phase reaction mechanisms can be reduced together for all the fuel-lean cases. On the other hand, when joint reduction is performed for low-pressure fuel-rich cases (using a strict threshold value to capture the relatively weak, yet still important coupling between the catalytic and gas-phase reaction pathways) the result is a less efficient reduction process. For the high-pressure fuel-rich cases the catalytic-gaseous chemical coupling is weak enough to be neglected such that the reduction can be conducted separately for higher reduction efficiency. The reduced mechanisms reproduced well the major gaseous species concentrations, gas temperatures and Homogeneous ignition distances obtained with the detailed mechanisms, thus demonstrating the capacity of the applied method in reducing catalytic/gas-phase reaction mechanisms. In addition, it is shown that for fuel-lean stoichiometries the reduction could provide a rapid indication if gas-phase Combustion is ignited, without the need of full simulations. The reduced mechanisms are expected to facilitate large-scale simulations, with fidelity, for the design and thermal management of practical catalytic Combustion systems.
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h2 and co heterogeneous kinetic coupling during Combustion of h2 co o2 n2 mixtures over rhodium
Combustion and Flame, 2019Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The chemical interactions between CO and H2 over rhodium were investigated for H2/CO/O2/N2 mixtures with H2:CO volumetric ratios 1:5–3:1, overall fuel-lean equivalence ratios φ = 0.13 and 0.23, a pressure of 5 bar, and surface temperatures 510-610 K. This temperature range was particularly important for catalytic ignition in hybrid hetero-/Homogeneous Combustion concepts of large gas-turbines operating at part-load or idling conditions and in recuperative micro-turbine-based microreactors at normal operation. In situ Raman measurements of major gas-phase species concentrations were carried out over the catalyst boundary layer, while 2-D simulations were performed with a detailed catalytic reaction scheme. Comparisons of simulations and measurements assessed the performance of the catalytic reaction mechanism for the oxidation of pure CO, pure H2 and H2/CO fuel blends. Transition temperatures were identified below (above) which H2 inhibited (promoted) the oxidation of CO. For a given equivalence ratio, the transition temperatures decreased significantly with increasing H2:CO volumetric ratio (595 K for H2:CO = 1:5 and less than 535 K for H2:CO = 3:1, at φ = 0.13) while for a given H2:CO volumetric ratio they dropped moderately with decreasing φ. This behavior was fundamentally different to that of platinum catalysts, whereby transition temperatures depended weakly on H2:CO volumetric ratio and stronger on equivalence ratio. The strong dependence of the transition temperatures on H2:CO volumetric ratio over rhodium pointed to the advantage of this catalyst when used for high-hydrogen-content (> 80% volume) fuels in power generation applications. The promotion effect of H2 on CO oxidation above the transition temperatures was a result of the increased importance of the indirect CO oxidation route via surface COOH.
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a comparative experimental and numerical investigation of the heterogeneous and Homogeneous Combustion characteristics of fuel rich methane mixtures over rhodium and platinum
Proceedings of the Combustion Institute, 2017Co-Authors: Ran Sui, John Mantzaras, Rolf BombachAbstract:Abstract The heterogeneous and Homogeneous Combustion of fuel-rich CH4/O2/N2/CO2 mixtures (equivalence ratios φ = 1.8–3.5) was investigated experimentally and numerically at 5 bar. Experiments were carried out in an optically accessible channel-flow reactor, which was coated with either rhodium or platinum, and involved in situ spatially-resolved Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous processes and planar laser induced fluorescence (LIF) of formaldehyde for the assessment of Homogeneous Combustion. Simulations were performed with an elliptic 2-D code that included detailed heterogeneous and Homogeneous chemical reaction mechanisms. The surface reaction mechanism for Rh modestly overpredicted the formation of partial oxidation products (H2/CO) and underpredicted the total oxidation products (H2O/CO2) at φ ≥ 3.0. Rhodium was shown superior to platinum in syngas production and, furthermore, it maintained a good catalytic partial oxidation (CPO) capacity even at the low φ = 1.8 where Pt showed minimal H2/CO yields. The higher syngas production in Rh, and in particular of the highly reactive hydrogen, had a drastic impact on the ensuing gas-phase Combustion characteristics. While vigorous Homogeneous Combustion was always established in Rh, it was altogether suppressed in Pt despite the higher attained surface temperatures in Pt. The agreement between LIF-measured and predicted flame anchoring positions and flame lengths in Rh was particularly good. The strong gaseous Combustion in Rh had profound implications, as it considerably reduced the length of the oxidation zone in CPO reactors such that the reforming zone could be initiated farther upstream. It was also shown that Homogeneous Combustion did not affect the reactor thermal management and that it promoted the syngas yields at the reactor outlet.
Jianfeng Pan - One of the best experts on this subject based on the ideXlab platform.
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comparison of the effect of heat release and products from heterogeneous reaction on Homogeneous Combustion of h2 o2 mixture in the catalytic micro combustor
International Journal of Hydrogen Energy, 2019Co-Authors: Jie Gou, Jianfeng Pan, Yi Zhang, Jian Zhu, Evans K QuayeAbstract:Abstract Numerical simulation was carried out to investigate the hetero-/Homogeneous Combustion of stoichiometric H2/O2 premixed flames in a platinum-coated planar micro channel. Three-dimensional Computational Fluid Dynamics (CFD) models with detailed reaction mechanisms for Homogeneous (gas phase, G) and heterogeneous (catalytic, C) reactions were adopted. The effects of the heat released and products from heterogeneous reaction (CR) on the Homogeneous reaction (GR) were analyzed and compared systematically. In the presence of additional released heat, the flame temperature, intermediate concentrations and product yield increased, especially near the inner wall. The promotion effect of heat released from the CR on the GR was indicated, and it mainly reflected in the increase of chemical reaction rate and fuel consumption. When the heat released and the products from the CR were added simultaneously, the flame temperature and species (OH) concentration were still low as compared with the model without addition. The inhibition effect of the product on the GR was larger than the promotion effect of the additional heat on the GR. The increase in the chemical reaction rate and fuel conversion rate demonstrated that, the heat released from the CR could improve the Combustion efficiency of the micro combustor.
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hetero Homogeneous Combustion characteristics of premixed hydrogen air mixture in a planar micro reactor with catalyst segmentation
Chemical Engineering Science, 2017Co-Authors: Jianfeng Pan, Wenming Yang, Aikun Tang, Stephen Bani, Xia ShaoAbstract:Abstract Numerical simulation of stoichiometric hydrogen-air premixed flame in a platinum-coated micro channel was performed to investigate hetero-/Homogeneous Combustion characteristics. An elliptical two-dimensional (2D) Computational Fluid Dynamics (CFD) model with detailed reaction mechanisms for Homogeneous (gas phase) and heterogeneous (catalytic) reactions was adopted. The hetero-/Homogeneous reaction characteristics with different inlet flow velocities and flame speeds were used to evaluate the effect of heterogeneous reaction on Homogeneous reaction in the combustor with 2 mm length of catalyst segmentation. The effect of heat generation of the heterogeneous reaction was also analyzed. The numerical results indicated that the highest temperature in the catalytic combustor was lower than that in the combustor without catalyst. In the presence of heterogeneous reaction, the species (OH) concentration near the catalytic surface decreased significantly due to the dominated heterogeneous reaction at that region. The Homogeneous ignition distance increased with increasing inlet flow velocity. The heat transfer from the catalytic surface to the gaseous mixture in the catalytic zone exhibited a high intensity under the large flow velocity, and the preheated incoming flow improved the heterogeneous reaction to inhibit the Homogeneous reaction. The decreased flame speed in the catalytic combustor further demonstrated that the Homogeneous reaction was suppressed by the heterogeneous reaction.
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interaction between heterogeneous and Homogeneous reaction of premixed hydrogen air mixture in a planar catalytic micro combustor
International Journal of Hydrogen Energy, 2017Co-Authors: Jianfeng Pan, Wenming Yang, Aikun Tang, Stephen Bani, Xia ShaoAbstract:Abstract Hetero-/Homogeneous Combustion of hydrogen–air mixture in a platinum-coated micro channel was studied by means of three-dimensional (3D) Computational Fluid Dynamics (CFD) model using detailed reaction mechanisms for Homogeneous (gas phase) and heterogeneous (catalytic) reactions. The influence of heterogeneous reaction on Homogeneous reaction was obtained by discussing the hetero-/Homogeneous reaction characteristics, the process and competitiveness of heterogeneous reaction. Intense depletion of fuel and product formation near the inlet has shown that fuel absorption reaction was predominant whiles there was no Homogeneous reaction. The free radicals from Homogeneous reaction near the catalytic surface were drained, resulting in the interruption of chain reaction. The desorbed product as the third-body promoted the chain terminating reaction to deactivate free radical. The competitiveness value of heterogeneous reaction for capturing fuel was 14.85%, indicating a weak reaction intensity in the catalytic combustor. The heterogeneous reaction presented an inhibition effect on Homogeneous reaction but greatly enhanced the Combustion efficiency in the micro channel.
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hetero Homogeneous Combustion of premixed hydrogen oxygen mixture in a micro reactor with catalyst segmentation
International Journal of Hydrogen Energy, 2016Co-Authors: Jianfeng Pan, Aikung Tang, Xia ShaoAbstract:Abstract Numerical simulations with detailed Homogeneous (gas phase) and heterogeneous (catalytic) chemistries of premixed hydrogen–oxygen mixture were performed inside a rectangular micro-combustor. The effects of catalytic walls on the Homogeneous Combustion were investigated via varying catalyst segment layouts and sizes. The interactions between heterogeneous and Homogeneous reactions were discussed. It was shown that the heterogeneous reactions become weak when the catalyst disposition is shifted toward the outlet along the streamwise. The Homogeneous Combustion also becomes obviously weakened downstream behind the catalyst segmentation, except the exit. Moreover, with increasing catalyst segment size, the hydrogen conversion ratio increases and the mean outlet temperature reduces. The competition of the fresh fuel between the heterogeneous and Homogeneous reactions result in the inhibition of heterogeneous reactions on Homogeneous Combustion. In summary, the heterogeneous reactions can obviously improve the Combustion efficiency in a micro catalytic combustor. As expected, the effects of catalytic walls were more pronounced for the micro combustor systems.
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effects of products from heterogeneous reactions on Homogeneous Combustion for h2 o2 mixture in the micro combustor
Applied Thermal Engineering, 2016Co-Authors: Jianfeng Pan, Wenming Yang, Aikun Tang, Zhenhua Pan, Yi ZhangAbstract:Abstract Three-dimensional computational fluid dynamics (CFD) models with detailed Homogeneous (gas phase) and heterogeneous (catalytic) chemistries were performed inside a rectangular micro-combustor. The simulation model, based on the chemical reaction kinetics, was validated by experimental data. The effects of the intermediate and final product from heterogeneous reactions on the Homogeneous Combustion in a catalytic combustor were discussed. The results of numerical simulation show that the presence of intermediate can promote the fuel conversion ratio. The addition of final product can significantly decrease the flame temperature and fuel conversion ratio attributed to the heat loss of reaction and weakness in the Combustion intensity. Similar results are obtained when all the products are added as compared to only the addition of the final product. Suppression effect of the final product on Homogeneous Combustion displays a dominant role among the effects of all products. The combustor performance can be commonly promoted in the hetero-/Homogeneous Combustion system due to the existence of catalysis.