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SAE 2015 World Congress and Exhibition

作者： Tang, Chenglong Si, Zhanbo Zhang, Shuang Huang, Zuohua Pan, Shiyi Wang, Jinhua Gong, Jing Xi'An Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xi'an710049 China

The specific heat ratio used in heat release calculation plays an important role and the mass fraction burned is also a crucial parameter in thermodynamics analysis for engine combustion. A research of high methane fraction natural gas was investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of the initial pressure, the specific heat ratio is decreased, and the time of the mixture burned up is postponed, while the peak heat release ratio is increased. With the increase of the methane fraction, the parameters have the opposite behavior. With the increase of the initial temperature, the specific heat ratio is decreased, and the time when the mixture is burned up is accelerated, and the peak heat release ratio has no obviously difference. With the increase of the dilution ratio or the CO2/N2 ratio, the specific heat ratio is decreased, and the peak heat release heat ratio is decreased. Meanwhile, the time of mixture burned up is postponed with the increase of dilute ratio or CO2/ N2 ratio. Copyright © 2015 SAE International.

关键词： Specific heat

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Burning velocity and flamelet structure of turbulent premixed CH4/H2/air flames with CO2 dilution 10

Burning velocity and flamelet structure of turbulent premixe...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Wang, Jinhua Yu, Senbin Zhang, Meng Jin, Wu Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Turbulent burning velocity and statistical flame front structure parameters of turbulent premixed CH4/H2/air flames diluted with CO2 were measured with OH-PLIF technique. Hydrogen fractions are up to 0.2 and CO2 dilution ratios are up to 0.1. The instantaneous flame front structure was detected using the OH-PLIF technique on a turbulent premixed Bunsen burner. Through image processing and statistic analysis, turbulent burning velocity ST and statistic quantitative parameters, i.e. flame surface density Σ and flame brush thickness δT were obtained. Results show that turbulent burning velocity ST normalized by laminar burning velocity SL decreases with CO2 dilution. Increased Markstein number LM and flame intrinsic instability li with CO2 dilution leads to the passive response of flame to turbulence wrinkling which resulting in less wrinkled flame front, smaller Σ, lower local burning velocity and ST/SL. Convex structure is more frequent than that of concave ones at normal pressure and the bias distribution is much weaker comparing to that of high pressure. The positive structure decreases while the negative structure increases slightly with CO2 dilution. This would be one of the mechanisms leading to the decrease of the effective contact surface between reaction zone and unburned mixture which resulting in the decrease of ST/SL with CO2 dilution.

关键词： Carbon dioxide

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Interfacial stability in vertical swirling annular two-phase flow 16

Interfacial stability in vertical swirling annular two-phase...

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16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2015

作者： Liu, Li Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9781510811843

The linear stability of liquid film flowing upward the inner surface of vertical cylinder under the action of the swirling gas core flow is investigated taking exactly the centrifugal force and curvature of the cylinder into account. Swirl has been considered by superposing a circular movement on the annular flow. The theoretical model of the stability of interface to small perturbation is established by analyzing the normal force balance condition at the wavy interface. The characteristic equation is solved and the stability criterion is obtained. The stability characteristics of neutral, growing and damped modes are presented showing the influences of swirl intensity, relative motion of gas-liquid flow, and the surface tension force. The modeling results indicate that the swirling of the gas phase stabilizes the film flow while the curvature of the cylinder destabilizes it. For strong swirling annular flow, it is found that there is a small influence of surface tension on the stability of interface because the stabilizing centrifugal force is dominant on this condition. The neutral wavelength is found to be very sensitive to the values of swirl intensity and cylinder radius when gas-liquid relative movement is small. However, when gas flow rate is large enough, there is no significant difference in its value.

关键词： Stability criteria

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Flame front structure and flame speed of turbulent premixed combustion under weak turbulence 10

Flame front structure and flame speed of turbulent premixed ...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Yu, Senbin Wang, Jinhua Jin, Wu Nie, Yaohui Zhang, Meng Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi China

Flame front structure of turbulent premixed CH4/air and C3H8/air flames was obtained using OH-PLIF technique, laminar flame properties were calculated and the effect of turbulence intensity on turbulent flame structure and flame speed was analyzed. The results showed that the flame front wrinkled was promoted as the turbulence intensity increases. The correlation between flame speed and turbulence intensity was obtained.

关键词： Turbulence

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Thermal-diffusive instabilities of laminar premixed CH4/H2/air flat flames 10

Thermal-diffusive instabilities of laminar premixed CH4/H2/a...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Jin, Wu Wang, Jinhua Yu, Senbin Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

As one of the most promising clean alternative fuels, natural gas has been widely used in automobile engines. However, due to the slow burning velocity of natural gas and its poor lean-burn ability, hydrogen is often added to improve its combustion behavior. Researches on the fundamental laminar premixed flame characteristics of CH4/H2 blends are of great significance to understand the combustion process in practical combustors. The intrinsic instability of laminar flame is one of the classic issues in flame dynamics, which presents the dynamic response of laminar premixed flamelets to weak perturbations. By studying dynamic mechanism of intrinsic instability, we can estimate the burning velocity more accurately and gain a deeper insight into the turbulent combustion process in spark ignition engines. In this study, the cellular instabilities of laminar premixed CH4/H2/air flat flames were studied using McKenna burner with OH-PLIF technique. It was found that the addition of H2 can broaden the lean combustion limit on flat flame burner with which the cellular instabilities were brought. The digital and OH-PLIF images were obtained to calculate the quantitative parameters of cellular length scale, which is associated with the properties of fuel mixtures such as Lewis number, Markstein number et al. Through the theoretic analysis, we make a thorough investigation on the mechanism about how the cellular scales were determined.

关键词： Natural gas

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Measurement on Turbulent Premixed Flame Structure of CH4/H2/Air Mixtures with CO2 Dilution

Measurement on Turbulent Premixed Flame Structure of CH4/H2/...

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JSAE/SAE 2015 International powertrains, Fuels and Lubricants Meeting, FFL 2015

作者： Wang, Jinhua Yu, Senbin Nie, Yaohui Jin, Wu Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an710049 China

Measurement on turbulent premixed CH4/H2/air flames was studied experimentally. Hydrogen blending ratio is defined as the ratio of hydrogen to fuel, while CO2 dilution ratio is defined as the mole fraction of CO2 to those of mixture. Hydrogen blending ratios up to 0.2 and CO2 dilution ratios up to 0.1 were studied. OH profile of the instantaneous flame front was detected using the OH-PLIF visualizations on a turbulent Bunsen burner. 500 OH-PLIF images were used to obtain the turbulent burning velocity and calculate flame surface density, and 280 images was used to calculate the local curvature radius. © 2015 SAE Japan.

关键词： Carbon dioxide

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Numerical modeling of heat transfer in a two-phase closed thermosyphon 24

Numerical modeling of heat transfer in a two-phase closed th...

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24th IIR International Congress of Refrigeration, ICR 2015

作者： Cao, Jing Li, Mei Li, Bowen Hou, Yu Zhang, Xingqun State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9782362150128

Heat pipe technology is widely applied in the heat transfer systems of many equipment. Two-phase closed thermosyphon (TPCT) is one of the heat pipes which could work with the help of natural gravity. TPCT is adopted in many occasions, such as the waste heat recovery system, the ground source heat pumps, the preservation of permafrost and the de-icing of roadways. In this paper, a comprehensive numerical model is established to describe the condensation and evaporation of thermosyphon. The volume of fluid (VOF) model is employed to describe the interface between vapor and liquid phases. The predicted temperature distribution on the thermosyphon wall agreed well with the published experimental data in the trend.

关键词： Thermosyphons

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Modeling and dynamic simulation on a three-stage feedwater heater with water level controlled

Modeling and dynamic simulation on a three-stage feedwater h...

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International Conference on power engineering, ICOPE 2015

作者： Mu, Qiwei Han, Xiaoqu Wang, Bingqi Yan, Junjie Chen, Weixiong State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Consisting of steam cooler, condensation zone and drain cooler, the three-stage feedwater heater is widely used in the thermal power plants. To study the variable condition characteristics of three-stage feedwater heater with water level controlled, a GSE simulation model of that in 300MW thermal system of power plant was established. Validated by the steady states of the heater, different dynamic characteristics were investigated when the load varied. The results revealed that the steam pressure, feedwater flow and feedwater inlet temperature drops would have a significant influence on the extracting steam flow, feedwater temperature increment and terminal temperature difference. The dynamic trends were intensified with the variation of the input condition enhanced. The response time of extracting steam pressure drops is 430s and that of feedwater flow drops would be prolonged to 600s. The dynamic processes with water level controlled were carried out and showed that adjusting flow valve could keep the water level stable and secure the operation of heater smooth and steady. However, frequently controlling the position of flow valve could impair the steady procedures of other parameters and prolonged the response time. © 2015 The Japan Society of Mechanical Engineers.

关键词： Water levels

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Shock-tube measurements and kinetic study of propanal ignition 10

Shock-tube measurements and kinetic study of propanal igniti...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Yang, Ke Tang, Chenglong Man, Xingjia Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi China

Ignition delay times of propanal were measured in a shock tube over the temperature range of 1050-1800 K, pressures of 1.2-16 atm, fuel concentrations of 0.5-2.0%, and equivalence ratios of 0.5-2.0. Through multiple linear regression, a correlation for the tested ignition delay times was obtained, and the measured data were also compared to the previous data. Two available models (Veloo mech and NUIG mech), were used to simulate the experimental data. Results suggest that both mechanisms has its own advantages and the Veloo mech exhibits a better prediction on the measured data than NUIG mech except for the fuel-rich condition. Reaction pathway analysis indicates that propanal molecule mainly breaks down through the H-abstraction reactions (accounting for around 80% propanal consumption), while reactions of unimolecular decomposition contribute a little part of the whole consumption.

关键词： Shock tubes

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Study on particle and photonic flux distributions in a magnetically stirred photocatalytic reactor

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Journal of Photonics for Energy 2015年第1期5卷

作者： Ren, Yuxun Jing, Dengwei Xi'An Jiaotong University International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering 28 Xianning West Road Xi'an Shaanxi710049 China

When dispersed in water, nanoscale photocatalysts can aggregate into microscale secondary particles due to their high surface energy. The interaction between the incident photons and the aggregated particles is expected to be significantly changed due to their comparable length scales. Hydrodynamics of the particles after aggregation and the resultant photonic flux distributions in slurry photocatalytic reactors are therefore essential. The magnetically stirred photocatalytic reactor is compact and simple for fabrication, and therefore can be readily employed in lab-scale photocatalytic tests. However, studies toward its optimization are rare. In our study, the photocatalyst distribution was simulated using a Eulerian-Lagrangian approach, while the evolution of free liquid surface led by magnetic stirring was modeled by volume of fluid method. Subsequently, based on the photocatalyst distribution, the photonic flux distribution was obtained through a mean free path-based Monte Carlo method. Outcomes suggest that at a stirring speed of 900 rpm, the 10 μm particles can be well suspended, and a moderate free liquid surface will also be present. Moreover, under sufficient stirring, larger catalyst particles are more likely to be densely distributed in the outer region, which contributes to an increase in the overall photonic absorption even higher than the one with evenly distributed photocatalysts. © The Authors.

关键词： Computational fluid dynamics

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