2001 - 2005 Bachelor Science in Power Engineering, University of Shanghai for Science and Technology 2005 - Project engineer in Tonghui CARRIER, Shanghai 2005 - 2007 Master degree in Energy Fluid Environment, University of Rouen 2007 - 2011 PhD in combustion science, specialized in fluid mechanics & heat transfer, INSA Rouen, France; Transitional and stabilization behavior of non-premixed flames by CO2 dilution. 2010 - 2011 Assistant professor in University of Rouen 2011 - 2012 Post-doc fellowship in Laboratory CORIA for french national aerospace center (CNES); Influence of high-frequency tranverse acoustic field on the jet atomization. 2012 - Computational Fluid Dynamics (CFD) research engineer in R&D center of EDF China division, Beijing
Abstract: Air-side dilution on laminar methane/air diffusion flames in the buoyant regime was extensively studied.
CO2, important for EGR and fire safety, was chosen as a diluent. It was complemented by N2 and Ar. Flame stability, its external aspect and inner structure were quantified by complementary experiments and simulations. Two flame-response categories were highlighted, depending on whether mechanisms relied on several effects or mainly on pure dilution. In the former case, physico-chemical properties of diluents were essential. The greatest influence was detected with CO2, the least one with Ar. No critical value of the initial molar O2-concentration (XO2;i) was found to control quantities involved in stability (lifting limit, standoff distance of the attached flame), soot formation and flame-tip opening. It was found a critical flowrate ratio from which flame-liftoff always occurred, crucial to describe lifting process induced by dilution. The reaction, naturally weak at the flame tip, led to an apparent open-tip with diluents. However, simulation showed the reaction, even weakened, persisted. On the contrary, pure dilution controlled flame length behavior. When XO2;i was decreased, length increased according to a unique evolution whatever the diluents. To measure flame length, several techniques were applied: OH Planar Laser Induced Fluorescence (Lf,OH), soot-Laser Induced Incandescence (Lf,LII), direct flame emission (Lf,luminous and Lf,peak). Length Lf,luminous was unable to correctly characterize flame lengthening. Lf,peak was the closest to the calculated stoichiometric length. So, the method giving Lf,peak appeared as the easiest and the most accurate one. Comparison between our data and correlations found in literature indicated Roper’s correlation was the most efficient to predict length evolution.
Abstract: The authors focused on how adding CO2 to the air influences the transition from an attached flame to a lifted flame issued from a coaxial nonpremixed methane-air jet. To discriminate between effects due to a diluent (dilution, thermal, or chemical impacts), chemically and thermally inert N2 and chemically inert Ar were also investigated. Flame lifting always occurs, essentially controlled by the critical flow-rate ratio, (Qdiluent/Qair)lifting. CO2 has the strongest ability to break flame stability, followed by N2, then by Ar. A unique attachment
height and OH thickness characterize lifting for all the diluents; lifting is attained once the same critical flame edge propagation speed is reached. (Qdiluent/Qair)/(Qdiluent/Qair)lifting is the affine parameter of similarity laws describing Ha and EpOH evolutions with dilution. Aerodynamics competes with dilution to impose lifting and boundary effects cannot be ignored in a fine analysis. The flame behaves differently according to whether lifting results from aerodynamics or dilution.
Abstract: The addition of exhaust gas to a combustor may cause liftoff of a diffusion flame due to several possible mechanisms. Understanding the relative influence of these mechanisms is of importance for the further development of exhaust gas recirculation combustion technology. The authors present a numerical study on the effects of CO2, N2 (two of primary exhaust gas components) and Ar addition on the liftoff of a laminar CH4/air diffusion flame. A gradual switch-off approach was used to identify the relative importance of the different
mechanisms. A detailed reaction scheme and complex thermal and transport properties were employed. The simulation results were validated by comparing the calculated and previously measured critical ratios of the 3 additives for liftoff. The results show that the numerical simulation successfully reproduced the previously
measured critical ratios of liftoff for all 3 studied additives. Detailed analysis of the numerical results suggests that the addition of N2 affects flame liftoff due to the sole effect of dilution. On the other hand, the addition of CO2 causes flame liftoff due to the dilution, thermal and chemical effects, with the dilution effect being the most significant one, followed by the thermal and chemical effects. All 3 effects tend to reduce combustion intensity
and cause flame liftoff, leading to the smaller critical ratio of CO2 than that of N2. The radiation and transport property effects are negligible for CO2 addition. Ar addition affects flame liftoff due to dilution, thermal, and transport property effects. However, whereas the dilution effect tends to reduce combustion intensity and cause flame liftoff, the thermal and transport property effects tend to increase combustion intensity and resist flame liftoff for Ar addition, which results in the greater critical ratio of Ar than that of N2. Therefore, for the 3 studied additives in this paper, CO2 has the minimum critical ratio, whereas Ar has the maximum for liftoff.
Abstract: Diluted combustion systems are widely used nowadays, such as: (i) in exhaust gas recirculation com-bustion systems which are proved to be an effective way to improve combustion efficiency and to reduce pollutant emissions, NOx; (ii) in fire extinguishment. Phenomena involved in flame stabiliza-tion, like liftoff and extinction remain real key points in the control of the diluted combustion. Previ-ous work (Min et al., 2010) highlighted the influence of a diluent addition on flame liftoff phenomena as well as its relative effects between dilution, thermal, and chemistry. This work aims to investigate the influence of different diluents (CO2, N2, Ar and CO2+Ar) on the lifted flame stabilization behavior, as well as the process of flame extinction within a large range of aerodynamic conditions.
Abstract: This study details the influence of reactant temperature on the stability of non-premixed CH4/air co-flow jet flames. Flame characteristics have been studied for five temperature levels (from 295 K to 600 K). The hysteresis zone formed by the limits between attached and lifted flame translates towards higher methane jet
velocities with an increase of initial temperature, independently of the air velocity range. Moreover, critical velocities vary linearly with initial temperature. In addition, attachment and lift-off heights have been obtained from CH* chemiluminescence visualization. Results point out that the attachment height decreases significantly with temperature. Observations also indicate that the intrinsic process of lifting is modified. Pre-lifting anchored flame instabilities, not observed at room-temperature, appear at higher initial temperatures; their occurrence increases with temperature. The lift-off height of turbulent lifted flames is also reduced with temperature. Overall, results show that increasing local temperature in the stabilization zone
enhances flame stability.
Abstract: Experiments were performed to analyze dilution effects of CO2, N2 (thermally inert), or Ar (chemically inert) injected in air side, on non-premixed CH4/air flames. The flow rate ratio (Qdiluent/Qair)lifting controls lifting process. Anchored flames stabilize more downstream as Qdiluent/Qair increases; under given aerodynamic conditions, the attachment height, Ha vs. (Qdiluent/Qair)/(Qdiluent/Qair)lifting follows a unique profile whatever the diluents. Flames lift off when Ha,lifting, unique value for different diluents, is attained. Flame bases turn blue by adding a diluent, caused by a reduction in soot formation (see LII images), largely marked at low velocities. It is particularly drastic with CO2. For naturally lifted flames, liftoff height (HL) increases by adding diluents too. Liftoff phenomenon, dependent on (Qdiluent/Qair)lifting, leads to a unique HL-evolution with (Qdiluent/Qair)/(Qdiluent/Qair)lifting for different diluents.
Abstract: The present study is focused on the influence of carbon dioxide added to the air on the transition from an attached flame to a lifted flame issued from a coaxial jet (inner methane and outer air). As known, main effects due to a diluent are induced not only by pure dilution, but also by thermal and chemical actions. In order to find features able to discriminate between them, two other diluents had also been investigated: nitrogen, thermally inert and argon, chemically inert. Firstly flame stability was analyzed; results show that flame lifting can always occur such that it is essentially controlled by the critical flow ratio, [Qdiluent/Qair]lifting even though aerodynamics from inner jet structure does also influence it. Attached flames can stabilize with dilution at a higher position, Ha. Ha-evolution is dictated by the normalized parameter [Qdiluent/Qair]/[Qdiluent/Qair]lifting for the three diluents, leading to a unique curve under given aerodynamic conditions . Modifications in inner flame structure (OH-zone) are totally different when lifting results from pure aerodynamics (no dilution) or from a diluted configuration. But for all the three diluents, effects on flame OH-zone are identical when lifting occurs.
Abstract: An experimental investigation analyzes the effects of CO2 as a diluent on non-premixed CH4/air flames for a large range of air and CH4 velocities. For a fixed CH4 velocity, lifting is mainly controlled by the flow rate ratio, QCO2/Qair. For Uair£0.27m/s, the anchored flame stabilizes more and more far from the burner as QCO2/Qair increases. The changes in flame flickering (reduction of amplitude, slight increase in frequency) with CO2 are due to the variation in the oxide density. The flame stability is analyzed by means of two other diluents, N2 and Ar.
Abstract: The serious environment regulations request us to develop new combustion technologies with a higher efficiency. Since more than ten years, the great effect de combustion products on combustion it-self has been discovered. This paper deals with the influence of CO2 on the stability of a non-premixed flame (CH4/Air).
First of all, some definitions of non-premixed attached et lifted flame have been presented, as well the mechanisms which concern the effect of CO2 on the non-premixed flame. Secondly, the stability and the transition between attached flame and lifted flame have been analyzed with the help of the techniques of image and the measure of velocity. It includes some essential points: the hysteresis zone which is the key to limit the zones of attachment and lift; for attached flame: height of attachment, flickering phenomenon; for lifted flame: lift height. The stability of flame has been greatly influenced by adding CO2, which will reduce the ability of flame to keep attached at burner. At a fixed velocity of methane, it is the ratio of flux between CO2/Air which control the attachment and detachment of the flame. And the heights of attachment and lift increase by adding CO2. As well, the flickering phenomenon is delayed. Finally, the appearance of the soot is put off.
Abstract: This work focuses on the understanding of the behaviours of non-premixed methane-jet flames placed in an air coflow diluted by carbon dioxide (CO2) or by other chemically inert gases (nitrogen, argon, CO2+Ar mixture and helium) in order to discriminate between different phenomena involved in dilution. Diluent addition destabilizes the flame by reducing the flame burning velocity (SL). Transitional phenomena, such as liftoff and extinction, quantified through the stability limits, are systematically analyzed by means of representative physical quantities. The flame stability domain is limited by 3D-surfaces (liftoff and extinction) in the physical domain (Qdiluent/Qair (dilution level), Uair (air velocity), UCH4 (methane velocity)) revealing a competitive effect between aerodynamics and dilution. Results obtained with the tested diluents allow to propose generic diagrams of flame liftoff and extinction for all the diluents by using the comparative parameter Kdiluent defined as (Qdiluant/Qair)lifting/(QCO2/Qair)lifting ≡ (Qdiluant/Qair)extinction/(QCO2/Qair)extinction. This parameter compares the capability of a diluent to destabilize the flame to that of CO2. Hence, a relative ranking of diluents is obtained from the most effective to the least one : CO2 > CO2+Ar > He > N2 > Ar. A classification of representative quantities studied is proposed on the basis of phenomena which dominate the flame responses as a diluent is injected : pure dilution (flame length), chemistry (emission pollutants), oxidizer density (flickering) and coupled effects (stabilization). Physical quantities related to flame stabilization process are all submitted to, regardless of diluent, self-similar laws dependent on the affine parameter (Qdiluent/Qair)/Kdiluent. This is explained by SL which is considered as the key element in the mechanism of flame stabilization in the presence of dilution in the air.
