On the effective Lewis number formulations for lean hydrogen/hydrocarbon/air mixtures

Bouvet, N.,Halter, F.,Chauveau, C.,Yoon, Y. Pergamon Press ; Elsevier Science Ltd 2013 International journal of hydrogen energy Vol.38 No.14

Decades of research have underlined the undeniable importance of the Lewis number (Le) in the premixed combustion field. From early experimental observations on laminar flame propagation to the most recent DNS studies of turbulent flames, the unbalanced influence of thermal to mass diffusion (i.e. Le ≠ 1), known as nonequidiffusion, has shed the light on a wide range of combustion phenomena, especially those involving stretched flames. As a result the determination of the Lewis number has become a routine task for the combustion community. Recently, the growing interest in hydrogen/hydrocarbon (HC) fuel blends has produced extensive studies that have not only improved our understanding of H<SUB>2</SUB>/HC flame dynamics, but also, in its wake, raised a fundamental question: which effective Lewis number formulation should we use to characterize the combustion of hydrogen/hydrocarbon/air blends? While the Lewis number is unambiguously defined for combustible mixtures with a single fuel reactant, the literature is unclear regarding the appropriate equivalent formulation for bi-component fuels. The present paper intends to clarify this aspect. To do so, effective Lewis number formulations for lean (φ = 0.6 and 0.8) premixed hydrogen/hydrocarbon/air mixtures have been investigated in the framework of an existing outwardly propagating flame theory. Laminar burning velocities and burned Markstein lengths of H<SUB>2</SUB>/CH<SUB>4</SUB>, H<SUB>2</SUB>/C<SUB>3</SUB>H<SUB>8</SUB>, H<SUB>2</SUB>/C<SUB>8</SUB>H<SUB>18</SUB> and H<SUB>2</SUB>/CO fuel blends in air were experimentally and numerically determined for a wide range of fuel compositions (0/100% → 100/0% H<SUB>2</SUB>/HC). By confronting the two sets of results, the most appropriate effective Lewis number formulation was identified for conventional H<SUB>2</SUB>/HC/air blends. Observed deviations from the validated formulation are discussed for the syngas (H<SUB>2</SUB>/CO) flame cases.

Stability characteristics of non-premixed turbulent jet flames of hydrogen and syngas blends with coaxial air

Hwang, J.,Bouvet, N.,Sohn, K.,Yoon, Y. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.12

The stability characteristics of attached hydrogen (H<SUB>2</SUB>) and syngas (H<SUB>2</SUB>/CO) turbulent jet flames with coaxial air were studied experimentally. The flame stability was investigated by varying the fuel and air stream velocities. Effects of the coaxial nozzle diameter, fuel nozzle lip thickness and syngas fuel composition are addressed in detail. The detachment stability limit of the syngas single jet flame was found to decrease with increasing amount of carbon monoxide in the fuel. For jet flames with coaxial air, the critical coaxial air velocity leading to flame detachment first increases with increasing fuel jet velocity and subsequently decreases. This non-monotonic trend appears for all syngas composition herein investigated (50/50 → 100/0% H<SUB>2</SUB>/CO). OH<SUP>*</SUP> chemiluminescence imaging was performed to qualitatively identify the mechanisms responsible for the flame detachment. For all fuel compositions, local extinction close to the burner rim is observed at lower fuel velocities (ascending stability limit), while local flame extinction downstream of the burner rim is observed at higher fuel velocities (descending stability limit). Extrema of the non-monotonic trends appear to be identical when the nozzle fuel velocity is normalized by the critical fuel velocity obtained for the single jet cases.

H2/CO 합성가스 비예혼합 난류 제트화염에서 부착화염의 화염안정화

황정재,Nicolas Bouvet,손기태,윤영빈 한국연소학회 2012 한국연소학회지 Vol.17 No.1

The detachment stability characteristics of syngas H2/CO jet attached flames were studied. The flame stability was observed while varying the syngas fuel composition, coaxial nozzle diameter and fuel nozzle rim thickness. The detachment stability limit of the syngas single jet flame was found to decrease with increasing mole fraction of carbon monoxide in the fuel. In hydrogen jet flames with coaxial air, the flame detachment stability was found to be independent of the coaxial nozzle diameter. However, velocities of appearance of liftoff and blowout velocities of lifted flames have dependence. At lower fuel velocity range, the critical coaxial air velocity leading to flame detachment increases with increasing fuel jet velocity, whereas at higher fuel velocity range, it decreases. This increasing-decreasing non-monotonic trend appears for all H2/CO syngas compositions (50/50 ~ 100/0% H2/CO). To qualitatively understand the flame behavior near the nozzle rim, OH* chemiluminescence imaging was performed near the detachment limit conditions. For all fuel compositions, local extinction on the rim is observed at lower fuel velocities (increasing stability region), while local flame extinction downstream of the rim is observed at higher fuel velocities (decreasing stability region). Maximum values of the non-monotonic trends appear to be identical when the fuel jet velocity is normalized by the critical fuel velocity obtained in the single jet cases.

H<SUB>2</SUB>/CO 합성가스 비예혼합 난류 제트화염에서 부착화염의 화염안정화

황정재(Jeongjae Hwang),Nicolas Bouvet,손기태(Kitae Sohn),윤영빈(Youngbin Yoon) 한국연소학회 2012 한국연소학회지 Vol.17 No.1

The detachment stability characteristics of syngas H2/CO jet attached flames were studied. The flame stability was observed while varying the syngas fuel composition, coaxial nozzle diameter and fuel nozzle rim thickness. The detachment stability limit of the syngas single jet flame was found to decrease with increasing mole fraction of carbon monoxide in the fuel. In hydrogen jet flames with coaxial air, the flame detachment stability was found to be independent of the coaxial nozzle diameter. However, velocities of appearance of liftoff and blowout velocities of lifted flames have dependence. At lower fuel velocity range, the critical coaxial air velocity leading to flame detachment increases with increasing fuel jet velocity, whereas at higher fuel velocity range, it decreases. This increasing-decreasing non-monotonic trend appears for all H2/CO syngas compositions (50/50~100/0% H2/CO). To qualitatively understand the flame behavior near the nozzle rim, OH<SUP>*</SUP> chemilumi-nescence imaging was performed near the detachment limit conditions. For all fuel compositions, local extinction on the rim is observed at lower fuel velocities(increasing stability region), while local flame extinction downstream of the rim is observed at higher fuel velocities(decreasing stability region). Maximum values of the non-monotonic trends appear to be identical when the fuel jet velocity is normalized by the critical fuel velocity obtained in the single jet cases.

동축공기 조건에서 H₂/CO 난류 제트 확산화염의 화염길이

황정재(Jeongjae Hwang),Nicolas Bouvet,손기태(Kitae Sohn),윤영빈(Youngbin Yoon) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.42

The effect of fuel composition and coaxial air on the flame length was studied in a non-premixed turbulent jet flame. Three cases(100% H₂, 75% H2 / 25% CO, and 50% H₂ / 50% CO) were determined to investigate effects of the fuel composition and fuel velocity and coaxial velocity were varied Uf = 40-140 m/s and Ua = 1.7-11.2 m/s each other to investigate effects of the coaxial velocity. And for excluding the partial premixing effect of the lifted flame, experiments on flame length were conducted in the attached flame region. The flame length is decreased with coaxial air increasing since the air entrainment for reacting is supplied with coaxial air instead of ambient air. In this study, we confirmed that the scaling correlation for predicting the flame length in a jet flame with coaxial air has good agrees with far field concept for relatively low Ua/Uf and near field concept for relatively high Ua/Uf.

동축공기가 있는 H₂/CO 비예혼합 난류 제트화염의 화염 안정성에 대한 실험적 연구

황정재(Jeongjae Hwang),Nicolas Bouvet,손기태(Kitae Sohn),윤영빈(Youngbin Yoon) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.43

The research on the stability characteristics of the H₂/CO syngas jet flame in the turbulent region was conducted. Syngas fuel composition fraction, nozzle diameter, fuel velocity and coaxial air velocity were varied to investigate the effects of those on the characteristics of stability and mechanism of blowoff/liftoff. For higher CO content fuel, blowoff/liftoff is occurred at relatively low fuel velocity. But for all case of composition of fuel and all case of nozzle geometry, they have similar trend of blowoff/liftoff limit which is like a C-curve in fuel-air velocity diagram. The coaxial air diameter does not effect on the blowoff/liftoff coaxial air velocity in case of same fuel nozzle geometry.

NOx Scaling of Syngas H2/CO Turbulent Non-Premixed Jet Flames

Hwang, Jeongjae,Sohn, Kitae,Bouvet, Nicolas,Yoon, Youngbin Taylor Francis 2013 Combustion science and technology Vol.185 No.12

H₂/CO 합성가스의 비예혼합 난류 제트화염에서 화염 길이와 EINOx 스케일링

황정재(Jeongjae Hwang),손기태(Kitae Sohn),Nicolas Bouvet,윤영빈(Youngbin Yoo) 한국연소학회 2012 한국연소학회지 Vol.17 No.4

The flame lengths and NOx emission characteristics of syngas H₂/CO turbulent non-premixed jet flames were investigated. The flame length which is the main parameter governs NOx emission was studied for various syngas compositions. The flame length was compared with previous correlation between Froude number and flame height and it shows that they have good agreements. It was confirmed that the turbulent jet flames herein investigated are in the region of buoyancy-momentum transition. NOx emission was reduced with increased Reynolds number and CO contents in syngas fuel and with decreased fuel nozzle diameter which is attributed by decreased flame residence time. Previous EINOx scaling based on flame residence time of Lf³/(df²Uf) satisfies only the jet flame in momentum-dominated region, not buoyancy-momentum transition region. The simplified flame residence time (Lf/Uf) was adopted in modified EINOx scaling. The modified scaling satisfies the jet flames not only in momentum-dominated region but in buoyancy-momentum transition region. The scaling is also satisfied with H₂/CO syngas jet flames.

동축공기가 있는 H<SUB>2</SUB>/CO 비예혼합 난류 제트화염의 질소산화물 배출 상사식에 대한 실험적 연구

손기태(Kitae Sohn),황정재(Jeongjae Hwang),Nicolas Bouvet,윤영빈(Youngbin Yoon) 한국연소학회 2012 KOSCOSYMPOSIUM논문집 Vol.- No.44

Effect of Particle Loading Ratio and Orifice Exit Velocity on a Particle-Laden Jet

Paik, Kyong-Yup,Yoon, Jung-Soo,Hwang, Jeong-Jae,Chung, Jae-Mook,Bouvet, Nicolas,Yoon, Young-Bin The Korean Society for Aeronautical and Space Scie 2011 International Journal of Aeronautical and Space Sc Vol.12 No.3

In order to design a shear coaxial injector of solid particles with water, basic experiments on a particle laden jet are necessary. The purpose of the present study is to understand the effect of particle loading ratio on the particle spray characteristics (i.e. spreading angle, distribution of particle number density, velocity profiles, and particle developing region length). Hydro-reactive Al2O3 particles with a primary particle diameter of 35~50 ${\mu}m$ are used in this experiment. An automated particle feeder was designed to supply constant particle mass flowrates. Air is used as the carrier gas. To determine the air velocity at the orifice exit, tracers (aluminum oxide, 0.5~2 ${\mu}m$ primary diameter) are also supplied by a tracer feeder. A plain orifice type injector with 3 mm diameter, and 20 mm length was adopted. Particle image velocimetry is used to measure the mean and fluctuating velocity components along the axial and radial directions.