• Energy Research

Experiments were carried out on relatively large vertical propane sonic and subsonic exit velocity jet fires (up to approximately 10 m in length and 1.5 m in width). The main geometrical features of jet fires (flame shape, length and width) were determined by analyzing infrared images. From the observations of visible and infrared images, the flame boundary was defined as that corresponding to a temperature of 800 K. Results were compared with the shapes proposed in previous research projects. In the present study, data for sonic and subsonic exit velocity flames indicated that a cylindrical shape could accurately describe the shape of a vertical propane jet fire in still air. The length of such a cylindrical jet fire was the radiant flame length and the equivalent diameter was that corresponding to a volume equal to that surrounded by the aforementioned boundary. The ratio of flame length to diameter was found to be 7. Expressions are proposed to predict the values of jet flame length and width as a function of orifice exit diameter and Reynolds number. Peer Reviewed

Abstract This paper investigates the flame size (i.e. envelop surface area and flame volume) and the volumetric heat release rate of turbulent jet diffusion flames, in both normal and in a sub-atmospheric pressure. Experiments on turbulent jet diffusion flames, produced with nozzles of 4, 5, 6 and 8 mm in diameter and using propane as fuel, have been carried out at two different altitudes: Hefei, 50 m and 100 kPa and Lhasa, 3650 m and 64 kPa. Results have shown both the flame envelope surface area, Af, and the flame volume, Vf, to be much larger in the sub-atmospheric pressure than in the normal pressure (i.e. Af ∼ p − 4/5; Vf ∼ p−7/5). The flame envelope surface area has been found to scale with the heat release rate, Q , by the power of 4/5, Af ∼ Q 4 / 5 . The flame volume, Vf, has also been found to scale with the heat release rate by the power of 9/10, Vf ∼ Q 9 / 10 . The volumetric heat release rate, Q ‴ , has been found to be a function of both the heat release rate, Q , and the ambient pressure, p ( Q ‴ ∼ Q 0.1 ; Q ‴ ∼ p 7 / 5 ). General non-dimensional correlations for all the present data, obtained for the different nozzle diameters and the two ambient pressures, have also been proposed for the flame envelope surface area and the flame volume, respectively.

AbstractAlthough jet fires are usually smaller than other fires, they may lead to a destructive chain of events that can increase the scale of an accident. Therefore, their size should be predicted for accurate risk assessment. In the literature, most of the proposals for estimating jet fire size concern small jet fires (up to 2.5 m in length) or subsonic flames. In this study, experiments on relatively large propane jet fires in still air were performed. Vertical turbulent diffusion flames up to 10 m in length, with sonic and subsonic mass flow rates, were obtained using six different orifice exit diameters. The experiments were filmed with video and thermographic cameras and the resulting visible and infrared images were used to determine flame length and lift‐off distance. Expressions for estimating jet length as a function of several variables (mass flow rate, orifice exit diameter, Froude and Reynolds numbers) are also proposed. © 2008 American Institute of Chemical Engineers AIChE J, 2009

Achieving carbon peaking and carbon neutrality is crucial to accelerating the construction of ecological civilization and promoting high-quality national development. Carbon dioxide as an additive in industrial combustion can effectively reduce soot production. The main background of the paper is derived from industrial flares, which are devices that convert unrecoverable combustible gasses produced in industrial production into environmentally friendly combustion products through combustion. The paper presents the effect of cross airflow on the flame characteristics and flame radiation fraction of ethylene jet fires with carbon dioxide addition. The experiments were carried out on the test bench at one end of a wind tunnel facility with size of 22 m (length) × 1.2 m (width) × 0.8 m (height). The flame geometrical features (i.e. flame length and lift-off height) and flame radiation fraction of ethylene jet fires with carbon dioxide addition under cross airflow were analyzed. It was found that the flame lift-off height of ethylene gas and carbon dioxide is a linear function with the fuel ejection velocity, which is consistent with the pure fuel phenomenon studied by previous researchers. For the same heat release rate, the flame radiation fraction decreases with the increase of the volume flow of CO2 added to ethylene. Moreover, for the given test conditions, the flame radiation fraction of ethylene jet fires with carbon dioxide addition decreases with the increase of cross airflow speeds. A model for the dimensionless flame length of ethylene jet fires with carbon dioxide addition was obtained. Finally, a new global model is also proposed to characterize the flame radiation fraction of ethylene jet fires with carbon dioxide addition by accounting for the effect of cross airflows.

Abstract Flame downwash behavior (flame pulled by the wake flow and attached to the leeward side of the nozzle) of gaseous fuel jets in cross-flow is of much practical importance in the design of burners as well as industrial flare, and thus important for energy conversion and conservation; however, the studies are still very limited. The critical condition (i.e., critical cross-flow air speed) for flame downwash occurrence as well as the evolution of flame downwash length for various fuel jet exit velocities has not been quantified yet. In this work, the flame downwash length evolution of non-premixed jets for different pipe nozzle diameters at various fuel discharge velocities and cross-flow air speeds as well as the critical condition under which the flame downwash occurs have been quantified comprehensively. Pipe nozzles with inner diameters of 8, 10, 13 and 15 mm were employed in the experiments, using propane as the fuel and with fuel jet velocities ranging between 0.38 and 2.42 m/s. The experimental results showed that the flame downwash length increased with increasing cross-flow air speed for a given fuel jet exit velocity. It was also found that, with increasing cross-flow air speed, the downwash length increased more rapidly for the higher fuel jet exit velocity than that for the lower fuel jet velocity. The critical cross-flow air speed, when flame downwash occurs, was found to be little dependent on the nozzle diameter but increase with the fuel jet exit velocity following a linear relationship. A new correlation for flame downwash length was proposed based on physically the coupling effects due to the competition of the fuel jet momentum to the cross-flow momentum and the total fuel mass supply. The proposed correlation was shown to well characterize the flame downwash length in terms of nozzle inner diameters, dimensionless fuel mass flow rates and the jet momentum ratio. The findings of this work provide basic knowledge and have potential practical applications for burner design and flare implementation, which allow predictions to be made regarding the possible threat and the establishment of the necessary safety length for the stack to prevent the damage for reducing the potential risk.

Abstract This study reports experimental results and correlations for axisymmetric gaseous fuel jets restricted by parallel sidewalls at various separation distances. Although many investigations have been conducted to elucidate the flame height evolution of diffusion flames in an unrestricted environment; the restriction effect of sidewalls on diffusion flames, which occasionally occurs in accidental leakages of city natural gas pipelines, has received little attention. The underlying interaction dynamics of axisymmetric gaseous fuel jets with two parallel sidewalls at various separation distances has not been fully elucidated. In this work, a series of experiments on this issue were carried out with 3-, 6- and 10-mm nozzles. The sidewall separation distances were varied from 10 to 50 cm with a corresponding free condition. A series of new results and their interpretation are presented in this work. The results show that the flame height changes little when the sidewall separation distance reduces from +∞ to a critical value (Scri). Further reductions on the sidewall separation distance from Scri disturbed the evolution process of uprising vortexes and hindered air entrainment, leading to significant changes to the jet-flame shape by enlarging the flame height. The maximum flame heights had a linear relation with the critical separation distance of the sidewalls at the critical conditions, being consistent with the scaling analysis of the flow field. The dimensionless critical separation distance was found to be well correlated with the dimensionless heat release rate, Q D ∗ , with a 2/5 power law. A global model, characterizing the variation of the flame height with the dimensionless heat release rate, was proposed, showing good agreement with the experimental results. The results and the expressions obtained in this study contribute to a better understanding of jet fires, allowing a better prediction of flame height, relevant to the design of gas fuel storage systems and transportation systems in the city.